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ABSTRACT: Auditory verbal hallucinations (AVHs) are speech perceptions that lack an external source, phenomenologically experienced as "hearing voices". A perceptual origin of an AVH experience in patients with schizophrenia can however not explain why the "voices" drain the attentional and cognitive capacity of the patients, making them unable to direct attention away from the "voices" and to cognitively suppress the experience. We recently reported how AVHs interfere with the perception of speech sounds, using a dichotic listening experimental paradigm. We now extend this finding by reporting on the interference caused by AVHs on attention and cognitive control, using a slight variation of the same dichotic listening paradigm. The patients (N=148) were instructed to pay attention to and report from either the right or left ear syllable of the dichotic pair. We then correlated their PANSS score for the hallucination item (P3) with the performance score on the dichotic listening task. The results showed that AVHs interfered with the ability to report the right ear syllable when instructed to pay attention to the right side, which is a marker of inability to attend to an external speech stimulus. When instructed to pay attention to the left side, AVHs interfered with the ability to report the left ear syllable, which is a marker of inability to use cognitive control to suppress attending to the "voices". The corresponding correlations for the emotional withdrawal (N2) negative symptom were all non-significant. The correlations were substantiated in an ANOVA with corresponding significant group differences between high versus low symptom score groups. The results thus extend our previous findings of a perceptual origination for AVHs by showing that AVHs interfere with the ability to attend to the outer world around the patient, and the ability to inhibit, or suppress, the "voices" once they occur. Future research should pin down the neuronal basis of both the origination and the attentional and cognitive control aspects of AVHs.
Biological Psychiatry 05/2013; · 8.28 Impact Factor
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ABSTRACT: Most psychological experimentation takes place in laboratories aiming to maximize experimental control; however, this creates artificial environments that are not representative of real-life situations. Since cognitive processes usually take place in noisy environments, they should also be tested in these contexts. The recent advent of smartphone technology provides an ideal medium for such testing. In order to examine the feasibility of mobile devices (MD) in psychological research in general, and laterality research in particular, we developed a MD version of the widely used speech laterality test, the consonant-vowel dichotic listening (DL) paradigm, for use with iPhones/iPods. First, we evaluated the retest reliability and concurrent validity of the DL paradigm in its MD version in two samples tested in controlled, laboratory settings (Experiment 1). Second, we explored its ecological validity by collecting data from the general population by means of a free release of the MD version (iDichotic) to the iTunes App Store (Experiment 2). The results of Experiment 1 indicated high reliability (r(ICC) = 0.78) and validity (r(ICC) = 0.76-0.82) of the MD version, which consistently showed the expected right ear advantage (REA). When tested in real-life settings (Experiment 2), participants (N = 167) also showed a significant REA. Importantly, the size of the REA was not dependent on whether the participants chose to listen to the syllables in their native language or not. Together, these results establish the current MD version as a valid and reliable method for administering the DL paradigm both in experimentally controlled as well as uncontrolled settings. Furthermore, the present findings support the feasibility of using smartphones in conducting large-scale field experiments.
Frontiers in psychology. 01/2013; 4:42.
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Kristiina Kompus,
Liv E Falkenberg,
Josef J Bless,
Erik Johnsen,
Rune A Kroken,
Bodil Kråkvik,
Frank Larøi,
Else-Marie Løberg,
Einar Vedul-Kjelsås,
René Westerhausen,
Kenneth Hugdahl
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ABSTRACT: Auditory verbal hallucinations (AVHs) are a subjective experience of "hearing voices" in the absence of corresponding physical stimulation in the environment. The most remarkable feature of AVHs is their perceptual quality, that is, the experience is subjectively often as vivid as hearing an actual voice, as opposed to mental imagery or auditory memories. This has lead to propositions that dysregulation of the primary auditory cortex (PAC) is a crucial component of the neural mechanism of AVHs. One possible mechanism by which the PAC could give rise to the experience of hallucinations is aberrant patterns of neuronal activity whereby the PAC is overly sensitive to activation arising from internal processing, while being less responsive to external stimulation. In this paper, we review recent research relevant to the role of the PAC in the generation of AVHs. We present new data from a functional magnetic resonance imaging (fMRI) study, examining the responsivity of the left and right PAC to parametrical modulation of the intensity of auditory verbal stimulation, and corresponding attentional top-down control in non-clinical participants with AVHs, and non-clinical participants with no AVHs. Non-clinical hallucinators showed reduced activation to speech sounds but intact attentional modulation in the right PAC. Additionally, we present data from a group of schizophrenia patients with AVHs, who do not show attentional modulation of left or right PAC. The context-appropriate modulation of the PAC may be a protective factor in non-clinical hallucinations.
