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Visual dreams in the congenitally blind?

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Abstract

An EEG study of sleep in congenitally blind persons revealed a significant correlation between the visual activity reported during dreaming and the decrease of alpha strength recorded from the central and occipital regions of the scalp. This provides the first objective evidence that subjects who have never had visual experiences can have dreams with virtual images that are probably mediated by the activation of the cortical areas responsible for visual representations.

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... Therefore if dreams with visual content could be demonstrated in congenitally blind persons, this would imply that visual imagery is possible in subjects who have been prevented from having visual experiences. Furthermore, this would allow one to infer that visual imagery does not depend on specific visual perception, but can emerge from activation of visual cortex by nonvisual inputs (Lopes da Silva, 2003). ...
... It has in fact been established by several authors that congenitally blind subjects use the visual cortex to process different kinds of information, namely auditory (Kujala, Alho, Huotilainen, Ihmoniemi, Leinonen, Rinne, Salonen, Sinkkonen, Standertskjöld-Nordenstam & Näätänen, 1997;Kujala, Alho, Kekoni, Hämäläinen, Reinukainen, Salonen, Standertskjöld-Nordenstam & Näätänen, 1995), tactile (Sadato, Pascual-Leone, Grafman, Ibañez, Deibar, Dold & Hallett, 1996), somatosensitive (Röder, Rösler, Hennighausen & Näcker, 1996), and during the encoding and transformation of haptic images (Röder, Rösler & Hennighausen, 1997). Lopes da Silva defends that one possible conclusion from our study (Bértolo et al., 2003) is that auditory and tactile inputs can create virtual images in the brains of congenitally blind subjects which can be revealed in their dreams (Lopes da Silva, 2003). ...
Article
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The question regarding visual imagery and visual perception remain an open issue. Many studies have tried to understand if the two processes share the same mechanisms or if they are independent, using different neural substrates. Most research has been directed towards the need of activation of primary visual areas during imagery. Here we review some of the works providing evidence for both claims. It seems that studying visual imagery in blind subjects can be used as a way of answering some of those questions, namely if it is possible to have visual imagery without visual perception. We present results from the work of our group using visual activation in dreams and its relation with EEG’s spectral components, showing that congenitally blind have visual contents in their dreams and are able to draw them; furthermore their Visual Activation Index is negatively correlated with EEG alpha power. This study supports the hypothesis that it is possible to have visual imagery without visual experience.
... Dream content is creative and productive only insofar as reassembles previous perceptual content. For instance, congenitally born blind subjects do not dream of colors or visual content (Bértolo, Paiva et al. 2003;Lopes da Silva 2003;Kerr and Domhoff 2004). ...
... These cases can't be discussed at length here. Yet, just to have an idea how it could be difficult to interpret such remarkable findings, consider that it has hitherto been impossible to settle definitively the debate as to the visual content of congenitally blind subjects (Bértolo, Paiva et al. 2003;Lopes da Silva 2003;Kerr and Domhoff 2004) which is a relatively more common and well-known condition. By the way, on this last issue, the Spread Mind is unambiguous: a congenitally blind subject should not have any visual phenomenal content in her dreams or in other psychological states. ...
... Therefore if dreams with visual content could be demonstrated in congenitally blind persons, this would imply that visual imagery is possible in subjects who have been prevented from having visual experiences. Furthermore, this would allow one to infer that visual imagery does not depend on specific visual perception, but can emerge from activation of visual cortex by non-visual inputs 63 . ...
... It has in fact been established by several authors that congenitally blind subjects use the visual cortex to process different kinds of information, namely auditory 77,78 , tactile 79 , somatosensitive 80 , and during the encoding and transformation of haptic images 81 . Lopes da Silva defends that one possible conclusion from our study 72 is that auditory and tactile inputs can create virtual images in the brains of congenitally blind subjects which can be revealed in their dreams 63 . ...
