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Genuine and drug-induced synesthesia: A comparison
Abstract
Despite some principal similarities, there is no systematic comparison between the different types of synesthesia (genuine, acquired and drug-induced). This comprehensive review compares the three principal types of synesthesia and focuses on their phenomenological features and their relation to different etiological models. Implications of this comparison for the validity of the different etiological models are discussed. Comparison of the three forms of synesthesia show many more differences than similarities. This is in contrast to their representation in the literature, where they are discussed in many respects as being virtually similar. Noteworthy is the much broader spectrum and intensity with the typical drug-induced synesthesias compared to genuine and acquired synesthesias. A major implication of the phenomenological comparison in regard to the etiological models is that genuine and acquired synesthesias point to morphological substrates, while drug-induced synesthesia appears to be based on functional changes of brain activity.
... It has been objected, however, that there are important phenomenological differences between these forms of synesthesia. Due to such differences, according to Sinke et al. (2012), we should expect that such states are most likely related to different neural mechanisms. The main phenomenological difference between the two types of experience, according to this study, is intensity, i.e., drug induced synesthetic states are more intense. ...
... Other types of synesthetic experience seem to exhibit an emotional component(Cytowic, 2002). Since it is not clear the extent to which grapheme-color synesthesia exhibits emotions(Sinke, Halpern, Zedler, Neufeld, Emrich, and Passie, 2012), its emotional properties will not be discussed. For a discussion on the hedonic and emotional tone of synesthesia and its relationship to aesthetic experience seeNikolinakos (2012). ...
... 14 For a similar point seeAizawa (2009).15 In order to defend the realistic nature of this scenario, we can point out the following with respect to theSinke et al. (2012) study which sets out to articulate the differences between genuine, drug induced, and acquired synesthesia. The study identifies a variety of phenomenological features that are used to characterize the differences among these types of synesthesia. ...
... The use of psychedelic drugs, such as psilocybin, LSD and mescaline, has a long history of reportedly inducing synaesthesia-like experiences, such as the cross-modal induction of colour experiences via auditory tones [51,52]. However, due to the methodological limitations of these studies, including lack of placebo controls and a failure to assess key hallmarks of synaesthesia within these experiences, it has been difficult to draw firm conclusions about the validity of these claims (for reviews, see [52,53]). For example, drug-induced synaesthesia-like experiences seem to lack consistency, do not occur automatically and can be influenced by the current state of the individual, whereas a (natural) synaesthetic concurrent is consistent, automatic and unaltered by an individual's current state of mind [53]. ...
... However, due to the methodological limitations of these studies, including lack of placebo controls and a failure to assess key hallmarks of synaesthesia within these experiences, it has been difficult to draw firm conclusions about the validity of these claims (for reviews, see [52,53]). For example, drug-induced synaesthesia-like experiences seem to lack consistency, do not occur automatically and can be influenced by the current state of the individual, whereas a (natural) synaesthetic concurrent is consistent, automatic and unaltered by an individual's current state of mind [53]. ...
... In summary, while there is ongoing debate about whether certain pharmacologically induced experiences should be described as synaesthesia-like [21,52,53], currently it appears that these experiences represent a more dynamic and flexible phenomenon, having only superficial similarities to natural synaesthesia. ...
People with synaesthesia have additional perceptual experiences, which are automatically and consistently triggered by specific inducing stimuli. Synaesthesia therefore offers a unique window into the neurocognitive mechanisms underlying conscious perception. A long-standing question in synaesthesia research is whether it is possible to artificially induce non-synaesthetic individuals to have synaesthesia-like experiences. Although synaesthesia is widely considered a congenital condition, increasing evidence points to the potential of a variety of approaches to induce synaesthesia-like experiences, even in adulthood. Here, we summarize a range of methods for artificially inducing synaesthesia-like experiences, comparing the resulting experiences to the key hallmarks of natural synaesthesia which include consistency, automaticity and a lack of ‘perceptual presence’. We conclude that a number of aspects of synaesthesia can be artificially induced in non-synaesthetes. These data suggest the involvement of developmental and/or learning components in the acquisition of synaesthesia, and they extend previous reports of perceptual plasticity leading to dramatic changes in perceptual phenomenology in adults.
This article is part of a discussion meeting issue ‘Bridging senses: novel insights from synaesthesia’.
... However, it could be argued that the complexity of psychedelic synaesthesia, while certainly reported by some (e.g., Klüver, 1966), is not obligatory (e.g., Simpson and McKellar, 1955). Sinke et al. (2012) further suggest that drug-induced synaesthesia lacks the automaticity and consistency of congenital synaesthesia, citing an older study which explored the consistency of sound-colour synaesthesia with mescaline (Beringer, 1927). Indeed, our study similarly found no effect of LSD on grapheme-or sound-colour consistency (Terhune et al., 2016). ...
... A final difference between congenital and drug-induced synaesthesias may be in the types of inducers and concurrents. Sinke et al. (2012) note that congenital synaesthesias typically have graphemes as inducers, whereas drug-induced synaesthesias do not. Although it's true that graphemes are frequent inducers, there is evidence that music and sound stimuli function as inducers in more than 25 per cent of cases of congenital synaesthesia (Hochel and Milán, 2008). ...
... Although it's true that graphemes are frequent inducers, there is evidence that music and sound stimuli function as inducers in more than 25 per cent of cases of congenital synaesthesia (Hochel and Milán, 2008). This is notable because soundcolour (or sound-visual) synaesthesia appears to be the most frequently observed type of drug-induced synaesthesia (Klüver, 1966;Luke et al., 2012;Pahnke and Richards, 1966;Simpson and McKellar, 1955;Sinke et al., 2012; for a review, see Luke and Terhune, 2013). Furthermore, approximately 1 per cent of recreational tryptamine psychedelic (e.g., psilocybin, LSD) users report spontaneous grapheme-colour synaesthesia (Luke et al., 2012) and at least one case of verified drug-induced graphemecolour synaesthesia has been reported (Brang and Ramachandran, 2008). ...
... After ingestion of LSD, increased visual imagery with eyes closed has been reported to be associated with increased functional connectivity between the visual cortex and the parahippocampus (Kaelen et al. 2016). Music and sounds are most often reported to induce synesthesia, but tactile, gustatory, olfactory, or emotional stimuli can also induce synesthesia, with the stimuli primarily being translated to the visual domain (Sinke et al. 2012). An experience that is only found in drug-induced synesthesia is the perception of an altered body image (e.g., the body morphs in form and size) in response to visual, acoustical, or tactile stimuli (Sinke et al. 2012). ...
... Music and sounds are most often reported to induce synesthesia, but tactile, gustatory, olfactory, or emotional stimuli can also induce synesthesia, with the stimuli primarily being translated to the visual domain (Sinke et al. 2012). An experience that is only found in drug-induced synesthesia is the perception of an altered body image (e.g., the body morphs in form and size) in response to visual, acoustical, or tactile stimuli (Sinke et al. 2012). Additionally, synesthesia comprising more than one modality has been described. ...
... Leuner (1962) described a visual-tactil-olfactory synesthesia experience: One subject reported that the blue color of a visual stimulus was associated with the perception of an ozone-like smell and the feeling of being electrically shocked. In contrast to acquired and genuine synesthesias, drug-induced synesthesias are highly dynamic and more flexible and show a high inter-and intrapersonal variance (Sinke et al. 2012). This may be one reason why experimental studies investigating drug-induced synesthesias and their underlying neural processes are very rare (Brogaard 2013). ...
... Increased visual imagery with closed eyes after the intake of LSD has been reported to be associated with increased functional connectivity between the visual cortex and the parahippocampus (Kaelen et al. 2016). Music and sounds are most often reported to induce synesthesia, but also tactile, gustatory, olfactory, or emotional stimuli can be translated, mostly to the visual domain (Sinke et al. 2012). An experience which is only found in drug-induced synesthesia is the perception of an altered body image (e.g., the body morphs in form and size) induced by visual, acoustical, or tactile stimuli (Sinke et al. 2012). ...
... Music and sounds are most often reported to induce synesthesia, but also tactile, gustatory, olfactory, or emotional stimuli can be translated, mostly to the visual domain (Sinke et al. 2012). An experience which is only found in drug-induced synesthesia is the perception of an altered body image (e.g., the body morphs in form and size) induced by visual, acoustical, or tactile stimuli (Sinke et al. 2012). Additionally, synesthesia comprising more than one modality has been described. ...
... Leuner (1962) described a visual-tactil-olfactory synesthesia experience: One subject reported that the blue color of a visual stimulus was associated with the perception of an ozone-like smell and a feeling of being electrified. In contrast to acquired and genuine synesthesia, drug-induced synesthesia are highly dynamic, more flexible, and show a high inter-and intrapersonal variance (Sinke et al. 2012). This may be one reason why experimental studies investigating drug-induced synesthesia and their underlying neural processes are very rare (Brogaard 2013). ...
Classic serotonergic hallucinogens or psychedelics produce an Altered States of Consciousness (ASC) that is characterized by profound alterations in sensory perception, mood, thought including the perception of reality, and the sense of self. Over the past years, there has been considerable progress in the search for invariant and common features of psychedelic states. In the first part of this review, we outline contemporary approaches to characterize the structure of ASCs by means of three primary etiology-independent dimensions including Oceanic Boundlessness, Anxious Ego Dissolution, and Visionary Restructuralization as well as by 11 lower order factors, all of which can be reliably measured by the Altered State of Consciousness questionnaire (APZ-OAV). The second part sheds light on the dynamic nature of psychedelic experiences. Frequently, psychedelic subjects progresses through different stages over time and levels of changes along a perception-hallucination continuum of increasing arousal and ego dissolution. We then review in detail the acute effects of psychedelics on sensory perception, emotion, cognition, creativity, and time perception along with possible neural mechanisms underlying them. The next part of this review outlines the influence of non-pharmacological factors (predictors) on the acute psychedelic experience, such as demographics, genetics, personality, mood, and setting, and also discusses some long-term effects succeeding the acute experience. The last part presents some recent concepts and models attempting to understand different facets of psychedelic states of consciousness from a neuroscientific perspective.
... These findings indicate that enhanced color perception and vividly colored visual disturbances typically associated with hallucinogens are not simply a case of increased sensitivity to spectral properties. Such visual disturbances are thus better understood as involving drug-induced synesthesia (Brogaard, 2013;Shanon, 2002Shanon, , 2003Sinke et al., 2012;Studerus et al., 2011). ...
... Subjects treated with such drugs frequently report experiencing an altered perception of the world that blends sensory modalities that normally are informationally encapsulated. Colored music is the most frequently reported type of drug-induced synesthesia (Shanon, 2002(Shanon, , 2003Sinke et al., 2012;Studerus et al., 2011). ...
... Because drug-induced synesthesia is transiently induced, it is likely that its occurrence cannot be attributed to altered structural connectivity in the brain. Whereas developmental and acquired synesthesias involve morphological substrates , drug-induced synesthesia is probably linked to functional changes in brain activity (Brogaard, 2013;Carhart-Harris et al., 2012;Sinke et al., 2012), although it may also reinforce existing morphological structures (Brogaard, 2013). The fact that hallucinogens can produce novel types of synesthesia in developmental synesthetes seems to provide evidential support for these hypotheses (Simpson & McKellar, 1955). ...
Studies have shown that both serotonin and glutamate receptor systems play a crucial role in the mechanisms underlying drug-induced synesthesia. The specific nature of these mechanisms, however, continues to remain elusive. Here we propose two distinct hypotheses for how synesthesia triggered by hallucinogens in the serotonin agonist family may occur. One hypothesis is that the drug-induced destabilization of thalamic projections via ?-aminobutyric acidergic neuronal circuits from sensory areas leads to a disruption of low-level, spontaneous integration of multisensory stimuli. This sort of integration regularly occurs when spatial and temporal attributes match. Destabilization of feedback loops, however, can result in incongruent experiences or binding of random thalamus activation with sensory input in a particular sensory modality. The second hypothesis builds on embodied cognition, cases in which visual images of external stimuli activate task-related neural regions. In this proposal, binding processes that do not normally generate awareness become accessible to consciousness as a result of decreased attentional discrimination among incoming stimuli.
... The explanations for different kinds and types of synaesthesia could depend on distinct neurocognitive and psychological mechanisms (Afra, Funke, and Matsuo, 2009;Novich, Cheng, and Eagleman, 2011;Sinke et al., 2012). In accordance with the idea of the integrative or compensatory function, different kinds of synaesthesia could appear during various periods of human life that are critical for the development of perception (Rogowska, 2011). ...
... Thus, if synaesthetic experiences are felt as pleasant, and are often and willingly used for daily activities, they become more stable over time or even increase, whereas disagreeable synaesthetic experiences may be less consistent over time or decrease. Indeed, emotional synaesthetes (proposed by Emrich, Schneider, and Zedler as a subtype of synaesthesia, as cited in Sinke et al., 2012) seem to demonstrate a generally low consistency over time in synaesthetic associations. Their inducer-concurrent pairing changes (leading to a high intrapersonal variance) are due to the constant modulation of their current affective state. ...
