Functional tests of the corpus callosum in schizophrenia

Alpha-gamma interactions are disturbed in schizophrenia: a fusion of electroencephalography and functional magnetic resonance imaging

OBJECTIVE

To delineate regional brain activity associated with the alpha oscillations related to perception of sensory stimuli, and test the hypothesis that the synchronisation of alpha oscillations with stimulus onset is impaired in schizophrenia.

METHODS

Joint independent component analysis was applied to electroencephalographic and functional magnetic resonance imaging data recorded in 19 individuals with schizophrenia and 19 healthy individuals during a vibrotactile somatosensory task.

RESULTS

In healthy individuals the strongest component was dominated by alpha oscillations, and was associated not only with activity in somatosensory regions but also in the insula and anterior cingulate cortex (the salience network). In schizophrenia, the strongest component had low alpha power and activity was limited mainly to somatosensory regions. Furthermore, in the healthy group, but not the patients, significant correlation was observed between the strongest component and evoked gamma power.

CONCLUSION

The correlation between the alpha-dominated component and evoked gamma power is consistent with the hypothesis that gamma localised to sensory cortex elicits stimulus-locking of spatially distinct, large-scale ongoing alpha oscillations. Furthermore, this hypothesised mechanism appears to be disrupted in schizophrenia.

SIGNIFICANCE

These findings suggest that a weakened alpha-gamma interaction underlies impaired recruitment of the brain during sensory information processing in schizophrenia.

Evidence for reduced somatosensory lateralisation and focalisation in schizophrenia

Neuroimaging studies indicate diminished lateralisation of cerebral activity during motor tasks and language processing in schizophrenia. Some evidence also indicates that decreased lateralisation is accompanied by more diffuse intra-hemispheric activation, suggesting that diminished lateralisation might be part of a more general diminution of regional functional specialisation. In the case of passive processing of elementary somatosensory stimuli, evidence for decreased lateralisation derived from event-related potential studies, is conflicting. The greater spatial resolution of functional magnetic resonance imaging (fMRI) offers the potential to resolve this conflict. We report an fMRI study of 22 right-handed individuals with schizophrenia, 21 right-handed healthy individuals and 10 non-right-handed healthy individuals, designed to test the hypothesis that in schizophrenia there is a diminution of both lateralisation and intra-hemispheric focalisation during the passive processing of vibrotactile stimuli delivered to the right index finger. Significantly reduced lateralisation of activity in primary somatosensory cortex (SI) was observed in the schizophrenia group as compared to the healthy right-handed group. There was a trend for a reduction in SI lateralisation in the schizophrenia group compared to the healthy non-right-handed group. Contralateral SI focalisation was also significantly reduced in the schizophrenia group compared to both healthy groups. SI focalisation was negatively correlated with severity of disorganisation symptoms in the schizophrenia group. These results support the hypothesis that a generalised loss of functional specialisation is fundamental to schizophrenia.

A case of schizophrenia with complete agenesis of the corpus callosum

OBJECTIVE

To describe the case of a person with schizophrenia and agenesis of the corpus callosum.

CONCLUSION

A 24-year-old Caucasian woman with schizophrenia was incidentally found to have complete agenesis of the corpus callosum. A comprehensive neuropsychiatric assessment allowed management to be specifically tailored to the patient's unique clinical profile.

A study of transcallosal inhibition in schizophrenia using transcranial magnetic stimulation

