Diffusion tensor imaging in schizophrenia

Fiber geometry in the corpus callosum in schizophrenia: evidence for transcallosal misconnection

BACKGROUND

Structural abnormalities in the callosal fibers connecting the heteromodal association areas of the prefrontal and temporoparietal cortices bilaterally have been suggested to play a role in the etiology of schizophrenia.

AIMS

To investigate for geometric abnormalities in these callosal fibers in schizophrenia patients by using a novel Diffusion-Tensor Imaging (DTI) metric of fiber geometry named Shape-Normalized Dispersion (SHD).

METHODS

DTIs (3T, 51 gradient directions, 1.7mm isotropic voxels) were acquired from 26 schizophrenia patients and 23 matched healthy controls. The prefrontal and temporoparietal fibers of the corpus callosum were extracted by means of whole-brain tractography, and their mean SHD calculated.

RESULTS

The schizophrenia patients exhibited subnormal levels of SHD in the prefrontal callosal fibers when controlling for between-group differences in Fractional Anisotropy. Reduced SHD could reflect either irregularly turbulent or inhomogeneously distributed fiber trajectories in the corpus callosum.

CONCLUSIONS

The results suggest that the transcallosal misconnectivity thought to be associated with schizophrenia could reflect abnormalities in fiber geometry. These abnormalities in fiber geometry could potentially be underpinned by neurodevelopmental irregularities.

Diffusion tensor imaging: exploring the motor networks and clinical applications

With the advances in diffusion magnetic resonance (MR) imaging techniques, diffusion tensor imaging (DTI) has been applied to a number of neurological conditions because DTI can demonstrate microstructures of the brain that are not assessable with conventional MR imaging. Tractography based on DTI offers gross visualization of the white matter fiber architecture in the human brain in vivo. Degradation of restrictive barriers and disruption of the cytoarchitecture result in changes in the diffusion of water molecules in various pathological conditions, and these conditions can also be assessed with DTI. Yet many factors may influence the ability to apply DTI clinically, so these techniques have to be used with a cautious hand.

Anatomical insights into disrupted small-world networks in schizophrenia

Schizophrenia is characterized by lowered efficiency in distributed information processing, as indicated by research that identified a disrupted small-world functional network. However, whether the dysconnection manifested by the disrupted small-world functional network is reflected in underlying anatomical disruption in schizophrenia remains unresolved. This study examined the topological properties of human brain anatomical networks derived from diffusion tensor imaging in patients with schizophrenia and in healthy controls. We constructed the weighted brain anatomical network for each of 79 schizophrenia patients and for 96 age and gender matched healthy subjects using diffusion tensor tractography and calculated the topological properties of the networks using a graph theoretical method. The topological properties of the patients' anatomical networks were altered, in that global efficiency decreased but local efficiency remained unchanged. The deleterious effects of schizophrenia on network performance appear to be localized as reduced regional efficiency in hubs such as the frontal associative cortices, the paralimbic/limbic regions and a subcortical structure (the left putamen). Additionally, scores on the Positive and Negative Symptom Scale correlated negatively with efficient network properties in schizophrenia. These findings suggest that complex brain network analysis may potentially be used to detect an imaging biomarker for schizophrenia.

The effects of hypertension and body mass index on diffusion tensor imaging in schizophrenia

Recently, the negative effects of hypertension and elevated body mass index on cognitive functioning in schizophrenia have been reported (Friedman et al., 2010). Data suggests that cognitive changes in hypertensive patients from the general population may be mediated, in part, by white matter damage. Therefore, we performed diffusion tensor imaging (DTI) in the same subjects studied by Friedman et al. (2010) to investigate the effects of hypertension and elevated body mass index on the fractional anisotropy (FA) of several major white matter tracts. Significant interactions between a diagnosis of schizophrenia and hypertension on FA in several white matter regions were detected. Hypertension was associated with lower FA in the schizophrenic group and higher FA in the same tracts in the non-schizophrenic subjects. These results suggest hypertension-induced compensatory mechanisms in the brains of non-schizophrenic patients with hypertension which may be impaired in persons with schizophrenia.

Abnormalities in connectivity of white-matter tracts in patients with familial and non-familial schizophrenia

BACKGROUND

Abnormalities in the connectivity of white-matter (WM) tracts in schizophrenia are supported by evidence from post-mortem investigations, functional and structural magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI). The aims of this study were to explore the microstructural changes in first-episode schizophrenia in a Han Chinese population and to investigate whether a family history of psychiatric disorder is related to the severity of WM tract integrity abnormalities in these patients.

METHOD

T1-weighted MR and DT images were collected in 68 patients with first-episode schizophrenia [22 with a positive family history (PFH) and 46 with a negative family history (NFH)] and 100 healthy controls. Voxel-based analysis was performed and WM integrity was quantified by fractional anisotropy (FA). Cluster- and voxel-level analyses were performed by using two-sample t tests between patients and controls and/or using a full factorial model with one factor and three levels among the three sample groups (patients with PFH or NFH, and controls), as appropriate.

RESULTS

FA deficits were observed in the patient group, especially in the left temporal lobe and right corpus callosum. This effect was more severe in the non-familial schizophrenia than in the familial schizophrenia subgroup.

CONCLUSIONS

Overall, these findings support the hypothesis that loss of WM integrity may be an important pathophysiological feature of schizophrenia, with particular implications for brain dysmaturation in non-familial and familial schizophrenia.

Brodmann area analysis of white matter anisotropy and age in schizophrenia

Diffusion tensor and structural MRI images were acquired on ninety-six patients with schizophrenia (69 men and 27 women) between the ages of 18 and 79 (mean=39.83, SD=15.16 DSM-IV diagnosis of schizophrenia according to the Comprehensive Assessment of Symptoms and History). The patients reported a mean age of onset of 23 years (range=13-38, SD=6). Patients were divided into an acute subgroup (duration ≤3 years, n=25), and a chronic subgroup (duration >3 years, n=64). Ninety-three mentally normal comparison subjects were recruited; 55 men and 38 women between the ages of 18 and 82 (mean=35.77, SD=18.12). The MRI images were segmented by Brodmann area, and the fractional anisotropy (FA) for the white matter within each Brodmann area was calculated. The FA in white matter was decreased in patients with schizophrenia broadly across the entire brain, but to a greater extent in white matter underneath frontal, temporal and cingulate cortical areas. Both normals and patients with schizophrenia showed a decrease in anisotropy with age but patients with schizophrenia showed a significantly greater rate of decrease in FA in Brodmann area 10 bilaterally, 11 in the left hemisphere and 34 in the right hemisphere. When the effect of age was removed, patients ill more than three years showed lower anisotropy in frontal motor and cingulate white matter in comparison to acute patients ill three years or less, consistent with an ongoing progression of the illness.

Positive symptoms and white matter microstructure in never-medicated first episode schizophrenia

BACKGROUND

We investigated cerebral structural connectivity and its relationship to symptoms in never-medicated individuals with first-onset schizophrenia using diffusion tensor imaging (DTI).

