The corpus callosum in schizophrenia-volume and connectivity changes affect specific regions

Resting-state functional network correlates of psychotic symptoms in schizophrenia

Schizophrenia has been associated with aberrant intrinsic functional organization of the brain but the relationship of such deficits to psychopathology is unclear. In this study, we investigated associations between resting-state networks and individual psychopathology in sixteen patients with paranoid schizophrenia and sixteen matched healthy control participants. We estimated whole-brain functional connectivity of multiple networks using a combination of spatial independent component analysis and multiple regression analysis. Five networks (default-mode, left and right fronto-parietal, left fronto-temporal and auditory networks) were selected for analysis based on their involvement in neuropsychological models of psychosis. Between-group comparisons and correlations to psychopathology ratings were performed on both spatial (connectivity distributions) and temporal features (power-spectral densities of temporal frequencies below 0.06 Hz). Schizophrenia patients showed aberrant functional connectivity in the default-mode network, which correlated with severity of hallucinations and delusions, and decreased hemispheric separation of fronto-parietal activity, which correlated with disorganization symptoms. Furthermore, the severity of positive symptoms correlated with functional connectivity of fronto-temporal and auditory networks. Finally, default-mode and auditory networks showed increased spectral power of low frequency oscillations, which correlated with positive symptom severity. These results are in line with findings from studies that investigated the neural correlates of positive symptoms and suggest that psychopathology is associated with aberrant intrinsic organization of functional brain networks in schizophrenia.

Abnormal neural oscillations and synchrony in schizophrenia

Converging evidence from electrophysiological, physiological and anatomical studies suggests that abnormalities in the synchronized oscillatory activity of neurons may have a central role in the pathophysiology of schizophrenia. Neural oscillations are a fundamental mechanism for the establishment of precise temporal relationships between neuronal responses that are in turn relevant for memory, perception and consciousness. In patients with schizophrenia, the synchronization of beta- and gamma-band activity is abnormal, suggesting a crucial role for dysfunctional oscillations in the generation of the cognitive deficits and other symptoms of the disorder. Dysfunctional oscillations may arise owing to anomalies in the brain's rhythm-generating networks of GABA (gamma-aminobutyric acid) interneurons and in cortico-cortical connections.

White matter connectivity and psychosis in ultra-high-risk subjects: a diffusion tensor fiber tracking study

This study assessed with diffusion tensor imaging (DTI) whether ultra-high-risk subjects who later develop a psychotic disorder (UHR-P) show abnormalities in association white matter fiber tracts as compared to UHR subjects who do not convert to psychosis (UHR-NP) and healthy controls. Participants comprised 17 male UHR subjects and 10 male healthy controls, who received baseline DTI scans before clinical follow-up. The uncinate and arcuate fasciculi, anterior and dorsal cingulate, and subdivisions of the corpus callosum were calculated and visualized, and tract-specific measurements were performed. At 24-month follow-up seven UHR subjects had developed a first psychotic episode. Fractional anisotropy in baseline DTI scans, including left-right asymmetry measures, did not differ between the groups. Thus, DTI measures of these association white matter tracts were not biological markers of psychosis in our UHR sample. Abnormalities of these fiber tracts may develop around or after onset of psychosis. However, further DTI studies in UHR subjects are needed in larger samples.

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

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

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Probabilistic topography of human corpus callosum using cytoarchitectural parcellation and high angular resolution diffusion imaging tractography