... Their inducer-concurrent pairing changes (leading to a high intrapersonal variance) are due to the constant modulation of their current affective state. Moreover, in drug-induced synaesthesia, the visual concurrent is mainly modulated by the affective state of the intoxicated person (Sinke et al., 2012). ...
Synaesthesia is a fascinating cognitive phenomenon where one type of stimulation evokes the sensation of another. For example, synaesthetes might perceive colours when listening to music, or tastes in the mouth when reading words. This book provides an insight into the idiosyncratic nature of synaesthesia by exploring its relationships with other dimensions of individual differences. Many characteristics of linguistic-colour synaesthetes are covered including personality, temperament, intelligence, creativity, emotionality, attention, memory, imagination, colour perception, body lateralization and gender. Aleksandra Rogowska proposes that linguistic-colour synaesthesia can be considered as an abstract form of a continuous variable in the broader context of cross- and intra-modal associations. There has been a resurgence of interest in synaesthesia and this book will appeal to students and scientists of psychology, cognitive science and social science, and to those who are fascinated by unusual states of mind.
... De manière cohérente, les synesthètes graphème-couleur présentent une augmentation du volume de matière grise non seulement au niveau du gyrus fusiforme mais aussi au niveau du cortex pariétal (par ex., Weiss & Fink, 2009). Il est intéressant de noter que l'implication des aires pariétales n'est pas spécifique de la synesthésie graphème-couleur, mais a aussi été observée dans d'autres formes de synesthésie impliquant la couleur, comme l'audition colorée (Beeli, Esslen, & Jäncke, 2008 ;Jäncke & Langer, 2011 ;Neufeld et al., 2012 ;Nunn et al., 2002 ;Paulesu et al., 1995). ...
... Néanmoins, ces arguments sont sujets à caution. Ainsi, Sinke, Halpern, Zelder, Neufeld, Emrich et Passie (2012) ont récemment relevé que la synesthésie induite par les drogues diffère de la synesthésie développementale, car notamment elle ne présente pas de constance (ni sur le long terme ni après un re-test immédiat), n'est pas automatique et arbore une phénoménologie différente tant au niveau des inducteurs que des concurrents. De même, dans l'étude de Cohen Kadosh et al. (2009), il n'y a pas de preuves tangibles que les participants qui ont eu une expérience synesthésique lors d'une suggestion post-hypnotique aient vécu une expérience semblable à celle de véritables synesthètes. ...
Résumé Ces dernières années, l’étude de la synesthésie a pris de l’ampleur au sein de la communauté scientifique. Cet article passe en revue certains aspects essentiels de la synesthésie. Après une description de ce phénomène, nous nous intéressons à son objectivation et à ses origines développementales. Ensuite, grâce aux données issues de divers articles, nous tentons de déterminer si l’acquisition d’associations synesthésiques s’arrête un jour et si des personnes qui ne sont pas synesthètes peuvent apprendre à le devenir. Nous discutons aussi des bénéfices cognitifs éventuels de la synesthésie et de ce que peut apporter l’étude de ce phénomène à la compréhension plus générale de la cognition.
... However, these aspects are only strongly associated with the experience of synaesthesia and their requirement as diagnostic criteria remains open to debate [12][13][14]. The ambiguity in what constitutes a 'genuine' form of synaesthesia has contributed to the question of whether the genetic form (developmental synaesthesia) is a phenomenon distinct from acquired or drug-induced types, with each arising through unique neural mechanisms [12,15,16]. ...
... The strength of the SRS is that it can explain developmental and acquired/induced synaesthesias in the same framework. The main argument against acquired synaesthesia being genuine is its inconsistent nature [15]. The SRS rather highlights this aspect and emphasizes that synaesthetic associations are not fixed at onset and stabilize over the course of development in all forms of synaesthesia. ...
In synaesthesia, stimulation of one sensory modality evokes additional experiences in another modality (e.g. sounds evoking colours). Along with these cross-sensory experiences, there are several cognitive and perceptual differences between synaesthetes and non-synaesthetes. For example, synaesthetes demonstrate enhanced imagery, increased cortical excitability and greater perceptual sensitivity in the concurrent modality. Previous models suggest that synaesthesia results from increased connectivity between corresponding sensory regions or disinhibited feedback from higher cortical areas. While these models explain how one sense can evoke qualitative experiences in another, they fail to predict the broader phenotype of differences observed in synaesthetes. Here, we propose a novel model of synaesthesia based on the principles of stochastic resonance. Specifically, we hypothesize that synaesthetes have greater neural noise in sensory regions, which allows pre-existing multisensory pathways to elicit supra-threshold activation (i.e. synaesthetic experiences). The strengths of this model are (a) it predicts the broader cognitive and perceptual differences in synaesthetes, (b) it provides a unified framework linking developmental and induced synaesthesias, and (c) it explains why synaesthetic associations are inconsistent at onset but stabilize over time. We review research consistent with this model and propose future studies to test its limits.
This article is part of a discussion meeting issue ‘Bridging senses: novel insights from synaesthesia’.
... For example, instead of abnormal connections enabling sounds to evoke conscious visual experiences in synesthetes (as in the cross-activation model), this model argues that these connections are present in all individuals and that synesthetes have less inhibition restricting how strongly sounds modulate visual activity. This model is supported by evidence from drug-induced synesthesia, wherein synesthetic-like experiences occur almost immediately after drug-ingestion, in too short a time period for new neural pathways to be generated (Brang & Ramachandran, 2008;Brogaard, 2013;Sinke et al., 2012). However, several limitations have led researchers to question whether drug-induced synesthesias are the same as developmental forms (Luke & Terhune, 2013;Sinke et al., 2012;Terhune et al., 2016). ...
... This model is supported by evidence from drug-induced synesthesia, wherein synesthetic-like experiences occur almost immediately after drug-ingestion, in too short a time period for new neural pathways to be generated (Brang & Ramachandran, 2008;Brogaard, 2013;Sinke et al., 2012). However, several limitations have led researchers to question whether drug-induced synesthesias are the same as developmental forms (Luke & Terhune, 2013;Sinke et al., 2012;Terhune et al., 2016). Specifically, there are self-selection biases in who chooses to take hallucinogenics, questions about the reliability of self-reports during drug-use, as well as the inability to rigorously verify and parameterize synesthesia induced by drugs due to ethical concerns. ...
... Dreamlike floating experiences resembling the pre-sleep hypnagogic state, changes in perception and thinking abilities, auditory and visual hallucinations, vivid colours, abstract and kaleidoscopic patterns, human and animal forms, and distorted surroundings were described by many. Experienced users described management of these states by refocusing or opening the eyes (Sinke et al., 2012). Reduced environmental stimuli in the advised setting were viewed to contribute to a focused and enhanced experience of these hallucinatory and synesthetic effects (see Sinke et al., 2012). ...
... Experienced users described management of these states by refocusing or opening the eyes (Sinke et al., 2012). Reduced environmental stimuli in the advised setting were viewed to contribute to a focused and enhanced experience of these hallucinatory and synesthetic effects (see Sinke et al., 2012). Out of body and perceived near death experiences (Greyson, 2003) whilst frightening were viewed thereafter as life changing (Shanon, 2002). ...
... However, a systematic review of these studies revealed that they suffered from numerous methodological limitations including the absence of placebo controls and the failure to use established behavioural measures of different features of synaesthesia including automaticity, inducer specificity, and consistency of inducer-concurrent associations (Luke and Terhune, 2013). For these reasons, controversy persists as to whether these drug-induced experiences qualify as genuine synaesthesia (Deroy and Spence, 2013;Luke and Terhune, 2013;Sinke et al., 2012). ...
... Third, it is plausible that drug-induced synaesthesia-like experiences are superficially similar to, but qualitatively distinct from, congenital synaesthesia and thus should not be expected to meet standard criteria for the latter. The present results are consistent with this interpretation and the related claim that the mechanisms and characteristics of drug-induced synaesthesia-like experiences are different from those of congenital synaesthesia (Deroy and Spence, 2013;Hubbard and Ramachandran, 2003;Sinke et al., 2012). This interpretation is perhaps further bolstered by the fact that participants were able to detect which condition they were in (see below) and yet still did not display response patterns similar to congenital synaesthetes. ...
... However, this model is not supported by the testimony of synesthetes, who generally report not perceiving any effect of synesthetic experiences on their affective states. 32 The models above emphasize either an anatomical or a physiological hypothesis, although they are unable to exclude either. The physiological hypothesis also explains adventitious synesthesias, which occur because of a failure in the mechanism of feedback inhibition. ...
... Hubbard 4 highlights that experiences triggered by psychedelic drugs are different from synesthesia because they are usually relatively more complex, pointing to different mechanisms. This notion is supported by Sinke et al. 32 who, In their review article, compare the phenomenological characteristics of three types of synesthesias-congenital, acquired, and drug-induced-highlighting the much greater complexity and intensity of drug-induced synesthesias relative to congenital or acquired synesthesias. However, Cohen Kadosh et al. 33 induced experiences similar to the grapheme-color synesthesia in non-synesthetes, through post-hypnotic suggestion. ...
No presente trabalho de revisão, investigamos o cruzamento de sensações e sua relação com a percepção musical. Inicialmente, nos debruçamos sobre o estudos da sinestesia, sua definição, incidência, formas, fatores genéticos e de desenvolvimento. Abordamos ainda as teorias sobre as bases neurais da sinestesia, comparando teorias que enfatizam os aspectos anatômicos a outras que reforçam a importância de processos fisiológicos. Numa segunda seção tratamos dos cruzamentos de modos sensoriais, seu papel na percepção e sua relação com a sinestesia. Cogitamos haver um grau de sinestesia mais baixo e inconsciente em não sinestetas, esta sinestesia latente (sem manifestações sensoriais explícitas) seria funcional, auxiliando na construção de associações abstratas entre campos perceptivos diferentes. A significação musical talvez seja construída, em grande parte, por processos sinestésicos, em que as associações sensoriais a partir do sonoro ativam memórias, imagens e emoções.
... 30 Psychedelic substances commonly produce audiovisual synesthesia, that is music inducing dynamic images, shapes, or colors. 31 Synesthesia can less commonly occur between other sensory modalities. Even though the term "hallucinogen" is often used to classify substances like psilocybin, LSD, DMT, and mescaline, they are unlikely to cause hallucinations such as those classically described in psychotic disorders. ...
Psilocybin therapy has recently emerged as a promising new treatment for depression and other mental health disorders. This chapter summarizes the most recent data on its safety and efficacy. The delivery of psilocybin therapy and its subjective effects are also presented. Furthermore, this chapter outlines our current understanding of psilocybin’s pharmacology and neurobiological effects. Other similar psychedelic substances with encouraging therapeutic potential are briefly presented.
... Since the rst studies by Bleuler, few have addressed if synesthesia is linked to more widespread abnormalities in perception in neuropsychiatric subjects in understanding the mechanisms that mediate the development of a possible typical and atypical perceptual experience [52,53,102]. On the other hand, since the beginning of scienti c research on psychedelic drugs [103], numerous observations attest that a wide range of chemical substances elicit synesthesia with a possible implication of the serotonergic system [104,105]. We need further studies on developmental and acquired pathological conditions to understand the neurophysiological and neurochemical mechanisms underlying the synesthesia phenomenon. ...
Synesthesia gave rise to an important debate in nineteenth-century Europe that was influenced by the Symbolist movement and research into the physiology of perception. Yet, efforts to understand sensory modalities and to pictorially translate musical effects, or vice versa, are very ancient in origin. For example, the ability to coordinate colors and sounds was well known in the ancient cultures of India and China. Similarly, in sixth-century Greece, Pythagoras (570 BC–495 BC) assigned numbers as well as colors to musical notes. There was also interest in how the various sensory modalities were able to reveal the distinctive properties of an object and if these experiences could be translated or shared with others. This chapter examines the foundations of the nineteenth-century debate, the importance of the cultural aspect of synesthesia, and the subsequent search for a neurological explanation. As we show, the lively European debate included Italian, French, English, Swiss, and German scientists who were stimulated to study the relationship between color and sound, music and painting, and the creativity associated with synesthetes. Among the researchers discussed are Carlo Botta (1766–1837), Alfred Vulpian (1826–1887), Filippo Lussana (1820–1897), and Eugene Bleuler (1857–1939). The paper also looks at the three forms of synesthesia related to the debate (metaphoric, constitutional, and pathological) from both historical and contemporary perspectives. Finally, we examine the role of emotion in the various forms of musical synesthesia and possible neuronal well-being.KeywordsMusic synesthesiaEmotionBrainWell-being
... In some cases, synesthesia is acquired after brain damage (Ro et al., 2007), drug usage (Luke and Terhune, 2013) or sensory loss (Afra et al., 2009;Armel and Ramachandran, 1999). However, many synesthetes report having this kind of experiences since they can remember (Sinke et al., 2012), qualifying as cases of 'developmental synesthesia' (Ward, 2013). ...
