Corpus callosum size and inter-hemispheric function in schizophrenia

Abnormalities in hemispheric lateralization of intra- and inter-hemispheric white matter connections in schizophrenia

Hemispheric lateralization is a prominent feature of the human brain and is grounded into intra- and inter-hemispheric white matter (WM) connections. However, disruptions in hemispheric lateralization involving both intra- and inter-hemispheric WM connections in schizophrenia is still unclear. Hence, a quantitative measure of the hemispheric lateralization of intra- and inter-hemispheric WM connections could provide new insights into schizophrenia. This work performed diffusion tensor imaging on 50 patients and 58 matched healthy controls. Using graph theory, the global and nodal efficiencies were computed for both intra- and inter-hemispheric networks. We found that patients with schizophrenia showed significantly decrease in both global and nodal efficiency of hemispheric networks relative to healthy controls. Specially, deficits in intra-hemispheric integration and inter-hemispheric communication were revealed in frontal and temporal regions for schizophrenia. We also found disrupted hemispheric asymmetries in brain regions associated with emotion, memory, and visual processes for schizophrenia. Moreover, abnormal hemispheric asymmetry of nodal efficiency was significantly correlated with the symptom of the patients. Our finding indicated that the hemispheric WM lateralization of intra- and inter-hemispheric connections could serve as a potential imaging biomarker for schizophrenia.

Altered interhemispheric signal propagation in schizophrenia and depression

OBJECTIVE

Altered interhemispheric connectivity is implicated in the pathophysiology of schizophrenia (SCZ) and major depressive disorder (MDD) and may account for deficits in lateralized cognitive processes. We measured transcranial magnetic stimulation evoked interhemispheric signal propagation (ISP), a non-invasive measure of transcallosal connectivity, and hypothesized that the SCZ and MDD groups will have increased ISP compared to healthy controls.

METHODS

We evaluated ISP over the dorsolateral prefrontal cortex in 34 patients with SCZ and 34 patients with MDD compared to 32 age and sex-matched healthy controls.

RESULTS

ISP was significantly increased in patients with SCZ and patients with MDD compared to healthy controls but did not differ between patient groups. There were no effects of antidepressant, antipsychotic, and benzodiazepine medications on ISP and our results remained unchanged after re-analysis with a region of interest method.

CONCLUSION

Altered ISP was found in both SCZ and MDD patient groups. This indicates that disruptions of interhemispheric signaling processes can be indexed with ISP across psychiatric populations.

SIGNIFICANCE

These findings enhance our knowledge of the physiological mechanisms of interhemispheric imbalances in SCZ and MDD, which may serve as potential treatment targets in future patients.

Corpus callosum microstructural and macrostructural abnormalities in schizophrenia according to the stage of disease

Corpus callosum (CC) volume and surface (macrostructural) studies remain controversial and have not considered the illness duration (ID) systematically. Regardless of ID, some CC macrostructural studies have shown no difference between SZ patients and healthy controls (HC), whereas others have reported macrostructural abnormalities in SZ. Conversely, CC microstructural studies are more in agreement with alterations in CC integrity regardless of the patients' ID, but the direction and degree of these abnormalities over time remain unknown. Moreover, no study has explored both the micro- and macrostructure of the CC in SZ by considering the stage of disease. Both CC micro- and macrostructural data were investigated in 43 SZ patients and compared between two patient groups (21 patients with a short ID and 22 with a long ID) and HC (23 participants) using diffusion tensor and structural imaging. CC microstructural alterations were detected in both SZ groups compared to the HC group, without differences between the SZ groups. In contrast, CC macrostructural alterations were only found in the long ID group. CC microstructural alterations might be detected in schizophrenia at an early stage, without an increase of magnitude thereafter, while CC macrostructural alterations might become apparent at later stages of the illness.

Scientific Evidence for the Evaluation of Neurological Soft Signs as Atypical Neurodevelopment Markers in Childhood Neuropsychiatric Disorders

Motor dysfunction is commonly present in children with neurodevelopmental disorders. Developmental changes in voluntary control of motor skills include improvements in speed and motor coordination as well as reduced frequency of neurological soft signs (NSS) that are commonly observed in typically developing younger children. NSS are motor and sensory conditions that cannot be linked to specific cerebral lesions. The persistence of NSS into later childhood and adolescence is linked with an increased risk of psychiatric disorders. This finding gives support to the neurodevelopmental model of NSS in which minor neurological impairments may be viewed as potential signs of deviant brain development and might represent trait markers of vulnerability for neurodevelopmental disorders. Given that NSS are easily detectable, it is important that clinicians increase their knowledge of the clinical presentation and research implications of the relationship between NSS and childhood neurodevelopmental disorders. To the best of our knowledge, this is the first review article to give an updated overview of the current knowledge of NSS in the most common neuropsychiatric disorders of childhood/adolescence, such as attention-deficit/hyperactivity disorder, autism spectrum disorder, obsessive-compulsive disorder, bipolar disorder, and first episode of psychosis. The article also presents key points for future research studies on this topic.

Decreased Resting-State Interhemispheric Functional Connectivity Correlated with Neurocognitive Deficits in Drug-Naive First-Episode Adolescent-Onset Schizophrenia

BACKGROUND

Given that adolescence is a critical epoch in the onset of schizophrenia, studying aberrant brain changes in adolescent-onset schizophrenia, particularly in patients with drug-naive first-episode schizophrenia, is important to understand the biological mechanism of this disorder. Previous resting-state functional magnetic resonance imaging studies have shown abnormal functional connectivity in separate hemispheres in patients with adult-onset schizophrenia. Our aim to study adolescent-onset schizophrenia can provide clues for the early aetiology of schizophrenia.

METHOD

A total of 48 drug-naïve, first-episode, adolescent-onset schizophrenia outpatients and 31 healthy controls underwent resting-state functional magnetic resonance imaging scans. Data were subjected to voxel-mirrored homotopic connectivity and support vector machine analyses.

RESULTS

Compared with the healthy controls, the adolescent-onset schizophrenia group showed significantly lower voxel-mirrored homotopic connectivity values in different brain regions, including the fusiform gyrus, superior temporal gyrus/insula, precentral gyrus, and precuneus. Decreased voxel-mirrored homotopic connectivity values in the superior temporal gyrus/insula were significantly correlated with Trail-Making Test: Part A performance (r = -0.437, P = .002). A combination of the voxel-mirrored homotopic connectivity values in the precentral gyrus and precuneus may be used to discriminate patients with adolescent-onset schizophrenia from controls with satisfactory classification results, which showed sensitivity of 100%, specificity of 87.09%, and accuracy of 94.93%.

CONCLUSION

Our findings highlight resting-state interhemispheric FC abnormalities within the sensorimotor network of patients with adolescent-onset schizophrenia and confirm the relationship between adolescent-onset schizophrenia and adult-onset schizophrenia. These findings suggest that reduced interhemispheric connectivity within the sensorimotor network has a pivotal role in the pathogenesis of schizophrenia.

