Mean diffusivity: a biomarker for CSF-related disease and genetic liability effects in schizophrenia

Comparison of Diffusion Tensor Imaging Metrics in Normal-Appearing White Matter to Cerebrovascular Lesions and Correlation with Cerebrovascular Disease Risk Factors and Severity

Alterations in tissue microstructure in normal-appearing white matter (NAWM), specifically measured by diffusion tensor imaging (DTI) fractional anisotropy (FA), have been associated with cognitive outcomes following stroke. The purpose of this study was to comprehensively compare conventional DTI measures of tissue microstructure in NAWM to diverse vascular brain lesions in people with cerebrovascular disease (CVD) and to examine associations between FA in NAWM and cerebrovascular risk factors. DTI metrics including fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were measured in cerebral tissues and cerebrovascular anomalies from 152 people with CVD participating in the Ontario Neurodegenerative Disease Research Initiative (ONDRI). Ten cerebral tissue types were segmented including NAWM, and vascular lesions including stroke, periventricular and deep white matter hyperintensities, periventricular and deep lacunar infarcts, and perivascular spaces (PVS) using T1-weighted, proton density-weighted, T2-weighted, and fluid attenuated inversion recovery MRI scans. Mean DTI metrics were measured in each tissue region using a previously developed DTI processing pipeline and compared between tissues using multivariate analysis of covariance. Associations between FA in NAWM and several CVD risk factors were also examined. DTI metrics in vascular lesions differed significantly from healthy tissue. Specifically, all tissue types had significantly different MD values, while FA was also found to be different in most tissue types. FA in NAWM was inversely related to hypertension and modified Rankin scale (mRS). This study demonstrated the differences between conventional DTI metrics, FA, MD, AD, and RD, in cerebral vascular lesions and healthy tissue types. Therefore, incorporating DTI to characterize the integrity of the tissue microstructure could help to define the extent and severity of various brain vascular anomalies. The association between FA within NAWM and clinical evaluation of hypertension and disability provides further evidence that white matter microstructural integrity is impacted by cerebrovascular function.

Clinical MRI morphological analysis of functional seizures compared to seizure-naïve and psychiatric controls

PURPOSE

Functional seizures (FS), also known as psychogenic nonepileptic seizures (PNES), are physical manifestations of acute or chronic psychological distress. Functional and structural neuroimaging have identified objective signs of this disorder. We evaluated whether magnetic resonance imaging (MRI) morphometry differed between patients with FS and clinically relevant comparison populations.

METHODS

Quality-screened clinical-grade MRIs were acquired from 666 patients from 2006 to 2020. Morphometric features were quantified with FreeSurfer v6. Mixed-effects linear regression compared the volume, thickness, and surface area within 201 regions-of-interest for 90 patients with FS, compared to seizure-naïve patients with depression (n = 243), anxiety (n = 68), and obsessive-compulsive disorder (OCD, n = 41), respectively, and to other seizure-naïve controls with similar quality MRIs, accounting for the influence of multiple confounds including depression and anxiety based on chart review. These comparison populations were obtained through review of clinical records plus research studies obtained on similar scanners.

RESULTS

After Bonferroni-Holm correction, patients with FS compared with seizure-naïve controls exhibited thinner bilateral superior temporal cortex (left 0.053 mm, p = 0.014; right 0.071 mm, p = 0.00006), thicker left lateral occipital cortex (0.052 mm, p = 0.0035), and greater left cerebellar white-matter volume (1085 mm³, p = 0.0065). These findings were not accounted for by lower MRI quality in patients with FS.

CONCLUSIONS

These results reinforce prior indications of structural neuroimaging correlates of FS and, in particular, distinguish brain morphology in FS from that in depression, anxiety, and OCD. Future work may entail comparisons with other psychiatric disorders including bipolar and schizophrenia, as well as exploration of brain structural heterogeneity within FS.

Microstructural white matter alterations associated with migraine headaches: a systematic review of diffusion tensor imaging studies

The pathophysiology of migraine as a headache disorder is still undetermined. Diffusion tensor imaging (DTI) has significantly improved our knowledge about brain microstructure in this disease. Here, we aimed to systematically review DTI studies in migraine and survey the sources of heterogeneity by investigating diffusion parameter changes associated with clinical characteristics and migraine subtypes. Microstructural changes, as revealed by widespread alteration of diffusion metrics in white matter (WM) tracts, subcortical and cortical regions, were reported by several migraine DTI studies. Specifically, we reported changes in the corpus callosum, thalamic radiations, corona radiata, and brain stem. These alterations showed high variability across migraine cycle phases. Additionally, migraine associated with depressive/anxiety symptoms revealed significant changes in the corpus callosum, internal capsule, and superior longitudinal fasciculus. No significant WM microstructural differences were observed between migraine patients with and without aura. Overall, differences between chronic and episodic migraine showed inconsistency across studies. Migraine is associated with microstructural changes in widespread regions including thalamic radiations, corpus callosum, and brain stem. These alterations can highlight neuronal damage and neuronal plasticity mechanisms either following pain stimulations occurring in migraine cycle or as a compensatory response to pain in chronic migraine. Longitudinal studies applying advanced modalities may shed new light on the underlying microstructural changes in migraine subtypes.