Synesthesia represents an atypical merging of percepts, in which a given sensory experience (e.g., words, letters, music) triggers sensations in a different perceptual domain (e.g., color). According to recent estimates, the vast majority of the reported cases of synesthesia involve a visual experience. Purely non-visual synesthesia is extremely rare and to date there is no reported case of a congenitally blind synesthete. Moreover, it has been suggested that congenital blindness impairs the emergence of synesthesia-related phenomena such as multisensory integration and cross-modal correspondences between non-visual senses (e.g., sound-touch). Is visual experience necessary to develop synesthesia? Here we describe the case of a congenital blind man (CB) reporting a complex synesthetic experience, involving numbers, letters, months and days of the week. Each item is associated with a precise position in mental space and with a precise tactile texture. In one experiment we empirically verified the presence of number-texture and letter-texture synesthesia in CB, compared to non-synesthete controls, probing the consistency of item-texture associations across time and demonstrating that synesthesia can develop without vision. Our data fill an important void in the current knowledge on synesthesia and shed light on the mechanisms behind sensory crosstalk in the human mind.
... Psychedelics may induce visual imagery (334)(335)(336), distortions in the perception of time and space (337,338) and synaesthesia (339,340). Auditory and tactile perceptual changes occur less frequently but can occur at higher doses (210,341). The implications of alterations in these systems for personalized psychedelic therapy are not fully clear, though it is interesting to note the recent proof of concept study showing a role for psilocybin therapy in migraine suppression (17), a condition known to be associated with aberrant connections from the somatosensory cortex to the frontal lobe (342). ...
Accumulating clinical evidence shows that psychedelic therapy, by synergistically combining psychopharmacology and psychological support, offers a promising transdiagnostic treatment strategy for a range of disorders with restricted and/or maladaptive habitual patterns of emotion, cognition and behavior, notably, depression (MDD), treatment resistant depression (TRD) and addiction disorders, but perhaps also anxiety disorders, obsessive-compulsive disorder (OCD), Post-Traumatic Stress Disorder (PTSD) and eating disorders. Despite the emergent transdiagnostic evidence, the specific clinical dimensions that psychedelics are efficacious for, and associated underlying neurobiological pathways, remain to be well-characterized. To this end, this review focuses on pre-clinical and clinical evidence of the acute and sustained therapeutic potential of psychedelic therapy in the context of a transdiagnostic dimensional systems framework. Focusing on the Research Domain Criteria (RDoC) as a template, we will describe the multimodal mechanisms underlying the transdiagnostic therapeutic effects of psychedelic therapy, traversing molecular, cellular and network levels. These levels will be mapped to the RDoC constructs of negative and positive valence systems, arousal regulation, social processing, cognitive and sensorimotor systems. In summarizing this literature and framing it transdiagnostically, we hope we can assist the field in moving toward a mechanistic understanding of how psychedelics work for patients and eventually toward a precise-personalized psychedelic therapy paradigm.
... Alterations in tactile perception are often associated with changes in self-experience and body experience 111 . Usually, alterations in these domains are experienced as synaesthesia, with mostly auditory sti muli being translated to the visual domain 157 . Under the influence of LSD, music-evoked visual imagery has been related to increased effective connectivity from the parahippocampal cortex to the visual cortex, suggesting that an increase in top-down information on early sensory regions may contribute to psychedelic-induced changes in perception 158 . ...
Renewed interest in the use of psychedelics in the treatment of psychiatric disorders warrants a better understanding of the neurobiological mechanisms underlying the effects of these substances. After a hiatus of about 50 years, state-of-the art studies have recently begun to close important knowledge gaps by elucidating the mechanisms of action of psychedelics with regard to their effects on receptor subsystems, systems-level brain activity and connectivity, and cognitive and emotional processing. In addition, functional studies have shown that changes in self-experience, emotional processing and social cognition may contribute to the potential therapeutic effects of psychedelics. These discoveries provide a scientific road map for the investigation and application of psychedelic substances in psychiatry.
... One of the most common synesthesia types is sequence-color synesthesia where linguistic sequences such as letters, numbers, or weekdays induce sensations of color [1,2]. Four main characteristics define developmental (in contrast to acquired or pharmacologically induced) synesthesia [3]. First, presence since childhood. ...
Background:
Synesthesia is a sensory phenomenon where certain domain-specific stimuli trigger additional sensations of e.g. color or texture. The condition occurs in about 4% of the general population, but is overrepresented in individuals with Autism Spectrum Disorder (ASD), where it might also be associated with the presence of prodigious talents.
Case presentation:
Here we describe the case of a young transsexual man with Asperger Syndrome, synesthesia and a prodigious talent for foreign language acquisition. In our case, not only letters, numbers, spoken words, music, noises, weekdays and months lead to highly consistent, vivid color sensations but also his own and others' emotions, geometric shapes, any mathematical symbol, and letters from an unfamiliar alphabet (Hebrew). These color associations seem to aid categorization, differentiation and storage of information and might thereby contribute to the young man's language acquisition ability. We investigated the young man's structural brain connectivity in comparison to adults with or without ASD, applying global fiber tracking to diffusion-weighted Magnetic Resonance Imaging (MRI) data. The case presented with increased connectivity, especially between regions involved in visual and emotion processing, memory, and higher order associative binding regions. An electroencephalography experiment investigating synesthetic color and shape sensations while listening to music showed a negligible occipital alpha suppression, indicating that these internally generated synesthetic sensations derive from a different brain mechanism than when processing external visual information.
Conclusions:
Taken together, this case study endorses the notion of a link between synesthesia, prodigious talent and autism, adding to the currently still sparse literature in this field. It provides new insights into the possible manifestations of synesthesia in individuals with ASD and its potential contribution to prodigious talents in people with an otherwise unexceptional cognitive profile. Additionally, this case impressively illustrates how synesthesia can be a key element not only of sensory perception but also social and emotional processing and contributes to existing evidence of increased brain connectivity in association with synesthesia.
... For example, people with this capacity might be able to "hear the sound of a color" or "see the color of a flavor". This is a very rare condition observed only on people who either were born with it (genuine synesthesia), acquired it as a consequence from brain damage, or people who temporarily forced it by using drugs such as LSD (lysergic acid diethylamide), mescaline, and psilocybin [65]. The exact mechanisms of how stimuli in a sensory channel triggers a different channel are still unclear. ...
Immersion is a quality that turns user experiences more appealing, despite the definition of immersion itself still being a source of controversy. Modern electronic games became a well-established immersive media which already has a number of consumer-level virtual reality hardware and software available. Endowing a game with immersion requires not only theoretical background found in literature but more practical guidelines for assisting developers to glimpse possibilities and make design decisions. In this paper, we investigate specific features that bestow immersion to an electronic game. So, we first analyzed game titles the audience, the critics and developers themselves consider immersive in order to enumerate potentially immersive features found in these games. We then developed a potentially immersive game prototype based on these features. Results of a comparative evaluation of our prototype and the selected titles under different settings suggest that six features were able to provide an immersive experience.
... La sinestesia es algo que se puede confirmar y los métodos de verificación los veremos más adelante, por ello, una de las suposiciones más aceptadas sobre el origen de la sinestesia, es que esta condición es un proceso sensorial que nace de En esta monografía nos limitaremos casi exclusivamente a describir los procesos y características de un sinestesico genuino o constitucional, es decir, aquel con la condición desde su nacimiento, no obstante, es indispensable aclarar que el fenómeno no sólo esta determinado desde la infancia sino que al menos se reconocen otras dos clasificaciones, las cuales son los denominados sinestesicos adquiridos, quienes no nacen con el fenómeno pero que por algún accidente o cambio neuronal obtienen el fenómeno, y los llamados sinestesicos inducidos por fármacos, los cuales son personas no sinestésicas que al consumir algún estupefaciente como el LSD, psilocibina o mescalina experimentan sensaciones conjuntas (Sinke et al, 2012). ...
La sinestesia es una extraña condición que genera una interconexión entre
modalidades sensoriales. Una persona con este fenómeno puede ser capaz de ver
colores en los números, degustar las palabras, oler los sonidos, entre muchos otros
tipos. En esta monografía se analiza el origen histórico de la sinestesia lo que nos
revela como se ha ido reuniendo información al respecto y además se presentan los
orígenes biológicos de esta (teoría de la poda axónica). También se observan las
posibles diferencias que pueden existir entre los sinestésicos tanto en su
neuroanatomía como en la fisiología, donde se examinan los distintos modelos
neuronales actuales.
Se analiza también la prevalencia y la genética de la condición, dos aspectos muy
relacionados entre sí y con grandes diferencias entre los artículos científicos, dando
como resultado que aún no se puede establecer una prevalencia exacta ni concluir
una base genética evidente.
En la parte final de este trabajo se consideran las consecuencias que esta condición
genera en aquellos involucrados. Tanto por el escepticismo como por
desconocimiento sobre la existencia y por las características de la sinestesia en
general que producen una percepción diferente de la realidad.
La sinestesia, cuyo estudio se puede considerar como reciente, es de gran aporte
al fenómeno del conocimiento y la subjetividad, se necesita mayor investigación y
divulgación del tema debido a que aún nos falta mucho por entender sobre todo
desde el área médica.
Palabras clave: Sinestesia, color, diferencias, neuroanatomía, percepción.
... Acquired synaesthesia in adults is rare and has been reported in very different contexts: following psychotropic and drug ingestion (Luke & Terhune, 2013;Sinke et al., 2012), migraine (Alstadhaug & Benjaminsen, 2010;Podoll & Robinson, 2002), after neuropathology involving the optic nerve and/or chiasm (Afra, Funke, & Matsuo, 2009) or blindness (Armel & Ramachandran, 1999;Niccolai, Jennes, Stoerig, & Van Leeuwen, 2012), after a head injury (but without visible lesions on MRI) (Brogaard, Vanni, & Silvanto, 2013) or a thalamic stroke (Ro et al., 2007;Schweizer et al., 2013). In most cases, no focal brain lesion could be identified and the diversity of the cases makes a common neurological substrate unlikely. ...
Several studies pertaining to déjà vu have consistently made a connection with the perirhinal region, a region located below the hippocampus. This idea is strengthened by the fact that déjà vu is an erroneous sense of familiarity and that familiarity appears to largely depend on the perirhinal region in healthy subjects. In this context, the role of the hippocampus is particularly unclear as it is unknown whether or not it plays a role in the genesis of déjà vu. We report on the case of OHVR, an epileptic patient who suffers from severe episodic amnesia related to massive isolated bilateral damage to the hippocampus. In contrast, the perirhinal region is intact structurally and functionally. This patient reports frequent déjà vu but also another experiential phenomenon with a prominent feeling of prescience, which shows some of the characteristics of déjà vécu. She clearly distinguishes both. She also developed a form of synaesthesia by attributing affective valence to numbers. This study shows that déjà vu can occur in cases of amnesia with massively damaged hippocampi and confirms that the perirhinal region is a core region for déjà vu, using a different approach from previous reports. It also provides clues about a potential influence of hippocampal alterations in déjà vécu.
... Synaesthesia of this kind may be achieved by unmasking the previously mentioned cross-modal connections and by further building neural links between the modalities [29]. Synaesthesia can be induced by the use of psychedelic drugs [30], including psilocybin, which has been shown to increase the excitability of the neural networks bridging between sensory regions [31]. ...
Tens of millions of people live blind, and their number is ever increasing. Visual-to-auditory sensory substitution (SS) encompasses a family of cheap, generic solutions to assist the visually impaired by conveying visual information through sound. The required SS training is lengthy: months of effort is necessary to reach a practical level of adaptation. There are two reasons for the tedious training process: the elongated substituting audio signal, and the disregard for the compressive characteristics of the human hearing system. To overcome these obstacles, we developed a novel class of SS methods, by training deep recurrent autoencoders for image-to-sound conversion. We successfully trained deep learning models on different datasets to execute visual-to-auditory stimulus conversion. By constraining the visual space, we demonstrated the viability of shortened substituting audio signals, while proposing mechanisms, such as the integration of computational hearing models, to optimally convey visual features in the substituting stimulus as perceptually discernible auditory components. We tested our approach in two separate cases. In the first experiment, the author went blindfolded for 5 days, while performing SS training on hand posture discrimination. The second experiment assessed the accuracy of reaching movements towards objects on a table. In both test cases, above-chance-level accuracy was attained after a few hours of training. Our novel SS architecture broadens the horizon of rehabilitation methods engineered for the visually impaired. Further improvements on the proposed model shall yield hastened rehabilitation of the blind and a wider adaptation of SS devices as a consequence.
... Synaesthesia of this kind may be achieved by unmasking the previously mentioned cross-modal connections and by further building neural links between the modalities [29]. Synaesthesia can be induced by the use of psychedelic drugs [30], including psilocybin, which has been shown to increase the excitability of the neural networks bridging between sensory regions [31]. ...
Tens of millions of people live blind, and their number is ever increasing. Visual-to-auditory sensory substitution (SS) encompasses a family of cheap, generic solutions to assist the visually impaired by conveying visual information through sound. The required SS training is lengthy: months of effort is necessary to reach a practical level of adaptation. There are two reasons for the tedious training process: the elongated substituting audio signal, and the disregard for the compressive characteristics of the human hearing system.
