Brain morphometry using diffusion-weighted magnetic resonance imaging: application to schizophrenia

Differentiating Individuals with and without Alcohol Use Disorder Using Resting-State fMRI Functional Connectivity of Reward Network, Neuropsychological Performance, and Impulsivity Measures

Individuals with alcohol use disorder (AUD) may manifest an array of neural and behavioral abnormalities, including altered brain networks, impaired neurocognitive functioning, and heightened impulsivity. Using multidomain measures, the current study aimed to identify specific features that can differentiate individuals with AUD from healthy controls (CTL), utilizing a random forests (RF) classification model. Features included fMRI-based resting-state functional connectivity (rsFC) across the reward network, neuropsychological task performance, and behavioral impulsivity scores, collected from thirty abstinent adult males with prior history of AUD and thirty CTL individuals without a history of AUD. It was found that the RF model achieved a classification accuracy of 86.67% (AUC = 93%) and identified key features of FC and impulsivity that significantly contributed to classifying AUD from CTL individuals. Impulsivity scores were the topmost predictors, followed by twelve rsFC features involving seventeen key reward regions in the brain, such as the ventral tegmental area, nucleus accumbens, anterior insula, anterior cingulate cortex, and other cortical and subcortical structures. Individuals with AUD manifested significant differences in impulsivity and alterations in functional connectivity relative to controls. Specifically, AUD showed heightened impulsivity and hypoconnectivity in nine connections across 13 regions and hyperconnectivity in three connections involving six regions. Relative to controls, visuo-spatial short-term working memory was also found to be impaired in AUD. In conclusion, specific multidomain features of brain connectivity, impulsivity, and neuropsychological performance can be used in a machine learning framework to effectively classify AUD individuals from healthy controls.

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.

Random Forest Classification of Alcohol Use Disorder Using fMRI Functional Connectivity, Neuropsychological Functioning, and Impulsivity Measures

Individuals with alcohol use disorder (AUD) are known to manifest a variety of neurocognitive impairments that can be attributed to alterations in specific brain networks. The current study aims to identify specific features of brain connectivity, neuropsychological performance, and impulsivity traits that can classify adult males with AUD (n = 30) from healthy controls (CTL, n = 30) using the Random Forest (RF) classification method. The predictor variables were: (i) fMRI-based within-network functional connectivity (FC) of the Default Mode Network (DMN), (ii) neuropsychological scores from the Tower of London Test (TOLT), and the Visual Span Test (VST), and (iii) impulsivity factors from the Barratt Impulsiveness Scale (BIS). The RF model, with a classification accuracy of 76.67%, identified fourteen DMN connections, two neuropsychological variables (memory span and total correct scores of the forward condition of the VST), and all impulsivity factors as significantly important for classifying participants into either the AUD or CTL group. Specifically, the AUD group manifested hyperconnectivity across the bilateral anterior cingulate cortex and the prefrontal cortex as well as between the bilateral posterior cingulate cortex and the left inferior parietal lobule, while showing hypoconnectivity in long-range anterior-posterior and interhemispheric long-range connections. Individuals with AUD also showed poorer memory performance and increased impulsivity compared to CTL individuals. Furthermore, there were significant associations among FC, impulsivity, neuropsychological performance, and AUD status. These results confirm the previous findings that alterations in specific brain networks coupled with poor neuropsychological functioning and heightened impulsivity may characterize individuals with AUD, who can be efficiently identified using classification algorithms such as Random Forest.

Positive symptoms and water diffusivity of the prefrontal and temporal cortices in schizophrenia patients: a pilot study

The development of diffusion tensor imaging (DTI) has provided information about microstructural changes in the brain. Most DTI studies have focused on white matter (WM). Few DTI studies have examined the gray matter (GM) in schizophrenia and, to date, there has been no attempt to identify the relationship between water diffusivity and symptom severity in schizophrenia. The present study aimed to examine microstructural deficits in the dorsal prefrontal cortex (DPFC) and temporal cortex in schizophrenia patients using fractional anisotropy (FA) and water diffusivity. This study also explored the relationship between DTI measurements and psychotic symptoms. Magnetic resonance imaging (MRI) and DTI were used to study 19 schizophrenia patients and 19 healthy controls. Fractional anisotropy, axial diffusivity, radial diffusivity, and regional volumes were measured in the prefrontal cortex and temporal cortex. On DTI measurements, patients showed increased axial and radial diffusivities in the prefrontal cortex and temporal cortex, but they did not demonstrate any difference in fractional anisotropy and regional volumes. Additionally, axial and radial diffusivities were significantly correlated with positive symptom scores in all regions of interest. These results indicate that water diffusivity measurements, including axial and radial diffusivities, can be used to identify microstructural changes in the gray matter in schizophrenia that may be related to symptom severity.

