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The white matter connections between the midbrain dopamine neurons and the striatum are part of a neural system involved in reward-based learning, a process that is impaired in patients with schizophrenia. The striato-nigro-striatal (SNS) tract, which participates in this process, has not as yet been explored. The present study aimed to use diffusion MRI (dMRI) to delineate the SNS tract, and to compare the application of two dMRI measures, Tract Dispersion (TD), an index of white matter morphology, and Fractional Anisotropy (FA), an index of white matter integrity, to detect group differences between patients with chronic schizophrenia (CSZ) and healthy controls (HC). dMRI scans were acquired in 22 male patients with CSZ and 23 age-matched HC. Two-tensor tractography was used in addition to manually-delineated regions of interest to extract the SNS tract. A mixed-model analysis of variance was used to investigate differences in TD and FA between CSZ patients and HC. The associations between TD and behavioral measures were also explored. Patients and controls differed significantly in TD (P = 0.04), but not in FA (P = 0.69). The group differences in TD were driven by a higher TD in the right hemisphere in the CSZ group. Higher TD correlated significantly with poorer performance in the Iowa Gambling Task (IGT) when combining the scores of both groups. The findings suggest that dysconnectiviy of the SNS tract which is associated with schizophrenia, could arise from abnormalities in white matter morphology. These abnormalities may potentially reflect irregularities in brain development.

In schizophrenia, abnormalities in structural connectivity between brain regions known to contain mirror neurons and their relationship to negative symptoms related to a domain of social cognition are not well understood. Diffusion tensor imaging (DTI) scans were acquired in 16 patients with first episode schizophrenia and 16 matched healthy controls. FA and Trace of the tracts interconnecting regions known to be rich in mirror neurons, i.e., anterior cingulate cortex (ACC), inferior parietal lobe (IPL) and premotor cortex (PMC) were evaluated. A significant group effect for Trace was observed in IPL-PMC white matter fiber tract (F (1, 28) = 7.13, p = .012), as well as in the PMC-ACC white matter fiber tract (F (1, 28) = 4.64, p = .040). There were no group differences in FA. In addition, patients with schizophrenia showed a significant positive correlation between the Trace of the left IPL-PMC white matter fiber tract, and the Ability to Feel Intimacy and Closeness score (rho = .57, p = 0.034), and a negative correlation between the Trace of the left PMC-ACC and the Relationships with Friends and Peers score (rho = remove -.54, p = 0.049). We have demonstrated disrupted white mater microstructure within the white matter tracts subserving brain regions containing mirror neurons. We further showed that such structural disruptions might impact negative symptoms and, more specifically, contribute to the inability to feel intimacy (a measure conceptually related to theory of mind) in first episode schizophrenia. Further studies are needed to understand the potential of our results for diagnosis, prognosis and therapeutic interventions.

Characterization of the default mode network (DMN) as a complex network of functionally interacting dynamic systems has received great interest for the study of DMN neural mechanisms. In particular, understanding the relationship of intrinsic resting-state DMN brain network with cognitive behaviors is an important issue in healthy cognition and mental disorders. However, it is still unclear how DMN functional connectivity links to cognitive behaviors during resting-state. In this study, we hypothesize that static and dynamic DMN nodal topology is associated with upcoming cognitive task performance. We used graph theory analysis in order to understand better the relationship between the DMN functional connectivity and cognitive behavior during resting-state and task performance. Nodal degree of the DMN was calculated as a metric of network topology. We found that the static and dynamic posterior cingulate cortex (PCC) nodal degree within the DMN was associated with task performance (Reaction Time). Our results show that the core node PCC nodal degree within the DMN was significantly correlated with reaction time, which suggests that the PCC plays a key role in supporting cognitive function.

We examined variability in performance on widely-used neuropsychological Wechsler tests of intelligence and memory in a large sample of persons with chronic schizophrenia, a subset of whom had also undergone prior studies of magnetic resonance imaging (MRI) of the orbital frontal cortex (OFC) gray matter and diffusion tensor imaging (DTI) of the cingulum bundle (CB) and the uncinate fasiculus (UF) white matter. In comparison to controls, persons with schizophrenia showed lower scores across neuropsychological tests, with most pronounced drops in processing speed and immediate memory, in relation to oral reading. For patients, greater declines in intelligence and memory each correlated with reduced CB white matter fractional anisotropy and reduced OFC gray matter, respectively. However, only memory decline correlated with severity of negative symptoms. Taken together, these data raise the intriguing question as to whether communication and motivational deficits expressed in negative symptoms may contribute to the relationship of auditory memory decline and OFC volume observed in this patient sample.

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

The current report used structural magnetic resonance imaging (MRI) to objectively measure olfactory bulb volume and olfactory sulcal depth in patients diagnosed with chronic schizophrenia and healthy controls. Additional measures were obtained to assess olfactory function. The olfactory bulb and sulcus were manually traced on structural 3T MRIs for 25 right-handed male patients diagnosed with chronic schizophrenia and 25 matched male healthy controls. A sub-set of subjects received the University of Pennsylvania Smell Identification Test (UPSIT). Olfactory bulb volume was significantly decreased in patients with schizophrenia compared to healthy controls, as was their performance on the UPSIT. Additionally, a positive correlation was seen in patients between right bulb volume and UPSIT scores. Overall, our findings support earlier research studies showing morphometric and functional changes in the olfactory system in patients with schizophrenia.