METHOD

We recruited subjects with first episode DSM-IV schizophrenia who had never been exposed to antipsychotic medication (n=34) and age-matched healthy volunteers (n=32). All subjects received DTI and structural magnetic resonance imaging scans. Patients' symptoms were assessed on the Positive and Negative Syndrome Scale. Voxel-based analysis was performed to investigate brain regions where fractional anisotropy (FA) values significantly correlated with symptom scores.

RESULTS

In patients with first-episode schizophrenia, positive symptoms correlated positively with FA scores in white matter associated with the right frontal lobe, left anterior cingulate gyrus, left superior temporal gyrus, right middle temporal gyrus, right middle cingulate gyrus, and left cuneus. Importantly, FA in each of these regions was lower in patients than controls, but patients with more positive symptoms had FA values closer to controls. We found no significant correlations between FA and negative symptoms.

CONCLUSIONS

The newly-diagnosed, neuroleptic-naive patients had lower FA scores in the brain compared with controls. There was positive correlation between FA scores and positive symptoms scores in frontotemporal tracts, including left fronto-occipital fasciculus and left inferior longitudinal fasciculus. This implies that white matter dysintegrity is already present in the pre-treatment phase and that FA is likely to decrease after clinical treatment or symptom remission.

Recovery of behavioral changes and compromised white matter in C57BL/6 mice exposed to cuprizone: effects of antipsychotic drugs

Recent animal and human studies have suggested that the cuprizone (CPZ, a copper chelator)-fed C57BL/6 mouse may be used as an animal model of schizophrenia. The goals of this study were to see the recovery processes of CPZ-induced behavioral changes and damaged white matter and to examine possible effects of antipsychotic drugs on the recovery processes. Mice were fed a CPZ-containing diet for 5 weeks then returned to normal food for 3 weeks, during which period mice were treated with different antipsychotic drugs. Various behaviors were measured at the end of CPZ-feeding phase as well as on the 14th and 21st days after CPZ withdrawal. The damage to and recovery status of white matter in the brains of mice were examined. Dietary CPZ resulted in white matter damage and behavioral abnormalities in the elevated plus-maze (EPM), social interaction (SI), and Y-maze test. EPM performance recovered to normal range within 2 weeks after CPZ withdrawal. Alterations in SI showed no recovery. Antipsychotics did not alter animals’ behavior in either of these tests during the recovery period. Altered performance in the Y-maze showed some recovery in the vehicle group; atypical antipsychotics, but not haloperidol, significantly promoted this recovery process. The recovery of damaged white matter was incomplete during the recovery period. None of the drugs significantly promoted the recovery of damaged white matter. These results suggest that CPZ-induced white matter damage and SI deficit may be resistant to the antipsychotic treatment employed in this study. They are in good accordance with the clinical observations that positive symptoms in schizophrenic patients respond well to antipsychotic drugs while social dysfunction is usually intractable.

Are there progressive brain changes in schizophrenia? A meta-analysis of structural magnetic resonance imaging studies

BACKGROUND

It is well established that schizophrenia is associated with structural brain abnormalities, but whether these are static or progress over time remains controversial.

METHODS

A systematic review of longitudinal volumetric studies using region-of-interest structural magnetic resonance imaging in patients with schizophrenia and healthy control subjects. The percentage change in volume between scans for each brain region of interest was obtained, and data were combined using random effects meta-analysis.

RESULTS

Twenty-seven studies were included in the meta-analysis, with 928 patients and 867 control subjects, and 32 different brain regions of interest. Subjects with schizophrenia showed significantly greater decreases over time in whole brain volume, whole brain gray matter, frontal gray and white matter, parietal white matter, and temporal white matter volume, as well as larger increases in lateral ventricular volume, than healthy control subjects. The time between baseline and follow-up magnetic resonance imaging scans ranged from 1 to 10 years. The differences between patients and control subjects in annualized percentage volume change were -.07% for whole brain volume, -.59% for whole brain gray matter, -.32% for frontal white matter, -.32% for parietal white matter, -.39% for temporal white matter, and +.36% for bilateral lateral ventricles.

CONCLUSIONS

These findings suggest that schizophrenia is associated with progressive structural brain abnormalities, affecting both gray and white matter. We found no evidence to suggest progressive medial temporal lobe involvement but did find evidence that this may be partly explained by heterogeneity between studies in patient age and illness duration. The causes and clinical correlates of these progressive brain changes should now be the focus of investigation.

Tract-based magnetic resonance spectroscopy of the cingulum bundles at 7 T

The cingulum bundle is a white matter fiber bundle in the human brain that is believed to be implicated in various neurological and psychiatric diseases. Subtle disease-related differences in metabolite concentrations in the cingulum tracts that may underlie these diseases may be detected using MR spectroscopic information. However, to date, limited signal to noise and lack of spatial resolution have prevented a reliable and reproducible measurement of metabolites in the cingulum bundle in vivo. Here we propose a new method that combines MR spectroscopic imaging at 7 T with fiber tracking to select only those MR spectroscopy voxels that are actually part of the cingulum bundles. The spectra of the selected spectroscopy voxels are processed per voxel and then combined yielding one spectrum at high spectral resolution for each cingulum bundle. In this way sensitivity is increased, as large parts of the cingulum are included while partial volume effects with both gray matter and white matter from other tracts is kept to a minimum. Three healthy volunteers were scanned to assess the feasibility of the method. For all three healthy volunteers spectra for the left and right cingulum tracts were computed, partial volume fractions calculated and metabolite fractions were quantified yielding similar results suggesting that tract-based MR spectroscopy allows us to study metabolic concentrations of individual white matter fiber bundles with high sensitivity and high specificity.

Neuroimaging study in subjects at high risk of psychosis revealed by the Rorschach test and first-episode schizophrenia

OBJECTIVE

There is increasing evidence of neuroanatomical pathology in schizophrenia, but it is unclear whether changes exist prior to disease onset. This study aimed to examine whether changes exist prior to disease onset, especially in the temporal lobes.

METHODS

T1-weighted and diffusion tensor magnetic resonance imaging were performed on 9 first-episode schizophrenia patients, 10 patients who were at high risk of schizophrenia and 10 healthy controls. Voxel-based analysis using the normalised images of cortical volume data was examined, and the fractional anisotropy value at three component fibres of the temporal lobes, inferior longitudinal fasciculus, superior longitudinal fasciculus (SLF) and cingulum hippocampal part was compared among the three groups.

RESULTS

There were statistically significant volume differences at the bilateral temporal lobe between the healthy subjects and high-risk group. Between the schizophrenic group and healthy subjects, statistically significant volume differences were detected at the bilateral temporal lobes and anterior cingulate cortex. The fractional anisotropy values of the SLF in the schizophrenic and high-risk groups were significantly lower than in the healthy subjects.

CONCLUSION

Our findings indicate that some brain alterations may progress in patients at psychosis pre-onset, possibly because of disrupted developmental mechanisms, and these pathological changes may be predictive of functional outcome.

