Diffusion tensor imaging of frontal lobe white matter tracts in schizophrenia

Changes in the superior longitudinal fasciculus and anterior thalamic radiation in the left brain are associated with developmental dyscalculia

Developmental dyscalculia is a neurodevelopmental disorder specific to arithmetic learning even with normal intelligence and age-appropriate education. Difficulties often persist from childhood through adulthood lowering the individual's quality of life. However, the neural correlates of developmental dyscalculia are poorly understood. This study aimed to identify brain structural connectivity alterations in developmental dyscalculia. All participants were recruited from a large scale, non-referred population sample in a longitudinal design. We studied 10 children with developmental dyscalculia (11.3 ± 0.7 years) and 16 typically developing peers (11.2 ± 0.6 years) using diffusion-weighted magnetic resonance imaging. We assessed white matter microstructure with tract-based spatial statistics in regions-of-interest tracts that had previously been related to math ability in children. Then we used global probabilistic tractography for the first time to measure and compare tract length between developmental dyscalculia and typically developing groups. The high angular resolution diffusion-weighted magnetic resonance imaging and crossing-fiber probabilistic tractography allowed us to evaluate the length of the pathways compared to previous studies. The major findings of our study were reduced white matter coherence and shorter tract length of the left superior longitudinal/arcuate fasciculus and left anterior thalamic radiation in the developmental dyscalculia group. Furthermore, the lower white matter coherence and shorter pathways tended to be associated with the lower math performance. These results from the regional analyses indicate that learning, memory and language-related pathways in the left hemisphere might be related to developmental dyscalculia in children.

Four-modality imaging of unmedicated subjects with schizophrenia: 18F-fluorodeoxyglucose and 18F-fallypride PET, diffusion tensor imaging, and MRI

Diminished prefrontal function, dopaminergic abnormalities in the striatum and thalamus, reductions in white matter integrity and frontotemporal gray matter deficits are the most replicated findings in schizophrenia. We used four imaging modalities (¹⁸F-fluorodeoxyglucose and ¹⁸F-fallypride PET, diffusion tensor imaging, structural MRI) in 19 healthy and 25 schizophrenia subjects to assess the relationship between functional (dopamine D₂/D₃ receptor binding potential, glucose metabolic rate) and structural (fractional anisotropy, MRI) correlates of schizophrenia and their additive diagnostic prediction potential. Multivariate ANOVA was used to compare structural and functional image sets for identification of schizophrenia. Integration of data from all four modalities yielded better predictive power than less inclusive combinations, specifically in the thalamus, left dorsolateral prefrontal and temporal regions. Among the modalities, fractional anisotropy showed highest discrimination in white matter whereas ¹⁸F-fallypride binding showed highest discrimination in gray matter. Structural and functional modalities displayed comparable discriminative power but different topography, with higher sensitivity of structural modalities in the left prefrontal region. Combination of functional and structural imaging modalities with inclusion of both gray and white matter appears most effective in diagnostic discrimination. The highest sensitivity of ¹⁸F-fallypride PET to gray matter changes in schizophrenia supports the primacy of dopaminergic abnormalities in its pathophysiology.

White Matter Correlates of Theory of Mind in Patients With First-Episode Psychosis

Deficits in theory of mind (ToM) are considered as a distinctive feature of schizophrenia. Functional magnetic resonance imaging (fMRI) studies have suggested that aberrant activity among the regions comprising the mentalizing network is related to observed ToM deficits. However, the white matter structures underlying the ToM functional network in schizophrenia remain unclear. To investigate the relationship between white matter integrity and ToM impairment, 35 patients with first-episode psychosis (FEP) and 29 matched healthy controls (HCs) underwent diffusion tensor imaging (DTI). Using tract-based spatial statistics (TBSS), fractional anisotropy (FA) values of the two regions of interest (ROI)-the cingulum and superior longitudinal fasciculus (SLF)-were acquired, and correlational analysis with ToM task scores was performed. Among the patients with FEP, ToM strange story scores were positively correlated with the FA values of the left cingulum and left SLF. There was no significant correlation between FA and ToM task scores in HCs. These results suggest that the left cingulum and SLF constitute a possible neural basis for ToM deficits in schizophrenia. Our study is the first to demonstrate the white matter connectivity underlying the mentalizing network, as well as its relation to ToM ability in patients with FEP.

Abnormalities in white matter tracts in the fronto-striatal-thalamic circuit are associated with verbal performance in 22q11.2DS

BACKGROUND

Abnormalities in fronto-striatal-thalamic (FST) sub-circuits are present in schizophrenia and are associated with cognitive impairments. However, it remains unknown whether abnormalities in FST sub-circuits are present before psychosis onset. This may be elucidated by investigating 22q11.2 deletion syndrome (22q11DS), a genetic syndrome associated with a 30% risk for developing schizophrenia in adulthood and a decline in Verbal IQ (VIQ) preceding psychosis onset. Here, we examined white matter (WM) tracts in FST sub-circuits, especially those in the dorsolateral (DLPFC) and ventrolateral prefrontal cortex (VLPFC) sub-circuits, and their associations with VIQ in young adults with 22q11DS.

METHODS

Diffusion MRI scans were acquired from 21 individuals with 22q11DS with prodromal symptoms of schizophrenia, 30 individuals with 22q11DS without prodromal symptoms, and 30 healthy controls (mean age: 21 ± 2 years). WM tracts were reconstructed between striatum and thalamus with rostral middle frontal gyrus (rMFG) and inferior frontal gyrus (IFG), representing DLPFC and VLPFC respectively. Fractional anisotropy (FA) and radial diffusivity (RD) were used for group comparisons. VIQ was assessed and associations with the diffusion measures were evaluated.

RESULTS

FA was significantly increased and RD decreased in most tracts of the DLPFC and VLPFC sub-circuits in 22q11DS. Verbal IQ scores correlated negatively with FA and, at trend level, positively with RD in the right thalamus-IFG tract in 22q11DS with prodromal symptoms.

CONCLUSIONS

While abnormalities in FST sub-circuits are associated with schizophrenia, we observed that these abnormalities are also present in 22q11DS individuals with prodromal symptoms and are associated with verbal performance in the right thalamus-IFG tract.

Relationship between white matter glucose metabolism and fractional anisotropy in healthy and schizophrenia subjects

Decreased fractional anisotropy and increased glucose utilization in the white matter have been reported in schizophrenia. These findings may be indicative of an inverse relationship between these measures of white matter integrity and metabolism. We used ¹⁸F-fluorodeoxyglucose positron emission tomography and diffusion-tensor imaging in 19 healthy and 25 schizophrenia subjects to assess and compare coterritorial correlation patterns between glucose utilization and fractional anisotropy on a voxel-by-voxel basis and across a range of automatically placed representative white matter regions of interest. We found a pattern of predominantly negative correlations between white matter metabolism and fractional anisotropy in both healthy and schizophrenia subjects. The overall strength of the relationship was attenuated in subjects with schizophrenia, who displayed significantly fewer and weaker correlations in all regions assessed with the exception of the corpus callosum. This attenuation was most prominent in the left prefrontal white matter and this region also best predicted the diagnosis of schizophrenia. There exists an inverse relationship between the measures of white matter integrity and metabolism, which may therefore be physiologically linked. In subjects with schizophrenia, hypermetabolism in the white matter may be a function of lower white matter integrity, with lower efficiency and increased energetic cost of task-related computations.

Diffusion tensor imaging in schizophrenia

Diffusion tensor imaging (DTI) is a magnetic resonance imaging technique that is increasingly being used for the non-invasive evaluation of brain white matter abnormalities. In this review, we discuss the basic principles of DTI, its roots and the contribution of European centres in its development, and we review the findings from DTI studies in schizophrenia. We searched EMBASE, PubMed, PsychInfo, and Medline from February 1998 to December 2006 using as keywords ‘schizophrenia’, ‘diffusion’, ‘tensor’, and ‘DTI’. Forty studies fulfilling the inclusion criteria of this review were included and systematically reviewed. White matter abnormalities in many diverse brain regions were identified in schizophrenia. Although the findings are not completely consistent, frontal and temporal white matter seems to be more commonly affected. Limitations and future directions of this method are discussed.

