Abnormalities of auditory evoked magnetic fields in the right hemisphere of schizophrenic females

Absence of auditory M100 source asymmetry in schizophrenia and bipolar disorder: a MEG study

Background

Whether schizophrenia and bipolar disorder are the clinical outcomes of discrete or shared causative processes is much debated in psychiatry. Several studies have demonstrated anomalous structural and functional superior temporal gyrus (STG) symmetries in schizophrenia. We examined bipolar patients to determine if they also have altered STG asymmetry.

Methods

Whole-head magnetoencephalography (MEG) recordings of auditory evoked fields were obtained for 20 subjects with schizophrenia, 20 with bipolar disorder, and 20 control subjects. Neural generators of the M100 auditory response were modeled using a single equivalent current dipole for each hemisphere. The source location of the M100 response was used as a measure of functional STG asymmetry.

Results

Control subjects showed the typical M100 asymmetrical pattern with more anterior sources in the right STG. In contrast, both schizophrenia and bipolar disorder patients displayed a symmetrical M100 source pattern. There was no significant difference in the M100 latency and strength in bilateral hemispheres within three groups.

Conclusions

Our results indicate that disturbed asymmetry of temporal lobe function may reflect a common deviance present in schizophrenia and bipolar disorder, suggesting the two disorders might share etiological and pathophysiological factors.

Brain imaging: on the way toward a therapeutic discipline

Brain imaging has proven its importance as an essential tool of neuroscientific research, especially in psychiatry. Several of these methods at hand promise to enhance our understanding of function and dysfunction of neural processes and their disturbances in mental disorders in the near future. But the convincing success of imaging tools in research has not yet answered the demand to lead to new therapies or to new and useful tools in the diagnosis and treatment of single subjects. This article tries to point out how new methodological developments are promising to lead to a further step in this way. This therapeutic option is based on technical developments like high-field magnetic resonance imaging (MRI) or the further development of neurofeedback. This concept might make brain imaging such as realtime fMRI a therapeutic option at least in specialized institutions in the foreseeable future, especially since MR-scanners are already widely available nowadays.

MEG auditory evoked fields suggest altered structural/functional asymmetry in primary but not secondary auditory cortex in bipolar disorder

OBJECTIVES

Objective physiological indices independently characterizing affective and schizophreniform psychoses would contribute to our understanding of the nature of their relationships. Magnetoencephalography (MEG)-based metrics of altered structural/functional asymmetry in the superior temporal gyrus have previously been found to characterize schizophrenia at the level of both the primary auditory (AI) and the secondary auditory (AII) cortex. This study examines these markers in patients with bipolar disorder, with the goal of improved understanding of the patterns of brain asymmetry that may independently characterize affective and schizophreniform psychosis.

METHODS

We studied 17 euthymic bipolar subjects and 17 matched controls. Auditory evoked fields were generated by both 40 Hz auditory stimuli eliciting steady state gamma band (SSR), activating the AI cortex, and discrete 1 kHz tone pips, activating the AII cortex. MEG was recorded from the hemisphere contralateral to the ear stimulated using a 37-channel MEG system. Source location estimates were calculated in both left and right hemispheres. Neuroanatomical location estimates for medial Heschl's gyri were determined from magnetic resonance images for correlation with MEG source locations.

RESULTS

Bipolar subjects failed to demonstrate normal laterality of SSR AI responses, indicating altered patterns of asymmetry at the level of AI cortex, but demonstrated normal asymmetry of AII responses (right anterior to left). Medial Heschl's gyri centroids were similarly lateralized in both groups, however (right anterior to left), dissociating function from structure in the AI cortex in the bipolar group.

CONCLUSIONS

The findings are compatible with altered functional/structural relationships, including diminished left-right hemisphere asymmetry of the AI, but not the AII cortex in bipolar disorder. In schizophrenia, both the AI and AII cortices exhibit such derangements; thus, the findings support both shared and nonshared features of auditory cortical disruption between the two disorders. This functional disorganization may help explain previously reported decreases in amplitude and phase synchrony of SSR gamma band responses in bipolar subjects, suggesting impaired neocortical synchrony in AI, possibly at a cortico-thalamic level, but perhaps not extending to heteromodal association cortex, and may relate to the cognitive impairments found in bipolar disorder.