Callosal size in first-episode schizophrenia patients with illness duration of less than one year: A cross-sectional MRI study

Previous studies have reported a reduction in the size of the corpus callosum (CC) on the mid-sagittal plane in patients with schizophrenia. However, findings for the size of the callosal area in patients with first-episode schizophrenia (FESz) are inconsistent. A possibility for these conflicting results is that the duration of illness in patients with FESz affects the CC size. The present study investigated the CC size abnormalities in patients with FESz. Forty-six patients with FESz whose duration of illness was less than 1year and 46 age-, sex-, and handedness-matched healthy controls were recruited to examine the CC size using magnetic resonance imaging. We measured the area of the CC using the Witelson's scheme, which divided the whole area into seven subdivisions. Analysis of covariance indicated there was no difference in the whole or regional areas of the CC between patients with FESz and healthy controls. The rostrum of the CC was significantly correlated with the total score for negative symptoms and some of the subtotal scores. Our findings indicate that there was no reduction in the whole or regional area of the CC among patients with FESz. When comparing the callosal morphology and symptoms, negative symptoms increased in severity as the rostrum area of the CC decreased in size. Further studies are needed to investigate whether the size of the anterior CC is associated with the pathology observed in the early stages of FESz.

Investigating the empirical support for therapeutic targets proposed by the temporal experience of pleasure model in schizophrenia: A systematic review

BACKGROUND

Anhedonia and amotivation are substantial predictors of poor functional outcomes in people with schizophrenia and often present a formidable barrier to returning to work or building relationships. The Temporal Experience of Pleasure Model proposes constructs which should be considered therapeutic targets for these symptoms in schizophrenia e.g. anticipatory pleasure, memory, executive functions, motivation and behaviours related to the activity. Recent reviews have highlighted the need for a clear evidence base to drive the development of targeted interventions.

OBJECTIVE

To review systematically the empirical evidence for each TEP model component and propose evidence-based therapeutic targets for anhedonia and amotivation in schizophrenia.

METHOD

Following PRISMA guidelines, PubMed and PsycInfo were searched using the terms "schizophrenia" and "anhedonia". Studies were included if they measured anhedonia and participants had a diagnosis of schizophrenia. The methodology, measures and main findings from each study were extracted and critically summarised for each TEP model construct.

RESULTS

80 independent studies were reviewed and executive functions, emotional memory and the translation of motivation into actions are highlighted as key deficits with a strong evidence base in people with schizophrenia. However, there are many relationships that are unclear because the empirical work is limited by over-general tasks and measures.

CONCLUSIONS

Promising methods for research which have more ecological validity include experience sampling and behavioural tasks assessing motivation. Specific adaptations to Cognitive Remediation Therapy, Cognitive Behavioural Therapy and the utilisation of mobile technology to enhance representations and emotional memory are recommended for future development.

Perception of emotion-related conflict in human communications: what are the effects of schizophrenia?

Our ability to make sense of emotional cues is of paramount importance for understanding state of mind and communicative intent. However, emotional cues often conflict with each other; this presents a significant challenge for people with schizophrenia. We conducted a theoretical review to determine the extent and types of impaired processing of emotion-related conflict in schizophrenia; we evaluated the relationship with medication and symptoms, and considered possible mediatory mechanisms. The literature established that people with schizophrenia demonstrated impaired function: (i) when passively exposed to emotion cues whilst performing an unrelated task, (ii) when selectively attending to one source of emotion cues whilst trying to ignore interference from another source, and (iii) when trying to resolve conflicting emotion cues and judge meta-communicative intent. These deficits showed associations with both negative and positive symptoms. There was limited evidence for antipsychotic medications attenuating impaired emotion perception when there are conflicting cues, with further direct research needed. Impaired attentional control and context processing may underlie some of the observed impairments. Neuroanatomical correlates are likely to involve interhemispheric transfer via the corpus callosum, limbic regions such as the amygdala, and possibly dorsolateral prefrontal and anterior cingulate cortex through their role in conflict processing.

Effects of eye dominance (left vs. right) and cannabis use on intermanual coordination and negative symptoms in schizophrenia patients

Based on the previous findings, it has been assumed that in schizophrenia patients, eye dominance and cannabis use will affect negative symptoms and intermanual coordination (IMC), an index of interhemispheric communication. But eye dominance, specifically the clinical findings for it, has been neglected in schizophrenia research. We therefore investigated its effects in 52 right-handed (36 right-eyed and 16 left-eyed) and 51 left-handed (35 left-eyed and 16 right-eyed) schizophrenia in-patients without and with drug use. Eye dominance affected IMC in all schizophrenia patients. When comparing right- and left-handers, we found that this result was only significant in the right-handed patients and in the smaller subgroup without drug use. In the right-handers, left eye dominance-like left-handedness-was associated with higher values in IMC and less pronounced manifestation of negative symptoms, right eye dominance was not. Thus, left-eyed right-handers may be more closely related to left-handers than to right-handers. In accordance with the results from the literature, we suggest that these findings are due to better interhemispheric connections and less impairment of white matter structures, especially in right-hemispheric regions. Moreover, cannabis use was related to higher scores in IMC and less pronounced negative symptoms, but only in the right-eyed and not in the left-eyed right-handers or in the left-handers. Hence, differences in eye dominance and handedness may be partially responsible for different results in interhemispheric connections among cannabis users. In conclusion, both eye dominance and use of cannabis should be taken into account when assessing clinical symptoms in schizophrenia patients.

Cerebral white matter abnormalities and their associations with negative but not positive symptoms of schizophrenia

Although diffusion tensor imaging (DTI) studies have reported fractional anisotropy (FA) abnormalities in multiple white matter (WM) regions in schizophrenia, relationship between abnormal FA and negative symptoms has not been fully explored. DTI data were acquired from twenty-four patients with chronic schizophrenia and twenty-five healthy controls. Regional brain abnormalities were evaluated by conducting FA comparisons in the cerebral and each lobar WMs between groups. Focal abnormalities were also evaluated with a voxel-wise tract specific method. Associations between structural WM changes and negative symptoms were assessed using the Scale for the Assessment of Negative Symptoms (SANS). The patient group showed decreased FA in the cerebrum, especially in the frontal lobe, compared with controls. A voxel-wise analysis showed FA decreases in almost all WM tracts in schizophrenia. Correlation analyses demonstrated negative relationships between FA in the cerebrum, particularly in the left hemisphere, and SANS global and global rating scores (Anhedonia-Asociality, Attention, and Affective-Flattening), and also associations between FA of left frontal lobe and SANS global score, Anhedonia-Asociality, and Attention. This study demonstrates that patients with chronic schizophrenia evince widespread cerebral FA abnormalities and that these abnormalities, especially in the left hemisphere, are associated with negative symptoms.