Putative diffusion tensor neuroimaging endophenotypes in schizophrenia: a review of the early evidence

Although schizophrenia has a high heritability, the genetic effects conferring diathesis to schizophrenia are thought to be complex and underlain by multifactorial polygenic inheritance. ‘Endophenotypes’, or ‘intermediate phenotypes’, are narrowed constructs of genetic risk that are assumed to be more proximal to the gene effects in the disease pathway than clinical phenotypes. A current aim in schizophrenia research is to identify promising putative endophenotypes for use in molecular genetics studies. Recently, much of the focus has been on neurocognitive, conventional T1-weighted structural MRI, functional MRI and electrophysiological endophenotypes. Diffusion tensor imaging has emerged as another important structural neuroimaging modality in the aim to identify abnormalities in brain connectivity and diffusivity in schizophrenia, and abnormalities detected via this method may be promising candidate endophenotypes. In this article, we present the first comprehensive review of the early evidence that qualifies diffusion tensor abnormalities as potentially appropriate endophenotypes of schizophrenia.

Electrophysiological and diffusion tensor imaging evidence of delayed corollary discharges in patients with schizophrenia

BACKGROUND

Patients with schizophrenia (SZ) characteristically exhibit supranormal levels of cortical activity to self-induced sensory stimuli, ostensibly because of abnormalities in the neural signals (corollary discharges, CDs) normatively involved in suppressing the sensory consequences of self-generated actions. The nature of these abnormalities is unknown. This study investigated whether SZ patients experience CDs that are abnormally delayed in their arrival at the sensory cortex.

METHOD

Twenty-one patients with SZ and 25 matched control participants underwent electroencephalography (EEG). Participants' level of cortical suppression was calculated as the amplitude of the N1 component evoked by a button press-elicited auditory stimulus, subtracted from the N1 amplitude evoked by the same stimulus presented passively. In the three experimental conditions, the auditory stimulus was delivered 0, 50 or 100 ms subsequent to the button-press. Fifteen SZ patients and 17 healthy controls (HCs) also underwent diffusion tensor imaging (DTI), and the fractional anisotropy (FA) of participants' arcuate fasciculus was used to predict their level of cortical suppression in the three conditions.

RESULTS

While the SZ patients exhibited subnormal N1 suppression to undelayed, self-generated auditory stimuli, these deficits were eliminated by imposing a 50-ms, but not a 100-ms, delay between the button-press and the evoked stimulus. Furthermore, the extent to which the 50-ms delay normalized a patient's level of N1 suppression was linearly related to the FA of their arcuate fasciculus.

CONCLUSIONS

These data suggest that SZ patients experience temporally delayed CDs to self-generated auditory stimuli, putatively because of structural damage to the white-matter (WM) fasciculus connecting the sites of discharge initiation and destination.

A voxel-based morphometry study of grey matter loss in fragile X-associated tremor/ataxia syndrome

Fragile X-associated tremor/ataxia syndrome is a neurodegenerative disorder that primarily affects older male premutation carriers of the fragile X mental retardation gene. Although its core symptoms are mainly characterized by motor problems such as intention tremor and gait ataxia, cognitive decline and psychiatric problems are also commonly observed. Past radiological and histological approaches have focused on prominent neurodegenerative changes in specific brain structures including the cerebellum and limbic areas. However, quantitative investigations of the regional structural abnormalities have not been performed over the whole brain. In this study, we adopted the voxel-based morphometry method together with regions of interest analysis for the cerebellum to examine the pattern of regional grey matter change in the male premutation carriers with and without fragile X-associated tremor/ataxia syndrome. In a comparison with healthy controls, we found striking grey matter loss of the patients with fragile X-associated tremor/ataxia syndrome in multiple regions over the cortical and subcortical structures. In the cerebellum, the anterior lobe and the superior posterior lobe were profoundly reduced in both vermis and hemispheres. In the cerebral cortex, clusters of highly significant grey matter reduction were found in the extended areas in the medial surface of the brain, including the dorsomedial prefrontal cortex, anterior cingulate cortex and precuneus. The other prominent grey matter loss was found in the lateral prefrontal cortex, orbitofrontal cortex, amygdala and insula. Although the voxel-wise comparison between the asymptomatic premutation group and healthy controls did not reach significant difference, a regions of interest analysis revealed significant grey matter reduction in anterior subregions of the cerebellar vermis and hemisphere in the asymptomatic premutation group. Correlation analyses using behavioural scales of the premutation groups showed significant associations between grey matter loss in the left amygdala and increased levels of obsessive-compulsiveness and depression, and between decreased grey matter in the left inferior frontal cortex and anterior cingulate cortex and poor working memory performance. Furthermore, regression analyses revealed a significant negative effect of CGG repeat size on grey matter density in the dorsomedial frontal regions. A significant negative correlation with the clinical scale for the severity of fragile X-associated tremor/ataxia syndrome was found in a part of the vermis. These observations reveal the anatomical patterns of the neurodegenerative process that underlie the motor, cognitive and psychiatric problems of fragile X-associated tremor/ataxia syndrome, together with incipient structural abnormalities that may occur before the clinical onset of this disease.

Regionally specific white matter disruptions of fornix and cingulum in schizophrenia

Limbic circuitry disruptions have been implicated in the psychopathology and cognitive deficits of schizophrenia, which may involve white matter disruptions of the major tracts of the limbic system, including the fornix and the cingulum. Our study aimed to investigate regionally specific abnormalities of the fornix and cingulum in schizophrenia using diffusion tensor imaging (DTI). We determined the fractional anisotropy (FA), radial diffusivity (RD), and axial diffusivity (AD) profiles along the fornix and cingulum tracts using a fibertracking technique and a brain mapping algorithm, the large deformation diffeomorphic metric mapping (LDDMM), in the DTI scans of 33 patients with schizophrenia and 31 age-, gender-, and handedness-matched healthy controls. We found that patients with schizophrenia showed reduction in FA and increase in RD in bilateral fornix, and increase in RD in left anterior cingulum when compared to healthy controls. In addition, tract-based analysis revealed specific loci of these white matter differences in schizophrenia, that is, FA reductions and AD and RD increases occur in the region of the left fornix further from the hippocampus, FA reductions and RD increases occur in the rostral portion of the left anterior cingulum, and RD and AD increases occur in the anterior segment of the left middle cingulum. In patients with schizophrenia, decreased FA in the specific loci of the left fornix and increased AD in the right cingulum adjoining the hippocampus correlated with greater severity of psychotic symptoms. These findings support precise disruptions of limbic-cortical integrity in schizophrenia and disruption of these structural networks may contribute towards the neural basis underlying the syndrome of schizophrenia and clinical symptomatology.