Increased and Decreased Superficial White Matter Structural Connectivity in Schizophrenia and Bipolar Disorder

Schizophrenia (SZ) and bipolar disorder (BD) are often conceptualized as "disconnection syndromes," with substantial evidence of abnormalities in deep white matter tracts, forming the substrates of long-range connectivity, seen in both disorders. However, the study of superficial white matter (SWM) U-shaped short-range tracts remained challenging until recently, although findings from postmortem studies suggest they are likely integral components of SZ and BD neuropathology. This diffusion weighted imaging (DWI) study aimed to investigate SWM microstructure in vivo in both SZ and BD for the first time. We performed whole brain tractography in 31 people with SZ, 32 people with BD and 54 controls using BrainVISA and Connectomist 2.0. Segmentation and labeling of SWM tracts were performed using a novel, comprehensive U-fiber atlas. Analysis of covariances yielded significant generalized fractional anisotropy (gFA) differences for 17 SWM bundles in frontal, parietal, and temporal cortices. Post hoc analyses showed gFA reductions in both patient groups as compared with controls in bundles connecting regions involved in language processing, mood regulation, working memory, and motor function (pars opercularis, insula, anterior cingulate, precentral gyrus). We also found increased gFA in SZ patients in areas overlapping the default mode network (inferior parietal, middle temporal, precuneus), supporting functional hyperconnectivity of this network evidenced in SZ. We thus illustrate that short U-fibers are vulnerable to the pathological processes in major psychiatric illnesses, encouraging improved understanding of their anatomy and function.

A longitudinal neurite and free water imaging study in patients with a schizophrenia spectrum disorder

Diffusion tensor imaging (DTI) studies show widespread white matter abnormalities in schizophrenia, but it is difficult to directly relate these parameters to biological processes. Neurite orientation dispersion and density imaging (NODDI) is geared toward biophysical characterization of white matter microstructure, but only few studies have leveraged this technique to study white matter alterations. We recruited 42 schizophrenia patients (30 antipsychotic-naïve and 12 currently untreated) and 42 matched controls in this prospective study. We assessed the orientation dispersion index (ODI) and extracellular free water (FW) using single-shell DTI data before and after a 6-week trial of risperidone. Longitudinal data were available for 27 patients. Voxelwise analyses showed significantly increased ODI in the posterior limb of the internal capsule in unmedicated patients (242 voxels; x = -24; y = 6; z = 6; p < 0.01; α < 0.04), but no alterations in FW. Whole brain measures did not reveal alterations in ODI but a 6.3% trend-level increase in FW in unmedicated SZ (t = -1.873; p = 0.07). Baseline ODI was negatively correlated with subsequent response to antipsychotic treatment (r = -0.38; p = 0.049). Here, we demonstrated altered fiber complexity in medication-naïve and unmedicated patients with a schizophrenia spectrum illness. Lesser whole brain fiber uniformity was predictive of poor response to treatment, suggesting this measure may be a clinically relevant biomarker. Interestingly, we found no significant changes in NODDI indices after short-term treatment with risperidone. Our data show that biophysical diffusion models have promise for the in vivo evaluation of brain microstructure in this devastating neuropsychiatric syndrome.

Common and distinct changes of default mode and salience network in schizophrenia and major depression

Brain imaging reveals schizophrenia as a disorder of macroscopic brain networks. In particular, default mode and salience network (DMN, SN) show highly consistent alterations in both interacting brain activity and underlying brain structure. However, the same networks are also altered in major depression. This overlap in network alterations induces the question whether DMN and SN changes are different across both disorders, potentially indicating distinct underlying pathophysiological mechanisms. To address this question, we acquired T1-weighted, diffusion-weighted, and resting-state functional MRI in patients with schizophrenia, patients with major depression, and healthy controls. We measured regional gray matter volume, inter-regional structural and intrinsic functional connectivity of DMN and SN, and compared these measures across groups by generalized Wilcoxon rank tests, while controlling for symptoms and medication. When comparing patients with controls, we found in each patient group SN volume loss, impaired DMN structural connectivity, and aberrant DMN and SN functional connectivity. When comparing patient groups, SN gray matter volume loss and DMN structural connectivity reduction did not differ between groups, but in schizophrenic patients, functional hyperconnectivity between DMN and SN was less in comparison to depressed patients. Results provide evidence for distinct functional hyperconnectivity between DMN and SN in schizophrenia and major depression, while structural changes in DMN and SN were similar. Distinct hyperconnectivity suggests different pathophysiological mechanism underlying aberrant DMN-SN interactions in schizophrenia and depression.

Alterations in prefrontal connectivity in schizophrenia assessed using diffusion magnetic resonance imaging

BACKGROUND

Spatial and biological characteristics of structural frontal disconnectivity in schizophrenia remain incompletely understood. Simultaneous streamline count (SC) and fractional anisotropy (FA) analyses may yield relevant complementary information to this end.

METHODS

Using 3T diffusion magnetic resonance imaging both SC and FA were calculated for the tracts linking lateral and medial subregions of prefrontal cortex (PFC) to cingulate, hippocampus, caudate and thalamus in 27 schizophrenia patients (14 first-episodes) and 27 controls. Relationships of these parameters with cognition, symptoms, treatment doses and illness duration were assessed where significant between-groups differences were detected.

RESULTS

Patients showed lower SC and FA in the tracts linking lateral and medial PFC to thalamus (likely corresponding to anterior thalamic peduncle) and lower FA in those linking PFC to caudate (likely through internal capsule), right caudal anterior cingulate and left hippocampus (likely corresponding to hippocampal-prefrontal pathway). Moreover, patients showed greater SC values for the tracts linking medial PFC and left caudal anterior cingulate. SC and FA values for the tracts linking PFC and caudal anterior cingulate were positively related to motor speed, executive function, problem solving and completed categories in WCST. FA for the tract linking right lateral PFC and caudate was directly related to positive symptoms and FA for the tract linking left medial PFC and left thalamus was inversely related to negative symptoms. Treatment doses were not associated with SC or FA values in any tract. Illness duration was negatively associated with SC and FA in the tracts linking PFC and subcortical areas.

CONCLUSIONS

Widespread alterations in frontal structural connectivity of PFC can be found in schizophrenia, and are related to cognition, symptoms and illness duration.

White matter integrity and symptom dimensions of schizophrenia: A diffusion tensor imaging study

Impaired fiber bundle connectivity between brain regions is a key neuropathological finding in schizophrenia. Symptom dimensions in schizophrenia can be clustered into factor models. Single syndromes have been related to grey and white matter brain structure alterations. We associated all core syndromes of schizophrenia in a single patient group with changes in white matter integrity. Diffusion weighted images (3T MRI) and SAPS/SANS scores were measured in 26 male patients and 26 healthy controls. First, group differences in fractional anisotropy (FA) were calculated with TBSS. Second, core symptom dimensions of schizophrenia were correlated with FA within these altered tracts. We found differences between groups in nine white matter tracts. Hallucinations were positively correlated with FA in the left uncinate fasciculus and left corticospinal tract. Ego-disturbances (passivity phenomena) showed a positive correlation with FA in the right anterior thalamic radiation. Positive formal thought disorders (FTD) corresponded negatively with FA in the right cingulum bundle. Negative symptoms were positively associated with the right anterior thalamic radiation and negatively with the right ventral cingulum bundle. For the first time, we analyzed the whole range of psychopathological factors in one schizophrenia patient group. We could validate our novel results for positive FTD and passivity phenomena by replicating findings for hallucinations and negative symptoms. Only those brain circuits which are most vulnerable at a given time during neurodevelopment are affected by a particular pathological impact (genetic, environmental). This scenario could explain the predominance of particular psychopathological syndromes related to specific white matter anomalies.