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.

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.

Magnetic resonance imaging correlates of first-episode psychosis in young adult male patients: combined analysis of grey and white matter

BACKGROUND

Several patterns of grey and white matter changes have been separately described in young adults with first-episode psychosis. Concomitant investigation of grey and white matter densities in patients with first-episode psychosis without other psychiatric comorbidities that include all relevant imaging markers could provide clues to the neurodevelopmental hypothesis in schizophrenia.

METHODS

We recruited patients with first-episode psychosis diagnosed according to the DSM-IV-TR and matched controls. All participants underwent magnetic resonance imaging (MRI). Voxel-based morphometry (VBM) analysis and mean diffusivity voxel-based analysis (VBA) were used for grey matter data. Fractional anisotropy and axial, radial and mean diffusivity were analyzed using tract-based spatial statistics (TBSS) for white matter data.

RESULTS

We included 15 patients and 16 controls. The mean diffusivity VBA showed significantly greater mean diffusivity in the first-episode psychosis than in the control group in the lingual gyrus bilaterally, the occipital fusiform gyrus bilaterally, the right lateral occipital gyrus and the right inferior temporal gyrus. Moreover, the TBSS analysis revealed a lower fractional anisotropy in the first-episode psychosis than in the control group in the genu of the corpus callosum, minor forceps, corticospinal tract, right superior longitudinal fasciculus, left middle cerebellar peduncle, left inferior longitudinal fasciculus and the posterior part of the fronto-occipital fasciculus. This analysis also revealed greater radial diffusivity in the first-episode psychosis than in the control group in the right corticospinal tract, right superior longitudinal fasciculus and left middle cerebellar peduncle.

LIMITATIONS

The modest sample size and the absence of women in our series could limit the impact of our results.

CONCLUSION

Our results highlight the structural vulnerability of grey matter in posterior areas of the brain among young adult male patients with first-episode psychosis. Moreover, the concomitant greater radial diffusivity within several regions already revealed by the fractional anisotropy analysis supports the idea of a late myelination in patients with first-episode psychosis.

White matter integrity, language, and childhood onset schizophrenia

BACKGROUND

The heterogeneity of symptoms and cognitive deficits in schizophrenia can be explained by abnormal connectivity between brain regions. Childhood-onset schizophrenia (COS) is a particularly severe form of schizophrenia, with an onset during a key time period for both cerebral pruning and myelination.

METHODS

Diffusion tensor images were acquired from 18 children and adolescents with COS and 25 controls. The COS group was divided into two sub-groups-one with linguistic impairment (LI) and the other without (NLI). The fractional anisotropy (FA), axial (AD), and radial diffusivity (RD) data from the two COS sub-groups were compared to each other and to the controls using tract-based spatial statistics (TBSS) analyses, which is a voxel-based method used to identify regions of white matter abnormalities.

RESULTS

TBSS identified several regions in the left hemisphere where the LI group had increased AD and RD relative to the NLI and the control groups. These areas primarily localized to linguistic tracts: left superior longitudinal fasciculus and left inferior longitudinal fasciculus/inferior fronto-occipital fasciculus. Regions of increased RD overlapped regions of increased AD, with the former showing more pronounced effects.

CONCLUSIONS

Studies of adult-onset schizophrenia typically identify areas of higher RD but unchanged AD; however, normal development studies have shown that while RD decreases are pronounced over this age range, smaller decreases in AD can also be detected. The observed increases in both RD and AD suggest that developmental disturbances affecting the structural connectivity of these pathways are more severe in COS accompanied by severe linguistic impairments.

