Modified activity of the human auditory cortex during auditory hallucinations

Pitch and Duration Mismatch Negativity and Heschl's Gyrus Volume in First-Episode Schizophrenia-Spectrum Individuals

Background. The mismatch negativity (MMN) brainwave indexes novelty detection. MMN to infrequent pitch (pMMN) and duration (dMMN) deviants is reduced in long-term schizophrenia. Although not reduced at first psychosis, pMMN is inversely associated with left hemisphere Heschl's gyrus (HG) gray matter volume within 1 year of first hospitalization for schizophrenia-spectrum psychosis, consistent with pathology of left primary auditory cortex early in disease course. We examined whether the relationship was present earlier, at first psychiatric contact for psychosis, and whether the same structural-functional association was apparent for dMMN. Method. Twenty-seven first-episode schizophrenia-spectrum (FESz) and 27 matched healthy comparison (HC) individuals were compared. EEG-derived pMMN and dMMN were measured by subtracting the standard tone waveform (80%) from the pitch- and duration-deviant waveforms (10% each). HG volumes were calculated from T1-weighted structural magnetic resonance imaging using Freesurfer. Results. In FESz, pMMN amplitudes at Fz were inversely associated with left HG (but not right) gray matter volumes, and dMMN amplitudes were associated significantly with left HG volumes and at trend-level with right HG. There were no structural-functional associations in HC. Conclusions. pMMN and dMMN index gray matter reduction in left hemisphere auditory cortex early in psychosis, with dMMN also marginally indexing right HG volumes. This suggest conjoint functional and structural pathology that affects the automatic detection of novelty with varying degrees of penetrance prior to psychosis. These brainwaves are sensitive biomarkers of pathology early in the psychotic disease course, and may serve as biomarkers of disease progression and as therapeutic outcome measures.

Language-Related Neurophysiological Deficits in Schizophrenia

Schizophrenia is a severe psychiatric disorder that affects all aspects of one's life with several cognitive and social dysfunctions. However, there is still no objective and universal index for diagnosis and treatment of this disease. Many researchers have studied language processing in schizophrenia since most of the patients show symptoms related to language processing, such as thought disorder, auditory verbal hallucinations, or delusions. Electroencephalography (EEG) and magnetoencephalography (MEG) with millisecond order high temporal resolution, have been applied to reveal the abnormalities in language processing in schizophrenia. The aims of this review are (a) to provide an overview of recent findings in language processing in schizophrenia with EEG and MEG using neurophysiological indices, providing insights into underlying language related pathophysiological deficits in this disease and (b) to emphasize the advantage of EEG and MEG in research on language processing in schizophrenia.

Psychosis Is Not Illness but a Survival Strategy in Severe Stress: A Proposal for an Addition to a Phenomenological Point of View

Phenomenology often looks at psychosis as a defined pathological state. In this paper, psychosis is not seen as a (pathological) state but as a way to respond in extreme stress. It is psychological functioning of the embodied and relational mind, and psychotic experience can be seen as one form of affective arousal among any other affects. Taken the point of views of Emmanuel Levinas and Mikhail Bakhtin about the primacy of living in responsive relationships, psychotic behavior is seen as emerging in relationships that do not guarantee adequate responses and thus the subject is imposed to isolate from social relationships and developing odd behavior. If dialogical responses are guaranteed, recovery from psychotic behavior can occur. Some guidelines for such dialogues are given.