Corpus callosum changes in euthymic bipolar affective disorder

BACKGROUND

Changes in corpus callosum area and thickness have been reported in bipolar disorder. Imaging and limited neuropathological data suggest possible abnormalities in myelination and/or glial function.

AIMS

To compare corpus callosum area, thickness and magnetic resonance imaging (MRI) T1 signal intensity in patients with bipolar disorder and healthy controls.

METHOD

A total of 48 patients with euthymic bipolar disorder and 46 healthy controls underwent MRI analysis of callosal midsagittal area, callosal thickness and T1 signal intensity.

RESULTS

The bipolar group had smaller overall and subregional callosal areas and correspondingly reduced callosal width than the control group. Age correlated negatively with callosal area in the control group but not in the bipolar group. Signal intensity was higher in women than in men in both groups. Signal intensity was reduced in women, but not in men, in the bipolar group.

CONCLUSIONS

Observed differences probably relate to diagnosis rather than mood state and bipolar disorder appears to result in morphometric change that overrides changes seen in normal ageing. Intensity changes are consistent with possible altered myelination or glial function. A gender-dependent factor appears to operate and to interact with diagnosis.

The diminished interhemispheric connectivity correlates with negative symptoms and cognitive impairment in first-episode schizophrenia

BACKGROUND

Previous studies imply that interhemispheric disconnectivity plays a more important role on information processing in schizophrenia. However, the role of the aberrant interhemispheric connection in the pathophysiology of this disorder remains unclear. Recently, resting-state functional Magnetic Resonance Imaging (fMRI) has reported to have potentials of mapping functional interactions between pairs of brain hemispheres.

METHODS

Resting-state whole-brain functional connectivity analyses were performed on 41 schizophrenia patients and 33 healthy controls.

RESULTS

The first-episode schizophrenia patients showed significant aberrant interhemispheric connection in the globus pallidus, medial frontal gyrus and inferior temporal gyrus. The correlation of Wechsler Adult Intelligence Scale scores with odds ratio of the aberrant interhemispheric connections revealed positive correlation in the pallidum (rho=0.335, p=.003) and medial frontal gyrus (rho=0.260, p=.025). The connection in the pallidum was also positively correlated with duration of illness (rho=-0.407, p=.009). Whereas, the aberrant interhemispheric connection in the inferior temporal gyrus was positively correlated with scores of Scale for the Assessment of Negative Symptoms (rho=0.393, p=.012).

CONCLUSION

The present study provides fMRI evidence for the aberrant interhemispheric resting-state functional connectivity within resting-state networks in first-episode schizophrenia patients. These aberrant interhemispheric connections, in particular the pallidum, due to its anatomical and functional connectivities, may be the primary disturbance for cognitive impairment, negative symptoms and chronicity of schizophrenia.

Microstructural white matter alterations in psychotic disorder: a family-based diffusion tensor imaging study

BACKGROUND

There is evidence for microstructural white matter alterations in patients with psychotic disorder, suggesting altered interregional connectivity. Less is known about the presence and role of white matter alterations in well individuals at higher than average genetic risk for psychotic disorder.

METHODS

85 patients with psychotic disorder, 93 non-psychotic siblings of patients with psychotic disorder and 80 healthy controls underwent a diffusion tensor imaging (DTI) scanning protocol. In a whole brain voxel-based analysis using Tract Based Spatial Statistics (TBSS), fractional anisotropy (FA) values were compared between the three groups. Effects of antipsychotic medication and drug use were examined.

RESULTS

The patients displayed significantly lower mean FA than the controls in the following regions: corpus callosum (genu, body, splenium), forceps major and minor, external capsule bilaterally, corona radiata (anterior, posterior) bilaterally, left superior corona radiata and posterior thalamic radiation bilaterally. Similar FA differences existed between the patients and siblings; the siblings did not differ from the controls.

CONCLUSION

Profound microstructural white matter alterations were found in the corpus callosum and other tracti and fasciculi in the patients with psychotic disorder, but not in siblings and the controls. These alterations may reflect brain pathology associated with the illness, illness-related environmental risk factors, or its treatment, rather than genetic risk.

Neuroleptic treatments and overflow movements in schizophrenia: are they independent?

Neurological soft signs (NSS) are minor neurological abnormalities that can be revealed by a clinical examination focused on sensory and motor information processing. NSS include overflow movements (OMs), which are defined as involuntary movements that may accompany the production of voluntary movements. OM is generally considered to be a characteristic feature of schizophrenia. White matter abnormalities might be involved in the pathogenesis of OMs. Dopamine receptors play a role in oligodendrocytes development. There is a direct link between antipsychotic agents that bind to dopamine receptors on oligodendrocytes and the development of oligodendrocytes and myelin formation. In this paper, we review the current knowledge of the effects of antipsychotic agents on NSS in schizophrenic patients. As a result of this critical review we hypothesize that the neuroleptic actions described in this paper could explain why antipsychotic agents have no effect on the resolution of NSS in patients with schizophrenia.

Reduced white matter fractional anisotropy and clinical symptoms in schizophrenia: a voxel-based diffusion tensor imaging study

Although not consistently replicated, diffusion tensor imaging (DTI) studies in schizophrenia have revealed lower fractional anisotropy (FA) in various white matter regions, a finding consistent with the disruption of white matter integrity. In this study, we used voxel-based DTI to investigate possible whole-brain differences in the white matter FA values between 58 schizophrenia patients and 58 healthy controls. We also explored the association between FA values and clinical symptoms in schizophrenia. Compared with the controls, the schizophrenia patients showed significant FA reductions in bilateral superior longitudinal fasciculus, bilateral inferior fronto-occipital fasciculus, and genu of right internal capsule. Furthermore, in the patient group, the FA value of the anterior part of the corpus callosum was negatively correlated with the avolition score on the Scale for the Assessment of Negative Symptoms. These findings suggest widespread disruption of white matter integrity in schizophrenia, which could partly explain the severity of negative symptomatology.

Age-related changes in the corpus callosum in early-onset bipolar disorder assessed using volumetric and cross-sectional measurements

Corpus callosum (CC) area abnormalities have been reported in magnetic resonance imaging (MRI) studies of adults and youths with bipolar disorder (BPD), suggesting interhemispheric communication may be abnormal in BPD and may be present early in the course of illness and affect normal neuromaturation of this structure throughout the lifecycle. Neuroimaging scans from 44 youths with DSM-IV BPD and 22 healthy controls (HC) were analyzed using cross-sectional area measurements and a novel method of volumetric parcellation. Univariate analyses of variance were conducted on CC subregions using both volume and traditional area measurements. Youths with BPD had smaller middle and posterior callosal regions, and reduced typical age-related increases in CC size. The cross-sectional area and novel volumetric methodologies resulted in similar findings. Future longitudinal assessments of CC development would track the evolution of callosal abnormalities in youths with BPD and allow exploration of the functional significance of these findings.