Reduced White Matter Integrity in Antisocial Personality Disorder: A Diffusion Tensor Imaging Study

Emerging neuroimaging research suggests that antisocial personality disorder (ASPD) may be linked to abnormal brain anatomy, but little is known about possible impairments of white matter microstructure in ASPD, as well as their relationship with impulsivity or risky behaviors. In this study, we systematically investigated white matter abnormalities of ASPD using diffusion tensor imaging (DTI) measures: fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD). Then, we further investigated their correlations with the scores of impulsivity or risky behaviors. ASPD patients showed decreased FA in multiple major white matter fiber bundles, which connect the fronto-parietal control network and the fronto-temporal network. We also found AD/RD deficits in some additional white matter tracts that were not detected by FA. More interestingly, several regions were found correlated with impulsivity or risky behaviors in AD and RD values, although not in FA values, including the splenium of corpus callosum, left posterior corona radiate/posterior thalamic radiate, right superior longitudinal fasciculus, and left inferior longitudinal fasciculus. These regions can be the potential biomarkers, which would be of great interest in further understanding the pathomechanism of ASPD.

Abnormal hippocampal-thalamic white matter tract development and positive symptom course in individuals at ultra-high risk for psychosis

Background/Objectives:

Abnormal development of the hippocampus has been reported in adolescents at ultra-high risk (UHR) for psychosis and thalamic abnormalities have been found. However, the white matter connections between the hippocampus and the thalamus have not been studied. The connections between these regions are of key importance to our understanding of the pathophysiology of psychosis.

Methods:

Twenty-six UHR and 21 healthy age-matched controls were tested at a baseline assessment and 12 months later. Symptoms were assessed at both the time points and all the participants underwent diffusion tensor imaging scans. We used tractography to trace the white matter connections in each individual between the thalamus and hippocampus and then extracted fractional anisotropy (FA) to assess white matter structural integrity.

Results:

There was a significant group by time interaction indicating that FA decreased in UHR, and increased in controls over 12 months. Across both groups, baseline FA of the thalamic–hippocampal tract was predictive of positive symptoms at 12-month follow-up. Critically, this pattern remained significant in UHR individual group alone. At baseline, those with higher FA, indicative of abnormal white matter development, show higher positive symptoms 1 year later.

Conclusions:

Here, we provide evidence to indicate that there are differences in white matter development in hippocampal–thalamic connections, both of which are important nodes in networks associated with schizophrenia. Furthermore, abnormal developmental patterns in UHR individuals are associated with positive symptom course.

Corpus callosum size and diffusion tensor anisotropy in adolescents and adults with schizophrenia

The corpus callosum has been implicated as a region of dysfunctional connectivity in schizophrenia, but the association between age and callosal pathology is unclear. Magnetic resonance imaging (MRI) and diffusion-tensor imaging (DTI) were performed on adults (n=34) and adolescents (n=17) with schizophrenia and adult (n=33) and adolescent (n=15) age- and sex-matched healthy controls. The corpus callosum was manually traced on each participant׳s MRI, and the DTI scan was co-registered to the MRI. The corpus callosum was divided into five anteroposterior segments. Area and anisotropy were calculated for each segment. Both patient groups demonstrated reduced callosal anisotropy; however, the adolescents exhibited reductions mostly in anterior regions while the reductions were more prominent in posterior regions of the adults. The adolescent patients showed greater decreases in absolute area as compared with the adult patients, particularly in the anterior segments. However, the adults showed greater reductions when area was considered relative to whole brain white matter volume. Our results suggest that the initial stages of the illness are characterized by deficiencies in frontal connections, and the chronic phase is characterized by deficits in the posterior corpus callosum; or, alternatively, adolescent-onset schizophrenia may represent a different or more severe form of the illness.

Neurocognitive similarities between severe chronic schizophrenia and behavioural variant frontotemporal dementia

This study focuses on a group of patients with chronic schizophrenia who have a more severe form of the disorder, as indicated by socio-functional decline, treatment resistance, and recurrent hospitalisation. Previous research has suggested that the pattern and severity of cognitive deficits in people with severe chronic schizophrenia is similar to that observed in behavioural variant frontotemporal dementia (bvFTD). In the current study, we compared neurocognitive performance in 16 cognitive domains in 7 inpatients with severe chronic schizophrenia, 13 community-dwelling outpatients with chronic schizophrenia, 12 patients with bvFTD, and 18 healthy controls. Our findings revealed more similar cognitive profiles between the schizophrenia inpatient and bvFTD groups compared to the schizophrenia outpatient group, who outperformed the former groups. The current results provide preliminary evidence for a distinct schizophrenia subgroup, distinguishable from other chronic schizophrenia patients by poorer clinical and functional status, who have levels of cognitive impairment comparable to those seen in bvFTD patients.

48 echo T₂ myelin imaging of white matter in first-episode schizophrenia: evidence for aberrant myelination

Myelin water imaging provides a novel strategy to assess myelin integrity and corresponding clinical relationships in psychosis, of particular relevance in frontal white matter regions. In the current study, T2 myelin water imaging was used to assess the myelin water fraction (MWF) signal from frontal areas in a sample of 58 individuals experiencing first-episode psychosis (FEP) and 44 healthy volunteers. No differences in frontal MWF were observed between FEP subjects and healthy volunteers; however, differences in normal patterns of associations between frontal MWF and age, education and IQ were seen. Significant positive relationships between frontal MWF and age, North American Adult Reading Test (NAART) IQ, and years of completed education were observed in healthy volunteers. In contrast, only the relationship between frontal MWF and NAART IQ was significant after Bonferroni correction in the FEP group. Additionally, significant positive relationships between age and MWF in the anterior and posterior internal capsules, the genu, and the splenium were observed in healthy volunteers. In FEP subjects, only the relationship between age and MWF in the splenium was statistically significant. Frontal MWF was not associated with local white matter volume. Altered patterns of association between age, years of education, and MWF in FEP suggest that subtle disturbances in myelination may be present early in the course of psychosis.

Translational studies of goal-directed action as a framework for classifying deficits across psychiatric disorders

The ability to learn contingencies between actions and outcomes in a dynamic environment is critical for flexible, adaptive behavior. Goal-directed actions adapt to changes in action-outcome contingencies as well as to changes in the reward-value of the outcome. When networks involved in reward processing and contingency learning are maladaptive, this fundamental ability can be lost, with detrimental consequences for decision-making. Impaired decision-making is a core feature in a number of psychiatric disorders, ranging from depression to schizophrenia. The argument can be developed, therefore, that seemingly disparate symptoms across psychiatric disorders can be explained by dysfunction within common decision-making circuitry. From this perspective, gaining a better understanding of the neural processes involved in goal-directed action, will allow a comparison of deficits observed across traditional diagnostic boundaries within a unified theoretical framework. This review describes the key processes and neural circuits involved in goal-directed decision-making using evidence from animal studies and human neuroimaging. Select studies are discussed to outline what we currently know about causal judgments regarding actions and their consequences, action-related reward evaluation, and, most importantly, how these processes are integrated in goal-directed learning and performance. Finally, we look at how adaptive decision-making is impaired across a range of psychiatric disorders and how deepening our understanding of this circuitry may offer insights into phenotypes and more targeted interventions.

Associations of white matter integrity and cortical thickness in patients with schizophrenia and healthy controls

Typical brain development includes coordinated changes in both white matter (WM) integrity and cortical thickness (CT). These processes have been shown to be disrupted in schizophrenia, which is characterized by abnormalities in WM microstructure and by reduced CT. The aim of this study was to identify patterns of association between WM markers and cortex-wide CT in healthy controls (HCs) and patients with schizophrenia (SCZ). Using diffusion tensor imaging and structural magnetic resonance imaging data of the Mind Clinical Imaging Consortium study (130 HC and 111 SCZ), we tested for associations between (a) fractional anisotropy in selected manually labeled WM pathways (corpus callosum, anterior thalamic radiation, and superior longitudinal fasciculus) and CT, and (b) the number of lesion-like WM regions ("potholes") and CT. In HC, but not SCZ, we found highly significant negative associations between WM integrity and CT in several pathways, including frontal, temporal, and occipital brain regions. Conversely, in SCZ the number of WM potholes correlated with reduced CT in the left lateral temporal gyrus, left fusiform, and left lateral occipital brain area. Taken together, we found differential patterns of association between WM integrity and CT in HC and SCZ. Although the pattern in HC can be explained from a developmental perspective, the reduced gray matter CT in SCZ patients might be the result of focal but spatially heterogeneous disruptions of WM integrity.