Serotonergic Hallucinogen-Induced Visual Perceptual Alterations

Serotonergic hallucinogens, such as lysergic acid diethylamide (LSD), psilocybin, and N,N-dimethyltryptamine (DMT), are famous for their capacity to temporally and profoundly alter an individual's visual experiences. These visual alterations show consistent attributes despite large inter- and intra-individual variances. Many reports document a common perception of colors as more saturated, with increased brightness and contrast in the environment ("Visual Intensifications"). Environmental objects might be altered in size ("Visual illusions") or take on a modified and special meaning for the subject ("Altered self-reference"). Subjects may perceive light flashes or geometrical figures containing recurrent patterns ("Elementary imagery and hallucinations") influenced by auditory stimuli ("Audiovisual synesthesia"), or they may envision images of people, animals, or landscapes ("Complex imagery and hallucinations") without any physical stimuli supporting their percepts. This wide assortment of visual phenomena suggests that one single neuropsychopharmacological mechanism is unlikely to explain such vast phenomenological diversity. Starting with mechanisms that act at the cellular level, the key role of 5-HT2A receptor activation and the subsequent increased cortical excitation will be considered. Next, it will be shown that area specific anatomical and dynamical features link increased excitation to the specific visual contents of hallucinations. The decrease of alpha oscillations by hallucinogens will then be introduced as a systemic mechanism for amplifying internal-driven excitation that overwhelms stimulus-induced excitations. Finally, the hallucinogen-induced parallel decrease of the N170 visual evoked potential and increased medial P1 potential will be discussed as key mechanisms for inducing a dysbalance between global integration and early visual gain that may explain several hallucinogen-induced visual experiences, including visual hallucinations, illusions, and intensifications.

Use of Multimodality Imaging and Neuropsychological Measures for the Assessment and Treatment of Auditory Verbal Hallucinations: A Brain to Behavior Approach

Patients suffering from auditory verbal hallucinations (AVHs) may utilize unique coping strategies in order to reduce distraction caused by the perception of internal speech. Behavioral strategies may include externalizing speech through self-talk. This paper examines the benefits of a multimodality brain to behavior approach applied to the outpatient psychiatric assessment of a 55-year-old Caucasian female presenting with auditory verbal hallucinations and challenges in attention, concentration, and emotional regulation, who employed self-talk as a coping strategy to focus her attention.

Distinct neural responses used to gain insight into hallucinatory perception in patients with schizophrenia

OBJECTIVE

Most patients with schizophrenia suffer from various types of hallucinations, which commonly produce distress, functional disability or behavioral dyscontrol. The neural process of adapting to hallucinations in patients with schizophrenia remains unknown.

METHODS

Functional magnetic resonance imaging (MRI) responses to an unusual threatening visual stimulus designed to simulate a hallucinatory experience were compared between 16 patients with schizophrenia and 17 healthy controls. Linear and quadratic repetition-variant as well as repetition-invariant responses to the stimulus were compared between the two groups.

RESULTS

Repetition-invariant responses were similar between patients with schizophrenia and healthy controls. Patients with schizophrenia exhibited a linear activation pattern in the anterior cingulate, whereas healthy controls exhibited a parabolic activation pattern in the anterior prefrontal cortex, occipito-temporal junction and amygdala.

CONCLUSIONS

These results provide us with a better understanding of the neural processes involved in gaining insight into unreality. Patients with schizophrenia may use a salience-related region instead of reality monitoring-related regions to react to the unusual stimuli, and this peculiarity of the neural processes may be related to vulnerability to psychosis.

Neurophysiological studies of auditory verbal hallucinations

We discuss 3 neurophysiological approaches to study auditory verbal hallucinations (AVH). First, we describe "state" (or symptom capture) studies where periods with and without hallucinations are compared "within" a patient. These studies take 2 forms: passive studies, where brain activity during these states is compared, and probe studies, where brain responses to sounds during these states are compared. EEG (electroencephalography) and MEG (magnetoencephalography) data point to frontal and temporal lobe activity, the latter resulting in competition with external sounds for auditory resources. Second, we discuss "trait" studies where EEG and MEG responses to sounds are recorded from patients who hallucinate and those who do not. They suggest a tendency to hallucinate is associated with competition for auditory processing resources. Third, we discuss studies addressing possible mechanisms of AVH, including spontaneous neural activity, abnormal self-monitoring, and dysfunctional interregional communication. While most studies show differences in EEG and MEG responses between patients and controls, far fewer show symptom relationships. We conclude that efforts to understand the pathophysiology of AVH using EEG and MEG have been hindered by poor anatomical resolution of the EEG and MEG measures, poor assessment of symptoms, poor understanding of the phenomenon, poor models of the phenomenon, decoupling of the symptoms from the neurophysiology due to medications and comorbidites, and the possibility that the schizophrenia diagnosis breeds truer than the symptoms it comprises. These problems are common to studies of other psychiatric symptoms and should be considered when attempting to understand the basic neural mechanisms responsible for them.