A considerable body of imaging research has demonstrated morphological changes in the corpus callosum (CC) of patients with schizophrenia. Transcranial magnetic stimulation (TMS) allows the possibility for the in vivo investigation of a variety of aspects of brain function including the spread of information across the CC. We aimed to investigate whether patients with schizophrenia demonstrate abnormalities of transcallosal inhibition (TCI), a TMS parameter measured with both single and paired pulse experiments. 25 patients with DSM-IV schizophrenia and 20 normal volunteers participated in the study. Electromyographic (EMG) recordings from the bilateral abductor pollicis brevis (APB) muscle were made during focal TMS stimulation to the motor cortex. Experimental paradigms were utilised to measure both the timing and degree of the effect of TCI. The patient group demonstrated a reduction in the degree of TCI at rest and during a sustained muscle contraction. TCI commenced at the same time in the patient and the control group but was of prolonged duration in the patient group although the length of TCI correlated with medication dose. Patients with schizophrenia demonstrate a reduction in the degree of TCI that appeared independent of medication dose. The latency of TCI is not altered in the patient group suggesting that cortical inhibitory mechanisms, rather than corpus callosal ones, are likely to be the cause of these TCI alterations.

Dysfunction of transcallosally mediated motor inhibition and callosal morphology in patients with schizophrenia

OBJECTIVE

In order to assess the functional integrity of motor pathways through the corpus callosum (CC) in patients with schizophrenia transcallosally mediated inhibition (TI) of voluntary tonic EMG activity of first dorsal interosseus muscle following ipsilateral focal transcranial magnetic stimulation (fTMS) was investigated. In addition thickness and length of CC were calculated.

METHOD

Twelve patients suffering from schizophrenia and 12 healthy controls were investigated. CC morphology was measured in mid-sagittal MRI-slices. Latency and duration of TI were calculated.

RESULTS

In schizophrenics the duration of TI was significantly prolonged, whereas latencies were not. In addition, a lack of TI was found unilaterally in three patients. Measurements of CC revealed a significantly reduction of the length and thickness in the anterior part of CC in patients.

CONCLUSION

These findings indicate that measurement of TI could be used to detect clinical silent affection of transcallosal motor pathways in schizophrenics. The effect of neuroleptic drugs has to be explored.

Transfer and interference of motor skills in people with intellectual disability

Atypical laterality (i.e. the lack of a clear pattern of lateralization) has been found to be a characteristic feature of individuals with intellectual disability (ID). The evidence for this has been based on 'handedness' studies which have contained little information about the ability of people with ID to carry out interhemispheric tasks reflecting bilateral transfer or interference. The present study examined this capacity in individuals with ID by utilizing bilateral transfer and interference paradigms. Right-handed subjects with ID (IQ = 55-76) and controls matched for age and sex were tested for bilateral transfer of motor skill in contralateral hands with a mirror-drawing task. The subjects were also tested for their ability to perform a finger-tapping task while processing verbal and non-verbal stimuli. The findings indicated that people with ID are significantly deficient relative to matched controls in bilateral transfer of motor skills from their non-preferred (left) hand to their preferred (right) one. The effect of interference during performance of the dual task was significantly greater in individuals with ID. Subjects with ID were found to perform better with their non-preferred than with their preferred hand. A within-group comparison revealed that right-handed performance was more affected by interference than left in these subjects.

Shape and size of the corpus callosum in schizophrenia and schizotypal personality disorder

The size and shape of the corpus callosum were assessed on sagittal section magnetic resonance images in 27 patients with schizophrenia, 13 patients with schizotypal personality disorder (SPD), and 30 healthy volunteers. High-resolution 1.2mm axial SPGR images were acquired and resectioned so that the sagittal plane passed through the anterior and posterior commissures and was parallel to the interhemispheric fissure. The corpus callosum and the whole brain were traced on midsagittal section slices of each brain, and the callosum was divided into 30 anteroposterior sectors. Pixel-by-pixel chi-square and thin-plate spline analyses were used to assess between-group shape differences. Size of the corpus callosum was smaller anteriorly in the genu of the corpus callosum and posteriorly in the splenium in schizophrenic patients than in normal controls. The genu of the corpus callosum was larger in SPD patients than in schizophrenic patients or normal controls. The posterior corpus callosum was largest in normal controls, smaller in SPD patients, and smallest in schizophrenic patients. Shape analysis was consistent with these size comparisons, and suggested a downward bowing of the corpus callosum in schizophrenic and SPD patients. SPD patients also had a region of the callosum just posterior to the genu that was narrower than in the other two groups. The decreases in corpus callosal size in schizophrenia varied directly with length of illness, perhaps indicative of a progressive process. The patient-control differences in callosal size and shape are consistent with a hypothesis of decreased connectivity between the left and the right hemispheres in schizophrenia and SPD.