Grey and white matter microstructure is associated with polygenic risk for schizophrenia

Recent discovery of approximately 270 common genetic variants associated with schizophrenia has enabled polygenic risk scores (PRS) to be measured in the population. We hypothesized that normal variation in PRS would be associated with magnetic resonance imaging (MRI) phenotypes of brain morphometry and tissue composition. We used the largest extant genome-wide association dataset (N = 69,369 cases and N = 236,642 healthy controls) to measure PRS for schizophrenia in a large sample of adults from the UK Biobank (N_max = 29,878) who had multiple micro- and macrostructural MRI metrics measured at each of 180 cortical areas, seven subcortical structures, and 15 major white matter tracts. Linear mixed-effect models were used to investigate associations between PRS and brain structure at global and regional scales, controlled for multiple comparisons. Polygenic risk was significantly associated with reduced neurite density index (NDI) at global brain scale, at 149 cortical regions, five subcortical structures, and 14 white matter tracts. Other microstructural parameters, e.g., fractional anisotropy, that were correlated with NDI were also significantly associated with PRS. Genetic effects on multiple MRI phenotypes were co-located in temporal, cingulate, and prefrontal cortical areas, insula, and hippocampus. Post-hoc bidirectional Mendelian randomization analyses provided preliminary evidence in support of a causal relationship between (reduced) thalamic NDI and (increased) risk of schizophrenia. Risk-related reduction in NDI is plausibly indicative of reduced density of myelinated axons and dendritic arborization in large-scale cortico-subcortical networks. Cortical, subcortical, and white matter microstructure may be linked to the genetic mechanisms of schizophrenia.

The clinical relevance of gray matter atrophy and microstructural brain changes across the psychosis continuum

Patients with psychotic spectrum disorders (PSD) exhibit similar patterns of atrophy and microstructural changes that may be associated with common symptomatology (e.g., symptom burden and/or cognitive impairment). Gray matter concentration values (proxy for atrophy), fractional anisotropy (FA), mean diffusivity (MD), intracellular neurite density (Vic) and isotropic diffusion volume (Viso) measures were therefore compared in 150 PSD (schizophrenia, schizoaffective disorder, and bipolar disorder Type I) and 63 healthy controls (HC). Additional analyses evaluated whether regions showing atrophy and/or microstructure abnormalities were better explained by DSM diagnoses, symptom burden or cognitive dysfunction. PSD exhibited increased atrophy within bilateral medial temporal lobes and subcortical structures. Gray matter along the left lateral sulcus showed evidence of increased atrophy and MD. Increased MD was also observed in homotopic fronto-temporal regions, suggesting it may serve as a precursor to atrophic changes. Global cognitive dysfunction, rather than DSM diagnoses or psychotic symptom burden, was the best predictor of increased gray matter MD. Regions of decreased FA (i.e., left frontal gray and white matter) and Vic (i.e., frontal and temporal regions and along central sulcus) were also observed for PSD, but were neither spatially concurrent with atrophic regions nor associated with clinical symptoms. Evidence of expanding microstructural spaces in gray matter demonstrated the greatest spatial overlap with current and potentially future regions of atrophy, and was associated with cognitive deficits. These results suggest that this particular structural abnormality could potentially underlie global cognitive impairment that spans traditional diagnostic categories.

Broad white matter impairment in multiple system atrophy

Multiple system atrophy (MSA) is a rare neurodegenerative disorder characterized by the widespread aberrant accumulation of α-synuclein (α-syn). MSA differs from other synucleinopathies such as Parkinson's disease (PD) in that α-syn accumulates primarily in oligodendrocytes, the only source of white matter myelination in the brain. Previous MSA imaging studies have uncovered focal differences in white matter. Here, we sought to build on this work by taking a global perspective on whole brain white matter. In order to do this, in vivo structural imaging and diffusion magnetic resonance imaging were acquired on 26 MSA patients, 26 healthy controls, and 23 PD patients. A refined whole brain approach encompassing the major fiber tracts and the superficial white matter located at the boundary of the cortical mantle was applied. The primary observation was that MSA but not PD patients had whole brain deep and superficial white matter diffusivity abnormalities (p < .001). In addition, in MSA patients, these abnormalities were associated with motor (Unified MSA Rating Scale, Part II) and cognitive functions (Mini-Mental State Examination). The pervasive whole brain abnormalities we observe suggest that there is widespread white matter damage in MSA patients which mirrors the widespread aggregation of α-syn in oligodendrocytes. Importantly, whole brain white matter abnormalities were associated with clinical symptoms, suggesting that white matter impairment may be more central to MSA than previously thought.

A multimodal imaging study of brain structural correlates of schizotypy dimensions using the MSS

Schizotypy is a multidimensional construct of subclinical schizophrenia-like behavioural traits and cognition. The recently developed multidimensional schizotypy scale (MSS) provides an improved psychometric assessment of the three main dimensions (positive, negative, and disorganised). We tested the hypothesis that the three dimensions are related to brain structural variation in the precuneus and fronto-thalamo-striatal system in a new non-clinical healthy cohort to support a dimensional model of the psychosis spectrum. We analysed data from 104 subjects with Multidimensional Schizotypy Scale (MSS) phenotyping and 3 Tesla magnetic resonance images using voxel-based morphometry (VBM) applying CAT12 software, and diffusion-tensor imaging (DTI) with TBSS in FSL to test for correlations with MSS scores. MSS subscales and total score were negatively associated with GMV in brain areas including the medial prefrontal cortex, anterior cingulate cortex, and lateral prefrontal and orbital cortex. MSS schizotypy was associated with white matter integrity in anterior thalamic radiation, uncinate fasciculus, and superior longitudinal fasciculus. Our findings provide first direct evidence for an association of schizotypy (as a psychosis risk phenotype) and the fronto-thalamo-striatal system, in both grey and white matter with regionally diverging effects across single dimensions. This provides new evidence arguing for the fronto-striatal system (rather than precuneus) in schizotypy.