The function of the corpus callosum (CC) is to distribute perceptual, motor, cognitive, learned, and voluntary information between the two hemispheres of the brain. Accurate parcellation of the CC according to fiber composition and fiber connection is of upmost important. In this work, population-based probabilistic connection topographies of the CC, in the standard Montreal Neurological Institute (MNI) space, are estimated by incorporating anatomical cytoarchitectural parcellation with high angular resolution diffusion imaging (HARDI) tractography. First, callosal fibers are extracted using multiple fiber assignment by continuous tracking algorithm based on q-ball imaging (QBI), on 12 healthy and young subjects. Then, the fiber tracts are aligned in the standard MNI coordinate system based on a tract-based transformation scheme. Next, twenty-eight Brodmann's areas on the surface of cortical cortex are registered to the MNI space to parcellate the aligned callosal fibers. Finally, the population-based topological subdivisions of the midsagittal CC to each cortical target are then mapped. And the resulting subdivisions of the CC that connect to the frontal and somatosensory associated cortex are also showed. To our knowledge, it is the first topographic subdivisions of the CC done using HARDI tractography and cytoarchitectonic information. In conclusion, this sophisticated topography of the CC may serve as a landmark to further understand the correlations between the CC, brain intercommunication, and functional cytoarchitectures.

Anatomical brain connectivity and positive symptoms of schizophrenia: a diffusion tensor imaging study

Structural brain changes in schizophrenia are well documented in the neuroimaging literature. The classical morphometric analyses of magnetic resonance imaging (MRI) data have recently been supplemented by diffusion tensor imaging (DTI), which mainly assesses changes in white matter (WM). DTI increasingly provides evidence for abnormal anatomical connectivity in schizophrenia, most often using fractional anisotropy (FA) as an indicator of the integrity of WM tracts. To better understand the clinical significance of such anatomical changes, we studied FA values in a whole-brain analysis comparing paranoid schizophrenic patients with a history of auditory hallucinations and matched healthy controls. The relationship of WM changes to psychopathology was assessed by correlating FA values with PANSS scores (positive symptoms and severity of auditory hallucinations) and with illness duration. Schizophrenic patients showed FA reductions indicating WM integrity disturbance in the prefrontal regions, external capsule, pyramidal tract, occipitofrontal fasciculus, superior and inferior longitudinal fasciculi, and corpus callosum. The arcuate fasciculus was the only tract which showed increased FA values in patients. Increased FA values in this region correlated with increased severity of auditory hallucinations and length of illness. Our results suggest that local changes in anatomical integrity of WM tracts in schizophrenia may be related to patients' clinical presentation.

Regional corpus callosum morphometry: effect of field strength and pulse sequence

PURPOSE

To investigate whether scanning at different field strengths and pulse sequences would influence reproducibility of corpus callosum (CC) morphometric measurements as variations in scanning parameters may result in differences in contrast properties between resulting images that are independent of the underlying tissue but rather reflect the physics of the imaging process.

MATERIALS AND METHODS

Ten subjects were scanned twice at 3T using magnetization-prepared rapid gradient-echo imaging (MPRAGE) and modified driven equilibrium Fourier transform (MDEFT) sequences and once at 1.5T using MPRAGE. Cross-sectional area measurements of four callosal regions were performed on midsagittal magnetic resonance imaging (MRI) sections.

RESULTS

Repeated measures analysis of variance with four regions as dependent variables and three scanning protocols (1.5T MPRAGE, 3T MPRAGE and 3T MDEFT) as independent variables revealed no significant region by protocol interaction: F(6,54) = 0.69, P = 0.52. Reliability measures for (3T MPRAGE/3T MDEFT) and (1.5T MPRAGE/3T MPRAGE; 1.5T MPRAGE/3T MDEFT) comparisons were high, ranging between 0.90 and 0.97.

CONCLUSION

Based on our results, combining and comparing CC morphometric data obtained at different field strengths and/or with different pulse sequences appears possible.