ADC changes in schizophrenia: a diffusion-weighted imaging study

Studies using diffusion tensor imaging (DTI) have shown multifocal reduction in anisotropy of white matter fibre tracts in schizophrenia, and a few of these also suggest changes in apparent diffusion coefficient (ADC). In this study, we assessed ADC in 18 patients with schizophrenia and 18 healthy controls using a voxel-based approach. We did not find evidence of statistically significant changes in ADC in either direction at P < 0.05 (FDR corrected) using different smoothing filter sizes; only at an uncorrected threshold of P < 0.001 did we find an increase in a small right prefrontal area close to our previous FA finding. Our findings therefore do not support ADC changes to be a marker of white matter or grey matter abnormalities in schizophrenia. Changes in other parameters like fractional anisotropy (FA) might be a more sensitive indicator of white matter pathology in this disorder.

Complementary diffusion tensor imaging study of the corpus callosum in patients with first-episode and chronic schizophrenia

BACKGROUND

Abnormalities in the corpus callosum have long been implicated in schizophrenia. Previous diffusion tensor imaging (DTI) studies in patients with different durations of schizophrenia yielded inconsistent results. By comparing patients with different durations of schizophrenia, we investigated if white matter abnormalities of the corpus callosum emerge at an early stage in the illness or result from pathological progression.

METHODS

We recruited patients with first-episode schizophrenia, patients with chronic schizophrenia and age-, sex- and handedness-matched healthy controls. We used 2 DTI techniques (voxel-based and fibre-tracking DTI) to investigate differences in corpus callosum integrity among the 3 groups.

RESULTS

With both DTI techniques, significantly decreased fractional anisotropy values were identified in the genu of corpus callosum in patients with chronic schizophrenia, but not first-episode schizophrenia, compared with healthy controls.

LIMITATIONS

This study was cross-sectional, and the sample size was relatively small.

CONCLUSION

Abnormalities in the genu of the corpus callosum might be a progressive process in schizophrenia, perhaps related to disease severity and prognosis.

Gyrification and neural connectivity in schizophrenia

There is emerging evidence for a connection between the surface morphology of the brain and its underlying connectivity. The foundation for this relationship is thought to be established during brain development through the shaping influences of tension exerted by viscoelastic nerve fibers. The tension-based morphogenesis results in compact wiring that enhances efficient neural processing. Individuals with schizophrenia present with multiple symptoms that can include impaired thought, action, perception, and cognition. The global nature of these symptoms has led researchers to explore a more global disruption of neuronal connectivity as a theory to explain the vast array of clinical and cognitive symptoms in schizophrenia. If cerebral function and form are linked through the organization of neural connectivity, then a disruption in neural connectivity may also alter the surface morphology of the brain. This paper reviews developmental theories of gyrification and the potential interaction between gyrification and neuronal connectivity. Studies of gyrification abnormalities in children, adolescents, and adults with schizophrenia demonstrate a relationship between disrupted function and altered morphology in the surface patterns of the cerebral cortex. This altered form may provide helpful clues in understanding the neurobiological abnormalities associated with schizophrenia.

Paradigm shift in translational neuroimaging of CNS disorders

During the last two decades, functional neuroimaging technology, especially functional magnetic resonance imaging (fMRI), has improved tremendously, with new attention towards resting-state functional connectivity of the brain. This development has allowed scientists to study changes in brain structure and function, and probe these two properties under conditions of evoked stimulation, disease and drug administration. In the domain of functional imaging, the identification and characterization of central nervous system (CNS) functional networks have emerged as potential biomarkers for CNS disorders in humans. Recent attempts to translate clinical neuroimaging methodology to preclinical studies have also been carried out, which offer new opportunities in translational neuroscience research. In this paper, we review recent developments in structural and functional MRI and their use to probe functional connectivity in various CNS disorders such as schizophrenia, mood disorders, Alzheimer's disease (AD) and pain.

Cortical thickness, gray matter volume, and white matter anisotropy and diffusivity in schizophrenia

INTRODUCTION

The study was conducted to evaluate simultaneously gray matter changes and white matter changes in patients with schizophrenia.

METHODS

Cortical thickness, gray matter volume, and white matter anisotropy and diffusivity changes in schizophrenic patients (n = 21) were assessed relative to age-, gender-, and parental socioeconomic status-matched healthy controls (n = 21). We used a newly described semi-automated method (FreeSurfer version 4.5) to determine cortical thickness and gray matter volume and used the tract-based spatial statistics method to evaluate white matter anisotropy and diffusivity.

RESULTS

Schizophrenic patients showed a significant decrease in hippocampal volume compared with healthy controls. No significant thickness deficits or anisotropy and diffusivity changes were found in schizophrenic patients compared with healthy controls. Stepwise multivariate analysis revealed that hippocampal volume was positively related to duration of illness in schizophrenic patients.

CONCLUSION

Our results suggest that hippocampal volume is smaller in schizophrenic patients compared with healthy controls and that progressive hippocampal volume loss occurs in the early course of illness in schizophrenic patients but not in the more chronic stages.

Disrupted axonal fiber connectivity in schizophrenia

BACKGROUND

Schizophrenia is believed to result from abnormal functional integration of neural processes thought to arise from aberrant brain connectivity. However, evidence for anatomical dysconnectivity has been equivocal, and few studies have examined axonal fiber connectivity in schizophrenia at the level of whole-brain networks.

METHODS

Cortico-cortical anatomical connectivity at the scale of axonal fiber bundles was modeled as a network. Eighty-two network nodes demarcated functionally specific cortical regions. Sixty-four direction diffusion tensor-imaging coupled with whole-brain tractography was performed to map the architecture via which network nodes were interconnected in each of 74 patients with schizophrenia and 32 age- and gender-matched control subjects. Testing was performed to identify pairs of nodes between which connectivity was impaired in the patient group. The connectional architecture of patients was tested for changes in five network attributes: nodal degree, small-worldness, efficiency, path length, and clustering.

RESULTS

Impaired connectivity in the patient group was found to involve a distributed network of nodes comprising medial frontal, parietal/occipital, and the left temporal lobe. Although small-world attributes were conserved in schizophrenia, the cortex was interconnected more sparsely and up to 20% less efficiently in patients. Intellectual performance was found to be associated with brain efficiency in control subjects but not in patients.

CONCLUSIONS

This study presents evidence of widespread dysconnectivity in white-matter connectional architecture in a large sample of patients with schizophrenia. When considered from the perspective of recent evidence for impaired synaptic plasticity, this study points to a multifaceted pathophysiology in schizophrenia encompassing axonal as well as putative synaptic mechanisms.

Diffusion tensor imaging, structural connectivity, and schizophrenia

A fundamental tenet of the "disconnectivity" theories of schizophrenia is that the disorder is ultimately caused by abnormal communication between spatially disparate brain structures. Given that the white matter fasciculi represent the primary infrastructure for long distance communication in the brain, abnormalities in these fiber bundles have been implicated in the etiology of schizophrenia. Diffusion tensor imaging (DTI) is a magnetic resonance imaging (MRI) technique that enables the visualization of white matter macrostructure in vivo, and which has provided unprecedented insight into the existence and nature of white matter abnormalities in schizophrenia. The paper begins with an overview of DTI and more commonly used diffusion metrics and moves on to a brief review of the schizophrenia literature. The functional implications of white matter abnormalities are considered, particularly with respect to myelin's role in modulating the transmission velocity of neural discharges. The paper concludes with a speculative hypothesis about the relationship between gray and white matter abnormalities associated with schizophrenia.