Magnetoencephalography: From SQUIDs to neuroscience. Neuroimage 20th anniversary special edition

Magnetoencephalography (MEG), with its direct view to the cortex through the magnetically transparent skull, has developed from its conception in physics laboratories to a powerful tool of basic and clinical neuroscience. MEG provides millisecond time resolution and allows real-time tracking of brain activation sequences during sensory processing, motor planning and action, cognition, language perception and production, social interaction, and various brain disorders. Current-day neuromagnetometers house hundreds of SQUIDs, superconducting quantum interference devices, to pick up signals generated by concerted action of cortical neurons. Complementary MEG measures of neuronal involvement include evoked responses, modulation of cortical rhythms, properties of the on-going neural activity, and interareal connectivity. Future MEG breakthroughs in understanding brain dynamics are expected through advanced signal analysis and combined use of MEG with hemodynamic imaging (fMRI). Methodological development progresses most efficiently when linked with insightful neuroscientific questions.

The 5-HT2A/1A agonist psilocybin disrupts modal object completion associated with visual hallucinations

BACKGROUND

Recent findings suggest that the serotonergic system and particularly the 5-HT2A/1A receptors are implicated in visual processing and possibly the pathophysiology of visual disturbances including hallucinations in schizophrenia and Parkinson's disease.

METHODS

To investigate the role of 5-HT2A/1A receptors in visual processing the effect of the hallucinogenic 5-HT2A/1A agonist psilocybin (125 and 250 μg/kg vs. placebo) on the spatiotemporal dynamics of modal object completion was assessed in normal volunteers (n = 17) using visual evoked potential recordings in conjunction with topographic-mapping and source analysis. These effects were then considered in relation to the subjective intensity of psilocybin-induced visual hallucinations quantified by psychometric measurement.

RESULTS

Psilocybin dose-dependently decreased the N170 and, in contrast, slightly enhanced the P1 component selectively over occipital electrode sites. The decrease of the N170 was most apparent during the processing of incomplete object figures. Moreover, during the time period of the N170, the overall reduction of the activation in the right extrastriate and posterior parietal areas correlated positively with the intensity of visual hallucinations.

CONCLUSIONS

These results suggest a central role of the 5-HT2A/1A-receptors in the modulation of visual processing. Specifically, a reduced N170 component was identified as potentially reflecting a key process of 5-HT2A/1A receptor-mediated visual hallucinations and aberrant modal object completion potential.

The neurophysiology of auditory hallucinations - a historical and contemporary review

Electroencephalography and magnetoencephalography are two techniques that distinguish themselves from other neuroimaging methodologies through their ability to directly measure brain-related activity and their high temporal resolution. A large body of research has applied these techniques to study auditory hallucinations. Across a variety of approaches, the left superior temporal cortex is consistently reported to be involved in this symptom. Moreover, there is increasing evidence that a failure in corollary discharge, i.e., a neural signal originating in frontal speech areas that indicates to sensory areas that forthcoming thought is self-generated, may underlie the experience of auditory hallucinations.

Reality of auditory verbal hallucinations

Distortion of the sense of reality, actualized in delusions and hallucinations, is the key feature of psychosis but the underlying neuronal correlates remain largely unknown. We studied 11 highly functioning subjects with schizophrenia or schizoaffective disorder while they rated the reality of auditory verbal hallucinations (AVH) during functional magnetic resonance imaging (fMRI). The subjective reality of AVH correlated strongly and specifically with the hallucination-related activation strength of the inferior frontal gyri (IFG), including the Broca's language region. Furthermore, how real the hallucination that subjects experienced was depended on the hallucination-related coupling between the IFG, the ventral striatum, the auditory cortex, the right posterior temporal lobe, and the cingulate cortex. Our findings suggest that the subjective reality of AVH is related to motor mechanisms of speech comprehension, with contributions from sensory and salience-detection-related brain regions as well as circuitries related to self-monitoring and the experience of agency.