Distribution of tract deficits in schizophrenia

BACKGROUND

Gray and white matter brain changes have been found in schizophrenia but the anatomical organizing process underlying these changes remains unknown. We aimed to identify gray and white matter volumetric changes in a group of patients with schizophrenia and to quantify the distribution of white matter tract changes using a novel approach which applied three complementary analyses to diffusion imaging data.

METHODS

21 patients with schizophrenia and 21 matched control subjects underwent brain magnetic resonance imaging. Gray and white matter volume differences were investigated using Voxel-based Morphometry (VBM). White matter diffusion changes were located using Tract Based Spatial Statistics (TBSS) and quantified within a standard atlas. Tracts where significant regional differences were located were examined using fiber tractography.

RESULTS

No significant differences in gray or white matter volumetry were found between the two groups. Using TBSS the schizophrenia group showed significantly lower fractional anisotropy (FA) compared to the controls in regions (false discovery rate <0.05) including the genu, body and splenium of the corpus callosum and the left anterior limb of the internal capsule (ALIC). Using fiber tractography, FA was significantly lower in schizophrenia in the corpus callosum genu (p = 0.003).

CONCLUSIONS

In schizophrenia, white matter diffusion deficits are prominent in medial frontal regions. These changes are consistent with the results of previous studies which have detected white matter changes in these areas. The pathology of schizophrenia may preferentially affect the prefrontal-thalamic white matter circuits traversing these regions.

White matter pathway organization of the reward system is related to positive and negative symptoms in schizophrenia

The reward system in schizophrenia has been linked to the emergence of delusions on the one hand and to negative symptoms such as affective flattening on the other hand. Previous Diffusion Tensor Imaging (DTI) studies reported white matter microstructure alterations of regions related to the reward system. The present study aimed at extending these findings by specifically investigating connection pathways of the reward system in schizophrenia. Therefore, 24 patients with schizophrenia and 22 healthy controls matched for age and gender underwent DTI-scans. Using a probabilistic fiber tracking approach we bilaterally extracted pathways connecting the ventral tegmental area (VTA) with the nucleus accumbens (NAcc), the medial and lateral orbitofrontal cortices (mOFC, lOFC), the dorsolateral prefrontal cortex (dlPFC) and the amygdala; as well as pathways connecting NAcc with mOFC, lOFC, dlPFC and amygdala resulting in a total of 18 connections. Probability indices forming part of a bundle of interest (PIBI) were compared between groups using independent t-tests. In 6 connection pathways PIBI-values were increased in schizophrenia. In 3 of these pathways the spatial extension of connection pathways was decreased. In schizophrenia patients, there was a negative correlation of PIBI-values and PANSS negative scores in the left VTA-amygdala and in the left NAcc-mOFC connection. A sum score of delusions and hallucinations correlated positively with PIBI-values of the left amygdala-NAcc connection. Structural organization of specific segments of white matter pathways of the reward system in schizophrenia may contribute to the emergence of delusions and negative symptoms in schizophrenia.

Increased stability of microtubules in cultured olfactory neuroepithelial cells from individuals with schizophrenia

Microtubules (MTs) are essential components of the cytoskeleton that play critical roles in neurodevelopment and adaptive central nervous system functioning. MTs are essential to growth cone advance and ultrastructural events integral to synaptic plasticity; these functions figure significantly into current pathophysiologic conceptualizations of schizophrenia. To date, no study has directly investigated MT dynamics in humans with schizophrenia. We therefore compared the stability of MTs in olfactory neuroepithelial (OE) cells between schizophrenia cases and matched nonpsychiatric comparison subjects. For this purpose, we applied nocodazole (Nz) to cultured OE cells obtained from tissue biopsies from seven living schizophrenia patients and seven matched comparison subjects; all schizophrenia cases were on antipsychotic medications. Nz allows MT depolymerization to be followed but prevents repolymerization, so that in living cells treated for varying time intervals, the MTs that are stable for a given treatment interval remain. Our readout of MT stability was the time at which fewer than 10 MTs per cell could be distinguished by anti-β-tubulin immunofluorescence. The percentage of cells with ≥10 intact MTs at specified intervals following Nz treatment was estimated by systematic uniform random sampling with Visiopharm software. These analyses showed that the mean percentages of OE cells with intact MTs were significantly greater for schizophrenia cases than for the matched comparison subjects at 10, 15, and 30min following Nz treatment indicating increased MT stability in OE cells from schizophrenia patients (p=0.0007 at 10min; p=0.0008 at 15min; p=0.036 at 30min). In conclusion, we have demonstrated increased MT stability in nearly all cultures of OE cells from individuals with schizophrenia, who received several antipsychotic treatments, versus comparison subjects matched for age and sex. While we cannot rule out a possible confounding effect of antipsychotic medications, these findings may reflect analogous neurobiological events in at least a subset of immature neurons or other cell types during gestation, or newly generated cells destined for the olfactory bulb or hippocampus, suggesting a mechanism that underlies findings of postmortem and neuroimaging investigations of schizophrenia. Future studies aimed at replicating these findings, including samples of medication-naïve subjects with schizophrenia, and reconciling the results with other studies, will be necessary. Although the observed abnormalities may suggest one of a number of putative pathophysiologic anomalies in schizophrenia, this work may ultimately have implications for an improved understanding of pathogenic processes related to this disorder.

Cuprizone-induced demyelination in mice: age-related vulnerability and exploratory behavior deficit

Schizophrenia is a mental disease that mainly affects young individuals (15 to 35 years old) but its etiology remains largely undefined. Recently, accumulating evidence indicated that demyelination and/or dysfunction of oligodendrocytes is an important feature of its pathogenesis. We hypothesized that the vulnerability of young individuals to demyelination may contribute to the onset of schizophrenia. In the present study, three different age cohorts of mice, i.e. juvenile (3 weeks), young-adult (6 weeks) and middle-aged (8 months), were subjected to a 6-week diet containing 0.2% cuprizone (CPZ) to create an animal model of acute demyelination. Then, age-related vulnerability to CPZ-induced demyelination, behavioral outcomes, and myelination-related molecular biological changes were assessed. We demonstrated: (1) CPZ treatment led to more severe demyelination in juvenile and young-adult mice than in middle-aged mice in the corpus callosum, a region closely associated with the pathophysiology of schizophrenia; (2) the higher levels of demyelination in juvenile and young-adult mice were correlated with a greater reduction of myelin basic protein, more loss of CC-1-positive mature oligodendrocytes, and higher levels of astrocyte activation; and (3) CPZ treatment resulted in a more prominent exploratory behavior deficit in juvenile and young-adult mice than in middle-aged mice. Together, our data demonstrate an age-related vulnerability to demyelination with a concurrent behavioral deficit, providing supporting evidence for better understanding the susceptibility of the young to the onset of schizophrenia.

Altered cortico-basal ganglia motor pathways reflect reduced volitional motor activity in schizophrenia

Little is known about the neurobiology of hypokinesia in schizophrenia. Therefore, the aim of this study was to investigate alterations of white matter motor pathways in schizophrenia and to relate our findings to objectively measured motor activity. We examined 21 schizophrenia patients and 21 healthy controls using diffusion tensor imaging and actigraphy. We applied a probabilistic fibre tracking approach to investigate pathways connecting the dorsolateral prefrontal cortex (dlPFC), the rostral anterior cingulate cortex (rACC), the pre-supplementary motor area (pre-SMA), the supplementary motor area proper (SMA-proper), the primary motor cortex (M1), the caudate nucleus, the striatum, the pallidum and the thalamus. Schizophrenia patients had lower activity levels than controls. In schizophrenia we found higher probability indices forming part of a bundle of interest (PIBI) in pathways connecting rACC, pre-SMA and SMA-proper as well as in pathways connecting M1 and pre-SMA with caudate nucleus, putamen, pallidum and thalamus and a reduced spatial extension of motor pathways in schizophrenia. There was a positive correlation between PIBI and activity level in the right pre-SMA-pallidum and the left M1-thalamus connection in healthy controls, and in the left pre-SMA-SMA-proper pathway in schizophrenia. Our results point to reduced volitional motor activity and altered motor pathway organisation in schizophrenia. The identified associations between the amount of movement and structural connectivity of motor pathways suggest dysfunction of cortico-basal ganglia pathways in the pathophysiology of hypokinesia in schizophrenia. Schizophrenia patients may use cortical pathways involving the supplementary motor area to compensate for basal ganglia dysfunction.