To overcome these obstacles, we developed a novel class of SS methods, by training deep recurrent autoencoders for image-to-sound conversion. We successfully trained deep learning models on different datasets to execute visual-to-auditory stimulus conversion. By constraining the visual space, we demonstrated the viability of shortened substituting audio signals, while proposing mechanisms, such as the integration of computational hearing models, to optimally convey visual features in the substituting stimulus as perceptually discernible auditory components. We tested our approach in two separate cases. In the first experiment, the author went blindfolded for 5 days, while performing SS training on hand posture discrimination. The second experiment assessed the accuracy of reaching movements towards objects on a table. In both test cases, above-chance-level accuracy was attained after a few hours of training.
Our novel SS architecture broadens the horizon of rehabilitation methods engineered for the visually impaired. Further improvements on the proposed model shall yield hastened rehabilitation of the blind and a wider adaptation of SS devices as a consequence.
... The sensory-aesthetic experience is characterized by perceptual changes such as increased vividness of colours, appearance of movement of static objects, fractal and kaleidoscopic imagery, enhanced sensitivity to music, altered sense of touch and texture, altered body awareness, and synesthesia (Pahnke et al., 1970;Richards, 2008;Sinke et al., 2012). These types of effects can occur at lower doses and are common in recreational use where structured psychedelic administration as described here is unusual. ...
Humans have used serotonergic hallucinogens (i.e. psychedelics) for spiritual, ceremonial, and recreational purposes for thousands of years, but their administration as part of a structured therapeutic intervention is still a relatively novel practice within Western medical and psychological frameworks. In the mid-20th century, considerable advances were made in developing therapeutic approaches integrating administration of low (psycholytic) and high (psychedelic) doses of serotonergic hallucinogens for treatment of a variety of conditions, often incorporating psychoanalytic concepts prevalent at that time. This work contributed seminal insights regarding how these substances may be employed with efficacy and safety in targeted therapeutic interventions, including the importance of optimizing set (frame of mind) and setting (therapeutic environment). More recently, clinical and pharmacological research has revisited the effects and therapeutic potential of psychedelics utilizing a variety of approaches. The current article provides an overview of past and present models of psychedelic therapy, and discusses important considerations for future interventions incorporating the use of psychedelics in research and clinical practice.
... Synesthesia is a phenomenon in which one stimulated sensory percept is experienced as another sensory percept that is internally produced (Sinke et al. 2012). The prevalence of all known types was reported to be 4.4% (Simner et al. 2006), and it is classified into 3 different types, by etiology: developmental (symptoms appear in early childhood under genetic influences), acquired (e.g. ...
... Synesthesia is a phenomenon in which one stimulated sensory percept is experienced as another sensory percept that is internally produced (Sinke et al. 2012). The prevalence of all known types was reported to be 4.4% (Simner et al. 2006), and it is classified into 3 different types, by etiology: developmental (symptoms appear in early childhood under genetic influences), acquired (e.g. ...
... Psychedelic mental imagery can be modulated by both verbal (Carhart-Harris et al., 2015) and musical auditory stimuli. Synaesthesia (Ward, 2013) has been reported, especially visual phenomena driven by auditory stimuli-'Sounds influenced the things I saw'-but classification of these effects as 'true' synaesthesia is actively debated (Sinke et al., 2012;Brogaard, 2013;Luke and Terhune, 2013;Terhune et al., 2016). ...
How do psychedelic drugs produce their characteristic range of acute effects in perception, emotion, cognition, and sense of self? How do these effects relate to the clinical efficacy of psychedelic-assisted therapies? Efforts to understand psychedelic phenomena date back more than a century in Western science. In this article I review theories of psychedelic drug effects and highlight key concepts which have endured over the last 125 years of psychedelic science. First, I describe the subjective phenomenology of acute psychedelic effects using the best available data. Next, I review late 19th-century and early 20th-century theories—model psychoses theory, filtration theory, and psychoanalytic theory—and highlight their shared features. I then briefly review recent findings on the neuropharmacology and neurophysiology of psychedelic drugs in humans. Finally, I describe recent theories of psychedelic drug effects which leverage 21st-century cognitive neuroscience frameworks—entropic brain theory, integrated information theory, and predictive processing—and point out key shared features that link back to earlier theories. I identify an abstract principle which cuts across many theories past and present: psychedelic drugs perturb universal brain processes that normally serve to constrain neural systems central to perception, emotion, cognition, and sense of self. I conclude that making an explicit effort to investigate the principles and mechanisms of psychedelic drug effects is a uniquely powerful way to iteratively develop and test unifying theories of brain function.
... This latter notion is supported by the result that discontinuous, incongruent imaginary content in terms of plot, character, objects or actions accounted for the largest component of cognitive bizarreness during LSD (Fig. 2). Furthermore, this is supported by a growing body of literature (Sweat et al. 2016;Baggott 2015;Sessa 2008;Leuner 1973) indicating that psychedelics induce a state of broadened consciousness that is associated with a different cognitive style, including facilitated access to remote semantic associations (Family et al. 2016;Spitzer et al. 1996;Rittenhouse et al. 1994); cross-modal fusion between sensory modalities (synaesthesia), perception and feeling (physiognomic perception) and imagery and perception (eidetic imagery) (Terhune et al. 2016;Sinke et al. 2012;Glicksohn 1992); thinking in metaphors and symbols (Lakoff 1993;Martindale and Fischer 1977;Landon and Fischer 1970); enhanced problem-solving capabilities (Sio et al. 2013;Frecska et al. 2012;Wagner et al. 2004); and increased topographically long-range neuronal connectivity in the brain (Achermann et al. 2016;Petri et al. 2014;Massimini et al. 2010). Taken together, these findings suggest that creative thinking may be an important mechanism behind cognitive bizarreness, where there is increased binding of logically incompatible, but associatively remotely connected, features into new phenomenological Gestalts (Rittenhouse et al. 1994). ...
RationaleAccumulating evidence indicates that the mixed serotonin and dopamine receptor agonist lysergic acid diethylamide (LSD) induces an altered state of consciousness that resembles dreaming. Objectives
This study aimed to test the hypotheses that LSD produces dreamlike waking imagery and that this imagery depends on 5-HT2A receptor activation and is related to subjective drug effects. Methods
Twenty-five healthy subjects performed an audiorecorded guided mental imagery task 7 h after drug administration during three drug conditions: placebo, LSD (100 mcg orally) and LSD together with the 5-HT2A receptor antagonist ketanserin (40 mg orally). Cognitive bizarreness of guided mental imagery reports was quantified as a standardised formal measure of dream mentation. State of consciousness was evaluated using the Altered State of Consciousness (5D-ASC) questionnaire. ResultsLSD, compared with placebo, significantly increased cognitive bizarreness (p < 0.001). The LSD-induced increase in cognitive bizarreness was positively correlated with the LSD-induced loss of self-boundaries and cognitive control (p < 0.05). Both LSD-induced increases in cognitive bizarreness and changes in state of consciousness were fully blocked by ketanserin. ConclusionsLSD produced mental imagery similar to dreaming, primarily via activation of the 5-HT2A receptor and in relation to loss of self-boundaries and cognitive control. Future psychopharmacological studies should assess the differential contribution of the D2/D1 and 5-HT1A receptors to cognitive bizarreness.
... It is also possible to interpret the drug effects reported here as supporting the neurochemical account of synaesthesia, though the diversity of pathways involved suggests another interpretation. Previous reports on the pharmacology of synaesthesia have focused mainly on the range of hallucinogenic drugs that can induce audiovisual synaesthesia-like experiences in non-synaesthetes or enhance them in synaesthetes, with a smaller number of reports of drugs that modulate the experience of developmental synaesthesia (see Sinke et al., 2012; for a recent review). Several authors have noted that many of these drugs, most notably the hallucinogens LSD, psilocybin and mescaline, act by modulating serotonin signalling (see Luke & Terhune, 2013) even leading to the proposal that mutations in serotonin pathway genes might underlie the condition (Brang & Ramachandran, 2008). ...
Synaesthesia is a developmental condition involving cross-communication between sensory modalities or substreams whereby an inducer (e.g. a sound) automatically evokes a concurrent percept in another modality (e.g. a colour). Whether this condition arises due to atypical structural connectivity (e.g., between normally unconnected cortical areas) or altered neurochemistry remains a central question. We report the exceptional cases of two synaesthetes – subjects AB and CD – both of whom experience coloured auras around individuals, as well as coloured perceptions in response to music. Both subjects have, in recent years, suffered a complete loss or reduction of their synaesthetic experiences, one (AB) through successive head traumas, including a lightning strike, followed by a number of medications, and the other (CD) while taking anxiolytic medications. Using semi-structured interviews and data from the Synaesthesia Battery and a colourpicker task, we characterise the phenomenological characteristics of their pre-loss synaesthesia, as well as the subsequent restoration of each subject's synaesthetic experiences (in the months post-trauma for AB, and after cessation of medication for CD). Even after years of suppression, the patterns of associations were highly consistent with those experienced pre-injury. The phenomenological experience of synaesthesia can, thus, like most conscious experiences, be modulated by pharmacologically diverse medications or head injury. However, the underlying neural substrates mediating specific synaesthetic pairings appear remarkably “hard-wired” and can persist over very long periods even under conditions that alter or completely suppress the conscious synaesthetic experience itself. This article is protected by copyright. All rights reserved.
... Synaesthesia-like experiences have been previously reported during the use of the psychedelic drug LSD (Luke and Terhune, 2013;Sinke et al., 2012a), which has prompted researchers to suggest that no special anatomical connections are necessary to elicit synaesthesia (e.g. Grossenbacher and Lovelace, 2001), i.e., that we are all synaesthetes in a way. ...
... perceptions in the absence of external stimuli), illusions (i.e. perceptual distortion of normal environmental stimuli), and 'pseudo-hallucinations' (hallucinations recognized by the patient not to be the result of external stimuli) [113][114][115], together with intense emotional responses and thoughts that may influence the human psyche [116]. ...
Over the last decade, the ‘traditional’ drug scene has been supplemented – but not replaced – by the emergence of a range of novel psychoactive substances (NPS), which are either newly created or existing drugs, including medications, now being used in novel ways. By the end of 2014, in excess of 500 NPS had been reported by a large number of countries in the world. Most recent data show, however, that synthetic cathinones, synthetic cannabinoids, and psychedelics/phenethylamines account for the largest number of NPS.
The present chapter aims at providing an overview of the clinical and pharmacological issues relating to these most popular NPS categories. Given the vast range of medical and psychopathological issues associated with the molecules here described, it is crucial for health professionals to be aware of the effects and toxicity of NPS. A general overview of the acute management of NPS adverse events is provided as well, although further studies are required to identify a range of evidence-based, index molecule-focused, treatment strategies. The rapid pace of change in the NPS online market constitutes a major challenge to the provision of current and reliable scientific knowledge on these substances.
... The hypothesis that the synesthetic effect of psychedelic substances, such as LSD or psilocybin, could be due to aberrant feedback connections has been taken to provide further evidence for the disinhibited feedback hypothesis (Shanon, 2002; Sinke et al., 2012. It is unknown, however, whether druginduced synesthesia and developmental synesthesia have the same underlying mechanism, as the former differs from the latter in nearly every respect (Sinke et al., 2012). Even the very experience of druginduced synesthesia at the time at which it occurs appears notably different from most cases of developmental synesthesia. ...
The phenomenon of synesthesia has undergone an invigorationof research interest and empirical progress over the past decade. Studies investigating the cognitive mechanisms underlying the condition have yielded insight into neural processes behind such cognitive operations as attention, memory, spatial phenomenologyand cross-modal processes. However, the structural and functional mechanisms underlying synesthesia still remain contentiousand hypothetical. In this chapter, BeritBrogaard, Kristian Marlow, and Kevin Rice critically review recent research on grapheme-color synesthesia, one of the most common forms of the condition, and address the ongoingdebate concerning the role of selective attention in eliciting synesthetic experience.
... De manière cohérente, les synesthètes graphème-couleur présentent une augmentation du volume de matière grise non seulement au niveau du gyrus fusiforme mais aussi au niveau du cortex pariétal (par ex., Weiss & Fink, 2009). Il est intéressant de noter que l'implication des aires pariétales n'est pas spécifique de la synesthésie graphème-couleur, mais a aussi été observée dans d'autres formes de synesthésie impliquant la couleur, comme l'audition colorée (Beeli, Esslen, & Jäncke, 2008 ;Jäncke & Langer, 2011 ;Neufeld et al., 2012 ;Nunn et al., 2002 ;Paulesu et al., 1995). ...
These last few years, the study of synaesthesia gained in importance in the scientific community. In this article, we present some essential aspects of synaesthesia. After describing this phenomenon, we discuss how to measure it in an objective way and what are its developmental origins. Then, based on data from various articles, we try to determine if the acquisition of synaesthetic associations stops one day and if non-synaesthete people can learn to become synaesthetes. We also discuss the possible cognitive benefits of synaesthesia and how the study of this phenomenon contributes to the more general comprehension of cognition.