Bilateral transfer deficit in schizophrenia: a trait marker

Schizophrenic patients who had shown improvement over a 6-week treatment period were tested for their bilateral transfer of skill with a mirror-drawing task. Compared with first degree relatives and normal control subjects, patients showed a significant deficit in bilateral transfer of skills in terms of response accuracy both before and after treatment. These findings indicate that the deficit is an enduring functional loss in schizophrenia.

A computerized magnetic resonance imaging study of corpus callosum morphology in schizophrenia

The hypothesis tested was that, in schizophrenia, corpus callosum size would be reduced, particularly in the region responsible for communication between both temporal lobes. This is supported by knowledge of: (a) anatomical homotopicity and functional specialization of fibres within the corpus callosum; (b) evidence linking structural and functional deficits of the corpus callosum and left temporal lobe with schizophrenia; and (c) that temporal lobe neuronal fibres pass through the middle region of the corpus callosum. Brain area and corpus callosum areas, widths and length were measured on mid-sagittal MRI scans using a computer outlining method. Scans from 30 schizophrenics and 44 normal subjects were compared. Mid-sagittal brain area, corpus callosum area, length and anterior widths were reduced in the schizophrenic group compared with controls. A significant area difference between schizophrenics and controls was seen in the mid-corpus callosum which communicates between the temporal lobes, including the superior temporal gyri. In schizophrenics, corpus callosum area reduction was not accounted for by brain area shrinkage alone. Differences between the two groups were accounted for by comparisons between males only. These findings support the hypothesis and the possibility that localized abnormalities of bilaterally connected brain regions might have secondary effects on their homotopically distributed fibres within the corpus callosum.

Early cortical tactile-evoked potentials, laterality and schizophrenia

No significant difference in the lateralisation of tactile-evoked potentials was found when a tactile stimulus was applied to the index finger of 14 schizophrenic patients and 14 age- and sex-matched controls. The early tactile responses, recorded from contralateral and ipsilateral parietal scalp electrodes, were compared. Our results differ from previously reported results.

Somatosensory evoked potentials in schizophrenia. A lateralisation study

The SSEPs obtained from 19 schizophrenics defined by RDC, DSM-III and PSE criteria were compared with those from a control group of healthy volunteers. Previous findings of an abnormal lack of lateralising response in schizophrenic patients were not replicated. No significant difference in either amplitude or morphology between the traces obtained from the two groups were recorded. Ipsilateral and contralateral latencies for stimulation of the left and right index finger showed no significant difference in peak latency for any component between patient and control group. When mean peak-to-peak amplitudes were plotted the contralateral component was always greater in amplitude than the ipsilateral one. An objective measure of the degree of lateralisation, the percentage lateralisation quotient, showed no lateralisation differences between the patient and control groups. A case of myogenic contamination of ipsilateral components was observed calling into doubt findings where no temporal region monitoring has been performed.

Schizophrenia, corpus callosum, and interhemispheric communication: a review

The literature suggests that some schizophrenic patients may have a dysfunction in the transfer of information between the two cerebral hemispheres via the corpus callosum (CC). The presence of an abnormally thickened CC in some schizophrenic patients and an abnormally thin CC in others suggests a possible anatomic basis for abnormal organization of cognitive functions in these patients resulting from either increased or decreased communication between the two cerebral hemispheres. The findings of the anatomic studies have suggested a connection between a thickened CC and both early onset and negative symptom patterns in schizophrenic patients. Similarly, onset of symptoms later in life and positive symptom patterns have been associated with a thinner CC. Behavioral and electrophysiological findings appear to support the idea that the same subgroups may be associated with opposite patterns of effective transfer of information between the cerebral hemispheres. Careful analysis of the transfer of information between the cerebral hemispheres for selected groups of schizophrenic patients and normal controls could provide important information about cerebral organization and possible mechanisms operative in schizophrenia.