Reduced auditory evoked potential component N100 in schizophrenia--a critical review

The role of a reduced N100 (or N1) component of the auditory event related potential as a potential trait marker of schizophrenia is critically discussed in this review. We suggest that the extent of the N100 amplitude reduction in schizophrenia depends on experimental and subject factors, as well as on clinical variables: N100 is more consistently reduced in studies using interstimulus intervals (ISIs) >1 s than in studies using shorter ISIs. An increase of the N100 amplitude by allocation of attention is often lacking in schizophrenia patients. A reduction of the N100 amplitude is nevertheless also observed when such an allocation is not required, proposing that both endogenous and exogenous constituents of the N100 are affected by schizophrenia. N100 is more consistently reduced in medicated than unmedicated patients, but a reduction of the N100 amplitude as a consequence of antipsychotic medication was shown in only two of seven studies. In line with that, the association between the N100 reduction and degree of psychopathology of patients appears to be weak overall. A reduced N100 amplitude is found in first degree relatives of schizophrenia patients, but the risk of developing schizophrenia is not reflected in the N100 amplitude reduction.

Competition for neuronal resources: how hallucinations make themselves heard

BACKGROUND

Hallucinations are perceptions in the absence of a corresponding external sensory stimulus. However, during auditory verbal hallucinations, activation of the primary auditory cortex has been described.

AIMS

The objective of this study was to investigate whether this activation of the auditory cortex contributes essentially to the character of hallucinations and attributes them to alien sources, or whether the auditory activation is a sign of increased general auditory attention to external sounds.

METHOD

The responsiveness of the auditory cortex was investigated by auditory evoked potentials (N100) during the simultaneous occurrence of hallucinations and external stimuli. Evoked potentials were computed separately for periods with and without hallucinations; N100 power, topography and brain electrical sources were analysed.

RESULTS

Hallucinations lowered the N100 amplitudes and changed the topography, presumably due to a reduced left temporal responsivity.

CONCLUSIONS

This finding indicates competition between auditory stimuli and hallucinations for physiological resources in the primary auditory cortex. The abnormal activation of the primary auditory cortex may thus be a constituent of auditory hallucinations.

Electromagnetic brain activity evoked by affective stimuli in schizophrenia

Schizophrenia is typically associated with cognitive deficits, but symptoms also point to alterations in the processing of affective material, with potential impact on behavioral performance. This impact may unfold on multiple time scales, but initial processing of rapidly unfolding social cues may be particularly important. MEG-assessed regional brain activity associated with the capacity to process the emotional content of rapid visual stimuli (3/s) was examined in 12 individuals with schizophrenia and 12 matched controls. Patients showed less differentiation of emotional versus neutral stimuli 90-300 ms following picture onset. Together with group differences in the lateral topography of valence effects, these results are discussed as evidence of deficient automatic processing of emotionally potent stimuli in schizophrenia.

Positive symptoms and duration of illness predict functional laterality and attention modulation in schizophrenia

OBJECTIVE

Dichotic listening (DL) performance in schizophrenia, reflecting hemispheric asymmetry and the functional integrity of the left temporal lobe, can vary with clinical characteristics. Previous studies have not taken the co-linearity of clinical variables into account. The aim of the present study was to evaluate the roles of positive symptoms and duration of illness in DL through Structural Equation Modeling (SEM), thus allowing for complex relationships between the variables.

METHOD

We pooled patients from four previous DL studies to create a heterogeneous group of 129 schizophrenic patients, all tested with a consonant-vowel syllables DL procedure that included attentional instructions.

RESULTS

A model where positive symptoms predicted a laterality component and duration of illness predicted an attention component in DL was confirmed.

CONCLUSION

Positive symptoms predicted reduced functional laterality, suggesting involvement of left temporal lobe language processing. Duration of illness predicted impaired attention modulation, possibly reflecting the involvement of frontotemporal networks.