Aberrant functional organization and maturation in early-onset psychosis: evidence from magnetoencephalography

Studies of the location of somatosensory and auditory cortical responses have shown anomalous hemispheric asymmetries in a variety of neurodevelopmental disorders. To date, abnormal asymmetries in the somatosensory region have shown greater specificity, being reported only in psychotic adults. This study examines the functional organization of the somatosensory cortices using magnetoencephalography in adolescents with childhood-onset psychotic disorders. Eighteen young outpatients with history of psychotic illness and 15 healthy adolescents participated. Both groups underwent stimulation of the index finger as magnetoencephalography was acquired from the contralateral hemisphere. Neural generators of the M50 somatosensory response were modeled using an equivalent current dipole for each hemisphere, and later investigated for systematic variation with diagnosis. Consistent with adult psychosis data, adolescent patients showed hemispheric symmetry in the anterior-posterior dimension. In controls, a reversed pattern of hemispheric asymmetry was observed relative to previous findings in normal adults [Reite, M., Teale, P., Rojas, D.C., Benkers, T.L., Carlson, J., 2003. Anomalous somatosensory cortical localization in schizophrenia. American Journal of Psychiatry 160, 2148-2153], but trend-level correlations suggested source location became more adult-like during the transition from adolescence to adulthood. Source parameters also exhibited robust inter-hemispheric correlations only in adolescent controls. In sum, source locations, patterns of cerebral lateralization, and inter-hemispheric correlations all distinguish patients from their normally developing cohort. These findings suggest aberrant maturation underlies the reduction in cerebral laterality associated with psychosis.

Right hemispheric dysfunction in schizophrenia

This study uses the Poffenberger (1912) paradigm, which compares the difference between "crossed" (stimuli and motor response areas are contralateral) and "uncrossed" (stimuli and motor response areas are ipsilateral) conditions to estimate interhemispheric transfer time. Simple reaction time (RT) was recorded to stimuli presented to the left visual field (LVF), right visual field (RVF), or bilaterally (BVF) in individuals with schizophrenia (n = 10) and controls (n = 14), who responded using either the left or right hand. While the results provide no evidence for differences between the groups in information transfer between the hemispheres, the schizophrenia group were significantly slower to respond to LVF stimuli, suggesting right hemisphere dysfunction.

Alterations in tonotopy and auditory cerebral asymmetry in schizophrenia

BACKGROUND

Deficits in basic auditory perception have been described in schizophrenia. Previous electrophysiologic imaging research has documented a structure-function disassociation in the auditory system in schizophrenia. This study examines whether the most fundamental level of auditory cortical organization, tonotopy, is altered in schizophrenia.

METHODS

The tonotopic organization for five tone frequencies in 19 patients with schizophrenia and 22 comparison subjects was evaluated using magnetoencephalography. Auditory evoked magnetic field dipole locations were examined for the N100m component for each frequency.

RESULTS

The expected linear relationship between depth and frequency was found in the comparison subjects but not in the schizophrenia group (p <.004). In addition, normal anterior-posterior asymmetry of the N100m was found to be reduced at all five stimulation frequencies employed in the study (p <.04). No relationships between clinical symptom ratings and either tonotopy or asymmetry were observed.

CONCLUSIONS

This finding suggests that the tonotopic organization of the auditory cortex in schizophrenia is disturbed and may help explain the relatively poor behavioral performance of schizophrenia patients on simple frequency discrimination tasks. Alterations in fundamental sensory organization may underlie or interact with higher order cognitive mechanisms to produce changes in cognitive task performance.

Schizotypy and patterns of lateral asymmetry on hemisphere-specific language tasks

Following the notion that abnormalities of hemispheric asymmetry may underlie schizophrenia, patterns of cognitive hemispheric asymmetries, as assessed by left and right hemisphere language tasks, were examined in relation to schizotypal symptoms. Ninety right-handed undergraduates completed the Oxford-Liverpool Inventory of Feelings and Experiences questionnaire (O-LIFE; Mason, O., Claridge, G., Jackson, M., 1995. New scales for the assessment of schizotypy. Personality and Individual Differences, Vol. 53, pp. 727-730), which measures different aspects of schizotypy symptomatology. Low scores on right, but not left, hemisphere language tasks were significant predictors of high scores on positive schizotypal symptomatology scales (Unusual Experiences and the STA) over and above the contributions of the left hemisphere language tasks and demographic variables. Low scores on both left and right hemisphere language tasks were significant predictors of high scores on the Cognitive Disorganisation factor, over and above the contributions of tasks related to the contralateral hemisphere and demographic variables. Neither the right nor the left hemisphere language tasks resulted in a significantly good degree of prediction of introvertive anhedonia (an index of negative schizotypal symptomatology) or impulsive non-conformity. The findings provide partial support for some current theories of hemispheric differences in schizophrenia and schizotypy.