Visuo-motor reaction times of normal subjects and schizophrenics using inverting prisms

The visuo-motor reaction times of normal subjects and schizophrenics were measured to investigate adaptation of eye-hand coordination in schizophrenics under modified vision. Reaction time was measured in 32 normal subjects and 32 schizophrenics by using a rectangular board with 24 illuminated buttons. Subjects' task was to press an illuminated button as quickly as possible under normal and modified vision. Time elapsed from when the light was switched on to when the button was pressed was measured as the visuo-motor reaction time in msec. Three conditions were set up: control in normal vision; inverted using an inverting goggle; reversed using a reversing goggle. In general the visuo-motor reaction times of schizophrenics were slower than those of normal subjects. But in the reversed condition, there was no significant difference between normal subjects and schizophrenics. The visuo-motor reaction times of schizophrenics in the reversed condition showed a large dispersion with the fastest being faster than that of any normal subjects. It is suggested that there may be a group among schizophrenics whose basic paradigm of visuo-motor association is different from that of normal subjects.

Agenesis of the corpus callosum and schizophrenia: a case report

Clinical, radiological and neuropsychological findings in the first reported case of schizophrenia with complete agenesis of the corpus callosum are described. Although causal inferences were made difficult by the co-existence of a left frontotemporal cyst and a family history of affective disorder, some theories of the role of callosal dysfunction in schizophrenia require revision in the light of this case.

Specific imbalance of right and left sided motor neuron excitability in schizophrenia

Fifty-three psychiatric patients, 16 with schizophrenia, 19 with affective disorder, and 19 with schizo-affective disorder were diagnosed by Research Diagnostic Criteria. Hoffmann reflex recovery curves were measured in the right and left legs of each patient. In both affective disorder and schizo-affective disorder, recovery curve height in the right and left legs was highly correlated. In schizophrenia, recovery curve height in the right and left legs was not correlated. These results demonstrate a right-left asymmetry in motor neuron excitability specific to schizophrenia. The findings are compatible with a deficit in hemispheric transfer that is unique to schizophrenia. Other interpretations can be made, including diffuse cortical or subcortical dysfunction in schizophrenia which disrupts transfer or interpretation or intrahemispheric communication.

Somatosensory evoked potential activity: a measure of interhemispheric transfer in schizophrenia?

Jones and Miller (1981) reported that schizophrenics could be distinguished from healthy controls by latency differences in their ipsilateral and contralateral somatosensory evoked potentials (SEPs), considered a measure of corpus callosum conduction time. Subsequent replication studies failed to follow the method of the original study. The present study represents a precise replication. An additional control for contamination of SEPs by an auditory stimulus generated by the vibrotactile stimulus was used. Ipsilateral SEP activity was identified but poor definition of a positive peak in the range of interest prevented measurement of peak latency. Evidence was advanced to suggest that such ipsilateral potentials result from activity at the vertex. It was concluded that this method is inappropriate for the investigation of interhemispheric transmission.

Tachistoscopic tests of colour naming and matching in schizophrenia: evidence for posterior callosum dysfunction?

Neuropsychological studies have shown that the integrity of the posterior corpus callosum is necessary for accurate colour naming in the left visual field (LVF) and colour matching across hemifields. Using this model, 22 schizophrenics, 14 depressive and 16 healthy matched controls were given a battery of tachistoscopic tests of colour perception. The schizophrenics made significantly more errors, in naming colours in the LVF compared to depressives, and in matching colours across fields compared to depressives and normals. There were no differences between groups for right visual (RVF) colour naming or matching within right and left visual fields. These findings support the hypothesis that trans-callosal transmission may be impaired in schizophrenia and are unlikely to be due to a specific disorder of colour perception, neuroleptic drugs or generally impaired performance. Those schizophrenics whose LVF naming errors exceeded RVF errors were more likely to have first rank symptoms and showed less cerebral atrophy but did not differ on other variables. The techniques described may be useful for further research into interhemispheric function in schizophrenia.