Dichotic listening in schizophrenic patients: effects of previous vs. ongoing auditory hallucinations

Auditory hallucinations (AH) in schizophrenia have been found to be related to both functional and structural brain abnormalities of left temporal lobe language areas. We do not know if these rain abnormalities are state or trait markers for AH. This study tested these alternatives by contrasting schizophrenic patients with ongoing AH and with a previous history of AH. A heterogeneous group of 26 schizophrenic patients was compared with a healthy control group matched for education and age. We used a verbal dichotic listening (DL) test with consonant-vowel syllables to study hemispheric asymmetry and the functional integrity of the left temporal lobe language areas. All subjects were tested during a divided and two focused attention conditions. Our data suggest that abnormal DL asymmetry for language stimuli is a state marker for AH, seen during the perception of AH. In contrast, problems of modulating DL performance by means of attentional control are a trait marker, seen both in patients with ongoing AH and only a history of AH.

The cognitive neuropsychiatry of auditory verbal hallucinations: an overview

INTRODUCTION

The cognitive neuropsychiatric approach to auditory verbal hallucinations (AVHs) attempts to explain the phenomena in cognitive or information-processing terms and ultimately their brain bases.

METHODS

A narrative review of the literature and an overview of this special issue of Cognitive Neuropsychiatry.

RESULTS

First, an operational definition of AVHs is offered. Next, clues to etiology are derived from a detailed consideration of the clinical phenomenology of "voices", their form and content. Functional and structural neuroimaging studies suggest the importance of left-side language areas in the generation/perception of AVHs.

CONCLUSIONS

Existing cognitive neuropsychiatric models provide a useful framework for the understanding of AVHs. However, data need to be applied more specifically to these models so that they may be refined.

Source distribution of neuromagnetic slow wave activity in schizophrenic and depressive patients

OBJECTIVE

Focal slow waves in the delta and theta frequency range frequently appear in psychopathological conditions. Due to their focal nature they can be localized by dipole modeling. We previously reported regional clustering of slow waves in temporal and parietal cortex of schizophrenic patients whereas such activity is largely absent in normals. Here we examine, to what extent distribution of slow wave generators differentiates schizophrenic from depressive syndromes.

METHODS

The regional densities of generators of focal slow waves were determined during resting conditions in patients with DSM-IV diagnoses of schizophrenia (N=25) and depression (N=27) and in 18 healthy controls.

RESULTS

Schizophrenic patients demonstrated accentuated temporal and parietal delta and theta dipole clustering, when compared to both the control and the depressive sample. In contrast, depressive patients had reduced frontal and prefrontal delta and theta dipole density relative to both schizophrenics and controls. This pattern was not related to age. Men generally displayed somewhat higher slow wave activity than women. For the areas of most pronounced slow wave deviances activity within each group was related to symptom scores: higher left-temporal slow wave activity was associated with hallucinations in schizophrenics, suppression of left-prefrontal slow wave activity correlated with depression scores.

CONCLUSIONS

Results suggest that slow wave distribution may assist in differentially diagnosing psychopathological conditions.

Increased susceptibility to auditory conditioning in hallucinating schizophrenic patients: a preliminary investigation

Auditory hallucinations have been elicited in the laboratory after repeated pairings of a tone (unconditioned stimulus) with a light (conditioned stimulus), until the presentation of the light alone resulted in subjects hearing the tone. This auditory sensory-conditioning phenomenon was first reported in normal subjects over a half-century ago. But the model remains, to date, untested in actively hallucinating patients. If sensory-conditioning mechanisms actually mediate the occurrence of clinical hallucinations, one would expect that hallucinating patients would more readily acquire and be more resistant to extinguish a conditioned hallucination than nonhallucinating psychotic patients. The present study examined the susceptibility of 15 hallucinating and 15 nonhallucinating acute schizophrenic inpatients to acquire and maintain a sensory-conditioned hallucination response. Consistent with the auditory sensory-conditioning model, evidence suggests that hallucinating patients acquire and maintain sensory-conditioned hallucinations more quickly than their nonhallucinating counterparts. Results are discussed in terms of hallucinators' susceptibility to sensory conditioning and suggestibility as important factors underlying hallucinatory behavior. The findings are interpreted with respect to the behavioral mechanisms underlying psychotic symptom formation.