White matter structure in schizophrenia and autism: Abnormal diffusion across the brain in schizophrenia

BACKGROUND

Schizophrenia and autism share many behavioral and neurological similarities, including altered white matter tract structure. However, because schizophrenia and autism are rarely compared directly, it is difficult to establish whether white matter abnormalities are disorder-specific or are common across these disorders that share some symptomatology.

METHODS

In the current study, we compared white matter water diffusion using tensor imaging in 25 adults with autism, 15 adults with schizophrenia, all with IQ scores above 88, and 19 neurotypical adults.

RESULTS

Although the three groups evinced no statistically significant differences in measures of fractional anisotropy (FA), the schizophrenia group showed significantly greater mean diffusivity (MD; Cohen's d > 0.77), due to greater radial diffusivity (RD; Cohen's d > 0.92), compared to both the autism and control groups. This effect was evident across the brain rather than specific to a particular tract.

CONCLUSIONS

The greater MD and RD in schizophrenia appears to be diagnosis-specific. The altered diffusion may reflect subtle abnormalities in myelination, which could be a potential mechanism underlying the widespread behavioral deficits associated with schizophrenia.

The details of structural disconnectivity in psychotic disorder: A family-based study of non-FA diffusion weighted imaging measures

BACKGROUND

Diffusion tensor imaging (DTI) studies in psychotic disorder have shown reduced FA, often interpreted as disturbed white matter integrity. The observed 'dysintegrity' may be of multifactorial origin, as changes in FA are thought to reflect a combination of changes in myelination, fiber organization and number of axons. Examining the structural substrate of the diffusion tensor in individuals with (risk for) psychotic disorder may provide better understanding of the underlying structural changes.

METHODS

DTI scans were acquired from 85 patients with psychotic disorder, 93 siblings of patients with psychotic disorder and 80 controls. Cross-sectional group comparisons were performed using Tract-Based Spatial Statistics (TBSS) on six DTI measures: axial diffusivity (AXD), radial diffusivity (RD), mean diffusivity (MD), and the case linear (CL), case planar (CP) and case spherical (CS) tensor shape measures.

RESULTS

AXD did not differ between the groups. RD and CS values were significantly increased in patients compared to controls and siblings, with no significant differences between the latter two groups. MD was higher in patients compared to controls (but not siblings), with no difference between siblings and controls. CL was smaller in patients than in siblings and controls, and CP was smaller in both patients and siblings as compared to controls.

CONCLUSION

The differences between individuals with psychotic disorder and healthy controls, derived from detailed diffusion data analyses, suggest less fiber orientation and increased free water movement in the patients. There was some evidence for association with familial risk expressed by decreased fiber orientation.

Studying Autism Spectrum Disorder with Structural and Diffusion Magnetic Resonance Imaging: A Survey

Magnetic resonance imaging (MRI) modalities have emerged as powerful means that facilitate non-invasive clinical diagnostics of various diseases and abnormalities since their inception in the 1980s. Multiple MRI modalities, such as different types of the sMRI and DTI, have been employed to investigate facets of ASD in order to better understand this complex syndrome. This paper reviews recent applications of structural magnetic resonance imaging (sMRI) and diffusion tensor imaging (DTI), to study autism spectrum disorder (ASD). Main reported findings are sometimes contradictory due to different age ranges, hardware protocols, population types, numbers of participants, and image analysis parameters. The primary anatomical structures, such as amygdalae, cerebrum, and cerebellum, associated with clinical-pathological correlates of ASD are highlighted through successive life stages, from infancy to adulthood. This survey demonstrates the absence of consistent pathology in the brains of autistic children and lack of research investigations in patients under 2 years of age in the literature. The known publications also emphasize advances in data acquisition and analysis, as well as significance of multimodal approaches that combine resting-state, task-evoked, and sMRI measures. Initial results obtained with the sMRI and DTI show good promise toward the early and non-invasive ASD diagnostics.

Hippocampal dysfunction during declarative memory encoding in schizophrenia and effects of genetic liability

Declarative memory (DM) impairments are reported in schizophrenia and in unaffected biological relatives of patients. However, the neural correlates of successful and unsuccessful encoding, mediated by the medial temporal lobe (MTL) memory system, and the influence of disease-related genetic liability remain under explored. This study employed an event-related functional MRI paradigm to compare activations for successfully and unsuccessfully encoded associative face-name stimuli between 26 schizophrenia patients (mean age: 33, 19m/7f), 30 controls (mean age: 29, 24m/6f), and 14 unaffected relatives of patients (mean age: 40, 5m/9f). Compared to controls or unaffected relatives, patients showed hyper-activations in ventral visual stream and temporo-parietal cortical association areas when contrasting successfully encoded events to fixation. Follow-up hippocampal regions-of-interest analysis revealed schizophrenia-related hyper-activations in the right anterior hippocampus during successful encoding; contrasting successful versus unsuccessful events produced schizophrenia-related hypo-activations in the left anterior hippocampus. Similar hippocampal hypo-activations were observed in unaffected relatives during successful versus unsuccessful encoding. Post hoc analyses of hippocampal volume showed reductions in patients, but not in unaffected relatives compared to controls. Findings suggest that DM encoding deficits are attributable to both disease-specific and genetic liability factors that impact different components of the MTL memory system. Hyper-activations in temporo-occipital and parietal regions observed only in patients suggest the influence of disease-related factors. Regional hyper- and hypo-activations attributable to successful encoding occurring in both patients and unaffected relatives suggest the influence of schizophrenia-related genetic liability factors.