Diffuse abnormality of low to moderately organized white matter in schizophrenia

Increasing evidence suggests that abnormal white matter is central to the pathophysiology and, potentially, the pathogenesis of schizophrenia (SCZ). The spatial distribution of observed abnormalities and the type of white matter involved remain to be elucidated. Seventeen chronically ill individuals with SCZ and 17 age- and gender-matched controls were studied using a 3T magnetic resonance imaging diffusion tensor imaging protocol designed to examine the abnormalities of white matter by region and by level of architectural infrastructure as assessed by fractional anisotropy (FA) in native space. After assessing whole-brain FA, FA was divided into quartiles, capturing all brain regions with FA values from 0 to 0.25, 0.25 to 0.5, 0.5 to 0.75, and 0.75 to 1.0. Mean whole-brain FA was 4.6% smaller in the SCZ group than in healthy controls. This difference was largely accounted for by FA values from the second quartile (between 0.25 and 0.5). Second quartile FA was decreased in all 130 brain regions of the template in the SCZ group, with the difference reaching statistical significance in 41 regions. Correspondingly, the amount of brain tissue with an FA of ∼0.4 was significantly reduced in the SCZ group, while the amount of brain tissue falling in the lowest quartile of FA was increased. These findings strongly imply a diffuse loss of white matter integrity in SCZ. Our finding that the loss of integrity disproportionately involves white matter of low to moderate organization suggests an approach to the specificity of white matter abnormalities in SCZ based on microstructure rather than spatial distribution.

Anterior limb of the internal capsule in schizophrenia: a diffusion tensor tractography study

Thalamo-cortical feedback loops play a key role in the processing and coordination of processing and integration of perceptual inputs and outputs, and disruption in this connection has long been hypothesized to contribute significantly to neuropsychological disturbances in schizophrenia. To test this hypothesis, we applied diffusion tensor tractography to 18 patients suffering schizophrenia and 20 control subjects. Fractional anisotropy (FA) was evaluated in the bilateral anterior and posterior limbs of the internal capsule, and correlated with clinical and neurocognitive measures. Patients diagnosed with schizophrenia showed significantly reduced FA bilaterally in the anterior but not the posterior limb of the internal capsule, compared with healthy control subjects. Lower FA correlated with lower scores on tests of declarative episodic memory in the patient group only. These findings suggest that disruptions, bilaterally, in thalamo-cortical connections in schizophrenia may contribute to disease-related impairment in the coordination of mnemonic processes of encoding and retrieval that are vital for efficient learning of new information.

Alterations in the cerebral white matter of genetic high risk offspring of patients with schizophrenia spectrum disorder

Alterations in white matter (WM) may be seen in young relatives at risk and may underlie vulnerability to schizophrenia. We were interested in exploring which of the WM regions were altered in adolescent offspring at familial risk for schizophrenia. We examined structural alterations in the offspring of subjects with schizophrenia or schizoaffective disorder (HR; n=65; 36 males) and healthy controls (HC; n=80: 37 males) matched for age and education. MRI images were collected using a GE 1.5 T scanner at the University of Pittsburgh Medical Center. Image processing was done using FreeSurfer (MGH) by an experienced rater blind to clinical data. We used multivariate analysis of covariance, with intracranial volume (p>0.05) and age as covariates. High Risk offspring had significant reductions in total WM, hemispheric WM and WM within left parietal and left cingulate cortices. Male offspring had more pronounced right hemisphere WM reductions than females.

Sexually dimorphic white matter geometry abnormalities in adolescent onset schizophrenia

The normal human brain is characterized by a pattern of gross anatomical asymmetry. This pattern, known as the "torque", is associated with a sexual dimorphism: The male brain tends to be more asymmetric than that of the female. This fact, along with well-known sex differences in brain development (faster in females) and onset of psychosis (earlier with worse outcome in males), has led to the theory that schizophrenia is a disorder in which sex-dependent abnormalities in the development of brain torque, the correlate of the capacity for language, cause alterations in interhemispheric connectivity, which are causally related to psychosis (Crow TJ, Paez P, Chance SE. 2007. Callosal misconnectivity and the sex difference in psychosis. Int Rev Psychiatry. 19(4):449-457.). To provide evidence toward this theory, we analyze the geometry of interhemispheric white matter connections in adolescent-onset schizophrenia, with a particular focus on sex, using a recently introduced framework for white matter geometry computation in diffusion tensor imaging data (Savadjiev P, Kindlmann GL, Bouix S, Shenton ME, Westin CF. 2010. Local white geometry from diffusion tensor gradients. Neuroimage. 49(4):3175-3186.). Our results reveal a pattern of sex-dependent white matter geometry abnormalities that conform to the predictions of Crow's torque theory and correlate with the severity of patients' symptoms. To the best of our knowledge, this is the first study to associate geometrical differences in white matter connectivity with torque in schizophrenia.

Reduced volume in the anterior internal capsule but its maintained correlation with the frontal gray matter in subjects at ultra-high risk for psychosis

The anterior limb of the internal capsule (ALIC), which interconnects with the frontal cortex and thalamus, is volumetrically altered in schizophrenia patients. However, it is unclear whether an abnormal ALIC volume is apparent prior to the onset of schizophrenia and whether this aberrant ALIC volume is related to the frontal gray matter in individuals at ultra-high risk (UHR) for psychosis. We used magnetic resonance imaging of 43 UHR subjects, 36 schizophrenia patients, and 42 healthy controls to investigate manually traced ALIC volumes. Additionally, we evaluated the correlation between the ALIC volume and the frontal gray matter. Significantly reduced ALIC volumes were observed in the UHR and schizophrenia groups compared to the healthy controls. However, the volume of the frontal gray matter was decreased only in the schizophrenia group. A positive correlation between the volumes in the ALIC and frontal gray matter found in healthy controls was maintained only in UHR subjects. In addition, a negative correlation between the total scores on the Positive and Negative Syndrome Scale and the ALIC volumes was observed only in schizophrenia patients. An aberrant ALIC volume but its maintained correlation with the interconnecting frontal lobe was present prior to the onset of full psychosis, indicating the prodromal phase of psychosis.

Anterior limb of the internal capsule in schizotypal personality disorder: fiber-tract counting, volume, and anisotropy

Mounting evidence suggests that white matter abnormalities and altered subcortical-cortical connectivity may be central to the pathology of schizophrenia (SZ). The anterior limb of the internal capsule (ALIC) is an important thalamo-frontal white-matter tract shown to have volume reductions in SZ and to a lesser degree in schizotypal personality disorder (SPD). While fractional anisotropy (FA) and connectivity abnormalities in the ALIC have been reported in SZ, they have not been examined in SPD. In the current study, magnetic resonance (MRI) and diffusion tensor imaging (DTI) were obtained in age- and sex-matched individuals with SPD (n=33) and healthy controls (HCs; n=38). The ALIC was traced bilaterally on five equally spaced dorsal-to-ventral axial slices from each participant's MRI scan and co-registered to DTI for the calculation of FA. Tractography was used to examine tracts between the ALIC and two key Brodmann areas (BAs; BA10, BA45) within the dorsolateral prefrontal cortex (DLPFC). Compared with HCs, the SPD participants exhibited (a) smaller relative volume at the mid-ventral ALIC slice level but not the other levels; (b) normal FA within the ALIC; (c) fewer relative number of tracts between the most-dorsal ALIC levels and BA10 but not BA45 and (d) fewer dorsal ALIC-DLPFC tracts were associated with greater symptom severity in SPD. In contrast to prior SZ studies that report lower FA, individuals with SPD show sparing. Our findings are consistent with a pattern of milder thalamo-frontal dysconnectivity in SPD than schizophrenia.

Fractional anisotropy and radial diffusivity: diffusion measures of white matter abnormalities in the anterior limb of the internal capsule in schizophrenia

INTRODUCTION

Higher cognitive functioning is mediated by frontal-subcortical cognitive and limbic feedback sub-loops. The thalamo-cortical projection through the anterior limb of the internal capsule (ALIC) serves as the final step in these feedback sub-loops. We evaluated abnormalities in the ALIC fiber tract in schizophrenia using both structural MRI and diffusion tensor imaging (DTI).