Auditory verbal hallucinations and dysfunction of the neural substrates of speech

OBJECTIVE

to evaluate the neural substrate of auditory verbal hallucinations (AVH), the correlation between AVH and subvocal speech (hereafter SVS), and the relationship between speech and AVH.

METHOD

we reviewed the papers found by an electronic literature search on hallucinations and speech. The review was extended to the papers cited in these publications and to classical works.

RESULTS

there is no conclusive evidence of structural abnormality of the speech perception area in hallucinating schizophrenic patients. However there is evidence of electrophysiological abnormalities of the auditory and speech perception cortices. Functional imaging data are inconsistent, yet point to the left superior temporal gyrus as one of the neural substrates for AVH. There is also evidence that SVS could accompany the experience of AVH.

CONCLUSION

there is evidence that dysfunction of brain areas responsible for speech generation is a fundamental mechanism for generating AVH in schizophrenia. It results in a secondary activation of Wernicke's area (speech perception) and Broca's area (speech expression). The first leading to the experience of hallucinations, and the second, eventually, gives rise to a variable degree of vocal muscle activity detectable by EMG, and/or faint vocalizations detectable by sensitive microphones placed at proximity of the larynx. Direct stimulation or disease of Wernicke's area produces AVH without SVS.

Audio-visual speech perception in schizophrenia: an fMRI study

Abnormalities in the integration of auditory and visual language inputs could underlie many core psychotic features. Perceptual confusion may arise because of the normal propensity of visual speech perception to evoke auditory percepts. Recent functional neuroimaging studies of normal subjects have demonstrated activation in auditory-linguistic brain areas in response to silent lip-reading. Three functional magnetic resonance imaging experiments were carried out on seven normal volunteers, and 14 schizophrenia patients, half of whom were actively psychotic. The tasks involved listening to auditory speech, silent lip-reading (visual speech), and perception of meaningless lip movements (visual non-speech). Subjects also undertook a behavioural study of audio-visual word identification designed to evoke perceptual fusions. Patients and controls both showed susceptibility to audio-visual fusions on the behavioural task. The patient group as a whole showed less activation relative to controls in superior and inferior posterior temporal areas while performing the silent lip-reading task. Attending to visual non-speech, the patients activated less posterior (occipito-temporal) and more anterior (frontal, insular and striatal) brain areas than controls. This difference was accounted for largely by the psychotic subgroup. Insular and striatal areas were also activated in both subject groups in the auditory speech perception condition, thus demonstrating the bimodal sensitivity of these regions. The results suggest that schizophrenia patients with psychotic symptoms respond to visually ambiguous stimuli (non-speech) by activation of polysensory structures. This could reflect particular processing strategies and may increase susceptibility to certain paranoid and hallucinatory symptoms.

Speaking modifies voice-evoked activity in the human auditory cortex

The voice we most often hear is our own, and proper interaction between speaking and hearing is essential for both acquisition and performance of spoken language. Disturbed audiovocal interactions have been implicated in aphasia, stuttering, and schizophrenic voice hallucinations, but paradigms for a noninvasive assessment of auditory self-monitoring of speaking and its possible dysfunctions are rare. Using magnetoencephalograpy we show here that self-uttered syllables transiently activate the speaker's auditory cortex around 100 ms after voice onset. These phasic responses were delayed by 11 ms in the speech-dominant left hemisphere relative to the right, whereas during listening to a replay of the same utterances the response latencies were symmetric. Moreover, the auditory cortices did not react to rare vowel changes interspersed randomly within a series of repetitively spoken vowels, in contrast to regular change-related responses evoked 100-200 ms after replayed rare vowels. Thus, speaking primes the human auditory cortex at a millisecond time scale, dampening and delaying reactions to self-produced "expected" sounds, more prominently in the speech-dominant hemisphere. Such motor-to-sensory priming of early auditory cortex responses during voicing constitutes one element of speech self-monitoring that could be compromised in central speech disorders.