Diffusion tensor imaging in first degree relatives of schizophrenia and bipolar disorder patients

OBJECTIVES

White matter (WM) abnormalities are one of the most widely and consistently reported findings in schizophrenia (SZ) and bipolar disorder (BD). If these abnormalities are inherited determinants of illness, suitable to be classified as an endophenotype, relatives of patients must also have them at higher rate compared to the general population. In this review, we evaluate published diffusion tensor imaging (DTI) studies comparing first degree relatives of SZ and BD patients and healthy control subjects.

METHODS

We searched PubMed, Embase and PsychInfo for DTI studies which included an unaffected relative and a healthy comparison group.

RESULTS

22 studies fulfilled the inclusion criteria. WM abnormalities were found in many diverse regions in relatives of SZ patients. Although the findings were not completely consistent across studies, the most implicated areas were the frontal and temporal WM regions and the corpus callosum. Studies in relatives of BD patients were fewer in number with less consistent findings reported across studies.

CONCLUSIONS

Our review supports the concept of WM abnormalities as an endophenotype in SZ, with somewhat weaker evidence in BD, but larger and higher quality studies are needed to make a definitive comment.

Cortical thinning, functional connectivity, and mood-related impulsivity in schizophrenia: relationship to aggressive attitudes and behavior

OBJECTIVE

Aggression in schizophrenia is a major societal issue, leading to physical harm, stigmatization, patient distress, and higher health care costs. Impulsivity is associated with aggression in schizophrenia, but it is multidetermined. The subconstruct of urgency is likely to play an important role in this aggression, with positive urgency referring to rash action in the context of positive emotion, and negative urgency referring to rash action in the context of negative emotion.

METHOD

The authors examined urgency and its neural correlates in 33 patients with schizophrenia or schizoaffective disorder and 31 healthy comparison subjects. Urgency was measured using the Urgency, Premeditation, Perseverance, and Sensation-Seeking scale. Aggressive attitudes were measured using the Buss-Perry Aggression Questionnaire.

RESULTS

Positive urgency, negative urgency, and aggressive attitudes were significantly and selectively elevated in schizophrenia patients (Cohen's d values, 1.21-1.50). Positive and negative urgency significantly correlated with the Aggression Questionnaire total score (r>0.48 in all cases) and each uniquely accounted for a significant portion of the variance in aggression over and above the effect of group. Urgency scores correlated with reduced cortical thickness in ventral prefrontal regions including the right frontal pole, the medial and lateral orbitofrontal gyrus and inferior frontal gyri, and the rostral anterior cingulate cortex. In patients, reduced resting-state functional connectivity in some of these regions was associated with higher urgency.

CONCLUSIONS

These findings highlight the key role of urgency in aggressive attitudes in people with schizophrenia and suggest neural substrates of these behaviors. The results also suggest behavioral and neural targets for interventions to remediate urgency and aggression.

Genome-wide schizophrenia variant at MIR137 does not impact white matter microstructure in healthy participants

A single nucleotide polymorphism (SNP rs1625579) within the micro-RNA 137 (MIR137) gene recently achieved strong genome-wide association with schizophrenia (SZ). However, the mechanisms by which SZ risk may be mediated by this variant are unknown. As miRNAs have the potential to influence oligodendrocyte development, we investigated whether this SNP was associated with variability in white matter (WM) microstructure. Diffusion tensor imaging (DTI) was conducted on 123 healthy participants genotyped for rs1625579. The analysis consisted of whole-brain tract-based spatial statistics and atlas-based tractography analysis of six major WM tracts known to be affected in SZ - the inferior longitudinal fasciculus, the uncinate fasciculus, the inferior fronto-occipital fasciculus, the anterior thalamic radiation, the cingulum bundle and the corpus callosum. No significant differences in either whole-brain fractional anisotropy or mean diffusivity between MIR137 genotype groups were observed (p>0.05). Similarly, atlas-based tractography of particular tracts implicated in SZ failed to reveal any significant differences between MIR137 genotype groups on measures of WM connectivity (p>0.05). In the absence of WM effects comparable to those reported for other SZ associated genes, these data suggest that MIR137 alone may not confer variability in these WM measures and therefore may not act in isolation for any effects that the variant may have on WM microstructure in SZ samples.

Structural brain alterations associated with schizophrenia preceded by conduct disorder: a common and distinct subtype of schizophrenia?

