Volumetric abnormalities in connectivity-based subregions of the thalamus in patients with chronic schizophrenia.

OBJECTIVE: The thalamus, which consists of multiple subnuclei, has been of particular interest in the study of schizophrenia. This study aimed to identify abnormalities in the connectivity-based subregions of the thalamus in patients with schizophrenia. METHODS: Thalamic volume was measured by a manual tracing on superimposed images of T1-weighted and diffusion tensor images in 30 patients with schizophrenia and 22 normal volunteers. Cortical regional volumes automatically measured by a surface-based approach and thalamic subregional volumes measured by a connectivity-based technique were compared between the two groups and their correlations between the connected regions were calculated in each group. RESULTS: Volume reduction was observed in the bilateral orbitofrontal cortices and the left cingulate gyrus on the cortical side, whereas in subregions connected to the right orbitofrontal cortex and bilateral parietal cortices on the thalamic side. Significant volumetric correlations were identified between the right dorsal prefrontal cortex and its related thalamic subregion and between the left parietal cortex and its related thalamic subregion only in the normal group. CONCLUSIONS: Our results suggest that patients with schizophrenia have a structural deficit in the corticothalamic systems, especially in the orbitofrontal-thalamic system. Our findings may present evidence of corticothalamic connection problems in schizophrenia.

Prenatal cocaine exposure: long-term deficits in learning and motor performance.

We have developed a rabbit model of in utero exposure to intravenous injections of cocaine given twice daily to dams from gestational days 8-29. At the doses employed (4 mg/kg, injected twice daily), no differences were found in the body weight gain of dams, time to delivery, litter size, and body weight or other physical characteristics of the offspring. However, cocaine-exposed pups displayed an abnormal structural and neurochemical development of the anterior cingulate cortex which persisted into adulthood. In agreement with the known functions of the anterior cingulate cortex, we found that adult, sexually mature rabbits, exposed to cocaine prenatally, demonstrate impairments in motor function, alterations in associative learning and severe impairments in discrimination learning. Moreover, the alterations in discrimination learning were interpreted to be due to deficits in attentional processes. Specifically, cocaine progeny preferentially attend to more salient stimuli even when these are not relevant to the task. Consequently they have difficulty in attending to less salient but relevant stimuli when more salient but irrelevant stimuli occur in the same context. We concluded that the learning deficits are a reflection of the morphologic and neurochemical abnormalities of the anterior cingulate cortex. Alterations in dopamine function of the caudate nucleus may also contribute to the deficits in motor performance.