Conference Paper
The question regarding visual imagery and visual perception remain an open issue. Many studies have tried to understand if the two processes share the same mechanisms or if they are independent, using different neural substrates. Most research has been directed towards the need of activation of primary visual areas during imagery. Here we review some of the works providing evidence for both claims. It seems that studying visual imagery in blind subjects can be used as a way of answering some of those questions, namely if it is possible to have visual imagery without visual perception. We present results from the work of our group using visual activation in dreams and its relation with EEG’s spectral components, showing that congenitally blind have visual contents in their dreams and are able to draw them; furthermore their Visual Activation Index is negatively correlated with EEG alpha power. This study supports the hypothesis that it is possible to have visual imagery without visual experience.
... However, research also indicated that there are dream experiences that are clearly not continuous to waking life, for example, flying dreams (Schredl & Piel, 2007), walking dreams in congenital paraplegics (Saurat et al., 2011;Voss et al., 2011), being someone else, for example, someone of the opposite sex or an animal (Schredl, 2019), or visual dream content in congenital blind persons (Bertolo et al., 2003). The study of Bertolo et al. (2003), for example, was heavily criticized (Kerr & Domhoff, 2004;Lopes de Silva, 2003) as the authors inferred the presence of visual images based on dream reports and drawings, but blind persons do also have a spatial orientation without explicit visual experiences. This example highlights that it is not always easy to elicit experiences that are discontinuous to waking life, for example, what are the sensations, feeling when flying without any technical means in the dream (Schredl, 2011). ...
Article
Since the formulation of the continuity hypothesis in 1971, research findings have supported the thematic and emotional continuity between waking and dreaming. However, dreams that include experiences that never occurred in the dreamer’s waking life, this is, discontinuous dreams, have not been studied extensively. In a long series ( N = 11,575 dreams), elevator dreams (about 1% of the dreams) were analyzed whether they were continuous or discontinuous to the waking life of the dreamer. Although many elevator dreams are likely to reflect waking life, in over 40% of the elevator dreams the dreamer was using an elevator that showed unusual or even bizarre features, for example, elevator moving horizontally or flying, transforming into a subway, and so on. Often these dreams were associated with anxiety, and the question is whether these dreams—discontinuous on a thematic level—represent a continuity of emotions and/or are a metaphorical expression of the dreamer’s waking life situation, for example, ups and downs.
... Lopes da Silva (2003) was the first to provide empirical evidence (in a study based on EEG) for the decrease of alpha strength recorded from the central and occipital regions of blind subjects carrying out visual imagery tasks. In so doing he provides proof in support of the idea that «subjects who have never had visual experiences can have dreams with virtual images that are probably mediated by the activation of the cortical areas responsible for visual representations» (ivi: 328). ...
Article
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The aim of this paper is to justify the role of mental imagery in creativity. In more spe-cific terms the central idea of this paper is that the justification for the role of mental images in the creative process lies in the analysis of the relationship between vision and imagery. Mental images are present in thought just in those situations in which the ideal way to solve a problem would be the perception of those same things before our own eyes. The production of a mental image is, from this point of view, an analogous process to the perception of an object in its absence. In these cases the images become a good substitute for reality: this is possible because they share common structural elements with percepts. These shared common characteristics provide a validation to the idea that the role of imagery in creativity depends on the structural properties which mental images share with the representation of the perceived information. Such a result opens the way to the idea that there is a close link between imagery and vision and, thus, provide justification for the theory that imagery is closer to perceiving than to thinking.
... Along the same line, people who are blinded after the age of 5-7 seem to have visual imagination and dream with visual imagery throughout life, while blinding at an earlier age leads to absence of visualization in both waking and dreaming [121,122], though dreaming in blind individuals is a subject of debate [123][124][125]. Overall, dreaming appears to be a gradual cognitive development that is tightly linked to the development of visual imagination. ...
Article
Dreams are a remarkable experiment in psychology and neuroscience, conducted every night in every sleeping person. They show that the human brain, disconnected from the environment, can generate an entire world of conscious experiences by itself. Content analysis and developmental studies have promoted understanding of dream phenomenology. In parallel, brain lesion studies, functional imaging and neurophysiology have advanced current knowledge of the neural basis of dreaming. It is now possible to start integrating these two strands of research to address fundamental questions that dreams pose for cognitive neuroscience: how conscious experiences in sleep relate to underlying brain activity; why the dreamer is largely disconnected from the environment; and whether dreaming is more closely related to mental imagery or to perception.