Tonotopy of the Auditory-Evoked Field Component N100m in Patients with Schizophrenia

Abstract A number of clinical studies on the auditory neuromagnetic evoked field (AEF) component N100m have reported an altered lateralization in schizophrenic patients. This study addresses the problem of a possible functional reorganization of the temporal cortex in schizophrenia by examining the tonotopic organization of the N100m. Thirty-two patients with schizophrenia and 33 healthy controls of both sexes took part. Two tone frequencies (1000 and 5000 Hz tone) were applied for auditory stimuli, and AEF were recorded over both hemispheres successively using a 31-channel biomagnetometer. The comparison of N100m dipole location and orientation between hemispheres revealed no alterations in male or female patients. Between tone frequencies highly significant differences were found for N100m peak latency, mean global field power, dipole orientation, and dipole location in the anterior-posterior direction. Although the main effects of frequency were found to be the same in patients and controls, the balance between hemispheres was altered in patients with schizophrenia, with respect to the dependence between frequency and dipole location in the anterior-posterior direction as well as between frequency and latency. In patients, the influence of frequency on these variables was more pronounced in the right hemisphere and less pronounced in the left, compared to controls.

Habituation of the auditory evoked field component N100m in male patients with schizophrenia

The auditory evoked field (AEF) component N100m represents the most prominent and stable peak of the AEF, and its alterations in patients with schizophrenia are an extensive topic of neuropsychiatric research. In our current study, the degree of N100m habituation was investigated in 20 male schizophrenics and 19 healthy male controls. Participants were stimulated monaurally with 270 trials of 1000 Hz tones separated by an interstimulus interval between 800-1800 ms. The trial sample of the bilaterally recorded AEF was separated into three consecutive blocks of 90 trials and these blocks were compared with each other. The mean global field power (MGFP) of the N100m decreased on average 9.1% from the first to the third trial block, while the N100m latency was increasing. The analyses of the influence of habituation revealed a systematic change of dipole location in inferior-superior direction, mainly in the left hemisphere. This habituation effect was found to be the same for both groups. The groups also did not differ in the N100m latency increase and MGFP decrease, except for one parameter. The right-hemispheric MGFP decrease from the first to second block was found to be more pronounced in patients compared to controls. However, this difference was related to medication with clozapine. Overall, the habituation behaviour of the N100m seems to be undisturbed in schizophrenic patients.

Latency of the auditory evoked neuromagnetic field components: stimulus dependence and insights toward perception

This review will focus on investigations of the auditory evoked neuromagnetic field component, the M100, detectable in the magnetoencephalogram recorded during presentation of auditory stimuli, approximately 100 milliseconds after stimulus onset. In particular, the dependence of M100 latency on attributes of the stimulus, such as intensity, pitch and timbre will be discussed, along with evidence relating M100 latency observations to perceptual features of the stimuli. Comparison with investigation of the analogous electrical potential component, the N1, will be made. Parametric development of stimuli from pure tones through complex tones to speech elements will be made, allowing the influence of spectral pitch, virtual pitch and perceptual categorization to be delineated and suggesting implications for the role of such latency observations in the study of speech processing. The final section will deal with potential clinical applications offered by M100 latency measurements, as objective indices of normal and abnormal cortical processing.

Bipolar disorder: anomalous brain asymmetry associated with psychosis

OBJECTIVE

Anomalous cerebral asymmetry in schizophreniform disorders has been described, but its presence in psychotic mood disorders has not been established. Measures of cerebral asymmetry may distinguish patients with psychotic mood disorders from those with nonpsychotic mood disorders and from comparison subjects. To test this hypothesis, the authors examined functional cerebral asymmetry by using a metric based on magnetic source imaging.

