Sylvian fissure asymmetries in monozygotic twins: a test of laterality in schizophrenia

Brain features of nearly drug-naïve female monozygotic twins with first-episode schizophrenia and the classification accuracy of brain feature patterns: A pilot study

BACKGROUND

Data on differences in brain features between monozygotic (MZ) twins with and without schizophrenia are scarce.

METHODS

We compared brain features of female MZ twins with and without first-episode schizophrenia and healthy controls (n = 20 each). Voxel-based morphometry and tract-based spatial statistics were used to analyze differences in brain structure. Whole-brain effective connectivity (EC) and functional connectivity (FC) networks were constructed using resting-state functional magnetic resonance imaging (rs-fMRI) data.

RESULTS

Female twins with schizophrenia exhibited abnormal gray matter volume (GMV) in the basal ganglia and prefrontal and parietal cortices, impairments in the arcuate fasciculus, and significant disruptions (primarily decreases) in nine EC networks. They exhibited rs-EC alterations involving the limbic areas and subcortex. Combined rs-EC and rs-FC data distinguished twins with first-episode schizophrenia with high accuracy. Combined consideration of structural and functional features enabled the distinction of female MZ twins with schizophrenia from those without schizophrenia and healthy controls with 100% accuracy.

CONCLUSIONS

Female MZ twins with schizophrenia exhibited increased GMV, white matter impairment, and disruptions in EC and FC networks. The combination of rs-EC + rs-FC data could distinguish female twins with schizophrenia from twins without schizophrenia and healthy controls with 97.4% accuracy, and the addition of structural brain features yielded a 100% accuracy rate. These findings may provide pivotal insight for further study of the mechanisms underlying schizophrenia.

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

Background

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

Methods

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

Results

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

Conclusions

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

Handedness, heritability, neurocognition and brain asymmetry in schizophrenia

Higher rates of non-right-handedness (i.e. left- and mixed-handedness) have been reported in schizophrenia and have been a centrepiece for theories of anomalous lateralization in this disorder. We investigated whether non-right-handedness is (i) more prevalent in patients as compared with unaffected siblings and healthy unrelated control participants; (ii) familial; (iii) associated with disproportionately poorer neurocognition; and (iv) associated with grey matter volume asymmetries. We examined 1445 participants (375 patients with schizophrenia, 502 unaffected siblings and 568 unrelated controls) using the Edinburgh Handedness Inventory, a battery of neuropsychological tasks and structural magnetic resonance imaging data. Patients displayed a leftward shift in Edinburgh Handedness Inventory laterality quotient scores as compared with both their unaffected siblings and unrelated controls, but this finding disappeared when sex was added to the model. Moreover, there was no evidence of increased familial risk for non-right-handedness. Non-right-handedness was not associated with disproportionate neurocognitive disadvantage or with grey matter volume asymmetries in the frontal pole, lateral occipital pole or temporal pole. Non-right-handedness was associated with a significant reduction in left asymmetry in the superior temporal gyrus in both patients and controls. Our data neither provide strong support for 'atypical' handedness as a schizophrenia risk-associated heritable phenotype nor that it is associated with poorer neurocognition or anomalous cerebral asymmetries.

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.

General absence of abnormal cortical asymmetry in childhood-onset schizophrenia: a longitudinal study

BACKGROUND

Childhood-onset schizophrenia (COS) is a rare, severe form of the adult-onset illness, with more salient neurobiological causes. Previous cross-sectional structural neuroimaging research has suggested that normal cortical asymmetry patterns [(R-L)/(R+L)] may be altered in adult schizophrenia, although these findings were not well replicated. Recent studies show dynamic changes in brain asymmetry during childhood and adolescence. We hypothesized that COS patients would show a lack of normal development of asymmetry and decreased overall asymmetry.

METHODS

Prospective structural magnetic resonance scans were obtained at baseline and at two-year follow-up visits in 49 right-handed COS patients (mean baseline age: 14.72+/-2.63, 117 scans) and 50 age and sex-matched, right-handed healthy controls (mean baseline age: 15.15+/-3.37, 125 scans). Cortical thickness was calculated at 40,962 homologous points across each cerebral hemisphere using a fully automated, validated method. Differences in developmental asymmetry patterns across the cortical surface were analyzed using a linear mixed effects regression model.