METHODS

20 chronic schizophrenia patients and 22 male, normal controls group matched for handedness, age, and parental SES, underwent structural and DTI brain imaging on a 1.5 Tesla GE system. We manually measured ALIC volume normalized for intracranial contents (ICC) using structural brain images and then registered these high resolution structural brain scan derived ALIC label maps to DTI space allowing for the measurement in the ALIC of diffusion indices including, fractional anisotropy (FA) mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD).

RESULTS

We found in the ALIC of chronic schizophrenia subjects, compared with normal controls, bilaterally lower FA and bilaterally higher RD, but no differences in AD, MD, or relative volume. Cognitive correlations in schizophrenia patients showed, in particular, that higher left ALIC FA correlated positively with better verbal and nonverbal declarative/episodic memory performance.

DISCUSSION

Using a novel approach to assess both diffusion and volume measures in the ALIC in schizophrenia, we found abnormalities in measures of diffusion, but not volume, supporting their importance as sensitive indices of abnormalities in white matter fiber bundles in schizophrenia. Our findings also support the role of ALIC white matter tract FA abnormalities in declarative/episodic memory in schizophrenia.

Structural studies of the hypothalamus and its nuclei in mood disorders

A large body of evidence indicates that the hypothalamus is involved in pathogenetic mechanisms of mood disorders. It has been suggested that functional abnormalities of the hypothalamus are associated with structural hypothalamic changes. Structural neuroimaging allows in vivo investigation of the hypothalamus that may shed light on the underlying pathogenetic mechanisms of unipolar and bipolar disorder. Clearly, the detection of subtle structural cerebral changes depends on the limitations of the neuroimaging technique used. Making a comprehensive database search, we reviewed the literature on hypothalamic macrostructure in affective disorders, addressing the specific question of what structural magnetic resonance imaging might be expected to show. Studies with convincing methodology, although rare, suggest a global volume decrease in the hypothalamus in affective disorders, a decrease which is not shown by the two specific nuclei investigated, the paraventricular and supraoptic nuclei. We discuss the implications of these findings and provide directions for future research.

The effects of psychosis risk variants on brain connectivity: a review

In light of observed changes in connectivity in schizophrenia and the highly heritable nature of the disease, neural connectivity may serve as an important intermediate phenotype for schizophrenia. However, how individual variants confer altered connectivity and which measure of brain connectivity is more proximal to the underlying genetic architecture (i.e., functional or structural) has not been well delineated. In this review we consider these issues and the relative sensitivity of imaging methodologies to schizophrenia-related changes in connectivity. We searched PubMed for studies considering schizophrenia risk genes AND functional or structural connectivity. Where data was available, summary statistics were used to determine an estimate of effect size (i.e., Cohen's d). A random-effects meta-analysis was used to consider (1) the largest effect and (2) all significant effects between functional and structural studies. Schizophrenia risk variants involved in neurotransmission, neurodevelopment and myelin function were found to be associated with altered neural connectivity. On average, schizophrenia risk genes had a large effect on functional (mean d = 0.76) and structural connectivity (mean d = 1.04). The examination of the largest effect size indicated that the outcomes of functional and structural studies were comparable (Q = 2.17, p > 0.05). Conversely, consideration of effect size estimates for all significant effects suggest that reported effect sizes in structural connectivity studies were more variable than in functional connectivity studies, and that there was a significant lack of homogeneity across the modalities (Q = 6.928, p = 0.008). Given the more variable profile of effect sizes associated with structural connectivity, these data may suggest that structural imaging methods are more sensitive to a wider range of effects, as opposed to functional studies which may only be able to determine large effects. These conclusions are limited by methodological considerations, and require further investigation involving larger samples, multiple genes, and novel analysis techniques for confirmation.

Altered integrity of perisylvian language pathways in schizophrenia: relationship to auditory hallucinations

BACKGROUND

Functional neuroimaging supports the hypothesis that auditory verbal hallucinations (AVH) in schizophrenia result from altered functional connectivity between perisylvian language regions, although the extent to which AVH are also associated with an altered tract anatomy is less clear.

METHODS

Twenty-eight patients with schizophrenia subdivided into 17 subjects with a history of AVH and 11 without a history of hallucinations and 59 age- and IQ-matched healthy controls were recruited. The number of streamlines, fractional anisotropy (FA), and mean diffusivity were measured along the length of the arcuate fasciculus and its medial and lateral components.

RESULTS

Patients with schizophrenia had bilateral reduction of FA relative to controls in the arcuate fasciculi (p < .001). Virtual dissection of the subcomponents of the arcuate fasciculi revealed that these reductions were specific to connections between posterior temporal and anterior regions in the inferior frontal and parietal lobe. Also, compared with controls, the reduction in FA of these tracts was highest, and bilateral, in patients with AVH, but in patients without AVH, this reduction was reported only on the left.

CONCLUSIONS

These findings point toward a supraregional network model of AVH in schizophrenia. They support the hypothesis that there may be selective vulnerability of specific anatomical connections to posterior temporal regions in schizophrenia and that extensive bilateral damage is associated with a greater vulnerability to AVH. If confirmed by further studies, these findings may advance our understanding of the anatomical factors that are protective against AVH and predictive of a treatment response.

A polymorphism of the ABCA1 gene confers susceptibility to schizophrenia and related brain changes

OBJECTIVE

The ATP-binding cassette transporter A1 (ABCA1) mediates cellular cholesterol efflux through the transfer of cholesterol from the inner to the outer layer of the cell membrane and regulates extracellular cholesterol levels in the central nervous system. Several lines of evidence have indicated lipid and myelin abnormalities in schizophrenia.

METHOD

Initially, we examined the possible association of the polymorphisms of the ABCA1 gene (ABCA1) with susceptibility to schizophrenia in 506 patients with schizophrenia (DSM-IV) and 941 controls. The observed association was then subject to a replication analysis in an independent sample of 511 patients and 539 controls. We further examined the possible effect of the risk allele on gray matter volume assessed with magnetic resonance imaging (MRI) in 86 patients with schizophrenia (49 males) and 139 healthy controls (47 males).

RESULTS

In the initial association study, the 1587 K allele (rs2230808) was significantly more common in male patients with schizophrenia than in male controls. Although such a significant difference was not observed in the second sample alone, the increased frequency of the 1587 K allele in male patients remained to be significant in the combined male sample of 556 patients and 594 controls. Male schizophrenia patients carrying the 1587 K allele had a smaller amount of gray matter volume than those who did not carry the allele.

CONCLUSION

Our data suggest a male-specific association of the 1587 K allele of ABCA1 with susceptibility to schizophrenia and smaller gray matter volume in schizophrenia.

Automated probabilistic reconstruction of white-matter pathways in health and disease using an atlas of the underlying anatomy

We have developed a method for automated probabilistic reconstruction of a set of major white-matter pathways from diffusion-weighted MR images. Our method is called TRACULA (TRActs Constrained by UnderLying Anatomy) and utilizes prior information on the anatomy of the pathways from a set of training subjects. By incorporating this prior knowledge in the reconstruction procedure, our method obviates the need for manual interaction with the tract solutions at a later stage and thus facilitates the application of tractography to large studies. In this paper we illustrate the application of the method on data from a schizophrenia study and investigate whether the inclusion of both patients and healthy subjects in the training set affects our ability to reconstruct the pathways reliably. We show that, since our method does not constrain the exact spatial location or shape of the pathways but only their trajectory relative to the surrounding anatomical structures, a set a of healthy training subjects can be used to reconstruct the pathways accurately in patients as well as in controls.