Frontiers in Human Neuroscience 01/2013; 7:144. · 2.34 Impact Factor
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ABSTRACT: Experiencing auditory verbal hallucinations is a prominent symptom in schizophrenia that also occurs in subjects at enhanced risk for psychosis and in the general population. Drug treatment of auditory hallucinations is challenging, because the current understanding is limited with respect to the neural mechanisms involved, as well as how CNS drugs, such as antipsychotics, influence the subjective experience and neurophysiology of hallucinations. In this article, the authors review studies of the effect of antipsychotic medication on brain activation as measured with functional MRI in patients with auditory verbal hallucinations. First, the authors examine the neural correlates of ongoing auditory hallucinations. Then, the authors critically discuss studies addressing the antipsychotic effect on the neural correlates of complex cognitive tasks. Current evidence suggests that blood oxygen level-dependant effects of antipsychotic drugs reflect specific, regional effects but studies on the neuropharmacology of auditory hallucinations are scarce. Future directions for pharmacological neuroimaging of auditory hallucinations are discussed.
Expert Review of Neurotherapeutics 01/2013; 13(1):23-36.
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ABSTRACT: In schizophrenia research executive functions have been frequently reported to be impaired on a global level, largely ignoring the fact that the term executive functions refers to a collection of cognitive functions, which may be affected independently of each other. In the present meta-analysis we were able to show that an aspect of interference control, the ability to resist to distracting information, is not substantially affected in schizophrenia. Summarizing the results of 21 studies using a flanker task, we did not find an increased incompatibility slowing (relative to a compatible flanker condition). The mean effect size, integrating the data of 1029 schizophrenia and 848 controls, was with M(g) = 0.037 (95% confidence interval: -0.05 to 0.13) small and the test power was with 1-β = 0.991 sufficiently high to exclude even small population effects. A similar result was obtained when analyzing the incompatibility slowing relative to a neutral flanker condition (8 studies, M(g) = -0.032, 95% confidence interval: -0.16 to 0.09). In not being substantially affected in schizophrenia, the ability to resist distractor interference could serve as "scaffold function", which used by cognitive remediation programs, would allow to build up general functions, such as vigilance and attention, before the affected executive abilities would be addressed.
Journal of psychiatric research 11/2012; · 3.72 Impact Factor
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ABSTRACT: We report evidence that auditory verbal hallucinations (AVH) in schizophrenia patients are perceptual distortions lateralized to the left hemisphere. We used a dichotic listening task with repeated presentations of consonant-vowel syllables, a different syllable in the right and left ear. This task produces more correct reports for the right ear syllable in healthy individuals, indicative of left hemisphere speech processing focus. If AVHs are lateralized to the left hemisphere language receptive areas, then this should interfere with correct right ear reports in the dichotic task, which would result in significant negative correlations with severity of AVHs. We correlated the right and left ear correct reports with the PANSS hallucination symptom, and a randomly selected negative symptom, in addition to the sum total of the positive and negative symptoms, in 160 patients with schizophrenia. The results confirmed the predictions with significant negative correlations for the right ear scores with the PANSS hallucination item, and for the sum total of positive symptoms, while all other correlations were close to zero. The results are unambiguous evidence for AVHs as aberrant speech perceptions originating in the left hemisphere.