RESULTS

No significant asymmetry differences were found either for cross-sectional comparisons of COS and healthy controls across the lateral and medial cortical surfaces or with respect to timing of developmental changes in asymmetry.

CONCLUSIONS

The present findings do not support asymmetry differences for this severe, early form of schizophrenia.

Diffusion tractography of the fornix in schizophrenia

BACKGROUND

White matter fiber tracts, especially those interconnecting the frontal and temporal lobes, are likely implicated in pathophysiology of schizophrenia. Very few studies, however, have focused on the fornix, a compact bundle of white matter fibers, projecting from the hippocampus to the septum, anterior nucleus of the thalamus and the mamillary bodies. Diffusion Tensor Imaging (DTI), and a new post-processing method, fiber tractography, provides a unique opportunity to visualize and to quantify entire trajectories of fiber bundles, such as the fornix, in vivo. We applied these techniques to quantify fornix diffusion anisotropy in schizophrenia.

METHODS

DTI images were used to evaluate the left and the right fornix in 36 male patients diagnosed with chronic schizophrenia and 35 male healthy individuals, group matched on age, parental socioeconomic status, and handedness. Regions of interest were drawn manually, blind to group membership, to guide tractography, and fractional anisotropy (FA), a measure of fiber integrity, was calculated and averaged over the entire tract for each subject. The Doors and People test (DPT) was used to evaluate visual and verbal memory, combined recall and combined recognition.

RESULTS

Analysis of variance was performed and findings demonstrated a difference between patients with schizophrenia and controls for fornix FA (p=0.006). Protected post-hoc independent sample t-tests demonstrated a bilateral FA decrease in schizophrenia, compared with control subjects (left side: p=0.048; right side p=0.006). Higher fornix FA was statistically significantly correlated with DPT and measures of combined visual memory (r=0.554, p=0.026), combined verbal memory (r=0.647, p=0.007), combined recall (r=0.516, p=0.041), and combined recognition (r=0.710, p=0.002) for the control group. No such statistically significant correlations were found in the patient group.

CONCLUSIONS

Our findings show the utility of applying DTI and tractography to study white matter fiber tracts in vivo in schizophrenia. Specifically, we observed a bilateral disruption in fornix integrity in schizophrenia, thus broadening our understanding of the pathophysiology of this disease.

Exploiting human anatomical variability as a link between genome and cognome

Although talents and disabilities appear to run in families, direct links between genes and cognitive ability are difficult to establish. Investigators are currently searching for intermediate phenotypes with plausible links to both genome and cognome (the cognitive phenotype). Cortical anatomy could provide one such intermediate phenotype. Variation in cortical size, asymmetry and sulcal pattern is influenced by genetic variation in neurotrophic factors and can predict variation in verbal and mathematical talent. Anecdotal evidence suggests that individuals with a rare morphological variant of Sylvian fissure sometimes have superior visualization ability combined with verbal deficits. Documentation of such 'cognitive cortical syndromes' might prove as genetically informative as the identification of dysmorphic syndromes associated with mental retardation. A necessary prerequisite for the establishment of such syndromes is a reliable technique for the identification of cortical patterns. Recent technical advances in software for automatically labeling and measuring cortical sulci now provide the possibility of establishing standard measures for their shape, size and location. Such measures are a prerequisite for genetic studies of cortical patterns that could illuminate the neurodevelopmental pathways by which genes affect cognitive ability.

A 4.0-T fMRI study of brain connectivity during word fluency in first-episode schizophrenia

OBJECTIVE

To use functional magnetic resonance imaging (fMRI) to investigate functional connectivity, and hence, underlying neural networks, in never-treated, first-episode patients with schizophrenia using a word fluency paradigm known to activate prefrontal, anterior cingulate, and thalamic regions. Abnormal connectivity between the prefrontal cortex (PFC) and other brain regions has been demonstrated in chronic, medicated patients in previous positron emission tomography (PET) studies, but has not to our knowledge, previously been demonstrated using both first-episode, drug-naïve patients and fMRI technology.

METHODS

A 4.0-Tesla (T) fMRI was used to examine activation and functional connectivity [psychophysiological interactions (PPIs)] during a word fluency task compared to silent reading in 10 never-treated, first-episode patients with schizophrenia and 10 healthy volunteers of comparable age, sex, handedness, and parental education.