The impact of a Dysbindin schizophrenia susceptibility variant on fiber tract integrity in healthy individuals: a TBSS-based diffusion tensor imaging study

Schizophrenia is a severe neuropsychiatric disorder with high heritability, though its exact etiopathogenesis is yet unknown. An increasing number of studies point to the importance of white matter anomalies in the pathophysiology of schizophrenia. While several studies have identified the impact of schizophrenia susceptibility gene variants on gray matter anatomy in both schizophrenia patients and healthy risk variant carriers, studies dealing with the impact of these gene variants on white matter integrity are still scarce. We here present a study on the effects of a Dysbindin schizophrenia susceptibility gene variant on fiber tract integrity in healthy young subjects. 101 subjects genotyped for Dysbindin-gene variant rs1018381, though without personal or first degree relative history of psychiatric disorders underwent diffusion tensor imaging (DTI), 83 of them were included in the final analysis. We used Tract-Based Spatial Statistics (TBSS) analysis to delineate the major fiber tracts. Carriers of the minor allele T of the rs1018381 in the Dysbindin gene showed two clusters of reduced fractional anisotropy (FA) values in the perihippocampal region of the right temporal lobe compared to homozygote carriers of the major allele C. Clusters of increased FA values in T-allele carriers were found in the left prefrontal white matter, the right fornix, the right midbrain area, the left callosal body, the left cerebellum and in proximity of the right superior medial gyrus. Dysbindin has been implicated in neurite outgrowth and morphology. Impairments in anatomic connectivity as found associated with the minor Dysbindin allele in our study may result in increased risk for schizophrenia due to altered fiber tracts.

Neuroanatomical changes in a mouse model of early life neglect

Using a novel mouse model of early life neglect and abuse (ENA) based on maternal separation with early weaning, George et al. (BMC Neurosci 11:123, 2010) demonstrated behavioral abnormalities in adult mice, and Bordner et al. (Front Psychiatry 2(18):1-18, 2011) described concomitant changes in mRNA and protein expression. Using the same model, here we report neuroanatomical changes that include smaller brain size and abnormal inter-hemispheric asymmetry, decreases in cortical thickness, abnormalities in subcortical structures, and white matter disorganization and atrophy most severely affecting the left hemisphere. Because of the similarities between the neuroanatomical changes observed in our mouse model and those described in human survivors of ENA, this novel animal model is potentially useful for studies of human ENA too costly or cumbersome to be carried out in primates. Moreover, our current knowledge of the mouse genome makes this model particularly suited for targeted anatomical, molecular, and pharmacological experimentation not yet possible in other species.

Understanding aberrant white matter development in schizophrenia: an avenue for therapy?

Although historically gray matter changes have been the focus of neuropathological and neuroradiological studies in schizophrenia, in recent years an increasing body of research has implicated white matter structures and its constituent components (axons, their myelin sheaths and supporting oligodendrocytes). This article summarizes this body of literature, examining neuropathological, neurogenetic and neuroradiological evidence for white matter pathology in schizophrenia. We then look at the possible role that antipsychotic medication may play in these studies, examining both its role as a potential confounder in studies examining neuronal density and brain volume, but also the possible role that these medications may play in promoting myelination through their effects on oligodendrocytes. Finally, the role of potential novel therapies is discussed.

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.

Voxel-based morphometry (VBM) studies in schizophrenia-can white matter changes be reliably detected with VBM?

Voxel-based morphometry (VBM) is a hypothesis-free, whole-brain, voxel-by-voxel analytic method that attempts to compare imaging data between populations. Schizophrenia studies have utilized this method to localize differences in diffusion tensor imaging (DTI) derived fractional anisotropy (FA), a measure of white matter integrity, between patients and healthy controls. The number of publications has grown, although it is unclear how reliable and reproducible this method is, given the subtle white matter abnormalities expected in schizophrenia. Here we analyze and combine results from 23 studies published to date that use VBM to study schizophrenia in order to evaluate the reproducibility of this method in DTI analysis. Coordinates of each region reported in DTI VBM studies published thus far in schizophrenia were plotted onto a Montreal Neurological Institute atlas, and their anatomical locations were recorded. Results indicated that the reductions of FA in patients with schizophrenia were scattered across the brain. Moreover, even the most consistently reported regions were reported independently in less than 35% of the articles studied. Other instances of reduced FA were replicated at an even lower rate. Our findings demonstrate striking inconsistency, with none of the regions reported in much more than a third of the published articles. This poor replication rate suggests that the application of VBM to DTI data may not be the optimal way for finding the subtle microstructural abnormalities suggested in 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.

White matter microstructural abnormalities in the frontal lobe of adults with antisocial personality disorder

Antisocial personality disorder (ASPD) and psychopathy involve significant interpersonal and behavioural impairments. However, little is known about their underlying neurobiology and in particular, abnormalities in white matter (WM) microstructure. A preliminary diffusion tensor magnetic resonance imaging (DT-MRI) study of adult psychopaths employing tractography revealed abnormalities in the right uncinate fasciculus (UF) (Craig et al., 2009), indicating fronto-limbic disconnectivity. However, it is not clear whether WM abnormalities are restricted to this tract or are or more widespread, including other tracts which are involved in connectivity with the frontal lobe. We performed whole brain voxel-based analyses on WM fractional anisotropy (FA) and mean diffusivity (MD) maps acquired with DT-MRI to compare 15 adults with ASPD and healthy age, handedness and IQ-matched controls. Also, within ASPD subjects we related differences in FA and MD to measures of psychopathy. Significant WM FA reduction and MD increases were found respectively in ASPD subjects relative to controls. FA was bilaterally reduced in the genu of corpus callosum while in the right frontal lobe FA reduction was found in the UF, inferior fronto-occipital fasciculus (IFOF), anterior corona radiata and anterior limb and genu of the internal capsule. These differences negatively correlated with measures of psychopathy. Also in the right frontal lobe, increased MD was found in the IFOF and UF, and the corpus callosum and anterior corona radiata. There was a significant positive correlation between MD and psychopathy scores.

CONCLUSIONS

The present study confirms a previous report of reduced FA in the UF. Additionally, we report for the first time, FA deficits in tracts involved in interhemispheric as well as frontal lobe connectivity in conjunction with MD increases in the frontal lobe. Hence, we provide evidence of significant WM microstructural abnormalities in frontal brain regions in ASPD and psychopathy.

Stochastic tractography study of Inferior Frontal Gyrus anatomical connectivity in schizophrenia

BACKGROUND

Abnormalities within language-related anatomical structures have been associated with clinical symptoms and with language and memory deficits in schizophrenia. Recent studies suggest disruptions in functional connectivity within the Inferior Frontal Gyrus (IFG) network in schizophrenia. However, due to technical challenges, anatomical connectivity abnormalities within this network and their involvement in clinical and cognitive deficits have not been studied.

MATERIAL AND METHODS

Diffusion and anatomical scans were obtained from 23 chronic schizophrenia patients and 23 matched controls. The IFG was automatically segmented, and its white matter connections extracted and measured with newly-developed stochastic tractography tools. Correlations between anatomical structures and measures of semantic processing were also performed.

RESULTS

White Matter connections between the IFG and posterior brain regions followed two distinct pathways: dorsal and ventral. Both demonstrated left lateralization, but ventral pathway abnormalities were only found in schizophrenia. IFG volumes also showed left lateralization and abnormalities in schizophrenia. Further, despite similar laterality and abnormality patterns, IFG volumes and white matter connectivity were not correlated with each other in either group. Interestingly, measures of semantic processing correlated with white matter connectivity in schizophrenia and with gray matter volumes in controls. Finally, hallucinations were best predicted by both gray matter and white matter measures together.

CONCLUSIONS

Our results suggest abnormalities within the ventral IFG network in schizophrenia, with white matter abnormalities better predicting semantic deficits. The lack of a statistical relationship between coexisting gray and white matter deficits might suggest their different origin and the necessity for a multimodal approach in future schizophrenia studies.

Cingulate and temporal lobe fractional anisotropy in schizotypal personality disorder

BACKGROUND

Consistent with the clinical picture of milder symptomatology in schizotypal personality disorder (SPD) than schizophrenia, morphological studies indicate SPD abnormalities in temporal lobe regions but to a much lesser extent in prefrontal regions implicated in schizophrenia. Lower fractional anisotropy (FA), a measure of white-matter integrity within prefrontal, temporal, and cingulate regions has been reported in schizophrenia but has been little studied in SPD.

AIMS

The study aim was to examine temporal and prefrontal white matter FA in 30 neuroleptic-naïve SPD patients and 35 matched healthy controls (HCs). We hypothesized that compared with HCs, SPD patients would exhibit lower FA in temporal lobe and anterior cingulum regions but relative sparing in prefrontal regions.