Laterality effects in schizophrenia and bipolar disorder

There are numerous reports in the literature of lateralised structural cerebral abnormalities and alterations of the corpus callosum in the major psychoses. In the light of these findings the purpose of this study was to directly compare hemispheric differences and callosal interhemispheric transmission (IT) in schizophrenia and bipolar disorder. To do that we tested schizophrenic (SCZ), bipolar disorder (BD) patients and controls in a simple manual reaction time (RT) task with lateralised visual stimuli (Poffenberger paradigm) which enables one to test both laterality effects and IT time. We found an overall slowing of responses with the right hand in schizophrenics but not in bipolar patients, who, like controls, showed no hand differences. This selective slowing down of the right hand is likely to be related to abnormalities of intrahemispheric cortico-cortical connections in the left hemisphere. In contrast, IT time was similar in SCZ and BD patients and did not differ with respect to controls. Two are the novel findings of the present study: first both SZC and BD share a normal IT of visuomotor information despite the presence of callosal abnormalities. Second, an impairment of intrahemispheric left hemispheric processing is present only in SCZ patients. This represents a potentially important clue to a further understanding of the pathogenetic differences between the two major psychoses.

A longitudinal study of the corpus callosum in chronic schizophrenia

BACKGROUND

Decreased callosal size and anisotropy have been described in schizophrenia patients but their longitudinal progression remains poorly understood.

METHODS

We performed diffusion-tensor and structural magnetic resonance imaging at baseline and at follow-up four years later in 49 chronic schizophrenia patients and 16 healthy comparison subjects. Schizophrenia patients were subdivided into good-outcome (n=23) and poor-outcome (n=26) groups. Baseline-to-follow-up changes in size, shape, position and fractional anisotropy of the corpus callosum, divided into five sagittal sections and five rostro-caudal segments, were assessed.

RESULTS

At baseline scan and in comparison to healthy subjects, schizophrenia patients displayed 1) smaller callosal size, 2) lower average anisotropy in all sagittal sections except the midline, and 3) more dorsal average coordinate position. During the four years after the baseline scan, patients with schizophrenia exhibited a more pronounced decline in absolute size of the corpus callosum than healthy comparison subjects. As compared with the good-outcome group, the corpus callosum in poor-outcome patients at baseline was of smaller size and lower average anisotropy, more elongated and posteriorly positioned. During the follow-up interval, poor-outcome patients displayed a more pronounced decline in size but less pronounced decline in anisotropy of the corpus callosum than patients with good outcomes.

CONCLUSIONS

Differences in callosal size between schizophrenia patients and healthy subjects seen at baseline continue to widen in the chronic phase of the illness, especially in patients with poor functional outcome. Baseline differences in callosal anisotropy among patients with different outcomes, however, diminish over time.

Using diffusion tensor imaging and fiber tracking to characterize diffuse perinatal white matter injury: a case report

Prematurity is associated with white matter injury. Diffusion tensor imaging, a new magnetic resonance imaging technique, identifies white matter fiber tracts and quantifies structural properties. We used diffusion tensor imaging fiber tracking to compare white matter characteristics in a 12-year-old born prematurely and full-term control. We divided fibers passing through the corpus callosum into 7 segments based on cortical projection zones and analyzed them for fractional anisotropy, axial diffusivity, and radial diffusivity. We also compared corticospinal and somatosensory tracts in the participant and control. The participant had decreased fractional anisotropy in every callosal segment, particularly in superior and posterior parietal projections. Fractional anisotropy of the corticospinal and somatosensory tracts was not lower in the participant than control. Fiber tracking allowed precise localization and visualization of white matter injuries of the corpus callosum associated with prematurity. Quantitative measures suggested myelin deficiencies across the corpus callosum, particularly in parietal projections.

Polyunsaturated fatty acids and brain white matter anisotropy in recent-onset schizophrenia: a preliminary study

Brain white matter myelin abnormalities and cell membrane fatty acid abnormalities have been implicated in schizophrenia and other psychiatric disorders. We investigated in young adults with a psychotic disorder (n=12) whether (poly)unsaturated fatty acid concentrations in erythrocyte membranes are related to an MRI measure of brain white matter, which depends on the degree of myelination. A significant correlation was found between total (poly)unsaturated fatty acid concentration and fractional anisotropy of a fronto-temporal white matter tract (r=0.503, P=0.048). Unsaturated fatty acids may be necessary for the myelinating activity of oligodendrocytes or for myelin maintenance. These results warrant further investigation.