RESULTS

Compared to healthy volunteers, the schizophrenia patient group exhibited less activation during the word fluency task, mostly in the right anterior cingulate and prefrontal regions. Psychophysiological interactions between right anterior cingulate and other parts of the brain revealed a localized interaction with the left temporal lobe in healthy volunteers during the task and a widespread unfocussed interaction in patients.

CONCLUSION

These findings suggest anterior cingulate involvement in the neuronal circuitry underlying schizophrenia.

An in vivo MRI study of prefrontal cortical complexity in first-episode psychosis

OBJECTIVE

The purpose of this study was to investigate abnormalities in the surface complexity of the prefrontal cortex and in the hemispheric asymmetry of cortical complexity in first-episode patients with schizophrenia.

METHOD

An estimate of the surface complexity of the prefrontal cortex was derived from the number of voxels along the boundary between gray matter and CSF. Magnetic resonance imaging scans were acquired from patients with a first episode of schizophrenia (N=17), patients with a first episode of affective psychosis (N=17), and normal comparison subjects (N=17), age-matched within a narrow age range (18-29 years). This study group was the focus of a previous study that showed lower prefrontal cortical volume in patients with schizophrenia.

RESULTS

Prefrontal cortical complexity was not significantly different among the groups. However, the schizophrenia patients differed significantly from the normal comparison subjects in asymmetry, with the schizophrenia patients showing less left-greater-than-right asymmetry in cortical complexity than the comparison subjects.

CONCLUSIONS

An abnormal pattern of asymmetry in the prefrontal cortex of first-episode patients with schizophrenia provides evidence for a neurodevelopmental mechanism in the etiology of schizophrenia.

Neuronal substrates of sensory gating within the human brain

BACKGROUND

For the human brain, habituation to irrelevant sensory input is an important function whose failure is associated with behavioral disturbances. Sensory gating can be studied by recording the brain's electrical responses to repeated clicks: the P50 potential is normally reduced to the second of two paired clicks but not in schizophrenia patients. To identify its neural correlates, we recorded electrical traces of sensory gating directly from the human hippocampus and neocortex.

METHODS

Intracranial evoked potentials were recorded using hippocampal depth electrodes and subdural strip and grid electrodes in 32 epilepsy patients undergoing invasive presurgical evaluation.

RESULTS

We found evidence of sensory gating only in the hippocampus, the temporo-parietal region (Brodmann's areas 22 and 2), and the prefrontal cortex (Brodmann's areas 6 and 24); however, whereas neocortical habituating responses to paired clicks were peaking around 50 msec, responses within the hippocampus proper had a latency of about 250 msec.

CONCLUSIONS

Consistent with data from animal studies, our findings show that the hippocampus proper contributes to sensory gating, albeit during a time window following neocortical habituation processes. Thus, sensory gating may be a multistep process, with an early phase subserved by the temporo-parietal and prefrontal cortex and a later phase mediated by the hippocampus.

Language lateralization in schizophrenia, an fMRI study

Anatomical studies have shown that cerebral asymmetry is reduced in schizophrenia. Functional asymmetry appears to be reduced also, as was shown with dichotic listening studies. These studies, however, have not revealed whether reduced lateralization is the result of decreased language activity of the left hemisphere or whether it is the consequence of increased language-related activity in the right hemisphere. To elucidate this, we examined hemispheric dominance for language processing by means of functional MRI. Twelve schizophrenic patients and twelve healthy controls were scanned while they were engaged in a verb-generation and a semantic decision task. Activation was measured bilaterally in the frontal, temporal and temporo-parietal language areas, and a laterality index was derived from activity in these regions of interest in the left and the right hemispheres. Clinical symptoms were rated at the time of scanning. The results indicate that language processing is less lateralized in patients than in controls (a mean laterality index of 0.35 versus 0.63, respectively, difference p<0.01). Analysis of variance of the extent of activity, i.e. numbers of active voxels, revealed a significant hemisphere by group interaction (F(1,22)=11.2, p<0.001), which was due to increased activation in the right hemisphere of the patients (post hoc t-test p<0.05). We found no evidence of reduced activity in the left hemisphere. Further analysis of clinical symptoms rated prior to scanning revealed that decreased language lateralization was associated with more severe hallucinations (r=-0.54, p<0.05). We postulate that decreased language lateralization in schizophrenia may result from failure to inhibit the right hemisphere.