Impaired inter-hemispheric facilitatory connectivity in schizophrenia

OBJECTIVES

To investigate the inter-hemispheric connections between the dorsal premotor cortex (dPM) and contralateral primary motor cortex (M1) in schizophrenia.

METHODS

Sixteen medicated, nine unmedicated schizophrenia patients and 20 healthy age-matched subjects were studied by twin-coil Transcranial Magnetic Stimulation. To activate distinct facilitatory and inhibitory transcallosal pathways between dPM and the contralateral M1, the intensity of dPM stimulation was adjusted to be either suprathreshold (110% of resting motor threshold) or subthreshold (80% of active motor threshold). Interstimulus intervals between conditioning stimulus and test stimulus were 6, 8 and 15 ms.

RESULTS

Schizophrenia patients had comparable efficacy of the inhibitory pathway. On the other hand, medicated patients showed less facilitation of contralateral M1 following dPM stimulation at 80% of active motor threshold, at interstimulus interval=8 ms. The individual amount of facilitation induced by dPM conditioning at 80% of active motor threshold at interstimulus interval=8 ms correlated negatively with negative symptoms.

CONCLUSIONS

Inter-hemispheric facilitatory dPM-M1 connectivity is selectively altered in schizophrenia.

SIGNIFICANCE

This study produced evidence that dPM-M1 connectivity is dysfunctional and that correlates with negative symptoms. These results converge with previous studies which strongly hypothesize that inter- and intra-hemispheric connectivity disturbances may play a major role in schizophrenia.

Corpus callosum abnormalities and potential age effect in men with schizophrenia: an MRI comparative study

The goal of this investigation was to evaluate corpus callosum (CC) morphometry in schizophrenia. In consideration of possible confounders such as age, gender and handedness, our study sample was restricted to right-handed male subjects, aged 18-55 years. In addition, we controlled for age at onset, illness duration and exposure to antipsychotic medication. Midsagittal CC linear and area Magnetic Resonance Imaging (MRI) measurements were performed on 50 subjects with schizophrenia and 50 healthy controls. After controlling for midsagittal cortical brain area and age, Analysis of Covariance (ANCOVA) revealed an overall effect of diagnosis on CC splenium width and CC anterior midbody area and a diagnosis by age interaction. Independent Student t tests revealed a smaller CC splenium width in the 36- to 45-year-old age group among the patients with schizophrenia and a smaller CC anterior midbody area in the 18- to 25-year-old age group among the patients with schizophrenia compared with controls. Age, age at onset, illness duration and psychopathology ratings did not show any significant correlations with the whole CC MRI measurements. A negative correlation was found between CC rostrum area and the estimated lifetime neuroleptic consumption. The results are discussed in terms of the possibility that CC structural changes may underlie the functional impairments, frequently reported in schizophrenia, of the associated cortical regions.

Antithetical asymmetry in schizophrenia and bipolar affective disorder: a line bisection study

OBJECTIVE

Evolutionary theories link the pathogenesis of psychosis with anomalous brain asymmetry. Research shows that aberrant lateralization is linked to schizophrenia with elevated rates of left-handedness and reversal of normal cerebral asymmetries. However, lateralization is underexamined in bipolar affective disorder (BPAD) and the available literature suggests the possibility of greater lateralization, which is diametrically opposite to what is observed in schizophrenia. For the first time, we report concurrent analyses of asymmetry in BPAD and schizophrenia using a line bisection task.

METHODS

We examined 164 subjects (31 patients with BPAD in remission, 30 patients with schizophrenia, and 103 healthy controls) using a two-hand line bisection task with established methodology. Raters with good inter-rater reliability (intraclass correlation coefficient > 0.8) measured deviation from the center. Task performance was compared using analysis of covariance with age, sex, and education as covariates.

RESULTS

Study groups did not differ significantly on age, sex, and handedness (p > 0.06). Patients (both schizophrenia and BPAD) had significantly more errors in identifying the center than controls (p < 0.001). Patients with schizophrenia bisected fewer lines at center than controls and BPAD subjects (p < 0.001). Using their right hand, schizophrenia patients had significant rightward deviation and BPAD patients had leftward deviation (p = 0.001). A significant interaction between diagnosis and direction of deviation (p = 0.01) was noted, with significant rightward deviation in schizophrenia and a trend toward leftward deviation in BPAD.

CONCLUSIONS

Study findings suggest attenuation of normal pseudoneglect in schizophrenia and accentuation of normal pseudoneglect in BPAD, indicating lesser lateralization in schizophrenia and possibly greater lateralization in BPAD. From an evolutionary perspective, schizophrenia and BPAD might have antithetical origins.

Contribution of callosal connections to the interhemispheric integration of visuomotor and cognitive processes

In recent years, cognitive neuroscience has been concerned with the role of the corpus callosum and interhemispheric communication for lower-level processes and higher-order cognitive functions. There is empirical evidence that not only callosal disconnection but also subtle degradation of the corpus callosum can influence the transfer of information and integration between the hemispheres. The reviewed studies on patients with callosal degradation with and without disconnection indicate a dissociation of callosal functions: while anterior callosal regions were associated with interhemispheric inhibition in situations of semantic (Stroop) and visuospatial (hierarchical letters) competition, posterior callosal areas were associated with interhemispheric facilitation from redundant information at visuomotor and cognitive levels. Together, the reviewed research on selective cognitive functions provides evidence that the corpus callosum contributes to the integration of perception and action within a subcortico-cortical network promoting a unified experience of the way we perceive the visual world and prepare our actions.

Laterality effects in schizophrenia and bipolar disorder

There are numerous reports in the literature of lateralised structural cerebral abnormalities and alterations of the corpus callosum in the major psychoses. In the light of these findings the purpose of this study was to directly compare hemispheric differences and callosal interhemispheric transmission (IT) in schizophrenia and bipolar disorder. To do that we tested schizophrenic (SCZ), bipolar disorder (BD) patients and controls in a simple manual reaction time (RT) task with lateralised visual stimuli (Poffenberger paradigm) which enables one to test both laterality effects and IT time. We found an overall slowing of responses with the right hand in schizophrenics but not in bipolar patients, who, like controls, showed no hand differences. This selective slowing down of the right hand is likely to be related to abnormalities of intrahemispheric cortico-cortical connections in the left hemisphere. In contrast, IT time was similar in SCZ and BD patients and did not differ with respect to controls. Two are the novel findings of the present study: first both SZC and BD share a normal IT of visuomotor information despite the presence of callosal abnormalities. Second, an impairment of intrahemispheric left hemispheric processing is present only in SCZ patients. This represents a potentially important clue to a further understanding of the pathogenetic differences between the two major psychoses.