... However, activated emotional and reward networks as well as deactivated realitymonitoring structures in sleep could define a protoconscious state (Hobson, 2009), whose existence and roles may be completely independent of and distinct from the waking conscious state. This statement may be partially supported by evidence that congenitally blind people can have visual dreams (Lopes Da Silva, 2003). Similar findings have been demonstrated for congenitally paraplegic and deaf-mute persons, who have dreams with modalities not experienced during waking life (Voss et al., 2011). ...
Article
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A scientific study of consciousness should take into consideration both objective and subjective measures of conscious experiences. To this date, very few studies have tried to integrate , or data about the neurophysiological correlates of conscious states, with , or data about subjective experience. Inspired by Morel's invention (Casares, 1940), a literary machine capable of reproducing sensory-dependent external reality, this article suggests that combination of virtual reality techniques and brain reading technologies, that is, decoding of conscious states by brain activity alone, can offer this integration. It is also proposed that the multimodal, simulating, and integrative capacities of the dreaming brain render it an "endogenous" Morel's machine, which can potentially be used in studying consciousness, but not always in a reliable way. Both the literary machine and dreaming could contribute to a better understanding of conscious states.
... Neste estudo concluiu-se que os cegos congénitos não só são capazes de descrever verbalmente o conteúdo visual dos seus sonhos como também conseguem, através do desenho, representar graficamente esse conteúdo que em pouco difere das representações gráficas dos sujeitos "normovisuais". Lopes daSilva (2003), ao fazer uma análise sobre o tema dos sonhos visuais em cegos congénitos, conclui que os resultados apresentados porBértolo et al. (2003) são semelhantes aos resultados obtidos por Volder et al.(2001), ou seja, que os "inputs" táteis e auditivos conseguem criar imagens virtuais, sendo estas reveladas nos sonhos. Estes estudos levados a cabo por Bértolo foram fortemente criticados por Kerr & Domhoff (2004) que consideram que as conclusões apresentadas terão sido precoces e mal fundamentadas, uma vez que dão a entender que as imagens virtuais registadas durante o sonho são semelhantes às imagens visuais, quando a maioria dos estudos, incluindo os citados nos estudos de Bértolo concluem que essas imagens são apenas representações mentais. ...
Thesis
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Whereas the educational content and virtual environments often use pictures, which assume different functions, it is necessary to describe these elements so that they can be perceived by those who do not have visual access to them. Despite the Web Content Accessibility Guidelines (WCAG) explain technical issues relating to alternative text and give suggestions of how to describe; most images are not described or present useless alternate text. Thus, there are 2 problems: what to describe and which is for those who do not have visual contact with the image the most effective description. Faced with this problem, this study presents a matrix - a set of parameters to describe a digital image in the eLearning context. To validate these parameters were chosen 2 images, one of the "People" category and another of "Architecture" category. It was requested to 2 groups of "descriptors" to describe these images; 32 described the images based on the parameters (the matrix) and 34 subjects described the images freely. With the descriptions obtained based on the matrix, devised a parameterized description based on the frequency of words and for which we have developed some “memory”, “preference” and “match” tests, seeking to verify their effectiveness. To verify this effectiveness in a comparative way we draw the same tests with one of the free descriptions. These tests would have to be performed by 2 groups: one group that does not use the visual function and a group that uses the visual function. A questionnaire was elaborated to identify subjects that would be included in these 2 groups created on Moodle platform. 23 subjects who do not use the visual function (with congenital blindness and acquired blindness) were involved and performed the tests of auditory memory and preferably; and 97 subjects who use the visual function (without visual impairment, with moderate and severe visual impairment) were enrolled in the other group, half held the same tests that the group that does not use the visual function and the other half held the matching tests and visual memory. With the obtained results we can conclude that the description according to the parameters presented is more effective than "free" description and goes to meet the preference of individuals that do not use the visual function or do not have visual contact with the image.
... As for the arguments from dreams or hallucinations, they do not show the mind exists independently from physical reality any more that the argument from illusion. Dreams are closer to the perception of reality than is commonly assumed, and their basic building blocks seem to be always the result of direct acquaintance with the physical world (Bulkeley 2009;da Silva and Fernando 2003;Murzyn 2008). My fantasies about Tolkien's Middle Earth, or my druginduced apparitions of twelve-headed lions may be fanciful, but are surely grounded in my previous experience of reality, which scientists who have studied perception often refer to as a 'controlled hallucination' (Koenderink 2011). ...