Are auditory hallucinations the consequence of abnormal cerebral lateralization? A morphometric MRI study of the sylvian fissure and planum temporale

BACKGROUND

Auditory verbal hallucinations (AVHs) are a characteristic feature of schizophrenia. Patients with schizophrenia have been found to have reduced volumes of a variety of brain structures as well as a reduction in right-left asymmetries, using postmortem and magnetic resonance imaging (MRI) measures. There is also evidence that patients with AVHs differ in these structural asymmetries, relative to those patients who do not hallucinate. The aim of this study was to examine whether patients with and without a prominent history of AVHs differ, both from each other and in comparison with normal subjects, in the asymmetry of the sylvian fissure (SF) and planum temporale (PT).

METHODS

We recruited 74 DSM-IV male patients with schizophrenia (on the basis of their AVH history) and 32 matched normal control subjects. Thirty patients had no history of AVHs and 44 had a strong definitive history of AVHs. The SF length and PT area and volume were measured on a three-dimensional MRI spoiled GRASS volume sequence. Absolute measures and laterality coefficients were calculated.

RESULTS

: All groups had the normal leftward asymmetry in both the SF and PT. Planum temporale volume and surface area and SF length were all larger in the left hemisphere. There were no significant differences in any measures between the two patient groups or between schizophrenic patients and control subjects. Greater leftward asymmetry of the SF correlated with hallucinations and thought disorder within the prominent hallucinator group. An association was found between handedness and brain size, but this did not interact with diagnosis.

CONCLUSIONS

The results of this study do not confirm reports, based on smaller samples, of reduced structural asymmetries of either the SF or PT in schizophrenia, nor do they indicate a specific relationship to a propensity to experience AVHs. A modest correlation between leftward asymmetry of the SF and some positive symptomatology was found.

A review of MRI findings in schizophrenia

After more than 100 years of research, the neuropathology of schizophrenia remains unknown and this is despite the fact that both Kraepelin (1919/1971: Kraepelin, E., 1919/1971. Dementia praecox. Churchill Livingston Inc., New York) and Bleuler (1911/1950: Bleuler, E., 1911/1950. Dementia praecox or the group of schizophrenias. International Universities Press, New York), who first described 'dementia praecox' and the 'schizophrenias', were convinced that schizophrenia would ultimately be linked to an organic brain disorder. Alzheimer (1897: Alzheimer, A., 1897. Beitrage zur pathologischen anatomie der hirnrinde und zur anatomischen grundlage einiger psychosen. Monatsschrift fur Psychiarie und Neurologie. 2, 82-120) was the first to investigate the neuropathology of schizophrenia, though he went on to study more tractable brain diseases. The results of subsequent neuropathological studies were disappointing because of conflicting findings. Research interest thus waned and did not flourish again until 1976, following the pivotal computer assisted tomography (CT) finding of lateral ventricular enlargement in schizophrenia by Johnstone and colleagues. Since that time significant progress has been made in brain imaging, particularly with the advent of magnetic resonance imaging (MRI), beginning with the first MRI study of schizophrenia by Smith and coworkers in 1984 (Smith, R.C., Calderon, M., Ravichandran, G.K., et al. (1984). Nuclear magnetic resonance in schizophrenia: A preliminary study. Psychiatry Res. 12, 137-147). MR in vivo imaging of the brain now confirms brain abnormalities in schizophrenia. The 193 peer reviewed MRI studies reported in the current review span the period from 1988 to August, 2000. This 12 year period has witnessed a burgeoning of MRI studies and has led to more definitive findings of brain abnormalities in schizophrenia than any other time period in the history of schizophrenia research. Such progress in defining the neuropathology of schizophrenia is largely due to advances in in vivo MRI techniques. These advances have now led to the identification of a number of brain abnormalities in schizophrenia. Some of these abnormalities confirm earlier post-mortem findings, and most are small and subtle, rather than large, thus necessitating more advanced and accurate measurement tools. These findings include ventricular enlargement (80% of studies reviewed) and third ventricle enlargement (73% of studies reviewed). There is also preferential involvement of medial temporal lobe structures (74% of studies reviewed), which include the amygdala, hippocampus, and parahippocampal gyrus, and neocortical temporal lobe regions (superior temporal gyrus) (100% of studies reviewed). When gray and white matter of superior temporal gyrus was combined, 67% of studies reported abnormalities. There was also moderate evidence for frontal lobe abnormalities (59% of studies reviewed), particularly prefrontal gray matter and orbitofrontal regions. Similarly, there was moderate evidence for parietal lobe abnormalities (60% of studies reviewed), particularly of the inferior parietal lobule which includes both supramarginal and angular gyri. Additionally, there was strong to moderate evidence for subcortical abnormalities (i.e. cavum septi pellucidi-92% of studies reviewed, basal ganglia-68% of studies reviewed, corpus callosum-63% of studies reviewed, and thalamus-42% of studies reviewed), but more equivocal evidence for cerebellar abnormalities (31% of studies reviewed). The timing of such abnormalities has not yet been determined, although many are evident when a patient first becomes symptomatic. There is, however, also evidence that a subset of brain abnormalities may change over the course of the illness. The most parsimonious explanation is that some brain abnormalities are neurodevelopmental in origin but unfold later in development, thus setting the stage for the development of the symptoms of schizophrenia. Or there may be additional factors, such as stress or neurotoxicity, that occur during adolescence or early adulthood and are necessary for the development of schizophrenia, and may be associated with neurodegenerative changes. Importantly, as several different brain regions are involved in the neuropathology of schizophrenia, new models need to be developed and tested that explain neural circuitry abnormalities effecting brain regions not necessarily structurally proximal to each other but nonetheless functionally interrelated. (ABSTRACT TRUNCATED)