METHOD

A total of 33 subjects participated. Nine were patients with bipolar I disorder and a negative history of psychotic symptoms during mood disorder episodes, 12 were patients with bipolar I disorder and a positive history of psychotic symptoms during mood disorder episodes, and 12 were nonpsychiatric comparison subjects. Equivalent current dipole generators in both hemispheres were estimated for the 20-msec-latency somatosensory evoked field (M20) component produced by stimulation of the contralateral median nerve.

RESULTS

The comparison subjects demonstrated asymmetry in anterior-posterior equivalent current dipole locations of the M20 (right anterior to left), and the bipolar subjects with no history of psychosis were similarly asymmetric. The bipolar subjects with a history of psychosis during mood episodes, however, demonstrated a reversal of cerebral asymmetry of the M20 (left anterior to right).

CONCLUSIONS

Cerebral lateralization of the M20 distinguished bipolar subjects with psychosis from those without psychosis and comparison subjects. The M20 is generated in area 3b of the postcentral gyrus. These findings suggest anatomical displacement of the postcentral gyrus in psychotic disorders and support the hypothesis that anomalous cerebral asymmetry is a feature of psychotic disorders generally, including psychotic mood disorders.

Schizoaffective disorder: evidence for reversed cerebral asymmetry

BACKGROUND

Schizoaffective disorder is one of the most severe of the affective psychoses, but its pathophysiology is poorly understood. Because cerebral lateralization may be disturbed in psychotic disorders generally, studies examining cerebral asymmetry may improve understanding of the neurobiology specific to schizoaffective disorder. This study examines cerebral lateralization in this patient population using magnetic source localization.

METHODS

We studied 16 subjects with schizoaffective disorder and 16 controls. Magnetic source localization was used to identify the location of the 20 msec latency somatosensory evoked field component (M20).

RESULTS

In control subjects, the source location was further anterior in the right hemisphere. The subjects with schizoaffective disorder were reverse lateralized.

CONCLUSIONS

The findings of a reversed asymmetry of the M20 in patients with schizoaffective disorder suggest an anatomical shift in the placement of the post central gyrus in this disorder, compatible with a disorder of cerebral lateralization. Whether this finding converges or diverges with measurement of the M20 in other psychotic disorders will require further investigation.

Impaired sensory processing in male patients with schizophrenia: a magnetoencephalographic study of auditory mismatch detection

The generation of mismatch negativity (MMN) as a component of auditory evoked event-related brain potentials has been reported previously to be severely disturbed in patients with schizophrenia. In the present study, we extended these findings to magnetoencephalography and investigated the neuromagnetic mismatch field (MMNm) in 15 male schizophrenic inpatients as compared to 16 healthy male volunteers. A standard tone of 1000 Hz and three different types of mismatch (1050-Hz tone, 5000-Hz tone, tone omission) were employed within the same paradigm, each mismatch occurring with a 10% pseudorandom probability. After correction for eye artifacts, the mean global field power of the mismatch reaction was calculated. Mismatch generation in patients with schizophrenia proved to be significantly impaired for all three conditions. This result confirms the theory of impaired auditory information processing in patients with schizophrenia at the level of the primary auditory cortex. Deficient generation of MMNm probably represents an impaired generation and/or faster decay of the sensory memory trace on the basis of disturbed sensory processing in male patients with schizophrenia.

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.

Quantification and rejection of ocular artifacts in auditory evoked fields in schizophrenics

RESULTS

In a magnetoencephalographic investigation of the auditory evoked field (AEF) in 17 schizophrenics and 17 controls, 37% of the schizophrenics and 12% of the controls showed eye artifacts in every second trial or even more frequently. In the uncorrected average fields, the ratio between the power of artifacts and the power of the magnetoencephalogram (MEG) exceeded the value of 0.1 for 48% of the schizophrenics and for 29% of the controls. Ocular artifacts biased the locations of equivalent current dipoles of the M100 component towards deeper positions. A regression algorithm for the correction of ocular artifacts in raw data and an identification technique of ocular artifacts based on the topography of transmission coefficients is described.

CONCLUSIONS

A linear dependence of ocular artifacts in AEF on the electrooculogram (EOG) was confirmed. Possible errors introduced by the correction are discussed. Transmission coefficients should be calculated for several individual trials with the same type of artifact. Errors due to evoked potentials in the EOG were found to be comparable in amplitude to noise in the AEF. Examples of transmission coefficients from the EOG to the MEG are given.

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.