From revolution to evolution: the glutamate hypothesis of schizophrenia and its implication for treatment

Glutamate is the primary excitatory neurotransmitter in mammalian brain. Disturbances in glutamate-mediated neurotransmission have been increasingly documented in a range of neuropsychiatric disorders including schizophrenia, substance abuse, mood disorders, Alzheimer's disease, and autism-spectrum disorders. Glutamatergic theories of schizophrenia are based on the ability of N-methyl-D-aspartate receptor (NMDAR) antagonists to induce schizophrenia-like symptoms, as well as emergent literature documenting disturbances of NMDAR-related gene expression and metabolic pathways in schizophrenia. Research over the past two decades has highlighted promising new targets for drug development based on potential pre- and postsynaptic, and glial mechanisms leading to NMDAR dysfunction. Reduced NMDAR activity on inhibitory neurons leads to disinhibition of glutamate neurons increasing synaptic activity of glutamate, especially in the prefrontal cortex. Based on this mechanism, normalizing excess glutamate levels by metabotropic glutamate group 2/3 receptor agonists has led to potential identification of the first non-monoaminergic target with comparable efficacy as conventional antipsychotic drugs for treating positive and negative symptoms of schizophrenia. In addition, NMDAR has intrinsic modulatory sites that are active targets for drug development, several of which show promise in preclinical/early clinical trials targeting both symptoms and cognition. To date, most studies have been done with orthosteric agonists and/or antagonists at specific sites. However, allosteric modulators, both positive and negative, may offer superior efficacy with less danger of downregulation.

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.

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.

ADC changes in schizophrenia: a diffusion-weighted imaging study

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

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.

Altered microstructure integrity of the amygdala in schizophrenia: a bimodal MRI and DWI study

BACKGROUND

The amygdala plays a central role in the fronto-limbic network involved in the processing of emotions. Structural and functional abnormalities of the amygdala have recently been found in schizophrenia, although there are still contradictory results about its reduced or preserved volumes.

METHOD

In order to address these contradictory findings and to further elucidate the possibly underlying pathophysiological process of the amygdala, we employed structural magnetic resonance imaging (MRI) and diffusion weighted imaging (DWI), exploring amygdalar volume and microstructural changes in 69 patients with schizophrenia and 72 matched healthy subjects, relating these indices to psychopathological measures.

RESULTS

Measuring water diffusivity, the apparent diffusion coefficients (ADCs) for the right amygdala were found to be significantly greater in patients with schizophrenia compared with healthy controls, with a trend for abnormally reduced volumes. Also, significant correlations between mood symptoms and amygdalar volumes were found in schizophrenia.

CONCLUSIONS

We therefore provide evidence that schizophrenia is associated with disrupted tissue organization of the right amygdala, despite partially preserved size, which may ultimately lead to abnormal emotional processing in schizophrenia. This result confirms the major role of the amygdala in the pathophysiology of schizophrenia and is discussed with respect to amygdalar structural and functional abnormalities found in patients suffering from this illness.

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.

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.

Serotonin transporter polymorphisms, microstructural white matter abnormalities and remission of geriatric depression

OBJECTIVE

This study compared microstructural abnormalities in depressed elders and controls and studied the association of the serotonin transporter gene status to white matter abnormalities and to remission of depression.

METHODS

The subjects were Caucasians with non-psychotic major depression and normal elders. Depressed subjects received escitalopram 10 mg daily for 12 weeks. Remission was defined as a HDRS score of 7 or below for 2 consecutive weeks. Diffusion tensor imaging was performed and voxel-based analysis of fractional anisotropy (FA) was conducted using age and mean diffusivity as covariates.

RESULTS

Depressed elders (N=27) had lower FA than controls (N=27) in several frontolimbic areas. Depressed elderly S-allele carriers also had lower FA than L homozygotes in frontolimbic brain areas, including the dorsal and rostral anterior cingulate, posterior cingulate, dorsolateral prefrontal and medial prefrontal regions, thalamus, and in other regions. S-allele carriers had a lower remission rate than L homozygotes.

LIMITATIONS

Small number of subjects, lack of random sampling, fixed antidepressant dose, short follow-up.