... Other very interesting groups are paraplegics (Saurat et al., 2011), amputees (Mulder, Hochstenbach, Dijkstra, & Geertzen, 2008), mute-deaf persons (Voss, Tuin, Schermelleh-Engel, & Hobson, 2011) because their waking life differs in particular aspects compared to that of unaffected persons, especially if the handicap is congenital. Even though dreams of blind persons have been studied quite intensely, systematic research in linking their waking life experiences to their dream content is still lacking; the major focus was on the differences between the dreams of blind persons compared to those of seeing persons (Lopes de Silva, 2003). Another group which has been studied are patients with brain damage in order to test whether specific cognitive deficits found in the waking state are reflected in alterations of dream recall and dream content (Murri et al., 1989). ...
Article
The ten commentaries to my discussion with J. Allan Hobson about the continuity and discontinuity between waking and dreaming (Hobson & Schredl, 2011) are very stimulating and I would like to thank all contributors. This reply will focus on four aspects: Defining continuity and discontinuity, how does the relationship between waking and dreaming work, possible functions of dreaming, and how to study the continuity (or lack of) between waking and dreaming empirically. Even though the question about possible functions is the most interesting one, I believe that much research is needed before this enigma can be solved. As dream research is such a small field, it is necessary that researchers discuss their theories openly and replicate each other’s findings, applying different methodological approaches for studying the same phenomena.
... Regarding dreams in blind individuals, findings are less univocal. Hurovitz et al (1999) found no visual imagery in dreams of 6 of 14 blind subjects, Berger et al. (1962) in 2 of 5 individuals and Bertolo et al. (2003) report that blinds can not only see but produce drawings of their dream themes (see also da Silva, 2003). These studies do not, however, completely refute the concept of continuity. ...
Article
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REM sleep is a state of desynchronized electrophysiological activity of the brain. It is usually accompanied by mental activity characterized by a succession of complex visual experiences commonly referred to as dreaming. Although REM sleep and dreaming are not implicitly conjoined, when they co-occur, they have a very distinct phenomenology, as, typically, the dream plot is bizarre and incohesive which is mirrored in heightened brain activation coupled with strongly attenuated coherence levels. At the same time, owing to increased limbic system activity, REM sleep dreams are highly emotional. Moreover, concrete emotions are often unrelated to dream events. Nevertheless, REM sleep dreams are often subjectively perceived as story-like and autobiographically meaningful. Indeed, elements of salient life events, attachment figures, and personally relevant emotions, especially trauma, seem to have a higher probability of re-appearing in dreams, albeit the dream plot itself remains highly distorted. This has prompted several theories on the interpretability of dreams, some authors leaning towards dreams reflecting waking mentation, others suggesting complete dissociation between waking and dreaming, both sides not fully accounting for empirical findings. In this review, we provide an overview of recent findings on the factors mediating REM sleep neurophysiology and dream content. As a first step towards integration of conflicting research results, we introduce a testable model (Trace-Spur-model) based on Hebb’ian theory of neural networks, proposing that dream bizarreness is a function of state-related modulations in synaptic strength allowing for hyper-associative mental activity, possibly enabling either a restructuring and integrative consolidation or extinction of learning experiences acquired in waking. In this model, dreams are viewed as phenomenological expressions of this neurophysiologic activity where dream recall allows a fragmentary witnessing of such processes, similar to peeking into an enduring and complex networking system. However, the content of the recollected dream is probably strongly deterred by autobiographical memory bias, favoring those images we can form some sort of association with.
... Furthermore, those dream content reports correlate with the decrease in alpha strength recorded from occipital regions (Bértolo et al., 2003). This suggests visual imagery in dreaming of the congenitally blind, because alpha activity attenuation is regarded as an indicator of visual imagery in general (Lopes da Silva, 2003). Furthermore, REM-locked activation in visual brain areas in utero suggests a REM-locked primitive form of vision (Schöpf et al., 2014). ...