Aberrant frontal and temporal complex network structure in schizophrenia: a graph theoretical analysis

Brain regions are not independent. They are interconnected by white matter tracts, together forming one integrative complex network. The topology of this network is crucial for efficient information integration between brain regions. Here, we demonstrate that schizophrenia involves an aberrant topology of the structural infrastructure of the brain network. Using graph theoretical analysis, complex structural brain networks of 40 schizophrenia patients and 40 human healthy controls were examined. Diffusion tensor imaging was used to reconstruct the white matter connections of the brain network, with the strength of the connections defined as the level of myelination of the tracts as measured through means of magnetization transfer ratio magnetic resonance imaging. Patients displayed a preserved overall small-world network organization, but focusing on specific brain regions and their capacity to communicate with other regions of the brain revealed significantly longer node-specific path lengths (higher L) of frontal and temporal regions, especially of bilateral inferior/superior frontal cortex and temporal pole regions. These findings suggest that schizophrenia impacts global network connectivity of frontal and temporal brain regions. Furthermore, frontal hubs of patients showed a significant reduction of betweenness centrality, suggesting a less central hub role of these regions in the overall network structure. Together, our findings suggest that schizophrenia patients have a less strongly globally integrated structural brain network with a reduced central role for key frontal hubs, resulting in a limited structural capacity to integrate information across brain regions.

Dysconnectivity in schizophrenia: where are we now?

The disconnection hypothesis suggests that the core symptoms of schizophrenia (SZ) are related to aberrant, or 'dys-', connectivity between distinct brain regions. A proliferation of functional and structural neuroimaging studies have been conducted to investigate this hypothesis, across the full course of the disorder; from people at Ultra-High-Risk of developing psychosis to patients with chronic SZ. However the results of these studies have not always been consistent, and to date, there have been no attempts to summarise the results of both methodologies in conjunction. In this article, we systematically review both the structural and functional connectivity literature in SZ. The main trends to emerge are that schizophrenia is associated with connectivity reductions, as opposed to increases, relative to healthy controls, and that this is particularly evident in the connections involving the frontal lobe. These two trends appear to apply across all stages of the disorder, and to be independent of the neuroimaging methodology employed. We discuss the potential implications of these trends, and identify possible future investigative directions.

Schizophrenia patients show augmented spatial frame illusion for visual and visuomotor tasks

Previous research has identified several key processes of visual perception and visually guided action that are implicated in schizophrenia. Yet, it is not well understood whether similar or different brain mechanisms mediate the abnormalities in these two processes. To explore this issue, we examined visual and visuomotor processing in schizophrenia, utilizing an illusion known as the Roelofs effect. This illusion refers to the spatial mislocalization of an object within an off-centered frame, with the object appearing to be shifted towards the opposite direction of the frame offset. In this study, localization of the object was measured either by a direct visual response or by an immediate or delayed visuomotor (reaching-to-touch) response. Patients demonstrated significantly greater magnitudes of the Roelofs effect in all response modes, indicating the existence of excessive spatial contextual effects of the frame during the processing of visual and visuomotor information, and when the two types of information are integrated over a delayed visuomotor response condition. These results provide evidence for a hypothesis of improper inhibitory control as a common mechanism underpinning abnormal visual and visuomotor processes in this mental disorder.

Predicting inter-hemispheric transfer time from the diffusion properties of the corpus callosum in healthy individuals and schizophrenia patients: a combined ERP and DTI study

BACKGROUND

Several theories of schizophrenia have emphasized the role of aberrant neural timing in the etiology of the disease, possibly as a consequence of conduction delays caused by structural damage to the white-matter fasciculi. Consistent with this theory, increased inter-hemispheric transmission times (IHTTs) to unilaterally-presented visual stimuli have been reported in patients with schizophrenia. The present study investigated whether or not these IHTT abnormalities could be underpinned by structural damage to the visual fibers of the corpus callosum.

METHODS

Thirty three schizophrenia patients and 22 matched controls underwent Event Related Potential (ERP) recording, and a subset of 19 patients and 16 controls also underwent 3T Diffusion-Tensor Imaging (DTI). Unilateral visual stimuli (squares, 2×2 degrees) were presented 6 degrees lateral to either side of a central fixation point. IHTTs (ipsilateral minus contralateral latencies) were calculated for the P1 and N1 components at parietal-occipital sites in current source density-transformed ERPs. The visual fibers of the corpus callosum were extracted with streamline tractography and the diffusion metrics of Fractional Anisotropy (FA) and Mode calculated.

RESULTS

While both subject groups exhibited highly significant IHTTs across a range of posterior electrode pairs, and significantly shorter IHTTs from left-to-right hemisphere than vice versa, no significant groupwise differences in IHTT were observed. However, participants' IHTTs were linearly related to their FA and Mode, with longer IHTTs being associated with lower FA and more prolate diffusion ellipsoids.

CONCLUSIONS

These results suggest that IHTTs are estimable from DTI measures of white matter integrity. In light of the range of diffusion abnormalities that have been reported in patients with schizophrenia, particularly in frontal fasciculi, these results support the conjecture that schizophrenia is associated with abnormalities in neural timing.

Linking oligodendrocyte and myelin dysfunction to neurocircuitry abnormalities in schizophrenia

Multiple lines of evidence in schizophrenia, from brain imaging, studies in postmortem brains, and genetic association studies, have implicated oligodendrocyte and myelin dysfunction in this disease. Recent studies suggest that oligodendrocyte and myelin dysfunction leads to changes in synaptic formation and function, which could lead to cognitive dysfunction, a core symptom of schizophrenia. Furthermore, there is accumulating data linking oligodendrocyte and myelin dysfunction with dopamine and glutamate abnormalities, both of which are found in schizophrenia. These findings implicate oligodendrocyte and myelin dysfunction as a primary change in schizophrenia, not only as secondary consequences of the illness or treatment. Strategies targeting oligodendrocyte and myelin abnormalities could therefore provide therapeutic opportunities for patients suffering from schizophrenia.

Anterior thalamic radiation integrity in schizophrenia: a diffusion-tensor imaging study

The anterior limb of the internal capsule (ALIC) is a white matter structure, the medial portion of which includes the anterior thalamic radiation (ATR) carrying nerve fibers between thalamus and prefrontal cortex. ATR abnormalities have a possible link with cognitive abnormalities and negative symptoms in schizophrenia. We aimed to study the fiber integrity of the ATR more selectively by isolating the medial portion of the ALIC using region-of-interest based methodology. Diffusion-tensor imaging was used to measure the anisotropy of total ALIC (tALIC) and medial ALIC (mALIC) in 39 schizophrenia and 33 control participants, matched for age/gender/handedness. Relationships between anisotropy, psychopathology, and cognitive performance were analyzed. Compared with controls, schizophrenia participants had 4.55% lower anisotropy in right tALIC, and 5.38% lower anisotropy in right mALIC. There were no significant group anisotropy differences on the left. Significant correlations were observed between right ALIC integrity and relevant domains of cognitive function (e.g., executive function, working memory). Our study suggests an asymmetric microstructural change in ALIC in schizophrenia involving the right side, which is only minimally stronger in mALIC, and which correlates with cognitive impairment. Microstructural changes in the ALIC may be linked to cognitive dysfunction in schizophrenia.