CONCLUSIONS

Lower FA was observed in several frontolimbic and other regions in depressed elders compared to controls. Depressed S-allele carriers had both microstructural white matter abnormalities in frontolimbic networks and a low remission rate. It remains unclear whether the risk for chronicity of geriatric depression in S-allele carriers is mediated by frontolimbic compromise. However, these observations set the stage for studies aiming to identify the relationship of S allele to impairment in specific frontolimbic functions interfering with response of geriatric depression to antidepressants.

Serotonin transporter polymorphisms, microstructural white matter abnormalities and remission of geriatric depression

OBJECTIVE

This study compared microstructural abnormalities in depressed elders and controls and studied the association of the serotonin transporter gene status to white matter abnormalities and to remission of depression.

METHODS

The subjects were Caucasians with non-psychotic major depression and normal elders. Depressed subjects received escitalopram 10 mg daily for 12 weeks. Remission was defined as a HDRS score of 7 or below for 2 consecutive weeks. Diffusion tensor imaging was performed and voxel-based analysis of fractional anisotropy (FA) was conducted using age and mean diffusivity as covariates.

RESULTS

Depressed elders (N=27) had lower FA than controls (N=27) in several frontolimbic areas. Depressed elderly S-allele carriers also had lower FA than L homozygotes in frontolimbic brain areas, including the dorsal and rostral anterior cingulate, posterior cingulate, dorsolateral prefrontal and medial prefrontal regions, thalamus, and in other regions. S-allele carriers had a lower remission rate than L homozygotes.

LIMITATIONS

Small number of subjects, lack of random sampling, fixed antidepressant dose, short follow-up.

CONCLUSIONS

Lower FA was observed in several frontolimbic and other regions in depressed elders compared to controls. Depressed S-allele carriers had both microstructural white matter abnormalities in frontolimbic networks and a low remission rate. It remains unclear whether the risk for chronicity of geriatric depression in S-allele carriers is mediated by frontolimbic compromise. However, these observations set the stage for studies aiming to identify the relationship of S allele to impairment in specific frontolimbic functions interfering with response of geriatric depression to antidepressants.

Volume and neuron number of the lateral geniculate nucleus in schizophrenia and mood disorders

Subjects with schizophrenia show deficits in visual perception that suggest changes predominantly in the magnocellular pathway and/or the dorsal visual stream important for visiospatial perception. We previously found a substantial 25% reduction in neuron number of the primary visual cortex (Brodmann's area 17, BA17) in postmortem tissue from subjects with schizophrenia. Also, many studies have found reduced volume and neuron number of the pulvinar--the large thalamic association nucleus involved in higher-order visual processing. Here, we investigate if the lateral geniculate nucleus (LGN), the visual relay nucleus of the thalamus, has structural changes in schizophrenia. We used stereological methods based on unbiased principles of sampling (Cavalieri's principle and the optical fractionator) to estimate the total volume and neuron number of the magno- and parovocellular parts of the left LGN in postmortem brains from nine subjects with schizophrenia, seven matched normal comparison subjects and 13 subjects with mood disorders. No significant schizophrenia-related structural differences in volume or neuron number of the left LGN or its major subregions were found, but we did observe a significantly increased total volume of the LGN, and of the parvocellular lamina and interlaminar regions, in the mood group. These findings do not support the hypothesis that subjects with schizophrenia have structural changes in the LGN. Therefore, our previous observation of a schizophrenia-related reduction of the primary visual cortex is probably not secondary to a reduction in the LGN.

A voxel-based diffusion tensor imaging study of temporal white matter in patients with schizophrenia

Diffusion tensor imaging (DTI) is a relatively new technique used to detect changes in the anisotropic diffusion of white matter. The study of the disruption of brain connectivity may increase our understanding of cognitive deficits associated with schizophrenia. Here we analysed DTI data in 25 patients with DSM-IV schizophrenia and 24 healthy controls. Two complementary measures, fractional anisotropy (FA) and the apparent diffusion coefficient (ADC), were considered and analysed using voxel-based morphometry. Declarative memory functions were also investigated and their associations with DTI data were analysed. FA was significantly reduced, and the ADC increased in the left sub-gyral white matter of the temporal lobe, which involves the posterior part of the fornix. In the schizophrenic group, females had lower FA than males in the genu of the corpus callosum. Memory functions correlate with FA values. These data provide further evidence for the disruption of white matter connectivity in the left medial temporal lobe, and for its contribution to the declarative memory deficit in schizophrenia.