Conduct disorder (CD) prior to age 15 is a precursor of schizophrenia in a minority of cases and is associated with violent behavior through adulthood, after taking account of substance misuse. The present study used structural magnetic imaging to examine gray matter (GM) volumes among 27 men with schizophrenia preceded by CD (SZ+CD), 23 men with schizophrenia but without CD (SZ-CD), 27 men with CD only (CD), and 25 healthy (H) men. The groups with schizophrenia were similar in terms of age of onset and duration of illness, levels of psychotic symptoms, and medication. The 2 groups with CD were similar as to number of CD symptoms, lifelong aggressive behavior, and number of criminal convictions. Men with SZ+CD, relative to those with SZ-CD, displayed (1) increased GM volumes in the hypothalamus, the left putamen, the right cuneus/precuneus, and the right inferior parietal cortex after controlling for age, alcohol, and drug misuse and (2) decreased GM volumes in the inferior frontal region. Men with SZ+CD (relative to the SZ-CD group) and CD (relative to the H group) displayed increased GM volumes of the hypothalamus and the inferior and superior parietal lobes, which were not associated with substance misuse. Aggressive behavior, both prior to age 15 and lifetime tendency, was positively correlated with the GM volume of the hypothalamus. Thus, among males, SZ+CD represents a distinct subtype of schizophrenia. Although differences in behavior emerge in childhood and remain stable through adulthood, further research is needed to determine whether the differences in GM volumes result from abnormal neural development distinct from that of other males developing schizophrenia.

Overlapping and distinct gray and white matter abnormalities in schizophrenia and bipolar I disorder

OBJECTIVES

Schizophrenia and bipolar disorder may share common neurobiological mechanisms, but few studies have directly compared gray and white matter structure in these disorders. We used diffusion-weighted magnetic resonance imaging and a region of interest based analysis to identify overlapping and distinct gray and white matter abnormalities in 35 patients with schizophrenia and 20 patients with bipolar I disorder in comparison to 56 healthy volunteers.

METHODS

We examined fractional anisotropy within the white matter and mean diffusivity within the gray matter in 42 regions of interest defined on a probabilistic atlas following non-linear registration of the images to atlas space.

RESULTS

Patients with schizophrenia had significantly lower fractional anisotropy in temporal (superior temporal and parahippocampal) and occipital (superior and middle occipital) white matter compared to patients with bipolar disorder and healthy volunteers. By contrast, both patient groups demonstrated significantly higher mean diffusivity in frontal (inferior frontal and lateral orbitofrontal) and temporal (superior temporal and parahippocampal) gray matter compared to healthy volunteers, but did not differ from each other.

CONCLUSIONS

Our study implicates overlapping gray matter frontal and temporal lobe structural alterations in the neurobiology of schizophrenia and bipolar I disorder, but suggests that temporal and occipital lobe white matter deficits may be an additional risk factor for schizophrenia. Our findings may have relevance for future diagnostic classification systems and the identification of susceptibility genes for these disorders.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Disease and genetic contributions toward local tissue volume disturbances in schizophrenia: a tensor-based morphometry study

Structural brain deficits, especially frontotemporal volume reduction and ventricular enlargement, have been repeatedly reported in patients with schizophrenia. However, it remains unclear whether brain structural deformations may be attributable to disease-related or genetic factors. In this study, the structural magnetic resonance imaging data of 48 adult-onset schizophrenia patients, 65 first-degree nonpsychotic relatives of schizophrenia patients, 27 community comparison (CC) probands, and 73 CC relatives were examined using tensor-based morphometry (TBM) to isolate global and localized differences in tissue volume across the entire brain between groups. We found brain tissue contractions most prominently in frontal and temporal regions and expansions in the putamen/pallidum, and lateral and third ventricles in schizophrenia patients when compared with unrelated CC probands. Results were similar, though less prominent when patients were compared with their nonpsychotic relatives. Structural deformations observed in unaffected patient relatives compared to age-similar CC relatives were suggestive of schizophrenia-related genetic liability and were pronounced in the putamen/pallidum and medial temporal regions. Schizophrenia and genetic liability effects for the putamen/pallidum were confirmed by regions-of-interest analysis. In conclusion, TBM findings complement reports of frontal, temporal, and ventricular dysmorphology in schizophrenia and further indicate that putamen/pallidum enlargements, originally linked mainly with medication exposure in early studies, also reflect a genetic predisposition for schizophrenia. Thus, brain deformation profiles revealed in this study may help to clarify the role of specific genetic or environmental risk factors toward altered brain morphology in schizophrenia.

Association between white matter fiber integrity and subclinical psychotic symptoms in schizophrenia patients and unaffected relatives

In this study, we investigate whether aberrant integrity of white matter (WM) fiber tracts represents a genetically determined biological marker of schizophrenia (SZ), and its relation with clinical symptoms. We collected brain DTI data from 28 SZ patients, 18 first-degree relatives and 22 matched controls and used voxel-based analysis with tract-based spatial statistics (TBSS) in order to compare fractional anisotropy (FA) between groups. Mean voxel-based FA values from the entire skeleton of each group were compared. We did a multiple regression analysis, followed by single post-hoc contrasts between groups. FA values were extracted from the statistically significant areas. The results showed significantly smaller FA values for SZ patients in comparison with controls in cortico-spinal tracts, in commissural fibers, in thalamic projections, in association fibers and in cingulum bundles. A significant increase of FA in SZ patients in comparison with healthy controls was only found in the arcuate fasciculus. Relatives had intermediate values between patients and controls which were deemed significant in the comparison to patients and controls in association fibers, arcuate fasciculus and cingulum bundles. Lower FA values in association fibers were significantly associated with predisposition toward hallucinations (in SZ patients and relatives), with higher PANSS scores of positive symptoms and with duration of illness (SZ patients). Our results suggest that clinical and subclinical presentations of psychotic symptoms are associated with aberrant integrity of multiple WM tracts. This association may represent an endophenotype of schizophrenia, since it is present in unaffected relatives as well. Such endophenotypes may serve as quantitative traits for future genetic studies and as candidate markers for early and preclinical identification of subjects at risk.