Disrupted white matter integrity of corticopontine-cerebellar circuitry in schizophrenia

Evidence for white matter abnormalities in patients with schizophrenia is increasing. Decreased fractional anisotropy (FA) in interhemispheric commissural fibers as well as long-ranging fronto-parietal association fibers belongs to the most frequent findings. The present study used tract-based spatial statistics to investigate white matter integrity in 35 patients with schizophrenia and 35 healthy volunteers. We found that patients exhibited significantly decreased FA relative to healthy subjects in the corpus callosum, the cerebral peduncle, the left inferior fronto-occipital fasciculus, the anterior thalamic radiation, the right posterior corona radiata, the middle cerebellar peduncle, and the right superior longitudinal fasciculus. Increased FA was detectable in the inferior sections of the corticopontine-cerebellar circuit. Present data indicate extended cortical-subcortical alterations of white matter integrity in schizophrenia using advanced data analysis strategies. They corroborate preceding findings of white matter structural deficits in mainly long-ranging association fibers and provide first evidence for neuroplastic changes in terms of an increased directionality in more inferior fiber tracts.

Tract-based analysis of magnetization transfer ratio and diffusion tensor imaging of the frontal and frontotemporal connections in schizophrenia

BACKGROUND

In the pathophysiology of schizophrenia, aberrant connectivity between brain regions may be a central feature. Diffusion tensor imaging (DTI) studies have shown altered fractional anisotropy (FA) in white brain matter in schizophrenia. Focal reductions in myelin have been suggested in patients using magnetization transfer ratio (MTR) imaging but to what extent schizophrenia may be related to changes in MTR measured along entire fiber bundles is still unknown.

METHODS

DTI and MTR images were acquired with a 1.5-T scanner in 40 schizophrenia patients and compared with those of 40 healthy participants. The mean FA and mean MTR were measured along the genu of the corpus callosum and the left and right uncinate fasciculus.

RESULTS

A higher mean MTR of 1% was found in the right uncinate fasciculus in patients compared with healthy participants. A significant negative correlation between age and mean FA in the left uncinate fasciculus was found in schizophrenia patients but not in healthy participants.

CONCLUSIONS

Decreased FA in the left uncinate fasciculus may be more prominent in patients with longer illness duration. The increased mean MTR in the right uncinate fasciculus could reflect a compensatory role for myelin in these fibers or possibly represent aberrant frontotemporal connectivity.

Gene expression abnormalities and oligodendrocyte deficits in the internal capsule in schizophrenia

Deficits in the expression of oligodendrocyte (Ol) and myelin genes have been described in numerous brain regions in schizophrenia (SZ) in association with abnormalities of cell cycle markers. We have previously reported a SZ-associated decrease in the expression of genes expressed after, but not prior to, the terminal differentiation of Ols in the posterior limb of the internal capsule (ICp). This pattern of deficits could reflect a failure of Ol precursors to exit the cell cycle and differentiate to meet the demands imposed by the high rate of apoptosis among myelinating Ols. Here we explore this hypothesis using quantitative real time PCR to examine the mRNA expression of additional genes in the ICp of the previously examined sample of 14 subjects with SZ and 15 normal controls (NCs). The genes examined in the present study were chosen because they are associated with particular phases of the cell cycle (CCND1, CCND2, p21(Cip1), p27(Kip1), and p57(Kip2)), with DNA replication and repair (PCNA), apoptosis (CASP3), or the Notch signaling pathway (JAG1, HES1, HES5, andDTX1). The Notch pathway influences whether Ol precursors continue to proliferate or exit the cell cycle. We also determined the densities of Ols in the ICp. Genes associated with maintenance of the cell cycle tended to exhibit increased expression levels in SZ relative to NCs and to be negatively correlated with the expression levels of the previously assessed mature Ol genes. In contrast, genes associated with cell cycle arrest tended to show the opposite pattern (decreased expression in SZ and positive correlations with mature Ol genes). CASP3 and PCNA expression levels were significantly decreased in SZ and positively correlated with mature Ol genes, suggesting that myelinating Ols may turnover more rapidly in normal controls than in subjects with SZ. JAG1 expression was significantly increased in SZ and exhibited positive correlations with mediators of the canonical Notch pathway but negative correlations with mature Ol genes. Ol densities were significantly decreased in SZ. These data are consistent with the hypothesis that Ol and myelin deficits in SZ involve a failure of Ol precursors to appropriately exit the cell cycle in order to differentiate and mature into myelinating Ols.

Corpus callosum abnormalities and their association with psychotic symptoms in patients with schizophrenia

BACKGROUND

While the neuroanatomical underpinnings of the functional brain disconnectivity observed in patients with schizophrenia (SZ) remain elusive, white matter fiber bundles of the brain are a likely candidate, given that they represent the infrastructure for long-distance neural communication.

METHODS

This study investigated for diffusion abnormalities in 19 patients with chronic SZ, relative to 19 matched control subjects, across tractography-defined segments of the corpus callosum. Diffusion-weighted images were acquired with 51 noncollinear gradients on a 3T scanner (1.7 mm isotropic voxels). The corpus callosum was extracted by means of whole-brain tractography and automated fiber clustering and was parcelled into six segments on the basis of fiber trajectories. The diffusion indexes of fractional anisotropy (FA) and mode were calculated for each segment.

RESULTS

Relative to the healthy control subjects, the SZ patients exhibited mode increases in the parietal fibers, suggesting a relative absence of crossing fibers. Schizophrenia patients also exhibited FA reductions in the frontal fibers, which were underpinned by increases in radial diffusivity, consistent with myelin abnormalities. Significant correlations were observed between patients' degree of reality distortion and their FA and radial diffusivity, such that the most severely psychotic patients were the least abnormal in terms of their frontal fiber diffusivity.

CONCLUSIONS

The SZ patients exhibited a variety of diffusion abnormalities in the corpus callosum, which were related to the severity of their psychotic symptoms. To the extent that diffusion abnormalities influence axonal transmission velocities, these results provide support for those theories that emphasize neural timing abnormalities in the etiology of schizophrenia.

Brain connectivity is not only lower but different in schizophrenia: a combined anatomical and functional approach

BACKGROUND

Schizophrenia is hypothesized to involve disordered connectivity between brain regions. Currently, there are no direct measures of brain connectivity; functional and structural connectivity used separately provide only limited insight. Simultaneous measure of anatomical and functional connectivity and its interactions allow for better understanding of schizophrenia-related alternations in brain connectivity.