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

Mean diffusivity (MD), the rotationally invariant magnitude of water diffusion that is greater in cerebrospinal fluid (CSF) and smaller in organized brain tissue, has been suggested to reflect schizophrenia-associated cortical atrophy. Regional changes, associations with CSF, and the effects of genetic predisposition towards schizophrenia, however, remain uncertain. Six-direction diffusion tensor imaging DTI and high-resolution structural images were obtained from 26 schizophrenia patients, 36 unaffected first-degree patient relatives, 20 control subjects and 32 control relatives (N=114). Registration procedures aligned diffusion tensor imaging (DTI) data across imaging modalities. MD was averaged within lobar regions and the cingulate and superior temporal gyri. CSF volume and MD were highly correlated. Significant bilateral temporal, and superior temporal MD increases were observed in schizophrenia compared with unrelated control probands. First-degree relatives of schizophrenia probands showed larger MD measures compared with controls within bilateral superior temporal regions with CSF volume correction. Superior temporal lobe brain tissue deficits and proximal CSF enlargements are widely documented in schizophrenia. Larger MD indices in patients and their relatives may thus reflect similar pathophysiological mechanisms. However, persistence of regional MD effects after controlling for CSF volume, suggests that MD is a sensitive biological marker of disease and genetic liability, characterizing at least partially distinct aspects of brain structural integrity.

Multivariate analysis of structural and diffusion imaging in traumatic brain injury

RATIONALE AND OBJECTIVES

Diffusion tensor (DT) and T1 structural magnetic resonance images provide unique and complementary tools for quantifying the living brain. We leverage both modalities in a diffeomorphic normalization method that unifies analysis of clinical datasets in a consistent and inherently multivariate (MV) statistical framework. We use this technique to study MV effects of traumatic brain injury (TBI).

MATERIALS AND METHODS

We contrast T1 and DT image-based measurements in the thalamus and hippocampus of 12 TBI survivors and nine matched controls normalized to a combined DT and T1 template space. The normalization method uses maps that are topology-preserving and unbiased. Normalization is based on the full tensor of information at each voxel and, simultaneously, the similarity between high-resolution features derived from T1 data. The technique is termed symmetric normalization for MV neuroanatomy (SyNMN). Voxel-wise MV statistics on the local volume and mean diffusion are assessed with Hotelling's T(2) test with correction for multiple comparisons.

RESULTS

TBI significantly (false discovery rate P < .05) reduces volume and increases mean diffusion at coincident locations in the mediodorsal thalamus and anterior hippocampus.

CONCLUSIONS

SyNMN reveals evidence that TBI compromises the limbic system. This TBI morphometry study and an additional performance evaluation contrasting SyNMN with other methods suggest that the DT component may aid normalization quality.

The role of white matter for the pathophysiology of schizophrenia

Inter- and intra-hemispheric connectivity disturbances have been suggested to play a major role in schizophrenia. To this extent, diffusion weighted imaging (DWI) is a relatively new technique examining subtle white matter microstructure organization. DWI studies in schizophrenia strongly suggest that white matter communication is disrupted. This supports the hypothesis that there is a cortico-cortical and transcallosal altered connectivity in schizophrenia, which may be relevant for the pathophysiology and the cognitive disturbances of the disorder. Future longitudinal diffusion and functional imaging studies targeting brain communication together with genetic investigations should further characterize white matter pathology in schizophrenia and its relevance for the development of the illness.

Cortical white-matter microstructure in schizophrenia. Diffusion imaging study

BACKGROUND

Several, although not all, of the previous small diffusion-weighted imaging (DWI) studies have shown cortical white-matter disruption in schizophrenia.

AIMS

To investigate cortical white-matter microstructure with DWI in a large community-based sample of people with schizophrenia.

METHOD

Sixty-eight people with schizophrenia and 64 healthy controls underwent a session of DWI to obtain the apparent diffusion coefficient (ADC) of white-matter water molecules. Regions of interest were placed in cortical lobes.