Handedness, language lateralisation and anatomical asymmetry in schizophrenia: meta-analysis

BACKGROUND

Cerebral lateralisation appears to be decreased in schizophrenia. Results of studies investigating this, however, are equivocal.

AIMS

To review quantitatively the literature on decreased lateralisation in schizophrenia.

METHOD

Meta-analyses were conducted on 19 studies on handedness, 10 dichotic listening studies and 39 studies investigating anatomical asymmetry in schizophrenia.

RESULTS

The prevalence of mixed- and left-handedness ('non-right-handedness') was significantly higher in patients with schizophrenia as compared to healthy controls, and also as compared to psychiatric controls. The analysis of dichotic listening studies revealed no significant difference in lateralisation in schizophrenia. However, when analysis was restricted to studies using consonant-vowel or fused word tasks, significantly decreased lateralisation in schizophrenia emerged. Asymmetry of the planum temporale and the Sylvian fissure was significantly decreased in schizophrenia, while asymmetry of the temporal horn of the lateral ventricle was not.

CONCLUSION

Strong evidence is provided for decreased cerebral lateralisation in schizophrenia.

Three-dimensional mapping of gyral shape and cortical surface asymmetries in schizophrenia: gender effects

OBJECTIVE

People with schizophrenia exhibit abnormalities in brain structure, often in the left hemisphere. Disturbed structural lateralization is controversial, however, and effects appear mediated by gender. The authors mapped differences between schizophrenic and normal subjects in gyral asymmetries, complexity, and variability across the entire cortex.

METHOD

Asymmetry and shape profiles for 25 schizophrenic patients (15 men) and 28 demographically similar normal subjects (15 men) were obtained for 38 gyral regions, including the sylvian fissure and temporal and postcentral gyri, by using magnetic resonance data and a novel surface-based mesh-modeling approach. Cortical complexity was examined for sex and diagnosis effects in lobar regions. Intragroup variability was quantified and visualized to assess regional group abnormalities at the cortical surface.

RESULTS

The patients showed greater variability in frontal areas than the comparison subjects. They also had significant deviations in gyral complexity asymmetry in the superior frontal cortex. In temporoparietal regions, significant gyral asymmetries were present in both groups. Sex differences were apparent in superior temporal gyral measures, and cortical complexity in inferior frontal regions was significantly greater in men.

CONCLUSIONS

Cortical variability and complexity show regional abnormalities in the frontal cortex potentially specific to schizophrenia. The results indicate highly significant temporoparietal gyral asymmetries in both diagnostic groups, contrary to reports of less lateralization in schizophrenia. Substantially larger study groups are necessary to isolate smaller deviations in surface asymmetries, if present in schizophrenia, suggesting their diagnostic value is minimal.