Article
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The neural correlates of rapid eye movements (REMs) in sleep are extraordinarily robust; including REM-locked multisensory-motor integration and accompanying activation in the retrosplenial cortex, the supplementary eye field and areas encompassing cholinergic basal nucleus (Hong et al., 2009). The phenomenology of REMs speaks to the notion that perceptual experience in both sleep and wakefulness is a constructive process – in which we generate predictions of sensory inputs and then test those predictions through actively sampling the sensorium with eye movements. On this view, REMs during sleep may index an internalized active sampling or ‘scanning’ of self-generated visual constructs that are released from the constraints of visual input. If this view is correct, it renders REMs an ideal probe to study consciousness as “an exclusively internal affair” (Metzinger, 2009). In other words, REMs offer a probe of active inference – in the sense of predictive coding – when the brain is isolated from the sensorium in virtue of the natural blockade of sensory afferents during REM sleep. Crucially, REMs are temporally precise events that enable powerful inferences based on time series analyses. As a natural, task-free probe, (REMs) could be used in non-compliant subjects, including infants and animals. In short, REMs constitute a promising probe to study the ontogenetic and phylogenetic development of consciousness and perhaps the psychopathology of schizophrenia and autism, which have been considered in terms of aberrant predictive coding.
... However, activated emotional and reward networks as well as deactivated reality-monitoring structures in sleep could define a protoconscious state(Hobson, 2009), whose existence and roles may be completely independent of and distinct from the waking conscious state. This statement may be partially supported by evidence that congenitally blind people can have visual dreams(Lopes da Silva, 2003). Similar findings have been demonstrated for congenitally paraplegic and deaf-mute persons, who have dreams with modalities not experienced during waking life ...
Thesis
In this work, I analyze the problem of explaining subjective conscious experience, and how science has largely failed to resolve it due to its weak methods of describing the first-person ontology of conscious states. I will thus mainly ask if it is possible to 'objectify' subjectivity, and suggest how an integration of scientific and philosophical methods is needed for approaching the matter of consciousness and the first person perspective. More specifically, I will suggest that philosophers have a fundamental role in the development of such methods and that neurophenomenology, an approach combining and integrating third-person data with phenomenologically-acquired first-person data, may be the solution to the problem.
... To conclude, as individuals with no visual experiences can nevertheless experience dreams with visual imagery 10 the dreaming as a virtual reality would seem to not merely reflect waking experiences. In the congenitally blind the dream imagery seems to be mediated by cortical activation of areas responsible for visual representations in sighted participants (Fosse et al., 2003;da Silva, 2003). However, this doesn't mean the visual component to be necessary for dreaming, and studies have also reported the cessation of dreaming even in adventitiously blind people (see e.g., Charcot, 1883; Kerr, 1993;Solms, 2000;Windt, 2010) Such findings of dreams to contain never-experienced contents are not limited to the blind. ...
Thesis
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Every night during sleep we experience an immersive world of dreams, woven together by our sleeping brain unbound by external stimulation. Despite considerable effort the question of why we dream has eluded a conclusive answer. Understanding dreams also arguably makes progress toward answering the broader question of consciousness: why do we experience anything at all? I attempt to illuminate these questions by concentrating on the quintessentially social nature of dreams. First, in Study I a novel theoretical accountthe Social Simulation Theory of dreaming (SST)is proposed, together with the first outlines of a research program for its empirical study. SST suggests the world simulation form of dreams provides clues for its function by preferentially simulating certain kinds of scenariosnamely social interactions. Second, in Studies II and III specific hypotheses derived from the SST in Study I are empirically evaluated. These provide evidence for dreams to contain more social content than corresponding waking life and to remain so even when social interactions are removed from waking life (Sociality Bias). Furthermore, the Strengthening Hypothesis that suggests dreams serve to maintain and/or increase social bonding with close others gains partial support. The Practise and Preparation Hypothesis gained support as dreams simulated positive interactions in one fifth of dream interactions and overall simulate complex social behaviours. The Compensation Hypothesis suggests dreams simulations to increase when waking social contacts are abolished, but this was not supported in the data as dream sociality remained stable despite social seclusion. When excluded from others our dreams reconfigure to decrease simulations of interactions with strangers. However, dreams during normal day-to-day life do not preferentially simulate bond-strengthening interactions with close others. In opposition to previous findings, Study II found no differences in social dream contents between either stage of sleep or time of night. In Study III a short social seclusion showed not only differences in dream content, but also in sleep structure, with an increase in REM sleep. Third, methodological development was undertaken by, both, developing a content analysis method for extracting social episodes in narrative reports (Social Content Scale, SCS; Study II), and by assessing the validity of a novel home sleep monitor device, the Beddit Sleep Tracker (BST). While the SCS proved useful for categorizing the social features in both studies II and III, BST failed to provide accurate sleep data as measured against a polysomnogram. Overall, the development of SST and the initial empirical evidence for some of its hypotheses brings us closer to understanding the twin problems of dreaming and consciousness.