RESULTS

Compared with controls, the schizophrenia group had significantly greater ADCs in frontal, temporal and occipital white matter (analysis of covariance, P < 0.05).

CONCLUSIONS

Our findings confirm the presence of cortical white-matter microstructure disruption in frontal and temporo-occipital lobes in the largest sample of people with schizophrenia thus for studied with this technique. Future brain imaging studies, together with genetic investigations, should further explore white-matter integrity and genes encoding myelin-related protein expression in people with first-episode schizophrenia and those at high risk of developing the disorder.

Electrophysiological subtypes of psychotic states

OBJECTIVE

This research sought neurobiological features common to psychotic states displayed by patients with different clinical diagnoses.

METHOD

Cluster analysis with quantitative electroencephalographic (QEEG) variables was used to subtype drug-naïve, non-medicated, and medicated schizophrenic, depressed and alcoholic patients with psychotic symptoms, from the USA and Germany. QEEG source localization brain images were computed for each cluster.

RESULTS

Psychotic patients with schizophrenia, depression and alcoholism, and drug- naïve schizophrenic patients, were distributed among six clusters. QEEG images revealed one set of brain regions differentially upregulated in each cluster and another group of structures downregulated in the same way in every cluster.

CONCLUSION

Subtypes previously found among 94 schizophrenic patients were replicated in a sample of 390 non-schizophrenic as well as schizophrenic psychotics, and displayed common neurobiological abnormalities. Collaborative longitudinal studies using these economical methods might improve differential understanding and treatment of patients based upon these features rather than clinical symptoms.

Differential effects of typical and atypical antipsychotics on brain myelination in schizophrenia

CONTEXT

Imaging and post-mortem studies provide converging evidence that patients with schizophrenia have a dysregulated developmental trajectory of frontal lobe myelination even in adulthood. Atypical antipsychotics have been shown to have a wide spectrum of efficacy across multiple psychiatric diseases and to be particularly efficacious in treatment resistant cases of disorders such as schizophrenia.

OBJECTIVE

To test the a priori hypothesis that antipsychotic medications may differentially impact frontal lobe myelination in patients with schizophrenia.

DESIGN, SETTING, AND PARTICIPANTS

Participants ranged in age from 18-35 years, were all male, and were recruited by a single group of investigators using the same criteria. Two cohorts of subjects with schizophrenia early in their disease who were treated either with oral risperidone (Ris) or fluphenazine decanoate (Fd) were imaged in conjunction with cohorts of healthy controls. Each cohort was imaged using a different MRI instrument using identical imaging sequences.

MAIN OUTCOME MEASURE

MRI measures of frontal lobe white matter volume.

RESULTS

We estimated differences due to differences in the MRI instruments used in the two studies in the two healthy control groups matched to the patient samples, adjusting for age and other covariates. We then statistically removed those differences (which we assumed were due to instrument effects) from the data in the schizophrenia samples by subtraction. Relative to the differences seen in controls, the two groups of schizophrenic patients differed in their pattern of frontal lobe structure with the Ris-treated group having significantly larger white matter volume than the Fd group.

CONCLUSIONS

The results suggest that the choice of antipsychotic treatment may differentially impact brain myelination in adults with schizophrenia. Prospective studies are needed to confirm this finding. MRI can be used to dissect subtle differences in brain tissue characteristics and thus could help clarify the effect of pharmacologic treatments on neurodevelopmental and pathologic processes in vivo.

Diffusion tensor microscopy indicates the cytoarchitectural basis for diffusion anisotropy in the human hippocampus

BACKGROUND AND PURPOSE

Observing changes to water diffusivity and fractional anisotropy (FA) for particular hippocampal regions may improve the sensitivity and specificity of diffusion tensor MR imaging for hippocampal pathologies like Alzheimer disease and mesial temporal sclerosis. As a first step toward this goal, this study characterized the cytoarchitectural features underlying diffusion anisotropy in human hippocampus autopsy specimens at 60-microm in-plane resolution.