Brain connectivity in psychiatric imaging genetics

In the past decade, imaging genetics has evolved into a highly successful neuroimaging discipline with a variety of sophisticated research tools. To date, several neural systems mechanisms have been identified that mediate genetic risk for mental disorders linked to common candidate and genome-wide-supported variants. In particular, the examination of intermediate connectivity phenotypes has recently gained increasing popularity. This paper gives an overview of the scientific methods and evidence that link indices of neural network organization to the genetic susceptibility for mental illness with a focus on the effects of candidate genes and genome-wide supported risk variants on brain structure and function.

Increased executive functioning, attention, and cortical thickness in white-collar criminals

Very little is known on white-collar crime and how it differs to other forms of offending. This study tests the hypothesis that white-collar criminals have better executive functioning, enhanced information processing, and structural brain superiorities compared with offender controls. Using a case-control design, executive functioning, orienting, and cortical thickness was assessed in 21 white-collar criminals matched with 21 controls on age, gender, ethnicity, and general level of criminal offending. White-collar criminals had significantly better executive functioning, increased electrodermal orienting, increased arousal, and increased cortical gray matter thickness in the ventromedial prefrontal cortex, inferior frontal gyrus, somatosensory cortex, and the temporal-parietal junction compared with controls. Results, while initial, constitute the first findings on neurobiological characteristics of white-collar criminals. It is hypothesized that white-collar criminals have information-processing and brain superiorities that give them an advantage in perpetrating criminal offenses in occupational settings.

Mapping corticocortical structural integrity in schizophrenia and effects of genetic liability

BACKGROUND

Structural and diffusion tensor imaging studies implicate gray and white matter (WM) abnormalities and disruptions of neural circuitry in schizophrenia. However, the structural integrity of the superficial WM, comprising short-range association (U-fibers) and intracortical axons, has not been investigated in schizophrenia.

METHODS

High-resolution structural and diffusion tensor images and sophisticated cortical pattern matching methods were used to measure and compare global and local variations in superficial WM fractional anisotropy between schizophrenia patients and their relatives and community comparison subjects and their relatives (n = 150).

RESULTS

Compared with control subjects, patients showed reduced superficial WM fractional anisotropy distributed across each hemisphere, particularly in left temporal and bilateral occipital regions (all p < .05, corrected). Furthermore, by modeling biological risk for schizophrenia in patients, patient relatives, and control subjects, fractional anisotropy was shown to vary in accordance with relatedness to a patient in both hemispheres and in the temporal and occipital lobes (p < .05, corrected). However, effects did not survive correction procedures for two-group comparisons between patient relatives and control subjects.

CONCLUSIONS

Results extend previous findings restricted to deep WM pathways to demonstrate that disturbances in corticocortical connectivity are associated with schizophrenia and might indicate a genetic predisposition for the disorder. Because the structural integrity of WM plays a crucial role in the functionality of networks linking gray matter regions, disturbances in the coherence and organization of fibers at the juncture of the neuropil might relate to features of schizophrenia at least partially attributable to disease-related genetic factors.

Interhemispheric hypoconnectivity in schizophrenia: fiber integrity and volume differences of the corpus callosum in patients and unaffected relatives

Changes in hemispheric asymmetry and inter-hemispheric connectivity have been reported in schizophrenia. However, the genetic contribution to these alterations is still unclear. In the current study, we applied an automatic segmentation method to structural MRI and diffusion tensor imaging (DTI) data and examined volume and fiber integrity of the corpus callosum (CC), the main interhemispheric fiber tract, in 16 chronic schizophrenia (SZ) patients, matched first degree relatives and controls. SZ patients and relatives had smaller CC volumes than controls, particularly in the posterior genu, isthmus and splenium. Fractional anisotropy (FA), an indicator of fiber integrity, was reduced in patients and relatives in the whole CC, the inferior genu, the superior genu and the isthmus. Correspondingly, the mean diffusivity (MD) values of the whole CC and the isthmus were higher in patients and their unaffected relatives, indicating decreased compactness and increased intercellular space. Relatives had intermediate values in the volumetric and fiber integrity measurements between patients and controls. Lower CC volume and fiber integrity in SZ patients were associated with more severe auditory hallucinations. These results support the connectivity hypothesis of SZ (Friston, 1998) and particularly highlight the altered interhemispheric connectivity, which appears to be a genetic feature of SZ risk.

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.

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.