Comparative proteomics in the corpus callosal sub-regions of postmortem human brain

The corpus callosum (CC) is a single anatomical region with homologous cytoarchitecture and divided into four sub-regions such as the rostrum, the genu, the body and the splenium. Neuroimaging analysis revealed that susceptibility to clinical neurological diseases of these sub-regions is variable, indicating biochemical and physiological heterogenecity. To understand the biochemical make up of these regions, we compared the protein expression of these three sub-regional areas [the genu, the body and the splenium (n=9)] through 2D proteomics, which is a high-throughput global protein expression analysis technique. Normative proteomic comparison of gels, and analysis of spectra revealed that 17 (identified as 7 proteins), 35 (identified as 20 proteins) and 39 (identified as 21 proteins) protein spots were differentially expressed in the genu vs. the body, the genu vs. the splenium and the body vs. the splenium, respectively. These results suggest that the sub-regions of the CC differ at the level of protein expression. Identified proteins of the different groups belong to several functional classes such as cytoskeletal, metabolic, signaling, oxidative stress and calcium regulation. Interestingly, oxidative stress defense and glucose metabolic pathways of the splenium are quite different from the genu which might be correlated to region specific vulnerability of neuronal illness. Protein expression maps of these regions can be used as a reference source for future studies to investigate the molecular basis of functional differences and degree of pathogenesis of various neurodegenerative diseases of the CC.

Reduced fractional anisotropy of corpus callosum in first-contact, antipsychotic drug-naive patients with schizophrenia

BACKGROUND

Corpus callosum is the most important commissure of the brain and therefore represents a first-choice candidate to challenge hypotheses of disrupted inter-hemispheric connectivity and white matter pathology in patients with schizophrenia. Recent studies on diffusion tensor imaging (DTI) of corpus callosum yielded promising but equivocal evidence of reduced fractional anisotropy (FA) in schizophrenia patients who were, for the most part, chronic cases on medication for a lengthy period of time. To exclude potentially confounding effects of the course of the disorder and its treatment, we compared callosal FA of first-contact, antipsychotic drug-naive schizophrenia patients (n=21) and healthy controls (n=21).

METHODS

Splenium and genu FA were obtained by two independent observers utilizing large, rectangular, tractography-guided regions of interest outlined on directional color-coded maps. Inter-observer agreement on FA was evaluated by means of the Bland and Altman and the Passing and Bablok procedures together with an estimate of the intra-class correlation coefficient.

RESULTS

Strong inter-observer agreement of FA values emerged from each of the three statistical approaches utilized. ANCOVA showed a significant effect on FA for the interaction between patient-control membership and callosal region (F=5.354; p=0.026); post hoc multiple comparisons demonstrated that, when compared to the controls, the patients had lower mean FA values (p=0.005) in the splenium but not in the genu and that this difference tended to be more evident in males (p=0.090).

CONCLUSIONS

Lowered mean FA values in the splenium of first-contact, antipsychotic drug-naive patients with respect to healthy controls strongly support the hypothesis that processes operant at least since the earliest phases of the disorder and independent from exposition to antipsychotic drugs contribute to reduced anisotropy in schizophrenia.

A genome-wide association study of schizophrenia using brain activation as a quantitative phenotype

BACKGROUND

Genome-wide association studies (GWASs) are increasingly used to identify risk genes for complex illnesses including schizophrenia. These studies may require thousands of subjects to obtain sufficient power. We present an alternative strategy with increased statistical power over a case-control study that uses brain imaging as a quantitative trait (QT) in the context of a GWAS in schizophrenia.

METHODS

Sixty-four subjects with chronic schizophrenia and 74 matched controls were recruited from the Functional Biomedical Informatics Research Network (FBIRN) consortium. Subjects were genotyped using the Illumina HumanHap300 BeadArray and were scanned while performing a Sternberg Item Recognition Paradigm in which they learned and then recognized target sets of digits in an functional magnetic resonance imaging protocol. The QT was the mean blood oxygen level-dependent signal in the dorsolateral prefrontal cortex during the probe condition for a memory load of 3 items.