MATERIALS AND METHODS

Eight-millimeter coronal segments of the hippocampal body were dissected from 5 autopsy specimens (mean = 55.6 +/- 6.2 years of age) with short postmortem intervals to fixation (21.2 +/- 5.7 hours) and no histologic evidence of neuropathology. Diffusion tensor microscopy data were collected from hippocampal specimens by using a 14.1T magnet with a protocol that included 21 unique diffusion gradient orientations (diffusion time = 17 ms, b = 1250 s/mm(2)). The resulting images were used to determine the mean diffusivity, FA, and principal fiber orientation for manually segmented hippocampal regions that included the stratum oriens, stratum radiatum, stratum pyramidale (CA1 and CA3), stratum lacunosum-molecular, hilus, molecular layer, granule cell layer, fimbria, and subiculum.

RESULTS

Diffusion-weighted images had high signal-to-noise ratios (31.1 +/- 13.0) and delineated hippocampal anatomy well. Water diffusivity ranged from 1.21 +/- 0.22 x 10(-4) mm(2)/s in the fimbria to 3.48 +/- 0.72 x 10(-4) mm(2)/s in granule cells (analysis of variance, P<.001). Color fiber-orientation maps indicated the underlying microstructures responsible for diffusion anisotropy in the hippocampal lamina.

CONCLUSION

Diffusion tensor microscopy provided novel microstructural information about the different lamina of the human hippocampus. These ex vivo data obtained at high-magnetic-field strengths can be used to study injury-specific diffusion changes to susceptible hippocampal regions and may lead to more specific MR imaging surrogate markers for Alzheimer disease or epilepsy.

Cerebral atrophy and white matter disruption in chronic schizophrenia

Several magnetic resonance imaging (MRI) studies have shown cerebral atrophy in established schizophrenia, although not in all reports. Discrepancies may mostly be due to population and postprocessing differences. Recently, disruption of cortical white matter integrity has also been reported in chronic patients with schizophrenia. In this study we explored tridimensional (3D) cerebral volumes and white matter microstructure in schizophrenia with structural and diffusion magnetic resonance. Twenty-five patients with established schizophrenia and 25 1:1 matched normal controls underwent a session of MRI using a Siemens 1.5T-scanner. 3D brain volume reconstruction was performed with the semi-automatic software Amira (TGS, San Diego, CA), whereas the apparent diffusion coefficients (ADCs) of cortical white matter water molecules were obtained with in-house developed softwares written in MatLab (The Mathworks-Inc., Natick, MA). Compared to controls, patients with schizophrenia had significantly smaller gray matter intracranium and total brain volumes, increased 4th ventricle volumes, and greater temporal and occipital ADCs. Patients treated with typical antipsychotic medication (N = 9) had significantly larger right lateral and 4th ventricles compared to those on atypical antipsychotic drugs. Intracranial volumes significantly inversely correlated with left temporal ADC in patients with schizophrenia. Also, age correlated directly with right, left, and 3rd ventricle volumes and inversely with gray matter intracranium volumes in individuals with schizophrenia. This study confirmed the presence of cortical atrophy in patients with schizophrenia, especially in those on typical antipsychotic drugs, and the existence of white matter disruption. It also suggested that physiological aging effects on brain anatomy may be abnormally pronounced in schizophrenia.

Early detection of schizophrenia by diffusion weighted imaging

A novel magnetic resonance imaging method was used to determine whether it is feasible to detect early signs of cortical atrophy among individuals who are at high risk for developing schizophrenia. Fifteen individuals at high-risk for schizophrenia and 15 of their first degree relatives diagnosed with schizophrenia were compared with controls (n=25) who did not have a family history of psychiatric illness or psychiatric hospitalizations. On the basis of a voxelwise analysis of apparent diffusion coefficient (ADC) maps derived from diffusion weighted magnetic resonance imaging, these individuals showed evidence of deficits in four separate regions of the brain, all on the left side only: parahippocampal gyrus, lingual gyrus, superior frontal gyrus, and middle frontal gyrus. However, conventional volumetric quantification of ventricular space to detect atrophy failed to reveal differences between high-risk subjects and controls. It is concluded that ADC may be a more sensitive measure than ventricular volume assessments for use in future studies of early prediction of schizophrenia.