Biological Psychiatry 07/2012; 140(1-3):59-64. · 8.28 Impact Factor
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ABSTRACT: We report fMRI and behavioral data from 113 subjects on attention and cognitive control using a variant of the classic dichotic listening paradigm with pairwise presentations of consonant-vowel syllables. The syllable stimuli were presented in a block-design while subjects were in the MR scanner. The subjects were instructed to pay attention to and report either the left or right ear stimulus. The hypothesis was that paying attention to the left ear stimulus (FL condition) induces a cognitive conflict, requiring cognitive control processes, not seen when paying attention to the right ear stimulus (FR condition), due to the perceptual salience of the right ear stimulus in a dichotic situation. The FL condition resulted in distinct activations in the left inferior prefrontal gyrus and caudate nucleus, while the right inferior frontal gyrus and caudate were activated in both the FL and FR conditions, and in a non-instructed (NF) baseline condition.
Brain and Language 04/2012; 121(3):240-7. · 3.12 Impact Factor
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ABSTRACT: Schizophrenia has been consistently shown to be associated with impairment in executive functioning. However, although frequently treated as such, the term executive functioning does not refer to a unitary cognitive function; it rather represents a set of basic, lower-level cognitive sub-components, e.g. updating, shifting, and cognitive inhibition. This specification into sub-components allows for a further differentiation of the executive deficits found in schizophrenia. Focusing on the sub-component of cognitive inhibition, we here present a meta-analysis of interference effect as assessed with the Stroop Color-Word Interference paradigm. Including the results of 36 studies with 1081 schizophrenia patients and 1026 healthy control subjects, it was shown that schizophrenia patients exhibit an increased Stroop interference effect both in response time (mean effect size: M(g) = 0.43; 95% confidence interval, CI95%: 0.35-0.52) and accuracy (M(g) = 0.62; CI95%: 0.47-0.77) measures of interference. However, a meta-regression analysis revealed that the size of the effect varies depending on the version of the Stroop paradigm used. Regarding the response time measures of interference, studies using the classical card version of the paradigm showed a significantly larger effect size than studies using a single-trial computerized version of the paradigm (M(g) = 0.60 vs. M(g) = 0.19). Despite of the dissociation between the two versions of the paradigm, the results of the present meta-analysis indicate that the reported global deficits in executive functioning found to be associated with schizophrenia are at least partly due to a reduced ability of cognitive inhibition.
Biological Psychiatry 09/2011; 133(1-3):172-81. · 8.28 Impact Factor
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ABSTRACT: Functional lateralization of episodic memory processes in the frontal lobe is an area of intense study in the field of cognitive neuroimaging. Yet, to date there is insufficient knowledge of what role the interhemispheric structural connectivity plays in this lateralized organization. We analyzed functional and structural magnetic resonance imaging data from healthy adult volunteers who performed an associative encoding and retrieval task. We examined the relationship between functional voxel-based relative asymmetry of encoding and retrieval in the frontal lobes and the size of the anterior corpus callosum (antCC; corrected for brain size). The size of the antCC was strongly associated to the relative encoding-retrieval asymmetry in the ventrolateral prefrontal cortex (BA 47). These findings show that the functional asymmetry of episodic memory processes in the frontal lobes is associated with the structural connectivity between the hemispheres.
Brain research 08/2011; 1419:61-7. · 2.46 Impact Factor
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ABSTRACT: The existing literature on neuroimaging studies of auditory verbal hallucinations (AVHs) in patients with schizophrenia contains an apparent "paradox" in that the same areas in the auditory cortex seem to be both activated and deactivated in relation to AVHs, depending on whether an external auditory stimulus is present or not. We performed meta-analyses of neuroimaging studies examining patients with schizophrenia during the processing of auditory stimuli and in individuals experiencing hallucinations in the absence of auditory stimuli to examine whether the auditory cortex shows the paradoxical decrease/increase pattern across studies. Databases PubMed and ISI Web of Knowledge were queried with the combination of the keywords "auditory verbal hallucinations", "auditory hallucinations", "fMRI", "PET", "imaging", yielding 11 studies involving comparison between schizophrenia and control group during external auditory stimulation, and 12 studies of hallucinating subjects experiencing AVHs and resting in the absence of auditory stimulation. The data were analyzed using Activation Likelihood Estimation method. The results showed overlapping increased activation in the absence of an external stimulus, and decreased activation in the presence of an external auditory stimulus in the left primary auditory cortex and in the right rostral prefrontal cortex, confirming the "paradoxical" brain activation in relation to AVHs. It is suggested that the "paradox" may be caused by an attentional bias towards internally generated information and failure of down- and up-regulation of the default mode and auditory processing networks, respectively, with the consequence that the spontaneous activation in the absence of an external stimulus shuts down the perceptual apparatus for further processing.