RESULTS

Three genes or chromosomal regions were identified by having 2 single-nucleotide polymorphisms (SNPs) each significant at P < 10(-6) for the interaction between the imaging QT and the diagnosis (ROBO1-ROBO2, TNIK, and CTXN3-SLC12A2). Three other genes had a significant SNP at <10(-6) (POU3F2, TRAF, and GPC1). Together, these 6 genes/regions identified pathways involved in neurodevelopment and response to stress.

CONCLUSION

Combining imaging and genetic data from a GWAS identified genes related to forebrain development and stress response, already implicated in schizophrenic dysfunction, as affecting prefrontal efficiency. Although the identified genes require confirmation in an independent sample, our approach is a screening method over the whole genome to identify novel SNPs related to risk for schizophrenia.

Treatment-refractory schizoaffective disorder in a patient with dyke-davidoff-masson syndrome

Dyke-Davidoff-Masson syndrome, or cerebral hemiatrophy, is a pre- or perinatally acquired entity characterized by predominantly neurologic symptoms, such as seizures, facial asymmetry, contralateral hemiplegia, and mental retardation. Psychiatric symptoms are rarely reported. We report the first case of left cerebral hemiatrophy and a late onset of treatment-resistant schizoaffective disorder after a stressful life event. The patient finally responded well to clozapine. The clinical history and results from structural neuroimaging are highlighted to discuss the possible developmental bias for psychotic disorders.

Altered metabolic integrity of corpus callosum among individuals at ultra high risk of schizophrenia and first-episode patients

BACKGROUND

The disconnectivity hypothesis as part of the neurodevelopmental model of schizophrenia states that an abnormality in brain development causing impaired corticocortical or interhemispheric connectivity leads to cognitive deficits and symptoms of the illness. Previous studies showed the altered morphology of corpus callosum in patients with schizophrenia. We investigated the metabolic integrity of corpus callosum of individuals at ultra high risk (UHR) of developing schizophrenia and first-episode patients.

METHODS

We studied 17 individuals at UHR of developing schizophrenia, 14 first-episode schizophrenia patients, and 30 healthy control subjects. We measured the absolute concentrations of neurometabolites and T2 relaxation time of tissue water (T2(B)) in the genu region of corpus callosum by using proton magnetic resonance spectroscopy.

RESULTS

N-acetylaspartate (NAA) concentrations were decreased and T2(B) values were prolonged in the UHR cases as well as in the first-episode patients, compared with the control subjects. The difference between the NAA concentrations of the UHR cases and first-episode patients was also significant. The NAA concentrations of the UHR cases and first-episode patients were correlated with the severity of negative symptoms.

CONCLUSIONS

We demonstrated the disrupted metabolic integrity of corpus callosum among individuals at UHR of schizophrenia and the first-episode patients.

Diffusion tensor quantification of the macrostructure and microstructure of human midsagittal corpus callosum across the lifespan

The midsagittal cross-sectional area of the human corpus callosum (CC) has been used by many researchers as a marker of development, natural aging, and neurodegenerative and acquired pathologies. The availability of non-invasive MRI methods for quantifying the macrostructural and microstructural organization of the CC would help to clarify the CC contribution to behavior and cognition in both health and disease. In this report, we extended and validated the ability of a recently described semi-automated diffusion tensor imaging tissue segmentation method to utilize the high orientation contrast of the CC on diffusion tensor imaging. Using a cohort of healthy right-handed children and adults aged 7-59 years, we show gender-independent non-linear (quadratic) and strongly correlated growth trends in the CC area and the corresponding diffusion tensor fractional anisotropy (r = 0.67; P < 1 x 10(-10)). Our results provide preliminary evidence that diffusion tensor anisotropy in the living CC may be related to the number of small myelinated fibers.