METHOD

We acquired diffusion tensor imaging (DTI) in all participants and examined FA in the white matter underlying Brodmann areas (BAs) in dorsolateral prefrontal (BAs 44, 45, and 46), temporal lobe (BAs 22, 21, and 20), and cingulum (BAs 25, 24, 31, 23, and 29) regions with a series of analyses using multivariate analysis of variance.

RESULTS

Compared with HCs, the SPD group had significantly lower FA in the left temporal lobe but not prefrontal regions. In the cingulum, FA was lower in the SPD group in the posterior regions (BAs 31 and 23), higher in the anterior (BA 25) regions and lower overall in the right but not the left cingulum. Among the SPD group, lower FA in the cingulum was associated with more severe negative symptoms (e.g., odd speech).

CONCLUSIONS

Similar to schizophrenia, our results indicate cingulum-temporal lobe FA abnormalities in SPD and suggest that cingulum abnormalities are associated with negative symptoms.

A diffusion tensor imaging study of the anterior limb of the internal capsule in schizophrenia

Frontal-subcortical cognitive and limbic feedback loops modulate higher cognitive functioning. The final step in these feedback loops is the thalamo-cortical projection through the anterior limb of the internal capsule (AL-IC). Using diffusion tensor imaging (DTI), we evaluated abnormalities in the AL-IC fiber tract in schizophrenia. Participants comprised 16 chronic schizophrenia patients and 19 male, normal controls, who were group matched for handedness, age, and parental socioeconomic status, and underwent DTI on a 1.5 Tesla GE system. We measured the diffusion indices, fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD), and manually segmented, based on FA maps, AL-IC volume, normalized for intracranial contents (ICC). The results showed a significant reduction in the ICC-corrected volume of the AL-IC in schizophrenia, but did not show diffusion measure group differences in the AL-IC in FA, MD, RD or AD. In addition, in the schizophrenia patients, AL-IC FA correlated positively with performance on measures of spatial and verbal declarative/episodic memory, and right AL-IC ICC-corrected volume correlated positively with more perseverative responses on the Wisconsin Card Sort Test (WCST). We found a reduction in AL-IC ICC-corrected volume in schizophrenia, without FA, MD, RD or AD group differences, implicating the presence of a structural abnormality in schizophrenia in this subcortical white matter region which contains important cognitive, and limbic feedback pathways that modulate prefrontal cortical function. Despite not demonstrating a group difference in FA, we found that AL-IC FA was a good predictor of spatial and verbal declarative/episodic memory performance in schizophrenia.

High-definition fiber tracking guidance for intraparenchymal endoscopic port surgery

The authors have applied high-definition fiber tracking (HDFT) to the resection of an intraparenchymal dermoid cyst by using a minimally invasive endoscopic port. The lesion was located within the mesial frontal lobe, septal area, hypothalamus, and suprasellar recess. Using high-dimensional (256 directions) diffusion imaging, more than 250,000 fiber tracts were imaged before and after surgery. Trajectory planning using HDFT in a computer model was used to facilitate cannulation of the cyst with the endoscopic port. Analysis of the proposed initial surgical route was overlaid onto the fiber tracts and was predicted to produce substantial disruption to prefrontal projection fibers (anterior limb of the internal capsule) and the cingulum. Adjustment of the cannulation entry point 1 cm medially was predicted to cross the corpus callosum instead of the anterior limb of the internal capsule or the cingulum. Following cyst resection performed using endoscopic port surgery, postoperative imaging demonstrated accurate cannulation of the lesion, with improved quantitative signal from both the anterior limb of the internal capsule and the cingulum. The observed fiber preservation from the cingulum and the anterior limb of the internal capsule, with minor injury to the corpus callosum, was in close agreement with preoperative trajectory modeling. Comparison of pre- and postoperative HDFT data facilitated quantification of the benefits and costs of the surgical trajectory. Future studies will help to determine whether HDFT combined with endoscopic port surgery facilitates anatomical and functional preservation in such challenging cases.

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.

White matter microstructure in 22q11 deletion syndrome: a pilot diffusion tensor imaging and voxel-based morphometry study of children and adolescents

Young people with 22q11 Deletion Syndrome (22q11DS) are at substantial risk for developing psychosis and have significant differences in white matter (WM) volume. However, there are few in vivo studies of both WM microstructural integrity (as measured using Diffusion Tensor (DT)-MRI) and WM volume in the same individual. We used DT-MRI and structural MRI (sMRI) with voxel based morphometry (VBM) to compare, respectively, the fractional anisotropy (FA) and WM volume of 11 children and adolescents with 22q11DS and 12 controls. Also, within 22q11DS we related differences in WM to severity of schizotypy, and polymorphism of the catechol-O-methyltransferase (COMT) gene. People with 22q11DS had significantly lower FA in inter-hemispheric and brainstem and frontal, parietal and temporal lobe regions after covarying for IQ. Significant WM volumetric increases were found in the internal capsule, anterior brainstem and frontal and occipital lobes. There was a significant negative correlation between increased schizotypy scores and reduced WM FA in the right posterior limb of internal capsule and the right body and left splenium of corpus callosum. Finally, the Val allele of COMT was associated with a significant reduction in both FA and volume of WM in the frontal lobes, cingulum and corpus callosum. Young people with 22q11DS have significant differences in both WM microstructure and volume. Also, there is preliminary evidence that within 22q11DS, some regional differences in FA are associated with allelic variation in COMT and may perhaps also be associated with schizotypy.

Functional and anatomical connectivity abnormalities in left inferior frontal gyrus in schizophrenia

Functional studies in schizophrenia demonstrate prominent abnormalities within the left inferior frontal gyrus (IFG) and also suggest the functional connectivity abnormalities in language network including left IFG and superior temporal gyrus during semantic processing. White matter connections between regions involved in the semantic network have also been indicated in schizophrenia. However, an association between functional and anatomical connectivity disruptions within the semantic network in schizophrenia has not been established. Functional (using levels of processing paradigm) as well as diffusion tensor imaging data from 10 controls and 10 chronic schizophrenics were acquired and analyzed. First, semantic encoding specific activation was estimated, showing decreased activation within the left IFG in schizophrenia. Second, functional time series were extracted from this area, and left IFG specific functional connectivity maps were produced for each subject. In an independent analysis, tract-based spatial statistics (TBSS) was used to compare fractional anisotropy (FA) values between groups, and to correlate these values with functional connectivity maps. Schizophrenia patients showed weaker functional connectivity within the language network that includes left IFG and left superior temporal sulcus/middle temporal gyrus. FA was reduced in several white matter regions including left inferior frontal and left internal capsule. Finally, left inferior frontal white matter FA was positively correlated with connectivity measures of the semantic network in schizophrenics, but not in controls. Our results indicate an association between anatomical and functional connectivity abnormalities within the semantic network in schizophrenia, suggesting further that the functional abnormalities observed in this disorder might be directly related to white matter disruptions.

Thalamo-frontal white matter alterations in chronic schizophrenia: a quantitative diffusion tractography study

Diffusion tensor imaging (DTI) and fiber tractography are useful tools for reconstructing white matter tracts (WMT) in the brain. Previous tractography studies have sought to segment reconstructed WMT into anatomical structures using several approaches, but quantification has been limited to extracting mean values of diffusion indices. Delineating WMT in schizophrenia is of particular interest because schizophrenia has been hypothesized to be a disorder of disrupted connectivity, especially between frontal and temporal regions of the brain. In this study, we aim to differentiate diffusion properties of thalamo-frontal pathways in schizophrenia from normal controls. We present a quantitative group comparison method, which combines the strengths of both tractography-based and voxel-based studies. Our algorithm extracts white matter pathways using whole brain tractography. Functionally relevant bundles are selected and parsed from the resulting set of tracts, using an internal capsule (IC) region of interest (ROI) as "source", and different Brodmann area (BA) ROIs as "targets". The resulting bundles are then longitudinally parameterized so that diffusion properties can be measured and compared along the WMT. Using this processing pipeline, we were able to find altered diffusion properties in male patients with chronic schizophrenia in terms of fractional anisotropy (FA) decreases and mean diffusivity (MD) increases in precise and functionally relevant locations. These findings suggest that our method can enhance the regional and functional specificity of DTI group studies, thus improving our understanding of brain function.