The concept of informational encapsulation has been important in promoting a view of the mind that has dominated cognitive science. Multisensory phenomena, such as synaesthesia, have been used as evidence for challenging this view. The main objective of this paper is to provide a more detailed understanding of the nature of such a challenge by examining the two types of grapheme–colour synaesthesia, projectors and associators. It is argued that the phenomena under consideration exemplify partial encapsulation failure and that it is expressed in three forms: intramodal, intermodal, and top-down. Additional support for these claims is provided by considering some evidence on synaesthetic-like experiences in relation to the continuity thesis.
Drawing on perspectives from music psychology, cognitive neuroscience, philosophy, musicology, clinical psychology, and music education, Music and Mental Imagery provides a critical overview of cutting-edge research on the various types of mental imagery associated with music. The four main parts cover an introduction to the different types of mental imagery associated with music such as auditory/musical, visual, kinaesthetic, and multimodal mental imagery; a critical assessment of established and novel ways to measure mental imagery in various musical contexts; coverage of different states of consciousness, all of which are relevant for, and often associated with, mental imagery in music, and a critical overview of applications of mental imagery in health, educational, and performance settings.
By both critically reviewing up-to-date scientific research and offering new empirical results, this book provides a unique overview of the different types and origins of mental imagery in musical contexts, various ways to measure them, and intriguing insights into related mental phenomena such as mind-wandering and synaesthesia. This will be of particular interest for scholars and researchers of music psychology and music education. It will also be useful for practitioners working with music in applied health and educational contexts.
There are global concerns about the proliferation and misuse of club drugs and novel psychoactive substances, yet we know little about their harms and research on clinical management and treatment remains limited. This book fills the knowledge gap by providing a detailed overview of the research evidence available to date. The book provides a framework that allows readers to understand this large number of new drugs, using classifications based on primary psychoactive effect. Within this framework, the book provides detailed reviews of the more commonly used drugs. Each chapter explores pharmacology, patterns and mode of use, acute and chronic harms, and clinical interventions supported by research evidence. An invaluable resource for clinical staff, this book will support clinicians working in the emergency department, substance misuse and addiction services, mental health services, primary care, sexual health services and more. It will also be of interest to academics and those developing drug policy.
All over the world, parents sing to their babies to soothe them and help them fall asleep. Among adults, the use of music as a sleep aid is also common, and research suggests that music can be effective for improving sleep in various populations with sleep problems. A number of studies have evaluated the effect of music on sleep in elderly persons with sleep problems, insomnia related to mental disorders, and hospitalized patients. These studies suggest a potential for the use of music as an intervention to improve sleep, even though the effect on objective sleep measures remains unclear. Music may facilitate sleep through relaxation, distraction, and mood regulation, and the mechanisms can be considered from a neurological, physiological, and psychological level. To improve sleep, it has been suggested that sleep music should be slow and predictable, but studies on the music people use to sleep show a large variation in genres, artists, and music characteristics.
Cerebral plasticity induced by visual loss represents a poorly understood field of neuroscience, with numerous questions that don’t yet have an answer. Central and peripheral vision, the evolutionary compromise between spatial resolution and the sampled space volume, are processed in distinct areas of the brain. Understanding the impact of vision loss in theses regions, is of utmost interest for the study of visual brain. Herein, in two models of retinal disorders affecting central and peripheral vision (namely Stargardt macular dystrophy and retinitis pigmentosa), we specifically investigated the effects of the central and peripheral visual loss on brain morphology and its functional connectivity. 1. Morphological plastic changes induced by central and peripheral visual loss. We explored the effects of visual loss on cortical thickness (CoTks) and cortical entropy (CoEn, marker of synaptic complexity) in the cytoarchytectonic regions of the occipital lobe. Central visual loss associated thinning in dorsal stream regions, while peripheral visual loss in early visual cortex (EVC) and regions belonging both to dorsal and ventral stream. Theses effects were unpredicted by the canonical view “central vision – ventral stream”, “peripheral vision – dorsal stream”. Normal CoEn in theses areas suggests that synaptic complexity is preserved in the remaining networks. Only central visual field loss presented CoEn alterations, namely an increase in areas involved in object recognition, that likely reflects a synaptic complexity enhancement in response to the loss of the high spatial resolution of central vision. The gain in synaptic complexity could mask neuronal loss due to deafferentation and may account for the CoTks normality. 2. Plastic changes in the functional connectivity of central and peripheral EVC. We explored and compared to normally afferented EVC, the functional connectivity of afferented and deafferented parts of EVC and found that central and peripheral visual loss induce different patterns of reorganization. Residually afferented early visual cortex reinforce local connections presumably to enhance the processing of altered visual input, while deafferented EVC strengthen long-range connections presumably to assist high-order functions. Combined structural and functional data indicate that areas with reduced CoTks superpose with several areas presenting reduced functional connectivity with the peripheral EVC and that areas with increased CoEn superpose with several areas presenting increased functional connectivity with afferented peripheral EVC. These data point that alterations of the sensory input to the peripheral field are more prone to induce plastic changes. Overview : Data in the current work provide an interesting perspective about the plasticity following central or peripheral visual field loss and show that it is more complex than the canonical model would have let to presume.
WPROWADZENIE
Chociaż zjawisko synestezji znane jest od kilkuset lat, w ostatniej dekadzie zainteresowanie synestezją przeżywa niezwykły rozkwit. Aktualnie badania nad synestezją prowadzone są w wielu ośrodkach na świecie, w perspektywie psychologii, kognitywistyki, neurologii, genetyki, medycyny, jak również muzyki, sztuk pięknych i literatury. Niniejsza publikacja wpisuje się w ten nurt rozważań. Przybliża polskiemu czytelnikowi po raz pierwszy światową literaturę naukową, wyjaśniając synestezję z punktu widzenia psychologii różnic indywidualnych, nauk poznawczych i neuropsychologii. Zjawisko synestezji jest tu ukazane z perspektywy nauki i sztuki. Przegląd współczesnych badań naukowych nad synestezją został uzupełniony opisem i analizą własnych doznań synestetycznych autorów niniejszej publikacji, którzy wykorzystują nierzadko synestezję do własnej twórczości artystycznej w dziedzinie muzyki, plastyki czy poezji. Subiektywny opis doświadczeń „z pierwszej ręki” łączy się tu z obiektywnym wglądem w naturę synestezji w perspektywie naukowej, co stanowić może nieocenioną wartość dla badacza tego zjawiska. Czytelnik może porównać też własne doznania z synestetyczną percepcją świata, opisywaną przez autorów tej książki, aby przekonać się, do jakiego stopnia możemy różnie postrzegać otaczający nas świat, jak niezwykłe są nasze zmysły i jak fascynująca może być próba odkrycia zagadki ludzkiego umysłu.
Psychologowie dostarczają wyjaśnień teoretycznych, opisując zjawisko, klasyfikując rozliczne rodzaje i typy synestezji, ukazując możliwości jej diagnozy, dokonując przeglądu badań empirycznych. Artyści dostarczają wskazówek praktycznych, opierając się na autorefleksji, studiach przypadków i wywiadach z wybitnymi synestetykami, co pomaga zrozumieć, jak funkcjonuje synestetyk na co dzień, jak wykorzystuje swoje specyficzne możliwości w procesie twórczym. W ten sposób niniejsza książka prezentuje syntetyczny opis zjawiska synestezji, który może zaciekawić zarówno ekspertów, jak i nieprofesjonalistów.
Pierwsza część publikacji przedstawia zjawisko synestezji w świetle badań psychologicznych. Justyna Skowronek w artykule „Czy jesteś synestetykiem? O rodzajach i diagnozowaniu synestezji” ukazuje ogromne zróżnicowanie sposobów przejawiania się synestezji i dokonuje próby usystematyzowania jej licznych typów. Artykuł ten wprowadza Czytelnika w tematykę synestezji, prezentując krótką historię psychologicznych badań nad naturą synestezji, jak również przegląd metod badawczych, wykorzystywanych do diagnozowania tego zjawiska.
Artykuł Karoliny Czerneckiej „Biologiczne podłoże synestezji” doskonale wpisuje się w dominujący nurt współczesnych badań nad synestezją w perspektywie neuropsychologicznej. Autorka dokonała analizy badań nad biologicznymi korelatami synestezji z wykorzystaniem technik neuroobrazowania. Celem przeglądu rozmaitych teorii i modeli funkcjonowania mózgu synestetyka jest wykrycie neuronalnych mechanizmów powstawania doświadczeń synestetycznych. Wyjaśnienie biologicznych podstaw różnic indywidualnych wśród synestetyków wymaga też prezentacji badań nad odziedziczalnością synestezji i wyznaczenia kierunków dalszych badań.
Zwieńczeniem tej części publikacji jest artykuł Aleksandry Rogowskiej, zatytułowany „Czy synestezja jest normalna?” Autorka prezentuje wyniki badań własnych nad zjawiskiem synestezji, rozumianej jako cecha ciągła z silnym i słabym natężeniem na obu biegunach. Na podstawie przeglądu badań z zakresu psychopatologii argumentuje, aby synestezję traktować jako zjawisko normalne o charakterze kompensacyjnym.
Część druga książki odnosi się do historii związków między synestezją a sztuką. Iryna I. Boyczuk, w swym artykule pt. „Synestezja jako klucz do poszerzonego odbioru, poznawania i twórczości” prezentuje zjawisko synestezji w kontekście sztuki muzycznej i filmowej. Autorka stawia tezę, iż synestezja stanowi jedną z form abstrakcyjnego asocjacyjnego myślenia twórczego, a wszystkie wywołujące ją zjawiska są wynikiem wzajemnych relacji i wpływu sfery poznawczo-sensorycznej oraz emocjonalnej człowieka. Przegląd teorii, opierających się na wielomodalnym spostrzeganiu natury świata, ukazuje synestezję jako naturalny wytwór ludzkiego myślenia i twórczości w dziedzinie artystycznej jak i naukowej.
Rozwinięciem teorii sztuki, wykorzystującej wielomodalną synestezję, jest praca Joanny Ganczarek, zatytułowana „Synestezja w malarstwie jako doświadczenie protomentalne”. Synestezja protomentalna jest stosowana jako środek artystyczny, polegający na integracji informacji wzrokowych i proprioceptywnych. Zgodnie z teorią prezentowaną przez Autorkę, pierwotna synestezyjna fuzja zmysłów stanowi podstawę bardziej złożonych procesów, prowadzących do głębszego doświadczenia dzieła sztuki poprzez włączenie specyficznych odczuć i emocji. Zaprezentowane tu współczesne teorie z pogranicza estetyki i psychologii, kładą nacisk na rolę synestezji w formowaniu ucieleśnionego przeżycia estetycznego.
W trzeciej części Czytelnik może zapoznać się z przejawami synestezji w literaturze pięknej. Anna Ginter w rozdziale „Barwne synestezje Vladimira Nabokova” dokonuje szczegółowej analizy językoznawczej rozmaitych dzieł słynnego pisarza, w kontekście jego doznań synestezyjnych. Jak wykazuje Autorka, barwa i wielomodalne skojarzenia odegrały ogromną rolę w twórczości literackiej Nabokova. Niezwykle ciekawe są metapoznawcze próby uchwycenia natury i mechanizmu swych doznań, zaprezentowane przez Nabokova w książkach autobiograficznych.
Przejawów synestezji poszukuje też Zuzanna Kozłowska w poezji Haliny Poświatowskiej. W artykule „Synestezyjna poezja Haliny Poświatowskiej” zaprezentowane są dzieła poetki, w których zaznacza się fundamentalna egzaltacja ciała oraz zmysłów. Autorka przedstawia liczne przykłady synestetycznej sensualizacji mowy, pisma, emocji i czasu w twórczości Haliny Poświatowskiej. Synestezyjne splątanie zmysłów potęguje i pogłębia doznawanie rzeczywistości. Jak twierdzi Zuzanna Kozłowska, „synestezja staje się w poezji Poświatowskiej hiperbolą samego istnienia w świecie”.
Przykłady wykorzystania synestezji we własnej twórczości artystycznej stanowią zawartość ostatniej części tej publikacji. Cykl otwiera artykuł Szymona S. Strzelca i Anny Sztwiertni pt. „Tysiące odcieni czerni. Synestezja wielomodalna jako mechaniczna podstawa rozumienia w komunikacji i twórczości artystycznej”. Szymon Strzelec opisuje własne doznania synestezyjne w kontekście pracy kompozytorskiej. Autorzy przedstawiają wyniki własnego eksperymentu artystycznego, w którym muzyka, skomponowana przez Szymona Strzelca, została przetworzona na język graficzny przez Annę Sztwiertnię. Synestezja jest tu widziana jako jeden z głównych katalizatorów postępu twórczości w epoce wczesnego posthumanizmu.
W artykule „Barwna emanacja sztuki. Wykorzystanie polimodalnej synestezji w twórczości muzycznej i poetyckiej” Monika Kozakiewicz ukazuje zjawisko synestezji w twórczości kompozytorskiej Aleksandra Skriabina i Oliviera Messiaena. Synestezja nie zawsze pozytywnie wpływa na twórczość i codzienne życie, jak wynika z przeglądu studiów przypadków pacjentów Olivera Sacksa. Autorka przedstawia też przykłady przenikania wielomodalnych wrażeń synestetycznych do własnej twórczości muzycznej i poetyckiej, nadając doświadczeniom estetycznym nowego wymiaru.
