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 A new imaging technique called diffusion tensor imaging (DTI) is a type of magnetic resonance imaging (MRI) that is being used to assess specific brain areas for cognitive deficits. Various domains of cognition in schizophrenia have been studied and the most pronounced deficits are typically evident on measures of working memory, verbal memory, and learning and executive functions that serve to guide action and thought. According to an article in Neuropsychology, Paul G. Nestor, PhD and colleagues at Boston Veterans Affairs Health Care System-Brockton Division, Harvard Medical School, and University of Massachusetts-Boston, point out that "these various patterns of neuropsychological decline appear to have a relatively stable course and are not attributable to medication or changes in personality, motivation, or transient mental state. Rather, these neuropsychological deficits are thought to represent a central and enduring characteristic of the disease or what might be considered a signature disturbance in processing of information, elements of which might even predate illness onset."
DTI uses a regular MRI machine to analyze the movement of water molecules in and around the fibers that connect different parts of the brain. Neuroscientists use DTI to track indicators of brain "connectivity" - factors such as the number, thickness, density and arrangement of axons and thickness of the insulating/conducting fatty myelin sheath in which they are embedded. If weaker structural integrity reduces connectivity, then it could quite possibly mean that, different brain areas do not communicate as well and with less synchrony or harmony. This is described as being similar to an orchestra playing out of synch.
The researchers conducted neuropsychological tests on 41 patients with schizophrenia and 46 healthy controls, and used DTI scans on a 14-person subset of people with schizophrenia and healthy controls. Brain images from the schizophrenic patients showed abnormalities in two functionally and anatomically different neural pathways - the uncinate fasciculus (UF) and the cingulate bundle (CB). Compared with age-matched controls, patients had smaller UF and CB. These bunches of axons are wrapped in myelin sheaths and bundled like electrical wire. The UF connects different parts of the frontal and temporal lobes and the CB connects parts of the prefrontal-cingulate regions. Each of these fiber tracts may help to define distinct neural networks. These fibers allow different parts of the brain are able to communicate.
The high-tech scans support the concept of schizophrenia as a serious cognitive disorder whose diverse symptoms rest in diverse anatomical differences which, consistent with the current findings, are based in neural fiber networks. Symptoms may result not from faults in single "components" but rather from differences in webs of neural connections. For example, a smaller UF bundle might not do as well in orchestrating important signals related to verbal processes, such as using words to organize thoughts. Neural networks are known to contribute to a wide range of cognitive functions and there is a correlation between fiber-tract size and cognitive problems.
Cognition requires a complex interaction of different brain areas working in harmony. These researchers are delving into some of the more subtle differences and they are evaluating the neural connections that participate in the brain's communication system.
Technical Paper on diffusion tensor imaging (pdf)
A Primer on Diffusion Tensor Imaging of Anatomical Substructures
Neurosurgical Focus (from Medscape)
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