Corpus callosum function in schizophrenia: a neuropsychological assessment of interhemispheric information processing

Impaired corpus callosum function has been reported in schizophrenia. We measured intra- and interhemispheric visual information processing in 16 schizophrenic patients and 16 matched controls. Although the schizophrenics performed worse between than within cerebral hemispheres, this pattern was similar to that of the normal controls. Schizophrenics do not show particular dysfunction of the corpus callosum.

Biological substrates of schizophrenia

Schizophrenia is increasingly believed to represent a group of organic disorders which primarily, although not exclusively, affect the central nervous system. Our purpose is to review a representative sample of twentieth-century literature which speaks to the biological substrates of the syndrome. Subjects reviewed include genetic and environmental contributions to the onset of illness, early and recent findings of gross structural anomalies, and apparent histopathological alterations in cerebral cortex, cerebellar vermis, limbic system, and brain stem, as well as problems of cerebral asymmetry. Data from a diverse group of electrophysiological studies reveal several promising correlates of these areas of investigation. Despite the inconsistent nature of the findings to date, several themes have begun to emerge, including patterns of hypofrontal/hyperparietal regional cerebral flow and glucose utilization, left hemispheric dysfunction, and deficits of interhemispheric information processing. The interpretation and significance of these emerging patterns remains unclear and must await more profound insights into the nature of normal and abnormal cerebral function.

Density values of the corpus callosum in schizophrenic brains

Density values of the corpus callosum and ventricular brain ratio (VBR) were obtained by coronal computerized tomography (CT) in 16 chronic schizophrenic patients and 16 normal controls. The corpus callosum of schizophrenic brains showed no apparent density loss which could indicate a dysfunctional brain. A significant ventricular dilatation was found in the patient group compared with age-matched controls. This finding was compatible with several former observations with transverse scanning.

Interhemispheric transmission: assessment with vibratory somatosensory evoked potentials

Interhemispheric transmission time (ITT) was derived from vibratory somatosensory evoked potentials (VSEP) arising in homologous cortical sensory--association areas of normals. Two different vibratory sources, an audiometer bone oscillator or an Optacon, were used to stimulate each index finger independently. ITT was calculated by subtracting the latency of the first major peak over the contralateral cortex (CL) from the latency of the corresponding peak over the ipsilateral area (IL-CL = ITT). Readily identified aberrant values were observed and rejected from the series of measurements leaving clear normal ranges. In addition to providing normal ITT data, clinical correlations were illustrated in two different disorders. Results suggested that important information relating to diagnosis and therapy of brain pathologies affecting interhemispheric transmission can now be made available in both experimental and clinical situations.

Stable abnormalities in the lateralisation of early cortical somatosensory evoked potentials in schizophrenic patients

During the investigation of somatosensory evoked cortical potentials arising from a complex vibro-tactile stimulus to the forefingers, an abnormal lack of lateralisation of response was found in 10 out of 21 schizophrenic patients. Eight patients with severe affective illness all had the expected degree of lateralisation of cortical potentials, as did 12 out of 15 normals. Three normals and 3 schizophrenic patients had a loss of lateralisation of the evoked response on stimulation of one hand but a normal lateralisation on stimulation of the other. The considerable technical problems of this and related techniques are discussed, but it is suggested that further exploration of this technique is justified. At this stage, no conclusion can be drawn about the cause of the abnormalities.

Voluntary control of two lateralized conscious states: validation by electrical and behavioral studies

A subject is described who can voluntarily select and hold either of two qualitatively different states of consciousness. Evidence is presented which confirmed differential left or right hemisphere dominance in each state. Asymmetries of EEG alpha and task performance scores indicated a state-dependent shift in functional lateralization. Evoked response studies showed directional changes in rate of interhemispheric transmission correlated with state-related hemisphere dominance. These findings demonstrated that capability for voluntary endogenous control of cerebral dominance under natural conditions.