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The neural substrates of mental image generation were investigated with functional MRI. Subjects listened to words under two different instructional conditions: to generate visual mental images of the words' referents, or to simply listen to each word and wait for the next word. Analyses were performed which directly compared the regional brain activity during each condition, with the goal of discovering whether mental image generation engages modality-specific visual areas, whether it engages primary visual cortex, and whether it recruits the left hemisphere to a greater extent than the right. Results revealed that visual association cortex, and not primary visual cortex, was engaged during the mental image generation condition. Left inferior temporal lobe (Brodmann's area 37) was the most reliably and robustly activated area across subjects, had activity which extended superiorly into occipital association cortex (area 19). The results of this experiment support the hypothesis that visual mental imagery is a function of visual association cortex, and that image generation is asymmetrically localized to the left.
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Subjects participated in perceptual and imagery tasks while their brains were scanned using positron emission tomography. In the perceptual conditions, subjects judged whether names were appropriate for pictures. In one condition, the objects were pictured from canonical perspectives and could be recognized at first glance; in the other, the objects were pictured from noncanonical perspectives and were not immediately recognizable. In this second condition, we assume that top-down processing is used to evaluate the names. In the imagery conditions, subjects saw a grid with a single X mark; a lowercase letter was presented before the grid. In the baseline condition, they simply responded when they saw the stimulus, whereas in the imagery condition they visualized the corresponding block letter in the grid and decided whether it would have covered the X if it were physically present. Fourteen areas were activated in common by both tasks, only 1 of which may not be involved in visual processing (the precentral gyrus); in addition, 2 were activated in perception but not imagery, and 5 were activated in imagery but not perception. Thus, two-thirds of the activated areas were activated in common.
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Evidence suggests that an important contribution of spectral power in the alpha range is characteristic of human REM sleep. This contribution is, in part, due to the appearance of well-defined bursts of alpha activity not associated with arousals during both tonic and phasic REM fragments. The present study aims at determining if the REM-alpha bursts constitute a different alpha variant from the REM background alpha activity. Since previous findings showed a selective suppression of background alpha activity over occipital regions during phasic REM fragments and, on the other hand, the density of alpha bursts seem to be independent of the presence or absence of rapid eye movements, one expects to find the same spectral power contribution of alpha bursts in tonic and phasic REM fragments. The results indicated that REM-alpha bursts showed a similar power contribution and topographic distribution (maximum energy over occipital regions) both in tonic and phasic REM fragments. This suggests that two variants of alpha activity with different functional roles are present during the human REM sleep: i) background alpha activity, modulated over occipital regions by the presence of rapid eye movements, which may be an electrophysiological correlate of the visual dream contents; and ii) REM-alpha bursts, independent of the presence of rapid eye movements, which could be facilitating the connection between the dreaming brain and the external world, working as a micro-arousal in this brain state.