Mean diffusivity and fractional anisotropy as indicators of disease and genetic liability to schizophrenia

The goals of this study were to first determine whether the fractional anisotropy (FA) and mean diffusivity (MD) of major white matter pathways associate with schizophrenia, and secondly to characterize the extent to which differences in these metrics might reflect a genetic predisposition to schizophrenia. Differences in FA and MD were identified using a comprehensive atlas-based tract mapping approach using diffusion tensor imaging and high-resolution structural data from 35 patients, 28 unaffected first-degree relatives of patients, 29 community controls, and 14 first-degree relatives of controls. Schizophrenia patients had significantly higher MD in the following tracts compared to controls: the right anterior thalamic radiations, the forceps minor, the bilateral inferior fronto-occipital fasciculus (IFO), the temporal component of the left superior longitudinal fasciculus (tSLF), and the bilateral uncinate. FA showed schizophrenia effects and a linear relationship to genetic liability (represented by schizophrenia patients, first-degree relatives, and controls) for the bilateral IFO, the left inferior longitudinal fasciculus (ILF), and the left tSLF. Diffusion tensor imaging studies have previously identified white matter abnormalities in all three of these tracts in schizophrenia; however, this study is the first to identify a significant genetic liability. Thus, FA of these three tracts may serve as biomarkers for studies seeking to identify how genes influence brain structure predisposing to schizophrenia. However, differences in FA and MD in frontal and temporal white matter pathways may be additionally driven by state variables that involve processes associated with the disease.

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.

Statistical analysis of fiber bundles using multi-tensor tractography: application to first-episode schizophrenia

This work proposes a new method to detect abnormalities in fiber bundles of first-episode (FE) schizophrenia patients. Existing methods have either examined a particular region of interest or used voxel-based morphometry or used tracts generated using the single tensor model for locating statistically different fiber bundles. Further, a two-sample t test, which assumes a Gaussian distribution for each population, is the most widely used statistical hypothesis testing algorithm. In this study, we use the unscented Kalman filter based two-tensor tractography algorithm for tracing neural fiber bundles of the brain that connect 105 different cortical and subcortical regions. Next, fiber bundles with significant connectivity across the entire population were determined. Several diffusion measures derived from the two-tensor model were computed and used as features in the subsequent analysis. For each fiber bundle, an affine-invariant descriptor was computed, thus obviating the need for precise registration of patients to an atlas. A kernel-based statistical hypothesis testing algorithm, which makes no assumption regarding the distribution of the underlying population, was then used to determine the abnormal diffusion properties of all fiber bundles for 20 FE patients and 20 age-matched healthy controls. Of the 1254 fiber bundles with significant connectivity, 740 fiber bundles were found to be significantly different in at least one diffusion measure after correcting for multiple comparisons. Thus, the changes affecting first-episode patients seem to be global in nature (spread throughout the brain).

Hippocampal volume reduction in first-episode and chronic schizophrenia: a review and meta-analysis

Several magnetic resonance imaging studies have reported hippocampal volume reduction in patients with schizophrenia, but other studies have reported contrasting results. In this review and meta-analysis, the authors aim to clarify whether a reduction in hippocampal volume characterizes patients with schizophrenia by considering illness phase (chronic and first episode) and hippocampus side separately. They made a detailed literature search for studies reporting physical volumetric hippocampal measures of patients with schizophrenia and healthy control (HC) participants and found 44 studies that were eligible for meta-analysis. Individual meta-analyses were also performed on 13 studies of first-episode patients and on 22 studies of chronic patients. The authors also detected any different findings when only males or both males and females were considered. Finally, additional meta-analyses and analyses of variance investigated the role of the factors "illness phase" and "side" on hippocampal volume reduction. Overall, the patient group showed significant bilateral hippocampal volume reduction compared with HC. Interestingly, first-episode and chronic patients showed same-size hippocampal volume reduction. Moreover, the left hippocampus was smaller than the right hippocampus in patients and HC. This review and meta-analysis raises the question about whether hippocampal volume reduction in schizophrenia is of neurodevelopmental origin. Future studies should specifically investigate this issue.

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.

Diffusion tensor imaging reliably differentiates patients with schizophrenia from healthy volunteers

The objective of this research was to determine whether fractional anisotropy (FA) and mean diffusivity (MD) maps derived from diffusion tensor imaging (DTI) of the brain are able to reliably differentiate patients with schizophrenia from healthy volunteers. DTI and high resolution structural magnetic resonance scans were acquired in 50 patients with schizophrenia and 50 age- and sex-matched healthy volunteers. FA and MD maps were estimated from the DTI data and spatially normalized to the Montreal Neurologic Institute standard stereotactic space. Individuals were divided randomly into two groups of 50, a training set, and a test set, each comprising 25 patients and 25 healthy volunteers. A pattern classifier was designed using Fisher's linear discriminant analysis (LDA) based on the training set of images to categorize individuals in the test set as either patients or healthy volunteers. Using the FA maps, the classifier correctly identified 94% of the cases in the test set (96% sensitivity and 92% specificity). The classifier achieved 98% accuracy (96% sensitivity and 100% specificity) when using the MD maps as inputs to distinguish schizophrenia patients from healthy volunteers in the test dataset. Utilizing FA and MD data in combination did not significantly alter the accuracy (96% sensitivity and specificity). Patterns of water self-diffusion in the brain as estimated by DTI can be used in conjunction with automated pattern recognition algorithms to reliably distinguish between patients with schizophrenia and normal control subjects.

Neuroimaging correlates of aggression in schizophrenia: an update

PURPOSE OF REVIEW

Aggression in schizophrenia is associated with poor treatment outcomes, hospital admissions, and stigmatization of patients. As such it represents an important public health issue. This article reviews recent neuroimaging studies of aggression in schizophrenia, focusing on PET/single photon emission computed tomography and MRI methods.