Diffusion tensor tractography quantification of the human corpus callosum fiber pathways across the lifespan

Several anatomical attributes of the human corpus callosum (CC) including the midsagittal cross-sectional area, thickness, and volume, have been used to assess CC integrity. We extended our previous lifespan quantitative diffusion tensor imaging (DTI) study of the regional CC midsagittal areas to include the CC volumes obtained from DTI fiber tracking. In addition to the entire CC tracked subvolumes we normalized volume with respect to each subject's intracranial volume (ICV) and the corresponding DTI metrics of the different specialized fiber pathways of the CC on a cohort of 99 right-handed children and adults aged 7-59 years. Results indicated that the CC absolute volume, the normalized volume fraction, and the fractional anisotropy followed inverted U-shaped curves, while the radial diffusivities followed a U-shaped curve reflecting white matter progressive and regressive myelination dynamics that continue into young adulthood. Our study provides for the first time normative baseline macro- and microstructural age trajectories of the human CC subvolumes across the lifespan that can be helpful for normative behavioral and clinical studies.

Relationship between intelligence and the size and composition of the corpus callosum

We investigated the relationship between the morphology of the corpus callosum (CC) and IQ in a healthy sample of individuals in their late teens and early twenties. The relationship between the area of the CC, measured at the midline, and IQ showed regional differences. We observed that a higher estimated performance IQ was associated with smaller area in the posterior regions of the CC, a finding that differs from a positive association previously observed in a somewhat older adult sample. In contrast, higher estimated verbal IQ was associated with decreased fractional anisotropy of the genu, an anterior portion of the CC. Age effects were also observed such that older age was associated with larger CC area. Our results suggest that CC morphology is related to cognitive performance, which may have implications for clinical populations in whom CC morphology is atypical.

Diffusion tensor quantification of the human midsagittal corpus callosum subdivisions across the lifespan

The midsagittal corpus callosum (CC) cross-sectional area subdivisions have been used as early and sensitive markers of human brain white matter connectivity, development, natural aging and disease. Despite the simplicity and conspicuity of the appearance of the CC on anatomical magnetic resonance imaging (MRI), the published quantitative MRI literature on its regional sex and age trajectories are contradictory. The availability of noninvasive quantitative methods to assess the CC regions across the human lifespan would help clarify its contribution to behavior and cognition. In this report, we extended the utility of a recently described semi-automated diffusion tensor imaging (DTI) tissue segmentation method to utilize the high orientation contrast of the CC on DTI. Using optimized DTI methods on a cohort of 121 right-handed children and adults aged 6-68 years, we examined the CC areas and corresponding DTI metrics of the different functionally specialized sectors of the CC. Both the area and fractional anisotropy metrics followed inverted U-shaped curves, while the mean and radial diffusivities followed U-curves reflecting white matter progressive and regressive myelination dynamics that continue into young adulthood.

Application of principal component analysis to distinguish patients with schizophrenia from healthy controls based on fractional anisotropy measurements

Principal component analysis (PCA) is often used to reduce the dimension of data before applying more sophisticated data analysis methods such as non-linear classification algorithms or independent component analysis. This practice is based on selecting components corresponding to the largest eigenvalues. If the ultimate goal is separation of data in two groups, then these set of components need not have the most discriminatory power. We measured the distance between two such populations using Mahalanobis distance and chose the eigenvectors to maximize it, a modified PCA method, which we call the discriminant PCA (DPCA). DPCA was applied to diffusion tensor-based fractional anisotropy images to distinguish age-matched schizophrenia subjects from healthy controls. The performance of the proposed method was evaluated by the one-leave-out method. We show that for this fractional anisotropy data set, the classification error with 60 components was close to the minimum error and that the Mahalanobis distance was twice as large with DPCA, than with PCA. Finally, by masking the discriminant function with the white matter tracts of the Johns Hopkins University atlas, we identified left superior longitudinal fasciculus as the tract which gave the least classification error. In addition, with six optimally chosen tracts the classification error was zero.