A longitudinal study of the corpus callosum in chronic schizophrenia

BACKGROUND

Decreased callosal size and anisotropy have been described in schizophrenia patients but their longitudinal progression remains poorly understood.

METHODS

We performed diffusion-tensor and structural magnetic resonance imaging at baseline and at follow-up four years later in 49 chronic schizophrenia patients and 16 healthy comparison subjects. Schizophrenia patients were subdivided into good-outcome (n=23) and poor-outcome (n=26) groups. Baseline-to-follow-up changes in size, shape, position and fractional anisotropy of the corpus callosum, divided into five sagittal sections and five rostro-caudal segments, were assessed.

RESULTS

At baseline scan and in comparison to healthy subjects, schizophrenia patients displayed 1) smaller callosal size, 2) lower average anisotropy in all sagittal sections except the midline, and 3) more dorsal average coordinate position. During the four years after the baseline scan, patients with schizophrenia exhibited a more pronounced decline in absolute size of the corpus callosum than healthy comparison subjects. As compared with the good-outcome group, the corpus callosum in poor-outcome patients at baseline was of smaller size and lower average anisotropy, more elongated and posteriorly positioned. During the follow-up interval, poor-outcome patients displayed a more pronounced decline in size but less pronounced decline in anisotropy of the corpus callosum than patients with good outcomes.

CONCLUSIONS

Differences in callosal size between schizophrenia patients and healthy subjects seen at baseline continue to widen in the chronic phase of the illness, especially in patients with poor functional outcome. Baseline differences in callosal anisotropy among patients with different outcomes, however, diminish over time.

M, Jain S. Corpus callosal area differences and gender dimorphism in neuroleptic-naïve, recent-onset schizophrenia and healthy control subjects

The study of corpus callosal morphometry is important to unravel the underlying connectivity disturbance in schizophrenia. We studied the corpus callosal area in schizophrenia subjects compared to healthy subjects, while controlling for several confounders that could affect morphometric measures of the corpus callosum (CC). Areas of the whole CC and its sub-regions obtained by two geometric partitioning schemes were studied in 23 right-handed neuroleptic-naïve, recent-onset, schizophrenia patients and compared with 23 right-handed age-, sex- and education-matched healthy subjects. The patients did not differ from controls in whole CC area. On tripartite division of the CC, the area of the anterior sub-region was significantly higher in patients compared to controls. On radial division into 5 sub-regions, the anterior truncus area was significantly higher in patients compared to controls. There was a significant effect of gender (F>M) on the area measures; however there was no significant diagnosis()gender effect. Age, age of onset, duration of illness and psychopathology ratings did not show any significant correlations with whole CC area and area of CC sub-regions. The finding of increased area of the anterior truncus that possibly comprises white fibres connecting the temporal association cortices could be indicative of an "abnormal functional hyperconnection" involving these regions in positive symptom schizophrenia. Additionally, the finding of females having larger areas of the whole CC and of the anterior and middle sub-regions could reflect a "normal hyperconnection" underlying increased ambilaterality in females.

Morphology of the corpus callosum at different stages of schizophrenia: cross-sectional study in first-episode and chronic illness

BACKGROUND

The shape of the corpus callosum may differ in schizophrenia, although no study has compared first-episode with established illness.

AIMS

To investigate the size and shape of the corpus callosum in a large sample of people with first-episode and established schizophrenia.

METHOD

Callosal size and shape were determined using high-resolution magnetic resonance imaging on 76 patients with first-episode schizophrenia-spectrum disorders, 86 patients with established schizophrenia and 55 healthy participants.

RESULTS

There were no significant differences in total area across groups. Reductions in callosal width were seen in the region of the anterior genu in first-episode disorder (P<0.005). Similar reductions were seen in the chronic schizophrenia group in the anterior genu, but also in the posterior genu and isthmus (P=0.0005).

CONCLUSIONS

Reductions in anterior callosal regions connecting frontal cortex are present at the onset of schizophrenia, and in established illness are accompanied by changes in other regions of the callosum connecting cingulate, temporal and parietal cortices.

Meta-analysis of magnetic resonance imaging studies of the corpus callosum in schizophrenia

OBJECTIVES

The corpus callosum plays a pivotal role in inter-hemispheric transfer and integration of information. Magnetic resonance studies have reported callosal abnormalities in schizophrenia but findings have been inconsistent. Uncertainty has persisted despite a meta-analytic evaluation of this structure several years ago. We set out to perform a further meta-analysis with the addition of the numerous reports published on the subject to test the hypothesis that the corpus callosum is abnormal in schizophrenia.

METHOD

A systematic search was carried out to identify suitable magnetic resonance studies which reported callosal areas in schizophrenia compared to controls. Results from the retrieved studies were compared in a meta-analysis whilst the influence of biological and clinical variables on effect size was ascertained with meta-regression analysis.

RESULTS

Twenty-eight studies were identified. Corpus callosum area was reduced in schizophrenia in comparison to healthy volunteers. This effect was larger in first episode patients. Similarly, heterogeneity detected among the studies was associated with course of illness indicating that chronic subjects with schizophrenia showed larger callosal areas. There was no evidence of publication bias.

CONCLUSIONS

This study confirms the presence of reduced callosal areas in schizophrenia. The effect is of a larger magnitude at first presentation and less so in subjects with a chronic course generally medicated with antipsychotics.

Hemispheric cooperation--a crucial factor in schizophrenia? Neurophysiological evidence

Previous behavioural studies have demonstrated evidence for impaired interhemispheric cooperation in schizophrenia patients. The present study uses event-related brain potentials (ERPs) and source localisations to investigate the neurophysiological mechanisms underlying hemispheric cooperation. Fourteen schizophrenia patients and 15 healthy controls performed a lexical decision task on words and pseudowords presented tachistoscopically either unilaterally to the right or left visual field or bilaterally, with two identical copies, one in each visual field. Behavioural results confirmed earlier findings that healthy controls exhibit a significant bilateral redundancy gain (BRG) for words, which is absent for pseudowords. Schizophrenia patients failed to show the bilateral redundancy gain for words, consistent with a deficit in interhemispheric information exchange. ERPs revealed a significant increase in amplitude approximately 180 ms after stimulus onset, occurring specifically for words in the bilateral stimulation condition. This neurophysiological correlate of the behavioural BRG was absent in patients. Source localisation using minimum norm estimates demonstrated BRG-related enhanced activity in the left temporal cortex for healthy controls, but not schizophrenia patients. Interestingly, behavioural and ERP data indicated a clear left-hemispheric laterality for word processing in healthy participants as well as in patients. Our findings provide behavioural and neurophysiological evidence for reduced interhemispheric cooperation in schizophrenia which may be due to impaired transfer of information from the right to the left hemisphere.