METHODS

Twenty-seven schizophrenia patients and 27 healthy control subjects underwent magnetic resonance imaging with resting state functional magnetic resonance imaging and diffusion tensor imaging. Separate functional and anatomical connectivity maps were calculated and combined for each subject. Global, regional, and voxel measures and K-means network analysis were employed to identify group differences and correlation with clinical symptoms.

RESULTS

A global connectivity analysis indicated that patients had lower anatomical connectivity and lower coherence between the two imaging modalities. In schizophrenia these group differences correlated with clinical symptom severity. Although anatomical connectivity nearly uniformly decreased, functional connectivity in schizophrenia was lower for some connections (e.g., middle temporal gyrus) and higher for others (e.g., cingulate and thalamus). Within the default mode network (DMN) two separate subsystems can be identified. Schizophrenia patients showed decoupling between structural and functional connectivity that can be localized to networks originating in posterior cingulate cortex as well as in the task-positive network and one of the DMN components.

CONCLUSIONS

Combining two measures of brain connectivity provides more comprehensive descriptions of altered brain connectivity underlying schizophrenia. Patients show deficits in white matter anatomy, but functional connectivity alterations are more complex. Fusion of both methods allows identification of subsystems showing both increased and decreased functional connectivity.

Accurate anisotropic fast marching for diffusion-based geodesic tractography

Using geodesics for inferring white matter fibre tracts from diffusion-weighted MR data is an attractive method for at least two reasons: (i) the method optimises a global criterion, and hence is less sensitive to local perturbations such as noise or partial volume effects, and (ii) the method is fast, allowing to infer on a large number of connexions in a reasonable computational time. Here, we propose an improved fast marching algorithm to infer on geodesic paths. Specifically, this procedure is designed to achieve accurate front propagation in an anisotropic elliptic medium, such as DTI data. We evaluate the numerical performance of this approach on simulated datasets, as well as its robustness to local perturbation induced by fiber crossing. On real data, we demonstrate the feasibility of extracting geodesics to connect an extended set of brain regions.

White matter abnormalities in first-episode schizophrenia: a combined structural MRI and DTI study

This study examined white matter volume change and integrity jointly in patients with first-episode schizophrenia using an empirically derived region of interest approach and novel Diffusion Tensor Imaging (DTI) geometric indices. Structural images from 103 individuals comprising of 39 patients with first-episode schizophrenia and 64 healthy controls were examined for regions of white matter volume change using voxel-based morphometry (VBM). These regions were then further interrogated for group differences employing geometric indices in addition to fractional anisotropy (FA).VBM analyses revealed that patients with first-episode schizophrenia had lower white matter volume in the right temporal-occipital region (p<0.005) corresponding to the inferior longitudinal fasciculus. Further analyses of diffusion anisotropy in the right temporal-occipital region revealed lower planar anisotropy, and higher linear anisotropy (p=0.012) in patients. FA in the implicated region was also found to be correlated with severity of delusions (r=0.47, p=0.004).We confirmed previous findings of lower white matter volume in the region of inferior longitudinal fasciculus. The presence of changes in geometric diffusion indices in the implicated white matter region suggested that pathophysiological processes which underlie cerebral white matter volume reduction may not be reflected by changes in FA. Further research is needed to better understand the nature of these white matter changes and its progression in schizophrenia over time.

Update on the use of MR for assessment and diagnosis of psychiatric diseases

The lack of quantitative objective measures of psychiatric diseases such as anxiety and depression is one reason that the causative factors of psychiatric diseases remain obscure. The fact that human behavior is complex and cannot be easily tested in laboratories or reproduced in animal models further complicates our understanding of psychiatric diseases. During the past 3 decades, several magnetic resonance (MR)-based tools such as MR morphometry, diffusion-tensor imaging, functional MR imaging, and MR spectroscopy have yielded findings that provide tangible evidence of the neurobiologic manifestations of psychiatric diseases. In this article, we summarize major MR findings of schizophrenia, bipolar disorder, anxiety disorders, and attention deficit-hyperactivity disorder as examples to illustrate the promise that MR techniques hold for not only revealing the neurobiological underpinnings of psychiatric disorders but also enhancing our understanding of healthy human behavior. However, many radiologists remain skeptical about the diagnostic value of MR in psychiatric disease. Many inconsistent, noncomparable reports in the literature contribute to this skepticism. The aims of this article are to (a) illustrate the most reported MR findings of major psychiatric disorders such as schizophrenia, mood disorders, anxiety disorders, and attention deficit-hyperactivity disorder; (b) inform radiologists of the potential roles of MR imaging in psychiatric imaging research; and (c) discuss several confounding factors in the design and interpretation of MR imaging findings in psychiatry.

Training of working memory impacts structural connectivity

Working memory is the limited capacity storage system involved in the maintenance and manipulation of information over short periods of time. Individual capacity of working memory is associated with the integrity of white matter in the frontoparietal regions. It is unknown to what extent the integrity of white matter underlying the working memory system is plastic. Using voxel-based analysis (VBA) of fractional anisotropy (FA) measures of fiber tracts, we investigated the effect of working memory training on structural connectivity in an interventional study. The amount of working memory training correlated with increased FA in the white matter regions adjacent to the intraparietal sulcus and the anterior part of the body of the corpus callosum after training. These results showed training-induced plasticity in regions that are thought to be critical in working memory. As changes in myelination lead to FA changes in diffusion tensor imaging, a possible mechanism for the observed FA change is increased myelination after training. Observed structural changes may underlie previously reported improvement of working memory capacity, improvement of other cognitive functions, and altered functional activity following working memory training.

Polymorphisms in SREBF1 and SREBF2, two antipsychotic-activated transcription factors controlling cellular lipogenesis, are associated with schizophrenia in German and Scandinavian samples

Several studies have reported structural brain abnormalities, decreased myelination and oligodendrocyte dysfunction in schizophrenia. In the central nervous system, glia-derived de novo synthesized cholesterol is essential for both myelination and synaptogenesis. Previously, we demonstrated in glial cell lines that antipsychotic drugs induce the expression of genes involved in cholesterol and fatty acids biosynthesis through activation of the sterol regulatory element binding protein (SREBP) transcription factors, encoded by the sterol regulatory element binding transcription factor 1 (SREBF1) and sterol regulatory element binding transcription factor 2 (SREBF2) genes. Considering the importance of these factors in the lipid biosynthesis and their possible involvement in antipsychotic drug effects, we hypothesized that genetic variants of SREBF1 and/or SREBF2 could affect schizophrenia susceptibility. We therefore conducted a HapMap-based association study in a large German sample, and identified association between schizophrenia and five markers in SREBF1 and five markers in SREBF2. Follow-up studies in two independent samples of Danish and Norwegian origin (part of the Scandinavian collaboration of psychiatric etiology study, SCOPE) replicated the association for the five SREBF1 markers and for two markers in SREBF2. A combined analysis of all samples resulted in highly significant genotypic P-values of 9 x 10(-4) for SREBF1 (rs11868035, odd ration (OR)=1.26, 95% confidence interval (CI) (1.09-1.45)) and 4 x 10(-5) for SREBF2 (rs1057217, OR=1.39, 95% CI (1.19-1.63)). This finding strengthens the hypothesis that SREBP-controlled cholesterol biosynthesis is involved in the etiology of schizophrenia.