Artykuł Marty Mołodyńskiej-Wheeler, pt. „Synestezja – implikacje praktyczne w pracy muzyka i anglisty” jest swoistym „studium własnego przypadku”. Autorka przytacza liczne opisy własnych doznań synestezyjnych (językowych i muzycznych), jak również podaje wiele przykładów wykorzystywania synestezji w nauce języków obcych, zapamiętywaniu ważnych informacji i interpretacji utworów muzycznych. Niekiedy też synestezja prowadzi do zamieszania czy chaosu informacyjnego, prowokując dyskusję nad przydatnością tego zjawiska w codziennym życiu.
Niniejsza monografia jest jedną z nielicznych polskich publikacji na temat synestezji. Do zapoznania się z jej zawartością zachęcamy psychologów, pedagogów, artystów, osoby zainteresowane niezwykłymi zjawiskami percepcyjnymi oraz samych synestetyków. Mamy nadzieję, że książka ta przybliży szerokiemu gronu polskich czytelników to fascynujące zjawisko, jakim jest synestezja.
dr hab. Aleksandra Rogowska, prof. UO
Instytut Psychologii, Uniwersytet Opolski
dr Julia Kaleńska-Rodzaj,
Katedra Psychologii, Uniwersytet Pedagogiczny w Krakowie,
Krakowski Ośrodek Doradztwa dla Artystów "KODA"
Creative Dissociation: the artist’s “trip”. A consensual hallucination experienced
by surrendering to the oblivion of consciousness: a hallucinatory “trip” into the
depths of the unconscious, undertaken by the Artist in the dangerous attempt to reach
with no certainty a state of “higher” inspiration and mystical illumination, letting
hallucinations and inner visions emerge from the lysergic mists of a chemical ecstasy
up to reveal the unfathomable mystery of the artistic creation, sublime mirage in the
obscure desert of the being. A break in the fine consciousness veil looking for an irrational,
but extremely revealing ecstasy: this paper (in Italian) discusses the effects of drugs on artistic
creativity, based on the latest findings in the field of brain biochemistry and
neuroaesthetics.
This Doctoral Dissertation (in Italian) presents a new research hypothesis about the Psychic Phenomena in Art (so-called 'Mediumistic Art'), providing a different interpretation to creative dissociation and artistic automatisms that characterize these particular manifestations of Abnormal Psychology, and demonstrating the neuroscientific and psychobiological bases of such phenomena.
Synesthetic-pseudosynesthetic characteristics have been hypothesized to be a schizophrenia endophenotype, a developmental feature, and/or a symptom of psychosis. Few studies to date, however, have examined whether individuals at risk for psychosis have synesthetic symptoms. We examined the relationship between hue and pitch in high psychosis prone (HP; n = 30) and low psychosis prone individuals (LP; n = 31). Synesthesia was evaluated using self-report and two performance-based tasks. Results revealed that HP subjects experienced more synesthetic experiences than the LP only on the self-report measure. These results suggest that high psychotic prone patients report unusual experiences but are no more likely to exhibit synesthesia than LP individuals. HP individuals, however, were more likely to choose shorter wavelength colors than LP individuals on performance tasks. These results are consistent with the notion that psychosis vulnerability is associated with a preference to light wavelengths associated with increasing emotional valence and negative affect.
Synesthesia is a condition in which features that ordinarily are processed by distinct perceptual or cognitive streams are bound together in a single stream, yielding an aberrant perceptual, image-like or thought-like experience. One of the most common forms of synesthesia is grapheme-color synesthesia. It is divided into two distinct forms: Projector synesthesia, which tends to be perception-like, and associator synesthesia, which tends to be more like imagery or thought. There has been an ongoing debate in philosophy about whether synesthesia can provide any insight into the philosophical question of the nature of perception. I argue here that at least some forms of projector synesthesia provide a challenge for reductive representationalism, the view that the phenomenal properties of perceptual experience is exhausted by an externalist, representational content. I conclude by arguing that a rejection of representationalism does not saddle us with a peculiar qualia view.
In her response to my “Seeing as a Non-Experiental Mental State: The Case from Synesthesia and Visual Imagery” Ophelia Deroy presents an argument for an interesting new account of synesthesia. On this account, synesthesia can be thought of as “a perceptual state (e.g. of a letter)” that is “changed or enriched by the incorporation of a conscious mental image (e.g. a color).” Deroy argues convincingly that Perky cases, in which the content of visual imagery is partially constituted by the content of perceptual experience, possibly are best understood as incorporated, or mixed, mental states (Deroy, Chap. 27, this volume; Perky 1910). But even if Perky cases are not truly mixed conscious states, Deroy argues, it is quite plausible that some of our mental states have perceptual as well as imagistic elements. Cases of synesthesia are good candidates to be exactly these kinds of mixed states.
Recent research into synaesthesia has highlighted the role of learning, yet synaesthesia is clearly a genetic condition. Here we ask how can the idea that synaesthesia reflects innate, genetic differences be reconciled with models that suggest it is driven by learning. A number of lines of evidence suggest that synaesthesia relies on, or at least interacts with, processes of multisensory integration that are common across all people. These include multisensory activations that arise in early regions of the brain as well as feedback from longer-term cross-modal associations generated in memory. These cognitive processes may interact independently to influence the phenomenology of the synaesthetic experience, as well as the individual differences within particular types of synaesthesia. The theoretical framework presented here is consistent with both an innate difference as the fundamental driver of the condition of synaesthesia, and with experiential and semantic influences on the eventual phenotype that emerges. In particular, it proposes that the internally generated synaesthetic percepts are treated similarly to other sensory information as the brain is learning the multisensory attributes of objects and developing cross-modal associations that merge in the concept of the object.
Copyright © 2015. Published by Elsevier Ltd.
Synesthesia is experienced when sensory stimulation of one sensory modality (the inducer) elicits an involuntary or automatic sensation in another sensory modality or different aspect of the same sensory modality (the concurrent). Auditory synesthesias (AS) occur when auditory stimuli trigger a variety of concurrents, or when non-auditory sensory stimulations trigger auditory synesthetic perception. The AS are divided into three types: developmental, acquired, and induced. Developmental AS are not a neurologic disorder but a different way of experiencing one's environment. They are involuntary and highly consistent experiences throughout one's life. Acquired AS have been reported in association with neurologic diseases that cause deafferentation of anterior optic pathways, with pathologic lesions affecting the central nervous system (CNS) outside of the optic pathways, as well as non-lesional cases associated with migraine, and epilepsy. It also has been reported with mood disorders as well as a single idiopathic case. Induced AS has been reported in experimental and postsurgical blindfolding, as well as intake of hallucinogenics or psychedelics. In this chapter the three different types of synesthesia, their characteristics, and phenomologic differences, as well as their possible neural mechanisms are discussed.
© 2015 Elsevier B.V. All rights reserved.
We investigated grapheme--colour synaesthesia and found that: (1) The induced colours led to perceptual grouping and pop-out, (2) a grapheme rendered invisible through `crowding' or lateral masking induced synaesthetic colours --- a form of blindsight --- and (3) peripherally presented graphemes did not induce colours even when they were clearly visible. Taken collectively, these and other experiments prove conclusively that synaesthesia is a genuine perceptual phenomenon, not an effect based on memory associations from childhood or on vague metaphorical speech. We identify different subtypes of number--colour synaesthesia and propose that they are caused by hyperconnectivity between colour and number areas at different stages in processing; lower synaesthetes may have cross-wiring (or cross-activation) within the fusiform gyrus, whereas higher synaesthetes may have cross-activation in the angular gyrus. This hyperconnectivity might be caused by a genetic mutation that causes defective pruning of connections between brain maps. The mutation may further be expressed selectively (due to transcription factors) in the fusiform or angular gyri, and this may explain the existence of different forms of synaesthesia. If expressed very diffusely, there may be extensive cross-wiring between brain regions that represent abstract concepts, which would explain the link between creativity, metaphor and synaesthesia (and the higher incidence of synaesthesia among artists and poets). Also, hyperconnectivity between the sensory cortex and amygdala would explain the heightened aversion synaesthetes experience when seeing numbers printed in the `wrong' colour. Lastly, kindling (induced hyperconnectivity in the temporal lobes of temporal lobe epilepsy [TLE] patients) may explain the purp...
In this article, the authors introduce a new theoretical framework for understanding intersensory development. Their approach is based upon insights gained from adults who experience synesthesia, in whom sensory stimuli induce extra cross-modal or intramodal percepts. Synesthesia appears to represent one way that typical developmental mechanisms can play out by magnifying connections present in early life that are pruned and/or inhibited during development but persist in muted form in all adults. As such, the study of synesthesia provides valuable insights into the nature of intersensory development. The authors review evidence on the perceptual reality and neural basis of synesthesia, then summarize developmental models and evidence that its underlying mechanisms are universal in adults. They illustrate how evidence for consistent sensory associations in adults leads to predictions about toddlers’ perception and present 3 bodies of work that have confirmed those hypotheses. They end by describing novel hypotheses about intersensory development that arise from this framework. Such intersensory associations appear to reflect intrinsic sensory cortical organization that influences the development of perception and of language and that may constrain the learning of environmentally based associations.
In this review, we distinguish strong and weak forms of synesthesia. Strong synesthesia is characterized by a vivid image in one sensory modality in response to stimulation in another one. Weak synesthesia is characterized by cross-sensory correspondences expressed through language, perceptual similarity, and perceptual interactions during information processing. Despite important phenomenological dissimilarities between strong and weak synesthesia, we maintain that the two forms draw on similar underlying mechanisms. The study of strong and weak synesthetic phenomena provides an opportunity to enrich scientists' understanding of basic mechanisms involved in perceptual coding and cross-modal information processing.
Synesthesia is experienced when sensory stimulation of one sensory modality elicits an involuntary sensation in another sensory modality. Auditory-visual synesthesia occurs when auditory stimuli elicit visual sensations. It has developmental, induced and acquired varieties. The acquired variety has been reported in association with deafferentation of the visual system as well as temporal lobe pathology with intact visual pathways. The induced variety has been reported in experimental and post-surgical blindfolding, as well as intake of hallucinogenic or psychedelics. Although in humans there is no known anatomical pathway connecting auditory areas to primary and/or early visual association areas, there is imaging and neurophysiologic evidence to the presence of early cross modal interactions between the auditory and visual sensory pathways. Synesthesia may be a window of opportunity to study these cross modal interactions. Here we review the existing literature in the acquired and induced auditory-visual synesthesias and discuss the possible neural mechanisms.
This review focuses on recent brain imaging and behavioral studies of sensory gating functions, which assess similarities between the effects of classic hallucinogens (eg, psilocybin), dissociative anesthetics (eg, ketamine), and entactogens (eg, 3,4-methylenedioxymethamphetamine [MDMA]) in humans. Serotonergic hallucinogens and psychotomimetic anesthetics produce overlapping psychotic syndromes associated with a marked activation of the prefrontal cortex (hyperfrontality) and other overlapping changes in temporoparietal, striatal, and thalamic regions, suggesting that both classes of drugs act upon a common final pathway. Together with the observation that both hallucinogens and N-methyl-oaspartate (NMDA) antagonists disrupt sensory gating in rats by acting on 5-hydroxytryptamine (serotonin) 5-HT(2) receptors located in cortico-striato-thalamic circuitry these findings suggest that disruption of cortico-subcortical processing leading to sensory overload of the cortex is a communality of these psychoses. In contrast to hallucinogens, the entactogen MDMA produces an emotional state of positive mood, concomitant with an activation of prefrontolimbiclparalimbic structures and a deactivation of amygdala and thalamus.
Despite a recent upsurge of research, much remains unknown about the neurobiological mechanisms underlying synaesthesia. By integrating results obtained so far in Magnetic Resonance Imaging (MRI) studies, this contribution sheds light on the role of particular brain regions in synaesthetic experiences. First, in accordance with its sensory nature, it seems that the sensory brain areas corresponding to the type of synaesthetic experience are activated. Synaesthetic colour experiences can activate colour regions in occipito-temporal cortex, but this is not necessarily restricted to V4. Furthermore, sensory and motor brain regions have been obtained that extend beyond the particular type of synaesthesia studied. Second, differences in experimental setup, number and type of synaesthetes tested, and method to delineate regions of interest may help explain inconsistent results obtained in the BOLD-MRI (Blood Oxygen Level Dependent functional MRI) studies. Third, an overview of obtained results shows that a network of brain areas rather than a single brain region underlies synaesthesia. Six brain regions of overlapping results emerge, these regions are in sensory and motor regions as well as 'higher level' regions in parietal and frontal lobe. We propose that these regions are related to three different cognitive processes inherently part of synaesthesia; the sensory processes, the (attentional) 'binding' processes, and cognitive control processes. Finally, we discuss how these functional and structural brain properties might relate to the development of synaesthesia. In particular, we believe this relationship is better understood by separating the question what underlies the presence of synaesthesia ('trait') from what determines particular synaesthetic associations ('type').