The corpus callosum in schizophrenia-volume and connectivity changes affect specific regions

The corpus callosum (CC) is of great interest for pathophysiological models of schizophrenia. Volume and structural integrity of the CC have been examined by volumetric and diffusion tensor imaging (DTI) studies, but results were not consistent across methods or studies. A possible explanation may be varying methodologies and accuracy of measurements based on a single slice or small regions of interest. In addition, none of the studies examined volume and diffusion values in the same group of patients, and thus the relationship between these anatomical measures is not clear. We used an automatic algorithm to segment seven midline slices of the CC from DTI images. We compared volume and the DTI measures fractional anisotropy (FA) and mean diffusivity (MD) in the CC and its subdivisions in the schizophrenia patients and matched controls. Patients had decreased volume, decreased FA and increased MD of the whole CC. The important novel finding is, however, that not all regions were equally affected by anatomical changes. The results emphasize the importance of using different methods in evaluation of white matter (WM) in schizophrenia to avoid false negative findings. In addition, the measures were highly correlated with each other, implying a common pathological process influencing FA, MD and volume of the CC. Although we cannot rule out other mechanisms affecting volume, FA and MD, converging evidence from cytoarchitectonic and genetic studies suggests that WM changes observed in schizophrenia may involve disintegration of healthy, functional axons and strengthening of aberrant connections resulting in increased severity of clinical symptoms.

Shape-based normalization of the corpus callosum for DTI connectivity analysis

The continuous medial representation (cm-rep) is an approach that makes it possible to model, normalize, and analyze anatomical structures on the basis of medial geometry. Having recently presented a partial differential equation (PDE)-based approach for 3-D cm-rep modeling [1], here we present an equivalent 2-D approach that involves solving an ordinary differential equation. This paper derives a closed form solution of this equation and shows how Pythagorean hodograph curves can be used to express the solution as a piecewise polynomial function, allowing efficient and robust medial modeling. The utility of the approach in medical image analysis is demonstrated by applying it to the problem of shape-based normalization of the midsagittal section of the corpus callosum. Using diffusion tensor tractography, we show that shape-based normalization aligns subregions of the corpus callosum, defined by connectivity, more accurately than normalization based on volumetric registration. Furthermore, shape-based normalization helps increase the statistical power of group analysis in an experiment where features derived from diffusion tensor tractography are compared between two cohorts. These results suggest that cm-rep is an appropriate tool for normalizing the corpus callosum in white matter studies.

Internal capsule, corpus callosum and long associative fibers in good and poor outcome schizophrenia: a diffusion tensor imaging survey

BACKGROUND

Prior voxelwise studies of white matter anisotropy found widespread reductions involving all major fiber tracts of the schizophrenic brain. We set out to confirm these exploratory findings and evaluate their relation to illness severity using a hypothesis-driven region-of-interest approach.

METHODS

104 schizophrenia patients (51 with good outcomes, 53 with poor outcomes) and 41 matched comparison subjects participated in the study. Regions of interest were selected on the basis of published voxelwise findings and placed within major fiber tracts using Talairach's stereotaxic coordinates.

RESULTS

Fractional anisotropy reductions in schizophrenia patients were confirmed in the left cingulum, anterior thalamic radiation, fronto-occipital and inferior longitudinal fasciculi, as well as bilaterally in the corpus callosum, anterior and posterior limbs of internal capsule, superior longitudinal fasciculus, optic radiation, and frontotemporal extrafascicular white matter. Anisotropy reductions were more extensive in patients with poor outcomes ("Kraepelinian"), particularly in the posterior corpus callosum, fronto-occipital fasciculus, left optic radiation and frontotemporal white matter. Lower anisotropy in the right hemisphere tracts was associated with more prominent positive symptomatology, whereas negative symptoms were inversely associated with anisotropy values in both hemispheres.

CONCLUSIONS

These results support a global neural disconnectivity in schizophrenia patients, which is more severe in those with poor clinical outcomes.

Interhemispheric integration of visual processing during task-driven lateralization

The mechanisms underlying interhemispheric integration (IHI) remain poorly understood, particularly for lateralized cognitive processes. To test competing theories of IHI, we constructed and fitted dynamic causal models to functional magnetic resonance data from two visual tasks that operated on identical stimuli but showed opposite hemispheric dominance. Using a systematic Bayesian model selection procedure, we found that, in the ventral visual stream, which was activated by letter judgments, interhemispheric connections mediated asymmetric information transfer from the nonspecialized right to the specialized left hemisphere when the latter did not have direct access to stimulus information. Notably, this form of IHI did not engage all areas activated by the task but was specific for areas in the lingual and fusiform gyri. In the dorsal stream, activated by spatial judgments, it did not matter which hemisphere received the stimulus: interhemispheric coupling increased bidirectionally, reflecting recruitment of the nonspecialized left hemisphere. Again, not all areas activated by the task were involved in this form of IHI; instead, it was restricted to interactions between areas in the superior parietal gyrus. Overall, our results provide direct neurophysiological evidence, in terms of effective connectivity, for the existence of context-dependent mechanisms of IHI that are implemented by specific visual areas during task-driven lateralization.

Impaired hemispheric communication in schizophrenia: a study using the consonant-vowel-consonant task

The ability of the left and right hemispheres to interact and cooperate in the processing of information is important for normal brain functioning. Some investigators have suggested that this cooperation in functioning occurs through a process called "metacontrol." Because studies have suggested that patients with schizophrenia may have problems with interhemispheric interaction, we considered that it could be informative to study such patients from the viewpoint of interhemispheric cooperation, and more specifically that of metacontrol. To do this we utilized an assessment procedure called the consonant-vowel-consonant (CVC) task, in which nonsense three-letter combinations (trigrams) are presented vertically to the left, right and both visual fields. The pattern of errors can be used to determine the type of processing the hemispheres use under the different conditions of presentation. Previous studies have shown that when trigram information is presented to both hemispheres, the left hemisphere appears to switch into a mode that more resembles right hemisphere processing, and we wished to determine if evidence for this switch in the mode of processing also occurred in a sample of patients with schizophrenia. To determine the specificity of any findings to schizophrenia, we also studied a group of patients with bipolar disorder. For the control and bipolar groups, our results showed the typical finding of superior processing in the right visual field (left hemisphere) over the left visual field, with presentation to both visual fields demonstrating a qualitative error pattern resembling that of the left visual field (right hemisphere). Patients with schizophrenia, however, did not demonstrate this switching into a right hemisphere mode upon bilateral presentation of the trigrams and instead seemed to show no switching, or actually switching into more of a left hemisphere mode. Our results suggest that patients with schizophrenia (but not bipolar disorder) may have abnormalities in the cooperative processing of information when it is presented to both hemispheres, and that this disturbance may reflect problems with metacontrol of hemispheric processing.