Auditory hallucinations: phenomenology, neuropsychology and neuroimaging update

Auditory verbal hallucinations (AVHs) are a cardinal feature of psychosis. Recent research is reviewed which has attempted to advance our knowledge of the mechanisms underlying this symptom. Phenomenological surveys have confirmed the importance of the content of such hallucinations and their meaning to the voice-hearer. Psychological and neuroimaging studies of inner speech and source monitoring have provided a neuropsychological framework for AVHs as well as some novel therapeutic strategies. There have also been successful attempts to 'capture' neural activity coincident with the experience of hallucinations using PET, SPECT and functional magnetic resonance imaging (MRI). This body of knowledge in combination with work on in-vivo receptor binding (dopamine and GABA) provides the beginnings of a cognitive and neurophysiological understanding of this complex and intriguing phenomenon.

Activation of Heschl's gyrus during auditory hallucinations

Apart from being a common feature of mental illness, auditory hallucinations provide an intriguing model for the study of internally generated sensory perceptions that are attributed to external sources. Until now, the knowledge about the cortical network that supports such hallucinations has been restricted by methodological limitations. Here, we describe an experiment with paranoid schizophrenic patients whose on- and offset of auditory hallucinations could be monitored within one functional magnetic resonance imaging (fMRI) session. We demonstrate an increase of the blood oxygen level-dependent (BOLD) signal in Heschl's gyrus during the patients' hallucinations. Our results provide direct evidence of the involvement of primary auditory areas in auditory verbal hallucinations and establish novel constraints for psychopathological models.

Depressive symptoms and presynaptic dopamine function in neuroleptic-naive schizophrenia

We have previously reported aberrations in the striatal presynaptic dopamine function in neuroleptic-naive schizophrenic patients compared to healthy controls (Hietala, J., Syvälahti, E., Vuorio, K. et al., 1995. Lancet 346, 1130-1131). In this extended study we explore whether the altered presynaptic dopamine function correlates with the clinical symptomatology in schizophrenia. Striatal dopamine synthesis capacity (6-[18F]fluorodopa (FDOPA) uptake, Ki values) was studied with positron emission tomography in 10 neuroleptic-naive schizophrenic patients and 13 healthy controls. The clinical symptomatology was characterized with the Positive and Negative Symptom Scale (PANSS). The patients had an increased FDOPA uptake in striatum and lacked the asymmetry in caudate FDOPA uptake (p = 0.0005), confirming our earlier results. Left striatal FDOPA uptake (Ki) values correlated negatively with depressive symptoms in a highly significant manner. On the other hand, paranoid symptomatology correlated positively with right putamen FDOPA uptake at a trend level (rho = 0.73, p < 0.02). The lack of asymmetry in caudate Ki values did not associate with any dimension of psychopathology. The major finding in this study is that depressive symptoms in neuroleptic-naive first-admission schizophrenia are associated with low presynaptic dopamine function. This link appears to be hemisphere-related and may have drug-treatment implications, e.g., in prediction of response to D2 receptor blocking antipsychotic drugs. A possible connection between paranoid symptomatology and subcortical hyperdopaminergia is suggested, but this remains to be further verified.

Magnetoencephalography and magnetic source imaging: technology overview and applications in psychiatric neuroimaging

Magnetoencephalography (MEG) is an electrophysiologic brain imaging technology that has been applied to the study of mental illness, particularly schizophrenia. Like electroencephalography, it provides excellent temporal resolution, and in combination with magnetic resonance imaging, can also provide good spatial resolution. Studies of the auditory system in schizophrenia using MEG have demonstrated an abnormality in functional cerebral asymmetry, in which persons with schizophrenia typically show reduced, or reversed, cerebral asymmetry compared with normal subjects. This abnormality is sex-specific; it is more pronounced in males with schizophrenia. These findings have not been demonstrated using other neuroimaging strategies. Thus, MEG appears to offer a unique and valuable contribution to psychiatric neuroimaging. Current research and clinical applications of MEG are limited, however, by the high cost of instrumentation. The cost of MEG systems should improve as more applications are developed, in schizophrenia as well as other neuropsychiatric conditions, and hospitals begin to invest in the technology.