Invited commentary on: functional anatomy of verbal fluency in people with schizophrenia and those at genetic risk. The genetics of asymmetry and psychosis

Spence et al (2000, this issue) describe an original and incisive approach to the genetics of psychosis – an attempt to define brain connectivity in patients and family members closest to the genetic risk (‘obligate carriers’) by comparison with those remote from familial risk. Their findings are potentially important but I suggest an alternative interpretation: that words are simply less lateralised in those genetically predisposed to suffer from schizophrenic symptoms. This conclusion has, I believe, implications for understanding the organisation of the human brain.

Twin studies of psychosis and the genetics of cerebral asymmetry

Kläning (1999, this issue) reports that dizygotic twins are at increased risk of schizophrenia relative to the general population. Any departure from the first assumption of twin studies that the illness has the same origin in twins as it does in the general population might tell us something about aetiology. Kläning's expectation that monozygotic twins would be at increased risk because such pairs are at increased risk of perinatal complications was not confirmed, adding to the weight of evidence that such complications are unrelated to the origins of psychotic illness. The contrary finding that dizygotic twins are at increased risk draws attention to the nature of dizygotic twinning. Is there something about this process that yields a clue to the origins of psychosis?

Structural brain imaging in schizophrenia: a selective review

Structural neuroimaging studies have provided some of the most consistent evidence for brain abnormalities in schizophrenia. Since the initial computed tomography study by Johnstone and co-workers, which reported lateral ventricular enlargement in schizophrenia, advances in brain imaging technology have enabled further and more refined characterization of abnormal brain structure in schizophrenia in vivo. This selective review discusses the major issues and findings in structural neuroimaging studies of schizophrenia. Among these are evidence for generalized and regional brain volume abnormalities, the specificity of anatomic findings to schizophrenia and to men versus women with schizophrenia, the contribution of genetic influences, and the timing of neuroanatomic pathology in schizophrenia. The second section reviews new approaches for examining brain structure in schizophrenia and their applications to studies on the pathophysiology of schizophrenia.

The planum temporale: a systematic, quantitative review of its structural, functional and clinical significance

The planum temporale (PT) is a triangular area situated on the superior temporal gyrus (STG), which has enjoyed a resurgence of interest across several disciplines, including neurology, psychiatry and psychology. Traditionally, the planum is thought to be larger on the left side of the brain in the majority of normal subjects [N. Geschwind, W. Levitsky, Human brain: left-right asymmetries in temporal speech regions, Science 161 (1968) 186-87.]. It coincides with part of Wernicke's area and it is believed to consist cytoarchitectonically of secondary auditory cortex. Consequently, it has long been thought to be intimately involved in language function. The PT is, therefore, of relevance to disorders where language function is impaired, such as schizophrenia and dyslexia. The gross anatomical boundaries remain in dispute, and only recently has its cytoarchitecture begun to be studied again after 60 years silence, and finally its functional significance is only now being explored. In the first part of this review the structural aspects and anatomical boundaries of the PT in the normal brain from post mortem and magnetic resonance imaging (MRI) and methods of measurement are discussed. In the second part, studies of the functional significance of the PT in the normal brain are reviewed critically. Finally a meta-analysis of MRI measurements of the distribution of planum anatomy in normal subjects is presented. Comparison is made with clinical populations, including schizophrenia and dyslexia, and the influence of handedness and gender on such measurements is quantified. Although there are many ways of defining and measuring the PT with a wide variety of results, overall there is a significant leftward asymmetry in normals, which is reduced in left handers and females. The leftward asymmetry is much reduced in patients with schizophrenia due to a relatively larger right PT than normal controls. The review is intended to guide future researchers in this area.

Projecting the sulcal pattern of human brains onto a 2D plane--a new approach using potential theory and MRI

A new method is introduced to project the sulcal pattern of the brain surface onto a 2D plane. Twin brains are compared against each other using the planar representation. We obtained T1-weighted Flash-3D MRI volumes from 14 male twins (seven monozygotic, seven dizygotic) with 3 mm-thick coronal slices. The projection is based on potential theory: A virtual electrostatic field is calculated between the area of the segmented brain and a surrounding spherical electrode. Field lines starting from each border point of the segmented brain follow the gradient towards the sphere, leading to field line concentrations due to the underlying sulci. The unwrapped sphere surface with the number of field lines per area unit is used as the 2D representation of the sulcal pattern. The resulting brain projections show a distinctive pattern, and a visual assignment of the twin pairs from the unsorted set is possible because of a high similarity of the patterns between twin pairs. Global correlation coefficients for each pair of maps yield significantly higher values for matching monozygotic twin pairs (mean = 20.2, range 12.3-25.6) than for unmatched pairs (mean = 13.0, range 1.1-28.5). As a conclusion, our method allows us to map the location and depth of the sulci on a 2D plane. The resulting maps allow quantitative inter-individual comparisons on the entire brain or parts of the brain surface.