Small-world networks and disturbed functional connectivity in schizophrenia

Disturbances in "functional connectivity" have been proposed as a major pathophysiological mechanism for schizophrenia, and in particular, for cognitive disorganization. Detection and estimation of these disturbances would be of clinical interest. Here we characterize the spatial pattern of functional connectivity by computing the "synchronization likelihood" (SL) of EEG at rest and during performance of a 2Back working memory task using letters of the alphabet presented on a PC screen in subjects with schizophrenia and healthy controls. The spatial patterns of functional connectivity were then characterized with graph theoretical measures to test whether a disruption of an optimal spatial pattern ("small-world") of the functional connectivity network underlies schizophrenia. Twenty stabilized patients with schizophrenia, who were able to work, and 20 healthy controls participated in the study. During the working memory (WM) task healthy subjects exhibited small-world properties (a combination of local clustering and high overall integration of the functional networks) in the alpha, beta and gamma bands. These properties were not present in the schizophrenia group. These findings are in accordance with a partially inadequate organization of neuronal networks in subjects with schizophrenia. This method could be helpful for diagnosis and evaluation of the severity of the disease, as well as understanding the pathophysiologic mechanisms underlying cognitive dysfunction in schizophrenia.

Synaptic plasticity and dysconnection in schizophrenia

Current pathophysiological theories of schizophrenia highlight the role of altered brain connectivity. This dysconnectivity could manifest 1) anatomically, through structural changes of association fibers at the cellular level, and/or 2) functionally, through aberrant control of synaptic plasticity at the synaptic level. In this article, we review the evidence for these theories, focusing on the modulation of synaptic plasticity. In particular, we discuss how dysconnectivity, observed between brain regions in schizophrenic patients, could result from abnormal modulation of N-methyl-D-aspartate (NMDA)-dependent plasticity by other neurotransmitter systems. We focus on the implication of the dysconnection hypothesis for functional imaging at the systems level. In particular, we review recent advances in measuring plasticity in the human brain using functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) that can be used to address dysconnectivity in schizophrenia. Promising experimental paradigms include perceptual and reinforcement learning. We describe how theoretical and causal models of brain responses might contribute to a mechanistic understanding of synaptic plasticity in schizophrenia.

Neural activity in speech-sensitive auditory cortex during silence

That auditory hallucinations are voices heard in the absence of external stimuli implies the existence of endogenous neural activity within the auditory cortex responsible for their perception. Further, auditory hallucinations occur across a range of healthy and disease states that include reduced arousal, hypnosis, drug intoxication, delirium, and psychosis. This suggests that, even in health, the auditory cortex has a propensity to spontaneously "activate" during silence. Here we report the findings of a functional MRI study, designed to examine baseline activity in speech-sensitive auditory regions. During silence, we show that functionally defined speech-sensitive auditory cortex is characterized by intermittent episodes of significantly increased activity in a large proportion (in some cases >30%) of its volume. Bilateral increases in activity are associated with foci of spontaneous activation in the left primary and association auditory cortices and anterior cingulate cortex. We suggest that, within auditory regions, endogenous activity is modulated by anterior cingulate cortex, resulting in spontaneous activation during silence. Hence, an aspect of the brain's "default mode" resembles a (preprepared) substrate for the development of auditory hallucinations. These observations may help explain why such hallucinations are ubiquitous.

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.

Neuroimaging and personality disorders

Within the past several years, neuroimaging research on personality disorders has begun to develop. Personality disorders can be thought of as trait-like dysfunctional patterns in cognitive, affective, impulse control, and interpersonal domains. These domains of dysfunction have been linked to specific neural circuits. Developments in brain imaging techniques have allowed researchers to examine the neural integrity of these circuits in personality-disordered individuals. This article reviews the neuroimaging literature on borderline personality disorder, antisocial personality disorder (including psychopathy) and schizotypal personality disorder. Functional and structural studies provide support for dysfunction in fronto-limbic circuits in borderline and antisocial personality disorder, whereas temporal lobe and basal striatal-thalamic compromise is evident in schizotypal personality disorder.

Smaller corpus callosum subregions containing motor fibers in schizophrenia

Neuropsychological and neurophysiological studies provide evidence for abnormal interhemispheric communication in schizophrenia. These abnormalities may have a substrate in structural irregularities of the corpus callosum. This study investigated schizophrenia patients (n=27) and healthy comparison subjects (n=31). Global and regional measurements of the corpus callosum were acquired from one midsagittal SPGR slice. Eight subregions were approximately matched to fiber pathways from cortical regions. Overall effects of diagnosis [Wilks' Lambda F(8,46)=2.45, p=0.03] and diagnosis by age interaction [Wilks' Lambda F(8,46)=2.58, p=0.02] were found in a MANCOVA of the eight functionally specific subregions. Specifically, chronic schizophrenia was associated with a smaller rostral body [lower by 6.9%, F(1,53)=9.70, p=0.003] and anterior midbody [lower by 9.7%, F(1,53)=4.89, p=0.03] subregions. The rostral body and anterior midbody subregions of the corpus callosum primarily have premotor, supplementary motor, and motor cortical fibers transversing through them. Functional abnormalities of the associated cortical regions are reported in schizophrenia. These novel findings suggest that structural abnormalities of the corpus callosum exist in schizophrenia, with perhaps the motor-specific subregions affected more than others. Structural differences in the corpus callosum may be a substrate for interhemispheric functional dysconnectivity in schizophrenia.

Ventricular size mapping in a transgenic model of schizophrenia

Genetically engineered mice have been generated to model a variety of neurological disorders. The chakragati (ckr) mouse is beginning to provide valuable insights into the structural brain changes underlying certain manifestations of schizophrenia. For instance, these mice show enlargement of the lateral ventricles, an abnormality frequently reported as a structural aberration in the schizophrenic brain. As neither the anatomical pattern nor the timing of this ventricular enlargement is known, we used magnetic resonance imaging (MRI) techniques to non-invasively visualize the development of the ventricular system in 5-, 10- and 30-day-old ckr pups. High-resolution MR images obtained from these mutants showed a progressive enlargement of the lateral ventricles, starting at day 5 of postnatal life. These emerging deficits were associated with abnormalities in mid-saggital corpus callosum area and thickness, particularly in 30-day-old adolescent animals. At this time of development, aberrant behaviors that mimic certain symptoms of schizophrenia also appeared in ckr mice suggesting that structural changes in ventricular size predates the onset of psychotic-like behaviors. These results are viewed as further indication that pre- and peri-natal disturbances of the ventricular system and adjacent neural regions may be important pathogenic factors in schizophrenia. Application of MRI to the ckr mouse is relatively new but has great potential for clarifying the relationship between brain structure changes and genetically induced vulnerabilities to psychoses.