Tactile-evoked potentials in schizophrenia. Interhemispheric transfer and drug effects

EEG potentials evoked by tactile stimulation of the forearm (tactile-evoked potentials or TEPs) were recorded simultaneously from both cerebral hemispheres in a group of schizophrenics and a group of healthy control subjects. Differences between the groups were found for the early waves of the TEPs: in the control subjects the first two positive waves (P25 and P50) and the first negative wave (N35) recorded from the hemisphere on the same side as the stimulation were slower (i.e. had longer latency) than those recorded from the hemisphere contralateral to the stimulation. This 'lateralization effect' was not seen in the schizophrenic subjects. It was concluded that the TEPs recorded from the hemisphere ipsilateral to the stimulus were not being transmitted from the other hemisphere via the corpus callosum and must therefore have been transmitted via direct ipsilateral pathways from the periphery. In a second experiment the drug pindolol was administered to schizophrenic subjects but differences in P50 latency between ipsilateral and contralateral hemispheres were found equally in both drug and placebo groups. We also found slight evidence to suggest that the more severely ill the patient the more similar the TEP latencies recorded from the contralateral and the ipsilateral hemispheres.

Failure to replicate evoked potential observations suggesting corpus callosum dysfunction in schizophrenia

Somatosensory potentials (SEPs) evoked by vibrotactile finger stimulation have been reported to be the same in both hemispheres in schizophrenics, whereas they are asymmetrical in normals, with the contralateral hemisphere leading the ipsilateral (Jones and Miller, 1981). These findings were taken to indicate that the corpus callosum is nonfunctional in schizophrenics. To attempt replication of these results, vibrotactile SEPs of 6 schizophrenics and 6 normal controls were recorded with both bipolar and monopolar derivations. Asymmetrical bipolar SEPs were obtained in both schizophrenics and controls; previous observations of schizophrenic-control differences were not replicated. Acceptable evidence of ipsilateral early SEPs was not obtained; the test procedure seems inappropriate for measuring callosal conduction time.

EEG coherence, lateral preference and schizophrenia

The EEG synchrony between hemispheres during cognitive activity differs from that during rest. With common reference recording and a visual imagery task it increases in healthy right-handers and neurotic patients, and it decreases in healthy left-handers and schizophrenic patients. It is suggested that this implies a less lateralized brain organization in schizophrenia which may account for the often reported association with left-handedness. When associated with impaired corpus callosum transmission, it may contribute to the disturbed behaviour and thought processes in this condition.

A histological study of the corpus callosum in chronic schizophrenia

As a followup to a post-mortem study of the brains of schizophrenic and control subjects where the corpus callosum was found to be significantly thicker anteriorly in early onset compared to late onset schizophrenia, histological sections of 18 schizophrenic, 7 manic-depressive, and 11 medical/surgical control subjects were prepared using a stain for glia and a stain for callosal fibers. A quantitative study of the concentration of glial cells and interhemispheric callosal fibers revealed no difference between groups. A neuropathologist unaware of the tissue origin rated the histological sections for gliosis. There was significantly more severe gliosis in the callosi of the late onset schizophrenics compared to early onset schizophrenics as well as the control group. These preliminary findings suggesting callosal pathology are discussed, and the need for further studies is stressed.

Corpus callosum thickness in chronic schizophrenia

In an effort at replication of the original report (Rosenthal and Bigelow, 1972) of increased callosal thickness in schizophrenic brains, the corpus callosum was measured in a blind study of 64 brains autopsied between the years 1972 and 1976. Diagnosis was established by independent chart review. The mean corpus callosum mid sections of 21 early onset chronic schizophrenic brains were found to have a significantly greater thickness when compared with 8 subjects with late onset schizophrenia, 13 patients with neurological diagnoses, or 14 patients with other psychiatric diagnoses. These studies, if independently confirmed, should provide an impetus for testing the hypothesis that some chronic schizophrenic patients have an illness associated with a pathological process in the corpus callosum.