Cannabis use and callosal white matter structure and integrity in recent-onset schizophrenia

Adolescent-onset cannabis use, compared with adult-onset use, has been associated with a higher risk for developing symptoms of schizophrenia-like psychotic disorders. To test the hypothesis that onset of cannabis use in early adolescence in male schizophrenia patients is associated with abnormalities in white matter structure and integrity, we used high resolution structural and diffusion tensor brain images to compare three groups of patients: those who started regular use of cannabis (1) before the age of 15 years (early-onset cannabis users, n = 10) or (2) at the age of 17 years or later (late-onset cannabis users, n = 8), and (3) those who were cannabis naïve (n = 8). To verify patient findings, we also compared white matter integrity of the three patient groups with that of a healthy control group (n = 10). Cannabis naïve patients showed reduced white matter density and reduced fractional anisotropy, an indicator for white matter integrity, in the splenium of the corpus callosum compared with patients with early-onset cannabis use. In the same brain area, cannabis naïve patients showed reduced fractional anisotropy compared with healthy controls. Our results suggest that the age of onset of cannabis use is not an identifying characteristic for white matter abnormalities in schizophrenia patients; however, our results might indicate a more vulnerable brain structure in cannabis naïve schizophrenia patients.

Progressive brain changes in schizophrenia: a 1-year follow-up study of diffusion tensor imaging

OBJECTIVE

Recent cross-sectional studies suggest that brain changes in schizophrenia are progressive during the course of the disorder. However, it remains unknown whether this is a global process or whether some brain areas are affected to a greater degree. The aim of this study was to examine the longitudinal brain changes in patients with chronic older schizophrenia by magnetic resonance imaging (MRI).

METHODS

Three-dimensional (3D) T1-weighted and diffusion tensor (DT) MRI were performed twice on each of 16 chronic older schizophrenia patients (mean age = 58.1 ± 6.7 years ) with an interval of 1 year between imaging sessions. To clarify the longitudinal morphological and white matter changes, volume data and normalised diffusion tensor imaging (DTI) metrics were compared between the first and follow-up studies using a paired t-test.

RESULTS

Focal cortical volume loss was observed in the left prefrontal lobe and anterior cingulate on volumetric study. In addition, DTI metrics changed significantly at the bilateral posterior superior temporal lobes, left insula, genu of the corpus callosum and anterior cingulate.

CONCLUSION

There are ongoing changes in the brains of schizophrenic patients during the course of the illness. Discrepancies between volume data and DTI metrics may indicate that the pattern of progressive brain changes varies according to brain region.

Microstructural organization of cerebellar tracts in schizophrenia

BACKGROUND

Dysconnectivity theories of schizophrenia would suggest that the connectivity of the cerebellum is impaired and that the impairment may be restricted to certain tracts. Attempts to examine the structural connectivity of the cerebellum using diffusion tensor imaging have yielded conflicting results. However, previous studies have employed region-of-interest approaches or have used small or unmatched samples, with a consequent risk of type II error.

METHODS

We conducted an appropriately powered case-control study of 33 patients with schizophrenia and 33 matched healthy control subjects. We used tractography to dissect the four white matter tracts of the cerebellum and measured fractional anisotropy (FA) and mean diffusivity (MD) over each tract for each subject.

RESULTS

Repeated-measures analysis of variance found that FA was lower in the schizophrenia group compared with the control group, but there were no tract-specific differences between the groups. Mean diffusivity did not differ between the groups.

CONCLUSIONS

Though structural connectivity is impaired in the cerebellum, it is not local to any particular tract but appears to have a wider, possibly global, distribution. Reduced fractional anisotropy with normal MD would point to the differences being due to disordered neuronal architecture rather than disordered myelination.

White matter 'potholes' in early-onset schizophrenia: a new approach to evaluate white matter microstructure using diffusion tensor imaging

There is considerable evidence implicating white matter abnormalities in the pathophysiology of schizophrenia. Many of the recent studies examining white matter have utilized diffusion tensor imaging (DTI) using either region of interest (ROI) or voxel-based approaches. Both voxel-based and ROI approaches are based on the assumption that the abnormalities in white matter overlap spatially. However, this is an assumption that has not been tested, and it is possible that aberrations in white matter occur in non-overlapping regions. In order to test for the presence of non-overlapping regions of aberrant white matter, we developed a novel image processing technique that evaluates for white matter 'potholes,' referring to within-subject clusters of white matter voxels that show a significant reduction in fractional anisotropy. We applied this algorithm to a group of children and adolescents with schizophrenia compared to controls and found an increased number of 'potholes' in the patient group. These results suggest that voxel-based and ROI approaches may be missing some white matter differences that do not overlap spatially. This algorithm may be also be well suited to detect white matter abnormalities in disorders such as substance abuse, head trauma, or specific neurological conditions affecting white matter.

Imaging genetics of structural brain connectivity and neural integrity markers

We review studies that have used diffusion imaging (DI) and magnetic resonance spectroscopy (MRS) to investigate genetic associations. A brief description of the measures obtainable with these methods and of some methodological and interpretability limitations is given. The usefulness of DI and MRS in defining intermediate phenotypes and in demonstrating the effects of common genetic variants known to increase risk for psychiatric manifestations on anatomical and metabolic phenotypes is reviewed. The main focus is on schizophrenia where the greatest amount of data has been collected. Moreover, we present an example coming from a different approach, where the genetic alteration is known (the deletion that causes Williams syndrome) and the DI phenotype can shed new light on the function of genes affected by the mutation. We conclude that, although these are still early days of this type of research and many findings remain controversial, both techniques can significantly contribute to the understanding of genetic effects in the brain and the pathophysiology of psychiatric disorders.

White matter reduction in patients with schizophrenia as revealed by voxel-based morphometry: an activation likelihood estimation meta-analysis

Schizophrenia is thought to be a mental disorder caused by the disconnection of brain regions. Cumulative evidence of white matter deficit in patients with schizophrenia has been reported using voxel-based morphometry (VBM), but these studies have not been quantitatively reviewed. In the study reported herein, we used activation likelihood estimation (ALE) analysis to quantitatively estimate focal white matter abnormalities in patients with schizophrenia. Seventeen studies that compared the white matter deficit of patients with schizophrenia and healthy controls were ascertained. The frontal white matter regions and internal capsule revealed consistent white matter reduction in patient groups relative to healthy controls, suggesting a clear focal white matter deficit in patients with schizophrenia. These results support the macro-circuit theory of white matter change in schizophrenia.