Structural neuroimaging research methods in geriatric depression

Geriatric depression consists of complex and heterogeneous behaviors unlikely to be caused by a single brain lesion. However, there is evidence that abnormalities in specific brain structures and their interconnections confer vulnerability to the development of late-life depression. Structural magnetic resonance imaging methods can be used to identify and quantify brain abnormalities predisposing to geriatric depression and in prediction of treatment response. This article reviews several techniques, including morphometric approaches, study of white matter hyperintensities, diffusion tensor imaging, magnetization transfer imaging, t2 relaxography, and spectroscopy, that have been used to examine these brain abnormalities with a focus on the type of information obtained by each method as well as each method's limitations. The authors argue that the available methods provide complementary information and that, when combined judiciously, can increase the knowledge gained from neuroimaging findings and conceptually advance the field of geriatric depression.

Understanding structural brain changes in schizophrenia

Schizophrenia is a chronic progressive disorder that has at its origin structural brain changes in both white and gray matter. It is likely that these changes begin prior to the onset of clinical symptoms in cortical regions, particularly those concerned with language processing. Later, they can be detected by progressive ventricular enlargement. Current magnetic resonance imaging (MRI) technology can provide a valuable tool for detecting early changes in cortical atrophy and anomalous language processing, which may be predictive of who will develop schizophrenia.

A preliminary DTI study showing no brain structural change associated with adolescent cannabis use

Analyses were performed on brain MRI scans from individuals who were frequent cannabis users (N = 10; 9 males, 1 female, mean age 21.1 +/- 2.9, range: 18-27) in adolescence and similar age and sex matched young adults who never used cannabis (N = 10; 9 males, 1 female, mean age of 23.0 +/- 4.4, range: 17-30). Cerebral atrophy and white matter integrity were determined using diffusion tensor imaging (DTI) to quantify the apparent diffusion coefficient (ADC) and the fractional anisotropy (FA). Whole brain volumes, lateral ventricular volumes, and gray matter volumes of the amygdala-hippocampal complex, superior temporal gyrus, and entire temporal lobes (excluding the amygdala-hippocampal complex) were also measured. While differences existed between groups, no pattern consistent with evidence of cerebral atrophy or loss of white matter integrity was detected. It is concluded that frequent cannabis use is unlikely to be neurotoxic to the normal developing adolescent brain.

Increased water diffusivity in the frontal and temporal cortices of schizophrenic patients

Schizophrenia has been suggested to be the result of both macroscopic and microscopic abnormalities in the brain. Although no definitive clinico-pathological correlations have been found to reconcile the many facets inherent in this disorder, the recent development of the magnetic resonance diffusion tensor imaging (DTI) has allowed us to gather useful information regarding the microcircuitry of the brain. Specifically, the apparent diffusion coefficient (ADC) reflects the degree of diffusion barriers and heterosynaptic communication for the brain neurotransmitter. Nineteen patients with DSM-IV schizophrenia and 21 age- and sex-matched control subjects participated in DTI, and the severity of the patients' symptoms was evaluated according to the Positive and Negative Syndrome Scale (PANSS). The ADC values were determined and compared between patients and control subjects via voxel-based morphometry. The results show an increased ADC in the bilateral fronto-temporal regions of the schizophrenic patients, as compared with those of the control subjects. In addition, the ADC values in the area of the right insular were correlated with the negative syndromes from the PANSS. Our findings of increased water diffusivity in the fronto-temporal regions of schizophrenic patients and the correlation between negative symptom scales and the ADC in the right insular region indicate that damaged brain microcircuitry might contribute to the pathophysiology of schizophrenia. These findings contribute towards integrating micro and macrostructural abnormalities and syndromes of schizophrenia.

Understanding structural brain changes in schizophrenia

Schizophrenia is a chronic progressive disorder that has at its origin structural brain changes in both white and gray matter. It is likely that these changes begin prior to the onset of clinical symptoms in cortical regions, particularly those concerned with language processing. Later, they can be detected by progressive ventricular enlargement. Current magnetic resonance imaging (MRI) technology can provide a valuable tool for detecting early changes in cortical atrophy and anomalous language processing, which may be predictive of who will develop schizophrenia.