RECENT FINDINGS

The neuroimaging literature on aggression in schizophrenia is in a period of development. This is attributable in part to the heterogeneous nature and basis of that aggression. Radiological methods have consistently shown reduced activity in frontal and temporal regions. MRI brain volumetric studies have been less consistent, with some studies finding increased volumes of inferior frontal structures, and others finding reduced volumes in aggressive individuals with schizophrenia. Functional MRI studies have also had inconsistent results, with most finding reduced activity in inferior frontal and temporal regions, but some also finding increased activity in other regions. Some studies have made a distinction between types of aggression in schizophrenia in the context of antisocial traits, and this appears to be useful in understanding the neuroimaging literature.

SUMMARY

Frontal and temporal abnormalities appear to be a consistent feature of aggression in schizophrenia, but their precise nature likely differs because of the heterogeneous nature of that behavior.

Hippocampi, thalami, and accumbens microstructural damage in schizophrenia: a volumetry, diffusivity, and neuropsychological study

Volumetric abnormalities in the subcortical structures have been described in schizophrenia. However, it still has to be clarified if subtle microstructural damage is also present. Thus, we aimed to detect subcortical volume and mean diffusivity (MD) alterations in 45 patients with diagnosis of schizophrenia compared with 45 age-, gender-, and educational attainment-matched healthy comparison (HC) participants, by using a combined volumetry and diffusion tensor imaging (DTI) method. A secondary aim was to identify the neuropsychological correlates of subcortical abnormalities in the schizophrenic group. We found thalami and hippocampi bilaterally and left accumbens to show MD increase in the schizophrenic group. No volumetric decrease was found. Moreover, significant correlations between the MD values in subcortical structures (right thalamus and hippocampus and left accumbens) and working memory performance were found. Thus, subcortical microstructural alterations are present in schizophrenia even in absence of volumetric abnormalities. Furthermore, microstructural damage in subcortical areas is linked to working memory, suggesting the presence of a subtle microstructural subcortical dysfunction in the pathoetiological mechanism underlying high cognitive load performances in schizophrenia. Finally, our findings indicate that MD is a more sensitive marker of brain tissue deficits than signal intensity variations measured in T1-weighted imaging data, consistently with previous reports. Thus, DTI appears to be an invaluable tool to investigate subcortical pathology in schizophrenia, greatly enhancing the ability to detect subtle brain changes in this complex disorder.

The contributions of disease and genetic factors towards regional cortical thinning in schizophrenia: the UCLA family study

OBJECTIVE

Cortical thickness reductions in prefrontal and temporal cortices have been repeatedly observed in patients with schizophrenia. However, it remains unclear whether regional variations in cortical thickness may be attributable to disease-related or genetic-liability factors.

METHOD

The structural magnetic resonance imaging data of 48 adult-onset schizophrenia patients, 66 first-degree non-psychotic relatives of schizophrenia patients, 27 community comparison (CC) probands and 77 CC relatives were examined using cortical pattern matching methods to map and compare highly localized changes in cortical gray matter thickness between groups defined by biological risk for schizophrenia.

RESULTS

Schizophrenia patients showed marked cortical thinning primarily in frontal and temporal cortices when compared to unrelated CC probands. Results were similar, though less pronounced when patients were compared with their non-psychotic relatives. Cortical thickness reductions observed in unaffected relatives compared to age-similar CC relatives suggestive of schizophrenia-related genetic liability were marginal, surviving correction for the left parahippocampal gyrus and inferior occipital cortex only.

CONCLUSIONS

Observations of pronounced fronto/temporal cortical thinning in schizophrenia patients replicate prior findings. The lack of marked cortical thickness alterations in non-psychotic relatives of patients, suggests that disease processes are primary contributors toward cortical thickness reductions in the disorder. However, genetic factors may have a larger influence on abnormalities in the medial temporal lobe.

Updated meta-analyses reveal thalamus volume reduction in patients with first-episode and chronic schizophrenia

OBJECTIVES

Although several structural MRI studies report significant thalamus volume reduction in patients with schizophrenia, many other studies do not. Therefore, the present meta-analyses aimed to clarify whether a reduction in thalamic volume characterizes patients diagnosed with schizophrenia by considering first-episode and chronic phases of the illness and right and left thalamus separately.

METHODS

Using Pubmed databases, we made a detailed literature search for structural MRI studies on patients with schizophrenia that reported physical volumetric measures of the right and left thalamus. Thirteen structural MRI studies were considered eligible for meta-analysis of the entire sample of patients and of the healthy control subjects. Individual meta-analyses were also performed on 6 studies of first-episode patients only and on 7 studies of chronic patients only. These were followed by additional meta-analyses to investigate the role of the factors "illness phase" and "side" on thalamic volume reduction.

RESULTS

Overall, the patient group showed a significant bilateral thalamus volume reduction compared to healthy control subjects. This was found in both first-episode and chronic patients. Furthermore, left thalamus was smaller than right in both patients and healthy control subjects.

CONCLUSIONS

When only studies that used physical volumetric measures were considered, the present meta-analyses confirmed that thalamic volume reduction characterizes patients with schizophrenia, both at the first-episode and chronic phases of the illness.

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.