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The rolandic mu rhythm, a resting activity of somatosensory cortex, is a striking feature of the waking human electroencephalogram. This study will demonstrate that activity with identical features occurs during rapid eye movement (REM) sleep. Eye and chin leads were added during prolonged closed circuit television (video) electroencephalographic (EEG) recording with scalp (12 patients) or subdural electrodes including 64 contract grids over the frontoparietal cortices (5 patients). Sleep staging was performed by reformatting into standard polysomnography montages (using two EEG channels, and eye and chin channels) and applying standard scoring criteria. The recordings were then reviewed using all EEG channels to assess rhythmic EEG activity by a reader blinded to the sleep staging. During scalp recordings, 7-10 Hz central rhythms were seen during wakefulness in 7 patients, with 6 of these also having similar rhythms during REM sleep. Similar activity was seen over somatosensory cortex during wakefulness and REM in all invasively recorded patients. This activity was blocked by contralateral body movement or contralateral somatosensory stimuli, even during REM sleep. It was absent in other sleep stages. This REM sleep activity recapitulates all the characteristics of the waking rolandic mu rhythm. This demonstrates functional similarity between the states of wakefulness and REM sleep.
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Previous neuroimaging studies identified a large network of cortical areas involved in visual imagery in the human brain, which includes occipitotemporal and visual associative areas. Here we test whether the same processes can be elicited by tactile and auditory experiences in subjects who became blind early in life. Using positron emission tomography, regional cerebral blood flow was assessed in six right-handed early blind and six age-matched control volunteers during three conditions: resting state, passive listening to noise sounds, and mental imagery task (imagery of object shape) triggered by the sound of familiar objects. Activation foci were found in occipitotemporal and visual association areas, particularly in the left fusiform gyrus (Brodmann areas 19-37), during mental imagery of shape by both groups. Since shape imagery by early blind subjects does involve similar visual structures as controls at an adult age, it indicates their developmental crossmodal reorganization to allow perceptual representation in the absence of vision.
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Cortical oscillations in the range of alpha activity (8-13 Hz) are one of the fundamental electrophysiological phenomena of the human electroencephalogram (EEG). Evidence from quantitative EEG data has shown that their electrophysiological features, cortical generation mechanisms, and therefore, their functional correlates vary along the sleep-wake continuum. Specifically, spectral microstructure and EEG coherence levels between anterior and posterior cortical regions permit to differentiate among alpha activity spontaneously appearing in relaxed wakefulness with eyes closed, drowsiness period, and REM sleep, by reflecting distinct properties of neural networks involved in its cortical generation as well as a different interplay between cortical generators, respectively. Besides, the dissimilar spatiotemporal features of brain electrical microstates within the alpha range reveals a different geometry of active neural structures underlying each alpha variant or, simply, changes in the stability level of neural networks during each brain state. Studies reviewed in this paper support the hypothesis that two different alpha variants occur during human REM sleep: 'background responsive alpha activity', blocked over occipital regions when rapid eye movements are present, and 'REM-alpha bursts', non modulated by the alteration of tonic and phasic periods. Altogether, evidence suggests that electrophysiological features of human cortical oscillations in the alpha frequency range vary across different behavioural states, as well as within state, reflecting different cerebral phenomena with probably dissimilar functional meaning.
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It is currently claimed that congenitally blind do not have visual imagery and are therefore unable to present visual contents in their dreams. The aim of our study was to quantitatively evaluate the existence of visual imagery in born-blind dreams and to correlate it with objective measures, such as sleep EEG frequency components, namely with alpha attenuation (regarded as an indicator of visual activity), and graphical analysis of dream pictorial representations. The investigation was carried out via simultaneous recordings of dream reports and polysomnography, during nocturnal sleep at volunteers' homes; scheduled regular awakenings during the night provided the data for dream and EEG analysis. In the morning, subjects were asked to make a drawing of their dream images. Congenitally blind (n=10) were comparable to normal sighted subjects (n=9): the two groups presented equivalent visual activity indices, and no differences in the analysis of graphical representation of dreaming imagery. However, blind subjects presented a lower rate of dream recall than sighted (27% versus 42%). Both groups had significant negative correlation between Visual Activity Index (VAI) and alpha power in the central and occipital O2 derivations (blind: C4: r=-0.615, P<0.005; O2: r=-0.608, P<0.006; sighted: C4: r=-0.633, P<0.01; O2: r=-0.506, P<0.05). This correlation was weaker for the blind in O1 (r=-0.573, P<0.05) and non-existent for the sighted. Blind individuals have significantly lower alpha activity in the central derivation. In conclusion, the congenitally blind have visual content in their dreams and are able to draw it and, as expected, their VAI is negatively correlated with EEG alpha power.