Neuropsychologia 08/2011; 49(12):3361-9. · 3.64 Impact Factor
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ABSTRACT: Recent diffusion-tensor imaging (DTI) studies suggest sexual dimorphism in the micro-structural architecture of the corpus callosum. However, the corpus callosum is also found to be larger in males than in females, a fact that might introduce a systematic bias to the analysis of DTI parameters. Diffusion parameters obtained in the larger male corpus callosum could be less affected by partial-volume averaging with surrounding non-callosal tissue than respective parameters obtained in the smaller female corpus callosum, i.e. the sex of the subject and partial-volume effects would be confounded. The objective of the present DTI study was to re-examine microstructural sex differences in the corpus callosum, while controlling for corpus callosum size differences between sexes. We compared 41 female and 34 male participants using regional tract-based spatial statistics (TBSS) analysis. Clusters of significantly higher fractional anisotropy (FA) and lower diffusion strength in males compared to females were detected in the genu and truncus of the corpus callosum. However, only the sex difference located in the anterior genu subregions could be unequivocally interpreted. This was the only cluster where the diffusion parameters did not correlate with regional callosal size. The present results indicate a stronger inter-hemispheric connectivity between the frontal lobes in males than females, which might be related to sex differences in hemispheric asymmetry and brain size.
NeuroImage 03/2011; 56(3):874-80. · 5.89 Impact Factor
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ABSTRACT: Klinefelter syndrome (47, XXY) is a sex chromosome aneuploidy associated with mild deficits in cognitive and language functions. Dysfunctions have also been reported in performance of tasks which examine executive functions. However, it is unclear whether the impaired performance is caused or accentuated by problems with semantic processing and information processing speed. In the present study we used an experimental task which is relatively insensitive to these confounding factors. We examined inhibitory executive functions in a group of XXY males compared with male (XY) and female (XX) controls, using a dichotic listening speech sound task with instructions to focus attention on either the right or the left ear stimulus. With this task, inhibitory executive functions can be assessed separately from language, processing speed, and attention orientation abilities. We found that XXY males showed a selective deficit in inhibitory executive functions compared to both control groups, whereas attentional orientation was not impaired. The present findings suggest that executive dysfunctions associated to Klinefelter syndrome can be selectively identified, and are particularly accentuated in the inhibitory sub-component. Such improved understanding of the nature of executive dysfunctions in XXY males may aid the development of specific neuropsychological rehabilitation strategies.
Psychiatry Research 03/2011; 189(1):135-40. · 2.52 Impact Factor
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Kristiina Kompus
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ABSTRACT: Episodic memories can be retrieved by an intentional search for certain information. Alternatively, a past episode may enter our consciousness without any intention to retrieve it, prompted by a stimulus in our surroundings. Incidental retrieval does not occur upon each encounter with a familiar stimulus, suggesting that a gating mechanism exists which regulates incidental retrieval activity. We analyzed data from a functional magnetic resonance imaging study on incidental retrieval in healthy young adults and found that failure to incidentally retrieve was selectively associated with reduced activation of lateral and medial parietal regions as well as ventromedial frontal cortex, areas implicated in default mode network. This is the first demonstration that relative deactivation of the brain regions associated with the default mode gates the consciousness from currently irrelevant memories.
