In: Biology
How might abnormalities in lateral cortical connections produce positive symptoms in schizophrenia. Also, give specific example, and relate the example to abnormalities in cortical connections.
One of the key structural and functional abnormalities is Schizophrenia. It is a disorder of disrupted neural connectivity especially in cortical region. It is a hereditary disease. Because of the structural changes memory loss will occur. The impaired neural connection cause impaired communication between the neurons. This leads to the associated symptoms and congnitive changes.
The human brain cortex is a six-layered isocortex. Layers 2 and 4 are defined by a high density of small interneurons, ie, neurons that do not send long-ranging projections to other cortical or subcortical areas. In contrast, layers 3 and 5 are defined by a high density of pyramidal cells, which collect input through their dendrites and project to other cortical or subcortical areas. Interneurons are GABAergic cells (GABA: gamma-aminobu lyric acid) and exert an inhibitory influence on their targets (via GABAA receptors) whereas pyramidal cells are glutamatergic and have an excitatory influence. Normal cortical function depends on an intricate balance between GABAergic inhibition and glutamatergic excitation.
Neuroimaging studies have revealed dysfunctional cortical networks in schizophrenia. Regional cerebral blood flow and glucose metabolism were found to be abnormal in frontal cortex and temporal lobe structures at rest as well as during the performance of cognitive tasks. There is, however, no pattern that is diagnostic for schizophrenia. For example, frontal cortical activity at rest was found to be lower by some investigators but not by others and temporal lobe activity at rest was found' to be decreased, normal, or increased.
The clinical heterogeneity of schizophrenia might explain why schizophrenia as a whole is not associated with a pathognomonic abnormality of brain function. When the signs and symptoms of schizophrenia are used to categorize patients into two groups (positive and negative syndrome) or into distinct clusters, a more consistent pattern of neural dysfunction in schizophrenia emerges. Frontal cortex activity at rest correlates inversely with the degree of negative symptoms and left medial temporal lobe activity at rest correlates positively with the severity of psychopathology or the degree of reality distortion. Similarly, decreased frontal cortex recruitment during the performance of some cognitive tasks occurs primarily in patients with negative symptoms.
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