Relationships between brain morphology and behavioral measures of hemispheric asymmetry and interhemispheric interaction

Thirty adult males identified consonant-vowel-consonant nonword trigrams projected briefly to the left visual field (right hemisphere), the right visual field (left hemisphere) or to both visual fields (and hemispheres) simultaneously. Magnetic resonance images of the brains of these same individuals provided measurements of the length of the Sylvian fissure and surface area of the planum temporale within each hemisphere as well as measurements of the midsagittal area of the corpus callosum. Both behavioral and morphological asymmetries were consistent with those found in previous studies. In addition, there were several relationships between brain morphology and trigram naming. For example, as the length of the right-hemisphere Sylvian fissure increased to become more like the typical length of the left-hemisphere Sylvian fissure, there were fewer errors of trigram identification and attention was distributed more quickly or evenly across the three letters contained in the display. In addition, as the midsagittal area of the corpus callosum increased, the percentage of errors increased on left visual field trials, but not on right visual field or bilateral trials, suggesting that an increase in corpus callosum size may be indicative of greater functional isolation of the two hemispheres.

Schizophrenia and autism considered as the products of an agnosic right shift gene

Crow (1995a) has argued that schizophrenia is caused by a gene associated with the evolution of human language and cerebral specialisation. This paper suggests a mechanism for Crow's theory which requires only one new assumption for the right shift genetic model of handedness and cerebral dominance (Annett, 1978). The proposal is that the RS+ allele, whose normal function is to induce the left hemisphere to serve speech by impairing speech-related cortex in the right hemisphere, tends to lose its directional coding. It becomes agnosic (RS+ a) for right versus left and impairs the left or right hemisphere at random. Schizophrenia is likely to develop when the RS+ a gene is paired with a normal RS+ gene but only in the 50% of cases where both hemispheres are affected. In the 50% where RS+ a affects the right hemisphere, development is normal as in the RS+ RS+ genotype. The risks for schizophrenia in monozygotic and dizygotic twins and other relatives are as expected for 50% expression of a Mendelian gene which is paired with a particular allele, but not alternative alleles at the same locus. The frequency of homozygotes for the agnosic gene is about 4 in 10,000, the rate observed for autism. A random pattern of double hemisphere deficits would give scope for a range of developmental strengths and weaknesses as observed within the spectrum of autistic disorders. Tests of the model require brain-imaging studies sensitive to individual differences in hemisphere lateralisation and a search for a genetic locus with human and nonhuman primate alleles, together with a mutant of the human form with a frequency of about 2%.

The Maudsley Family Study. 4. Normal planum temporale asymmetry in familial schizophrenia. A volumetric MRI study

BACKGROUND

Loss or reversal of the normal asymmetry of the planum temporale (PT) has been reported in schicophrenia, and may be due to aberations in the gene(s) controlling the development of brain asymmetries. We tested this hypothesis in a sample of schizophrenics and their relatives from families multiply affected with the disorder.

METHOD

We compared 32 schizophrenics and 55 of their non-schizophrenic first-degree relatives with 39 matched community controls. Volumetric measurements of the cortical volume beneath the PT were obtained using the Cavalieri method from three-dimensionally reconstructed magnetic resonance imaging images.

RESULTS

PT volume asymmetry coefficients from patients and their relatives did not differ significantly from those of the controls. Gender-specific analysis did not revealany differences.

CONCLUSIONS

Abnormalities in PT volume asymmetry are not present in familial schizophrenia, where genetic factors appear to predominate.