The subjective experience of color by synesthetes when viewing achromatic letters and numbers supposedly relates to real color experience, as exemplified by the recruitment of the V4 color center observed in some brain imaging studies. Phenomenological reports and psychophysics tests indicate, however, that both experiences are different. Using functional magnetic resonance imaging, we tried to precise the degree of coactivation by real and synesthetic colors, by evaluating each color center individually, and applying adaptation protocols across real and synesthetic colors. We also looked for structural differences between synesthetes and nonsynesthetes. In 10 synesthetes, we found that color areas and retinotopic areas were not activated by synesthetic colors, whatever the strength of synesthetic associations measured objectively for each subject. Voxel-based morphometry revealed no white matter (WM) or gray matter difference in those regions when compared with 25 control subjects. But synesthetes had more WM in the retrosplenial cortex bilaterally. The joint coding of real and synesthetic colors, if it exists, must therefore be distributed rather than localized in the visual cortex. Alternatively, the key to synesthetic color experience might not lie in the color system.
Synesthesia provides an elegant model to investigate neural mechanisms underlying individual differences in subjective experience in humans. In grapheme-color synesthesia, written letters induce color sensations, accompanied by activation of color area V4. Competing hypotheses suggest that enhanced V4 activity during synesthesia is either induced by direct bottom-up cross-activation from grapheme processing areas within the fusiform gyrus, or indirectly via higher-order parietal areas. Synesthetes differ in the way synesthetic color is perceived: "projector" synesthetes experience color externally colocalized with a presented grapheme, whereas "associators" report an internally evoked association. Using dynamic causal modeling for fMRI, we show that V4 cross-activation during synesthesia was induced via a bottom-up pathway (within fusiform gyrus) in projector synesthetes, but via a top-down pathway (via parietal lobe) in associators. These findings show how altered coupling within the same network of active regions leads to differences in subjective experience. Our findings reconcile the two most influential cross-activation accounts of synesthesia.
Synesthesia is a perceptual phenomenon in which stimuli in one particular modality elicit a sensation within the same or another sensory modality (e.g., specific graphemes evoke the perception of particular colors). Grapheme-color synesthesia (GCS) has been proposed to arise from abnormal local cross-activation between grapheme and color areas because of their hyperconnectivity. Recently published studies did not confirm such a hyperconnectivity, although morphometric alterations were found in occipitotemporal, parietal, and frontal regions of synesthetes. We used magnetic resonance imaging surface-based morphometry and graph-theoretical network analyses to investigate the topology of structural brain networks in 24 synesthetes and 24 nonsynesthetes. Connectivity matrices were derived from region-wise cortical thickness correlations of 2366 different cortical parcellations across the whole cortex and from 154 more common brain divisions as well. Compared with nonsynesthetes, synesthetes revealed a globally altered structural network topology as reflected by reduced small-worldness, increased clustering, increased degree, and decreased betweenness centrality. Connectivity of the fusiform gyrus (FuG) and intraparietal sulcus (IPS) was changed as well. Hierarchical modularity analysis revealed increased intramodular and intermodular connectivity of the IPS in GCS. However, connectivity differences in the FuG and IPS showed a low specificity because of global changes. We provide first evidence that GCS is rooted in a reduced small-world network organization that is driven by increased clustering suggesting global hyperconnectivity within the synesthetes' brain. Connectivity alterations were widespread and not restricted to the FuG and IPS. Therefore, synesthetic experience might be only one phenotypic manifestation of the globally altered network architecture in GCS.
In the current study, we explored the influence of synesthesia on memory for word lists. We tested 10 grapheme-color synesthetes who reported an experience of color when reading letters or words. We replicated a previous finding that memory is compromised when synesthetic color is incongruent with perceptual color. Beyond this, we found that, although their memory for word lists was superior overall, synesthetes did not exhibit typical color- or semantic-defined von Restorff isolation effects (von Restorff, 1933) compared with control participants. Moreover, our synesthetes exhibited a reduced Deese-Roediger-McDermott false memory effect (Deese, 1959; Roediger & McDermott, 1995). Taken as a whole, these findings are consistent with the idea that color-grapheme synesthesia can lead people to place a greater emphasis on item-specific processing and surface form characteristics of words in a list (e.g., the letters that make them up) relative to relational processing and more meaning-based processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved).
This study shows that biases exist in the associations of letters with colours across individuals both with and without grapheme-colour synaesthesia. A group of grapheme-colour synaesthetes were significantly more consistent over time in their choice of colours than a group of controls. Despite this difference, there were remarkable inter-subject agreements, both within and across participant groups (e.g., a tends to be red, b tends to be blue, c tends to be yellow). This suggests that grapheme-colour synaesthesia, whilst only exhibited by certain individuals, stems in part from mechanisms that are common to us all. In addition to shared processes, each population has its own distinct profile. Synaesthetes tend to associate higher frequency graphemes with higher frequency colour terms. For control participants, choices are influenced by order of elicitation, and by exemplar typicality from the semantic class of colours.
This study reports a synaesthete, GW, who experiences synaesthetic colours in response to a limited range of stimuli-namely those that have an emotional connotation. GW is significantly more consistent than a group of controls, and shows a Stroop-like congruency effect when the text colour differs from that reported for her synaesthetic photisms. The names of people who are known personally to GW are more likely to induce a synaesthetic colour than names referring to people with whom she is not personally acquainted and other categories of word (including colour names themselves). This feature resembles a number of reports in the historical literature on synaesthesia. This is explained by the fact that these stimuli are more likely to elicit an emotional response. In support of this, other words that have an emotional connotation (e.g., "love") have a tendency to elicit a synaesthetic response. The valence of the emotion (positive vs. negative) may have some role to play in determining the colour of the stimulus. It is concluded that emotion-colour synaesthesia is a genuine, if unusual, form of synaesthesia.
Psilocybin and related hallucinogenic compounds are increasingly used in human research. However, due to limited information about potential subjective side effects, the controlled medical use of these compounds has remained controversial. We therefore analysed acute, short- and long-term subjective effects of psilocybin in healthy humans by pooling raw data from eight double-blind placebo-controlled experimental studies conducted between 1999 and 2008. The analysis included 110 healthy subjects who had received 1-4 oral doses of psilocybin (45-315 µg/kg body weight). Although psilocybin dose-dependently induced profound changes in mood, perception, thought and self-experience, most subjects described the experience as pleasurable, enriching and non-threatening. Acute adverse drug reactions, characterized by strong dysphoria and/or anxiety/panic, occurred only in the two highest dose conditions in a relatively small proportion of subjects. All acute adverse drug reactions were successfully managed by providing interpersonal support and did not need psychopharmacological intervention. Follow-up questionnaires indicated no subsequent drug abuse, persisting perception disorders, prolonged psychosis or other long-term impairment of functioning in any of our subjects. The results suggest that the administration of moderate doses of psilocybin to healthy, high-functioning and well-prepared subjects in the context of a carefully monitored research environment is associated with an acceptable level of risk.
Background:
The OAV questionnaire has been developed to integrate research on altered states of consciousness (ASC). It measures three primary and one secondary dimensions of ASC that are hypothesized to be invariant across ASC induction methods. The OAV rating scale has been in use for more than 20 years and applied internationally in a broad range of research fields, yet its factorial structure has never been tested by structural equation modeling techniques and its psychometric properties have never been examined in large samples of experimentally induced ASC.
Methodology/principal findings:
The present study conducted a psychometric evaluation of the OAV in a sample of psilocybin (n = 327), ketamine (n = 162), and MDMA (n = 102) induced ASC that was obtained by pooling data from 43 experimental studies. The factorial structure was examined by confirmatory factor analysis, exploratory structural equation modeling, hierarchical item clustering (ICLUST), and multiple indicators multiple causes (MIMIC) modeling. The originally proposed model did not fit the data well even if zero-constraints on non-target factor loadings and residual correlations were relaxed. Furthermore, ICLUST suggested that the "oceanic boundlessness" and "visionary restructuralization" factors could be combined on a high level of the construct hierarchy. However, because these factors were multidimensional, we extracted and examined 11 new lower order factors. MIMIC modeling indicated that these factors were highly measurement invariant across drugs, settings, questionnaire versions, and sexes. The new factors were also demonstrated to have improved homogeneities, satisfactory reliabilities, discriminant and convergent validities, and to differentiate well among the three drug groups.
Conclusions/significance:
The original scales of the OAV were shown to be multidimensional constructs. Eleven new lower order scales were constructed and demonstrated to have desirable psychometric properties. The new lower order scales are most likely better suited to assess drug induced ASC.
Background:
In synaesthesia, sensations in a particular modality cause additional experiences in a second, unstimulated modality (e.g., letters elicit colour). Understanding how synaesthesia is mediated in the brain can help to understand normal processes of perceptual awareness and multisensory integration. In several neuroimaging studies, enhanced brain activity for grapheme-colour synaesthesia has been found in ventral-occipital areas that are also involved in real colour processing. Our question was whether the neural correlates of synaesthetically induced colour and real colour experience are truly shared.
Methodology/principal findings:
First, in a free viewing functional magnetic resonance imaging (fMRI) experiment, we located main effects of synaesthesia in left superior parietal lobule and in colour related areas. In the left superior parietal lobe, individual differences between synaesthetes (projector-associator distinction) also influenced brain activity, confirming the importance of the left superior parietal lobe for synaesthesia. Next, we applied a repetition suppression paradigm in fMRI, in which a decrease in the BOLD (blood-oxygenated-level-dependent) response is generally observed for repeated stimuli. We hypothesized that synaesthetically induced colours would lead to a reduction in BOLD response for subsequently presented real colours, if the neural correlates were overlapping. We did find BOLD suppression effects induced by synaesthesia, but not within the colour areas.
Conclusions/significance:
Because synaesthetically induced colours were not able to suppress BOLD effects for real colour, we conclude that the neural correlates of synaesthetic colour experience and real colour experience are not fully shared. We propose that synaesthetic colour experiences are mediated by higher-order visual pathways that lie beyond the scope of classical, ventral-occipital visual areas. Feedback from these areas, in which the left parietal cortex is likely to play an important role, may induce V4 activation and the percept of synaesthetic colour.
Little is known about how the properties of our private mental world relate to the physical and functional properties of our brain. Studying synesthesia, where a particular experience evokes a separate additional sensory experience, offers the unique opportunity to study phenomenological experiences as a stable trait in healthy subjects. A common form of synesthesia is grapheme-color synesthesia, where a particular letter or number evokes a particular color experience. We studied the neural basis of qualitative different properties of the synesthetic experience by using individual differences in grapheme-color synesthesia. Specifically, the synesthetic color can be experienced "in the mind" (associator synesthetes) or "in the outside world" (projector synesthetes). Gray matter structure and functioning (imaged using voxel-based morphometry and functional magnetic resonance imaging, respectively) were examined in grapheme-color synesthetes (N = 42, 16 projectors and 26 associators) and nonsynesthetes. Results indicated partly shared mechanisms for all grapheme-color synesthetes, particularly in posterior superior parietal lobe, which is involved in the integration of sensory information. In addition, the nature of synesthetic experience was found to be mediated by distinct neural mechanisms. The outside-world experience is related to brain areas involved in perceiving and acting in the outside world (visual cortex, auditory cortex, motor cortex) as well as frontal brain areas. In contrast, the in-the-mind experience is related to the hippocampus and parahippocampal gyrus, known for their role in memory. Thus, the different subjective experiences are related to distinct neural mechanisms. Moreover, the properties of subjective experiences are in accordance with functional properties of the mediating brain mechanisms.
In synesthesia, a certain stimulus (e.g. grapheme) is associated automatically and consistently with a stable perceptual-like experience (e.g. color). These associations are acquired in early childhood and remain robust throughout the lifetime. Synesthetic associations can transfer to novel inducers in adulthood as one learns a second language that uses another writing system. However, it is not known how long this transfer takes. We found that grapheme-color associations can transfer to novel graphemes after only a 10-minute writing exercise. Most subjects experienced synesthetic associations immediately after learning a new Glagolitic grapheme. Using a Stroop task, we provide objective evidence for the creation of novel associations between the newly learned graphemes and synesthetic colors. Also, these associations generalized to graphemes handwritten by another person. The fast learning process and the generalization suggest that synesthesia begins at the semantic level of representation with the activation of a certain concept (the inducer), which then, uniquely for the synesthetes, activates representations at the perceptual level (the concurrent). Thus, the results imply that synesthesia is a much more flexible and plastic phenomenon than has been believed until now.
For people with synaesthesia letters and numbers may evoke experiences of colour. It has been previously demonstrated that these synaesthetes may be better at detecting a triangle made of 2s among a background of 5s if they perceive 5 and 2 as having different synaesthetic colours. However, other studies using this task (or tasks based on the same principle) have failed to replicate the effect or have suggested alternative explanations of the effect. In this study, we repeat the original study on a larger group of synaesthetes (n = 36) and include, for the first time, an assessment of their self-reported colour experiences. We show that synaesthetes do have a general advantage over controls on this task. However, many synaesthetes report no colour experiences at all during the task. Synaesthetes who do report colour typically experience around one third of the graphemes in the display as coloured. This is more consistent with theories of synaesthesia in which spatial attention needs to be deployed to graphemes for conscious colour experiences to emerge than the interpretation based on 'pop-out'.