Investigating the cortical origins of motor overflow

Motor overflow refers to the involuntary movements which may accompany the production of voluntary movements. While overflow is not usually seen in the normal population, it does present in children and the elderly, as well as those suffering certain neurological dysfunctions. Advancements in methodology over the last decade have allowed for more convincing conclusions regarding the cortical origins of motor overflow. However, despite significant research, the exact mechanism underlying the production of motor overflow is still unclear. This review presents a more comprehensive conceptualization of the theories of motor overflow, which have often been only vaguely defined. Further, the major findings are explored in an attempt to differentiate the competing theories of motor overflow production. This exploration is done in the context of a range of neurological and psychiatric disorders, in order to elucidate the possible underlying mechanisms of overflow.

Schizophrenia and the stroop effect

Conflict between irrelevant words and relevant colors in the Stroop task creates interference, long considered a measure of how well individuals focus attention. In the traditional card version of the Stroop task, schizophrenia patients exhibit increased interference, consistent with the distractibility they exhibit in everyday life. In contrast, on other versions of the Stroop task they show augmented facilitation (faster responding to congruent than to neutral trials). We suggest that schizophrenia patients possess adequate attentional resources to avoid interference when each letter string is presented individually but face difficulty when delays are imposed and multiple attentional demands appear. Although psychiatric symptomatology may contribute to different patterns of performance, there is no evidence that medication modulates this.

Abnormalities in MRI-measured signal intensity in the corpus callosum in schizophrenia

The microstructural integrity of the corpus callosum (CC) in first-episode schizophrenia patients was assessed by measuring the signal intensity (SI) in T1-weighted MRI images. Analyses revealed that compared to both healthy controls and non-schizophrenic patients, schizophrenia patients showed reductions in SI in all the callosal subregions, the genu, body, isthmus and splenium in first-episode schizophrenia. These results indicate that schizophrenia is characterized by pathology of this principal interhemispheric commissure; the abnormalities may reflect distributed (rather than localized) interhemispheric disconnectivity that extends beyond the heteromodal association cortices.

Motor overflow in schizophrenia

The occurrence of motor dysfunction as a sign of schizophrenia, in addition to being a side effect of medication, has received considerable support in recent years. The current study aimed to systematically investigate both the presence and pattern of one such motor dysfunction, motor overflow. It was hypothesised that patients with schizophrenia would show significantly greater motor overflow than controls, and that the pattern of motor overflow occurrence would also vary significantly between the groups. A finger flexion task was used to examine the presence and pattern of motor overflow. Subjects were asked to maintain target forces, using either their index or small finger, representing 25, 50 or 75% of the maximum strength capacity for whichever finger was performing the task. Patients were found to exhibit significantly greater motor overflow than controls. There were also significant findings with respect to the patterns of motor overflow produced, specifically in regards to fine motor control and performance variability. In summary, patients differed significantly from controls in both the degree and pattern of overflow exhibited.

Magnetic resonance imaging study of corpus callosum abnormalities in patients with bipolar disorder

BACKGROUND

This study was conducted to further examine the hypothesis of abnormalities in size of corpus callosum in subjects with bipolar disorder.

METHODS

Sixteen right-handed DSM-IV bipolar I patients and 27 right-handed healthy control subjects were studied. A 1.5-T GE Signa magnet was used, and three-dimensional gradient echo imaging (spoiled gradient recall acquisition) was conducted. Area measurements of corpus callosum were obtained blindly, with a semi-automated software, by a well-trained rater.

RESULTS

Right-handed bipolar I patients had significantly smaller total corpus callosum, genu, posterior body, and isthmus areas compared with right-handed healthy control subjects (analysis of covariance with age, gender, and intracranial volume as covariates, p <.05). Partial correlation analyses, controlled for intracranial volumes, found a significant inverse relationship between age and total callosal, genu, anterior body, isthmus, and circularity in healthy control subjects (p <.05) but not in bipolar patients (p >.05).

CONCLUSIONS

Smaller callosal areas may lead to altered inter-hemispheric communication and be involved in the pathophysiology and cognitive impairment found in bipolar disorder.

Corpus callosum development in childhood-onset schizophrenia

OBJECTIVE

Corpus callosum (CC) size and interhemispheric communication differences have been reported between patients with schizophrenia and normal controls. Childhood-onset schizophrenia (COS) is a severe form of the disorder that is continuous with later-onset disorder. Corpus callosal area was examined for COS at initial scan and prospectively through adolescence, and related to other developmental abnormalities for this group.

METHOD

A total of 113 anatomic brain MRI scans were obtained from 55 COS (22 female) and 110 scans from 56 age- and gender-matched healthy volunteers (22 female), across ages 8-24. Baseline and prospective rescans were obtained at approximately 2-year intervals. The midsagittal areas for total corpus callosum and seven subregions were calculated using an automated system. Cross-sectional and longitudinal data were combined using mixed model regression analysis to compare developmental changes for the two groups.

RESULTS

No diagnostic differences were seen at time of initial scan. Longitudinally, and in contrast to healthy volunteers, patients with schizophrenia showed a significant difference in developmental trajectory for the area of the splenium, both before (p=0.012) and after (p=0.05) adjustment for total cerebral volume. The area of the splenium becomes significantly smaller in COS, starting at about age 22.

CONCLUSION

Patients with schizophrenia showed a significant difference in developmental trajectory for the splenial area, which seems to decline for COS. If replicated, this may reflect anticipated late occipital and extrastriate changes in brain regions.

Schizophrenia, neurodevelopment and corpus callosum

The Zeitgeist favors an interpretation of schizophrenia as a condition of abnormal connectivity of cortical neurons, particularly in the prefrontal and temporal cortex. The available evidence points to reduced connectivity, a possible consequence of excessive synaptic pruning in development. A decreased thalamic input to the cerebral cortex appears likely, and developmental studies predict that this decrease should entail a secondary loss of both long- and short-range cortico-cortical connections, including connections between the hemispheres. Indeed, morphological, electrophysiological and neuropsychological studies over the last two decades suggest that the callosal connections are altered in schizophrenics. However, the alterations are subtle and sometimes inconsistent across studies, and need to be investigated further with new methodologies.

Lateralized Lexical Decision in Schizophrenia: Hemispheric Specialization and Interhemispheric Lexicality Priming

Reports of left-hemisphere dysfunction and abnormal interhemispheric transfer in schizophrenia are mixed. The authors used a unified paradigm, the lateralized lexical decision task, to assess hemispheric specialization in word recognition, hemispheric error monitoring, and interhemispheric transfer in male, right-handed participants with schizophrenia (n=34) compared with controls (n=20). Overall, performance and error monitoring were worse in patients. However, patients like controls showed left-hemisphere superiority for lexical processing and right-hemisphere superiority for error monitoring. Only patients showed selective-interhemispheric lexicality priming for accuracy, in which performance improved when the lexical status of target and distractor stimuli presented to each hemifield was congruent. Results suggest that schizophrenia is associated with impaired monitoring and with increased interhemispheric automatic information transfer rather than with changed hemispheric specialization for language or error monitoring.