The fornix of the human brain: evidence of left/right asymmetry on axial MRI scans

This article reports the observation that there is a left/right asymmetry of the anterior columns of the fornix in the human brain. This asymmetry is present in the position of the two columns of the fornix in relation to the septum pellucidum. The left columna fornicis was found to be located caudal to the right, and this can be readily visualized on axial MRI scans. This difference was seen in most of the subjects, but in some subjects there was no left/right-difference and in a few the asymmetry was inverse. The asymmetry of the fornix with respect to the anterior-posterior axis was independent of the well-known dissimilar lateral ventricular volumes. However, the left/right difference in the position of the fornix was evident in subjects with or without differences in ventricular volumes. This suggests that the mechanism underlying the development of asymmetry of the fornix is independent of the mechanism leading to ventricular asymmetry. So far, no functional relevance has been ascribed to such differences in location. The finding is gaining interest in connection with recent reports of asymmetries in hippocampal subfields. Studies of fornical lesions should therefore give attention to possible side-to-side differences.

Cortical gyral anatomy and gross brain dimensions in monozygotic twins discordant for schizophrenia

BACKGROUND

This study combines recent advances in three-dimensional neuroimaging technology and the genetic constraints inherent in monozygotic (MZ) twins to examine surface gyral anatomy and gross brain dimensions in monozygotic twin pairs discordant for schizophrenia. Results are presented and evaluated with respect to prior observations of cortical anomalies in schizophrenia and the hypothesis that schizophrenia involves cortical maldevelopment.

DESIGN

Three-dimensional renderings from volumetric magnetic resonance imaging (MRI) data of 13 MZ twin pairs discordant for schizophrenia and nine normal MZ pairs were studied. Qualitative assessments of left and right hemisphere surfaces were made by raters blind to diagnosis in an effect to identify developmental gyral abnormalities such as vertical temporal gyri or microgyria. Measurement of brain hemisphere length, area, and volume were also determined. These data were compared within discordant MZ schizophrenia pairs, within normal MZ pairs, and between matched unaffected discordant and normal MZ groups.

RESULTS

Raters did not identify qualitatively abnormal gyri in the schizophrenia subjects to enable distinction from their unaffected co-twins or from normal controls. Brain hemisphere volumes in the affected DS were significantly smaller bilaterally by about 3% compared with their unaffected DS co-twins, who did not differ from normals on this measure.

CONCLUSIONS

We were unable to confirm previous reports of vertical gyri or localized gyral thinning as being characteristic of the cortical anatomy of schizophrenia. If cortical maldevelopment is associated with schizophrenia it does not appear to disrupt gross gyral pattern formation in these ways. The quantitative results of diminished hemisphere volume and length in the twins with schizophrenia are consistent with previous reports of smaller brain size in schizophrenia. Our results suggest that this is a bilateral phenomenon that may be dependent, at least in part, on environmental factors.

The temporal lobes, reversed asymmetry and the genetics of schizophrenia

Mechanisms determining temporal lobe structural asymmetries may be involved in the pathogenesis of schizophrenia. To investigate the temporal lobes in familial schizophrenia, computed tomographic scans were obtained from 51 subjects (seven families). Enlargement of sylvian fissures and temporal lobe sulcal spaces was observed in family members with schizophrenia. The posterior one-third of the sylvian fissure was larger on the left side in subjects with schizophrenia, and larger on the right side in unaffected individuals. This disturbed pattern of posterior sylvian fissure asymmetry suggests that adjacent language regions may be affected in schizophrenia. An intermediate degree of disturbance in subjects who had schizophrenia-related illnesses or were obligate carriers suggests that genetic factors may be important determinants of temporal lobe asymmetries in familial schizophrenia.

Normal asymmetry of the planum temporale in patients with schizophrenia. Three-dimensional cortical morphometry with MRI

BACKGROUND

Abnormal cerebral anatomical lateralisation has been reported in schizophrenia and may implicate anomalous neurodevelopment in the aetiology of this disease. A popular recent hypothesis has predicted that such disturbances in normal lateralisation should be especially apparent in the morphology of the temporal lobes.

METHOD

A temporal cortical region lying in the plane of the Sylvian fissure--known as the planum temporale--exhibits pronounced leftward asymmetry in normal right-handed males. We compared lateralisation of the planum temporale in schizophrenic and control males using MRI surface-rendering morphometry of the supratemporal cortex.

RESULTS

Contrary to the lateralisation hypothesis, normal patterns of leftward planum asymmetry were detected in both the schizophrenic and control groups. Schizophrenics and controls also exhibited a predicted symmetry in the bilateral areas of Heschl's gyrus, a supratemporal cortical structure immediately anterior to the planum.

CONCLUSION

These data do not support the notion that neurodevelopmental mechanisms of cerebral asymmetry are abnormal in schizophrenia.