Owing to its bizarre nature and its implications for understanding how brains work, synesthesia has recently received a lot of attention in the popular press and motivated a great deal of research and discussion among scientists. The questions generated by these two communities are intriguing: Does the synesthetic phenomenon require awareness and attention? How does a feature that is not present become bound to one that is? Does synesthesia develop or is it hard wired? Should it change our way of thinking about perceptual experience in general? What is its value in understanding perceptual systems as a whole? This volume brings together a distinguished group of investigators from diverse backgrounds--among them neuroscientists, novelists, and synesthetes themselves--who provide fascinating answers to these questions. Although each approaches synesthesia from a very different perspective, and each was curious about and investigated synesthesia for very different reasons, the similarities between their work cannot be ignored. The research presented in this volume demonstrates that it is no longer reasonable to ask whether or not synesthesia is real--we must now ask how we can account for it from cognitive, neurobiological, developmental, and evolutionary perspectives. This book will be important reading for any scientist interested in brain and mind, not to mention synesthetes themselves, and others who might be wondering what all the fuss is about.
Owing to its bizarre nature and its implications for understanding how brains work, synesthesia has recently received a lot of attention in the popular press and motivated a great deal of research and discussion among scientists. The questions generated by these two communities are intriguing: Does the synesthetic phenomenon require awareness and attention? How does a feature that is not present become bound to one that is? Does synesthesia develop or is it hard wired? Should it change our way of thinking about perceptual experience in general? What is its value in understanding perceptual systems as a whole? This volume brings together a distinguished group of investigators from diverse backgrounds--among them neuroscientists, novelists, and synesthetes themselves--who provide fascinating answers to these questions. Although each approaches synesthesia from a very different perspective, and each was curious about and investigated synesthesia for very different reasons, the similarities between their work cannot be ignored. The research presented in this volume demonstrates that it is no longer reasonable to ask whether or not synesthesia is real--we must now ask how we can account for it from cognitive, neurobiological, developmental, and evolutionary perspectives. This book will be important reading for any scientist interested in brain and mind, not to mention synesthetes themselves, and others who might be wondering what all the fuss is about.
Synaesthesia is a condition in which a mixing of the senses occurs; for example, sounds trigger the experience of colour. Previous reports suggest this may be familial, but no systematic studies exist. In addition, there are no reliable prevalence or sex-ratio figures for the condition, which is essential for establishing if the reported sex ratio (female bias) is reliable, and if this implicates a sex-linked genetic mechanism. Two independent population studies were conducted in the city of Cambridge, England (studies 1 and 2 here), as necessary background to the family genetic study of synaesthesia (study 3). Studies 1 and 2 arrived at an almost identical prevalence rate for synaesthesia: approximately 1 case in 2000. The sex ratio found was 6:1 (female:male). A third of cases also reported familial aggregation. In study 3 six families were examined, and first-degree relatives were tested for genuineness of the condition. All six families were indeed multiplex for synaesthesia. Alternative modes of inheritance are discussed.
Synesthesia is experienced when sensory stimulation of one sensory modality elicits an involuntary sensation in another sensory modality. Auditory-visual synesthesia occurs when auditory stimuli elicit visual sensations. It has developmental, induced and acquired varieties. The acquired variety has been reported in association with deafferentation of the visual system as well as temporal lobe pathology with intact visual pathways. The induced variety has been reported in experimental and post-surgical blindfolding, as well as intake of hallucinogenic or psychedelics. Although in humans there is no known anatomical pathway connecting auditory areas to primary and/or early visual association areas, there is imaging and neurophysiologic evidence to the presence of early cross modal interactions between the auditory and visual sensory pathways. Synesthesia may be a window of opportunity to study these cross modal interactions. Here we review the existing literature in the acquired and induced auditory-visual synesthesias and discuss the possible neural mechanisms. © 2009 Afra et al, publisher and licensee Dove Medical Press Ltd.
Two experiments tested the effect that synaesthesia has on the processing of digits for a single participant, a 22-year-old female college student, who experiences colour mental images (photisms) for digits, music, sounds, etc. The experiments used Stroop-type materials that were digits in the colours of her photisms for two tasks: colour naming and digit naming. For colour naming, the hypothesis was that when the colour of the actual print of the digit mismatched the colour of the participant's digit photism, colour naming times would be slower than when the print and digit photism matched, or when the digit was in black print. For digit naming, it was predicted that naming the digit corresponding to a coloured circle (that corresponded to one of her photisms for digits) would take longer than naming digits printed in any colour. ANOVAs and Tukey tests supported these hypotheses (P Document Type: Research Article DOI: http://dx.doi.org/10.1080/026432999380951 Publication date: March 1, 1999 (document).ready(function() { var shortdescription = (".originaldescription").text().replace(/\\&/g, '&').replace(/\\, '<').replace(/\\>/g, '>').replace(/\\t/g, ' ').replace(/\\n/g, ''); if (shortdescription.length > 350){ shortdescription = "" + shortdescription.substring(0,250) + "... more"; } (".shortdescription a").click(function() { (".originaldescription").slideDown(); return false; }); }); Related content In this: publication By this: publisher In this Subject: Anatomy & Physiology By this author: Mills, Carol Bergfeld ; Boteler, Edith Howell ; Oliver, Glenda K. GA_googleFillSlot("Horizontal_banner_bottom");
Patient PH developed retinitis pigmentosa in childhood and progressively lost his vision until he became completely blind at 40 years old. At age 42, he started experiencing vivid ‘synesthesia’+ADs- tactile stimuli on the hand evoked a vivid visual sensation of ‘movement’, ‘expansion’ or ‘jumping’. Intriguingly, the synesthesia was much more vivid when the hand was in front of the face rather than behind. The effect is unlikely to be confabulatory since touch thresholds (Semmes Monofilaments) were normal and identical for hand in front versus hand behind the head, while ‘thresholds’ for evoked visual sensations were significantly higher for the ‘behind’ condition. Also, the critical fusion frequency for the tactile sensation was much higher than the visually evoked ones. We propose three explanations. (i) ‘Remapping’ or ‘cross-talk’. As a result of de-afferentation, sensory input to the somatosensory pathways (e.g. insular cortex) also innervates extrastriate visual areas. (ii) When a person is touched, there may be spontaneously evoked tactile associative ‘memories’ that would not normally evoke actual visual qualia because of competing ‘spontaneous activity’ from the visual pathways. However, upon de-afferentation, the associations may be experienced as synesthesia. (iii) After de-afferentation, the ‘back projections’ to somatosensory areas from visual areas may be strengthened.
Using event-related fMRI, we investigated the neural correlates of letter detection and identification. Participants were required to detect or identify a single target letter embedded in noise. Prior to experimental runs, psychophysical contrast thresholds for letter detection (“Is a letter present or absent?”) and for identification (“If a letter is present, which letter is it?”, 8 letter choice) were determined. Experimental runs were divided into detection and identification runs and letters were presented in random order at four levels of contrast for both detection and identification. The four levels of contrast were based on individual threshold measurements and included two below threshold levels, far below (FB) and just below (JB), and two above threshold levels, far above (FA) and just above (JA). The FA contrast for detection was also the JA contrast for identification, and the JA contrast for detection was also the JB contrast for identification. A noise-only stimulus (N) with no embedded letter was included as a control. In the left anterior fusiform gyrus (LAF), a region known to be involved in letter processing, letters above detection threshold (FAD and JAD) produced more activation than letters below detection threshold (FBD and JBD). FBD and JBD letters did not differ from each other and also did not differ from the N stimulus. In contrast, FAD letters, that were also just above identification threshold, produced more activation than JAD letters, that were below identification threshold. Thus, we found that activation in the letter selective LAF region is driven only by detectable letters, and responds in a graded fashion to detectable letters depending on whether or not the letters are identified.
The article on synaesthesia by Ramachandran and Hubbard (2001; henceforth, R&H) is comprehensive and intellectually stimulating. In this commentary, I would like to present some empirical data not discussed in R&H and to raise some theoretical questions relating to ideas proposed in this article. My comments will be divided into three sections, or - rather - three stories, which correspond to three, independent and different, occasions in my career in which I found myself dealing with synaesthesia. Each of these stories carries a moral that adds to the picture of synaesthesia drawn in R&H.
This investigator briefly reviews the literature on the cerebral cortex. He discusses his observations on the stimulation of this area in conscious patients. Response is obtained most easily from the vicinity of the fissure of Rolando, but the responses were not obtained from exactly fixed areas. Penfield describes vocalization which he produced with the use of a thyratron stimulator, especially when area 12 was stimulated. Simple movements appeared to be involuntary in nature. Sensation, when produced electrically, was referred to the periphery but unexplained. In the dream state of an epileptic patient, a hallucination was presented by discharge within one portion of the cerebral cortex, but the patient retained insight into his real environment since other portions of the cortex retained their normal functions. Penfield supports the view of Hughlings Jackson that the sensorimotor cerebral cortex represents only a middle level of integration. There seems to be no reason why the neural mechanism of consciousness should migrate outward into the newer exfoliated hemisphere with the acquisition of man's new skills and new adjustments to his environment. This level of integration may lie below the cortex and above the midbrain. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Objective
The ventrolateral nucleus of the thalamus (VL), based on its connectivity with the cerebellum and motor cortex, has long been considered to be involved with motor functions. We show that the human VL also plays a prominent role in sensory processing.Methods
Structural magnetic resonance imaging and diffusion tensor imaging were used to localize a small lesion restricted to the right VL in a patient with contralesional sensory processing deficits. Systematic assessments of anatomic brain organization and behavioral measurements of somatosensory and visual processing were conducted at several time points after stroke.ResultsInitially, the patient was more likely to detect events on the contralesional side when a simultaneous ipsilesional event was presented within the same, but not different, sensory modality. This perceptual phenomenon, which we refer to as unisensory antiextinction, persisted for several months before transforming into a form of synesthesia in which auditory stimuli produced tactile percepts. Tractography performed on the diffusion tensor imaging data showed altered connections from the lesioned thalamus to the cerebral cortex, suggesting a neural basis for these sensory changes.InterpretationThese results demonstrate a role for the VL in sensory processing and suggest that reorganization of thalamocortical axonal connectivity can lead to major changes in perception. Ann Neurol 2007
Coloured hearing synaesthesia (from the Greek syn (union) and aisthesis (sensation)), has been known to the scientific community for over 300 years and yet has gone relatively uninvestigated. This review charts recent progress in the investigation of synaesthesia and discusses the consequences of this research for our understanding of the condition.
Studies investigating developmental synaesthesia have sought to describe a number of qualities that might capture in behavioural terms the defining characteristics of this unusual phenomenon. The task of generating a definition is made more difficult by the fact that any description of synaesthesia must be broad enough to capture the 61 different variants of the condition already reported to date. Given these difficulties, the current literature now contains a number of conflicting assumptions about the nature of this condition. Here, I attempt to address several of these divisive areas from a set of contemporary definitions. I present evidence that might argue against previous claims that synaesthesia is (a) a 'merging of the senses', which (b) gives rise to consistent synaesthetic associations over time, with (c) synaesthetic associations that are spatially extended. I then investigate the possible benefits of moving from a behavioural definition to a neurobiological one and explore the ways in which this might force a rethink about the potential outermost boundaries of this fascinating condition.
In auditory-visual synaesthesia, all kinds of sound can induce additional visual experiences. To identify the brain regions mainly involved in this form of synaesthesia, functional magnetic resonance imaging (fMRI) has been used during non-linguistic sound perception (chords and pure tones) in synaesthetes and non-synaesthetes. Synaesthetes showed increased activation in the left inferior parietal cortex (IPC), an area involved in multimodal integration, feature binding and attention guidance. No significant group-differences could be detected in area V4, which is known to be related to colour vision and form processing. The results support the idea of the parietal cortex acting as sensory nexus area in auditory-visual synaesthesia, and as a common neural correlate for different types of synaesthesia.
Synaesthesia is a broadly defined neural phenomenon in which stimulation of a sense or concept triggers a second perception not normally associated with the stimulus. For example, letters or numbers may trigger a colour experience, sounds may trigger a taste sensation, or tastes may trigger a feeling of touch. Dozens of forms of synaesthesia have been reported, but the relationship between the different forms has not been studied: is someone with a particular form of synaesthesia likely to possess other types? If so, which ones? As an inroad to illuminating underlying mechanisms, we here examine which different synaesthesia types tend to co-occur. We analyzed reports of the forms of synaesthesia experienced by 19,133 participants who completed the Synaesthesia Battery (Eagleman, Kagan, Nelson, Sagaram, & Sarma, 2007), using correlation analysis, exploratory factor analysis (EFA), confirmatory factor analysis (CFA), and multidimensional scaling (MDS). Our analyses converged on the finding of five distinct groupings of synaesthesia forms. We label these coloured sequence synaesthesias (CSSs), coloured music synaesthesias, non-visual sequela synaesthesias, spatial sequence synaesthesia (SSS), and coloured sensation synaesthesias. Collectively, our findings reveal that synaesthesia is an umbrella term that encompasses several distinct groups with independent probabilities of expression, and this may in turn suggest distinct underlying mechanisms and the possibility of different genetic bases.