Underconstrained perception: a theoretical approach to the nature and function of verbal hallucinations

We do not see the world as it is. Perception forms a subjective image of the world in a language that has proven to be adaptive to our interaction with the external world. Perception is mainly determined by current needs of the organism and goals of behavior. Sensory processing itself does not culminate in perception and is not essential for perception, since perception derives from representations of internal symbols and their features. The current stimulation of sensory organs does, however, constrain our perception. Perception might be less constrained by the external world in cases of (1) increased attention, (2) decreased sensory stimulation, or (3) facilitated formation of cortical associations between representations of expectations and internal symbols. Hallucinations are perceptions that are underconstrained by external sensory stimulation. Verbal hallucinations that allow the patient to infer about his self-image might constitute the core psychopathology in a subset of schizophrenia. Commenting and discussing voices might be perceived under the pressure of increased attention to environmental factors that relate to the patient's social fears and wishes. Secondarily, delusions about the possession of thoughts and disorders of self-experience may develop.

Reversal of cerebral asymmetry in schizophrenia measured with magnetoencephalography

It has been suggested that schizophrenic patients fail to develop left-hemisphere dominance because of an early disturbance in neuronal development. This hypothesis has been supported by some post-mortem. CT and magnetic resonance imaging (MRI) studies, while other in-vivo studies have given contradicting results. We used 122-channel whole-head magnetoencephalography and MRI to locate the sources of auditory evoked responses in 19 schizophrenic patients and in 20 healthy controls. Auditory evoked responses were detected in all subjects. The left-right hemisphere asymmetry of cerebral sources for auditory evoked responses was markedly dispersed among patients when compared with controls. The source locations for left auditory cortex were clearly anterior with respect to the right hemisphere in 32% of the patients, while the corresponding prevalence of this abnormal asymmetry was 0% in controls (p = 0.008. Fisher's exact test). The reversed asymmetry appeared to be associated with a shorter anterior-posterior distance between the auditory cortex and the anterior tip of the temporal lobe in the left side when compared with the right side. The reversed asymmetry was associated with higher PANSS general psychopathological score, and especially with higher guilt feelings and motor retardation scores. The large 2.5-fold standard deviation in the inter-hemispheric anterior posterior difference in the location of the auditory cortex among patients (p 0.001 for the difference in the magnitude of variance between controls and patients) clearly reflects the dispersion of the left right asymmetry into both direction, and three of the patients with 'normal asymmetry' had a greater left-right asymmetry than any of the controls. Markedly greater reversal of hemispheric asymmetry among patients implies that regulation of the development of brain asymmetry is disturbed among schizophrenic patients. Abnormality in the cerebral asymmetry may be a crucial factor in the development of schizophrenic disorder in a substantial proportion of patients. The results suggest that the reversed asymmetry is associated with the higher severity of general psychopathological symptoms.

Abnormalities of auditory evoked magnetic fields and structural changes in the left hemisphere of male schizophrenics--a magnetoencephalographic-magnetic resonance imaging study

Functional and structural changes in 10 DSM-III-R male schizophrenics and 10 healthy volunteers were investigated using magnetoencephalographically (MEG) detected long-latency (N100 m) auditory evoked fields (AEFs) and magnetic resonance imaging (MRI). The AEFs were characterized by single moving equivalent dipoles, which were superimposed on MRIs. There were significant differences in dipole orientations and in AEF latencies in the left hemisphere of schizophrenics, when compared to the controls. The MEG-detected alterations were found to be associated with a bilateral volume reduction of the posterior superior temporal gyrus (pSTG), which was more pronounced in the left hemisphere. Separate analysis of white and gray matter has shown that the pSTG volume reduction resulted from decreased gray matter volumes without white matter changes. Both the functional and the morphological data indicate a left-hemispheric disturbance in our patients.