Neuroscience Letters 10/2010; 487(3):318-21. · 2.11 Impact Factor
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ABSTRACT: Previous studies have shown that information that currently cannot be retrieved but will be retrieved on a subsequent, more supported task (i.e. is available but not accessible) has a distinct neural signature compared with non-available information. For verbal paired-associates, an availability signal has been revealed in left middle temporal cortex, an area potentially involved in the storage of such information, raising the possibility that availability signals are expressed in modality-specific storage sites. In the present study subjects encoded pictures and sounds representing concrete objects. One day later, during fMRI scanning, a verbal cued-recall task was administrated followed by a post-scan recognition task. Items remembered on both tasks were classified as accessible; items not remembered on the first but on the second task were classified as available; and items not remembered on any of the tasks were classified as not available. Multivariate partial-least-squares analyses revealed a modality-independent accessibility network with dominant contributions of left inferior parietal cortex, left inferior frontal cortex, and left hippocampus. Additionally, a modality-specific availability network was identified which included increased activity in visual regions for available pictorial information and in auditory regions for available sound information. These findings show that availability in memory, at least in part, is characterized by systematic changes in brain activity in sensory regions whereas memory access reflects differential activity in a modality-independent, conceptual network, thus indicating qualitative differences between availability and accessibility in memory.
NeuroImage 08/2010; 52(2):686-98. · 5.89 Impact Factor
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ABSTRACT: Memories of past episodes frequently come to mind incidentally, without directed search. It has remained unclear how incidental retrieval processes are initiated in the brain. Here we used fMRI and ERP recordings to find brain activity that specifically correlates with incidental retrieval, as compared to intentional retrieval. Intentional retrieval was associated with increased activation in dorsolateral prefrontal cortex. By contrast, incidental retrieval was associated with a reduced fMRI signal in posterior brain regions, including extrastriate and parahippocampal cortex, and a modulation of a posterior ERP component 170 msec after the onset of visual retrieval cues. Successful retrieval under both intentional and incidental conditions was associated with increased activation in the hippocampus, precuneus, and ventrolateral prefrontal cortex, as well as increased amplitude of the P600 ERP component. These results demonstrate how early bottom-up signals from posterior cortex can lead to reactivation of episodic memories in the absence of strategic retrieval attempts.
Journal of Cognitive Neuroscience 03/2010; 23(4):947-60. · 5.18 Impact Factor
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ABSTRACT: The activation of dorsolateral prefrontal cortex (dlPFC) has been suggested to reflect the engagement of a control mechanism for top-down biasing of context processing in resource-demanding memory tasks. Here we tested the hypothesis that the dlPFC subserves a similar function also in attention and emotion tasks. 18 healthy young adults were tested in a functional magnetic resonance imaging (fMRI) study where the demands for context processing were manipulated in three different cognitive domains: auditory attention, episodic retrieval, and emotion regulation. We found that the right dlPFC was jointly sensitive to increased cognitive demands in the attention and memory tasks. By contrast, increased demands in the emotion task (reappraisal) were associated with increased activity in ventromedial PFC along with decreased amygdala activity. Our findings of divergent prefrontal control networks for cognitive and emotional control extend previous separations of cognition and emotion in the anterior cingulate cortex.
Neuroscience Letters 10/2009; 467(2):76-80. · 2.11 Impact Factor
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ABSTRACT: It has been suggested that episodic and semantic long-term memory systems interact during retrieval. Here we examined the flexibility of memory retrieval in an associative task taxing memories of different strength, assumed to differentially engage episodic and semantic memory. Healthy volunteers were pre-trained on a set of 36 face-name pairs over a 6-week period. Another set of 36 items was shown only once during the same time period. About 3 months after the training period all items were presented in a randomly intermixed order in an event-related fMRI study of face-name memory. Once presented items differentially activated anterior cingulate cortex and a right prefrontal region that previously have been associated with episodic retrieval mode. High-familiar items were associated with stronger activation of posterior cortices and a left frontal region. These findings fit a model of memory retrieval by which early processes determine, on a trial-by-trial basis, if the task can be solved by the default semantic system. If not, there is a dynamic shift to cognitive control processes that guide retrieval from episodic memory.
Neuropsychologia 01/2009; 47(11):2252-60. · 3.64 Impact Factor
