Abnormal brain connectivity in schizophrenia : investigations into episodic memory networks

Abnormal connectivity between the prefrontal cortex (PFC) and other brain regions has been demonstrated in subjects with schizophrenia. We tested if abnormal connectivity, particularly between PFC and the medial temporal lobes (MTL), underlies the reduced brain activity and level of accuracy observed in schizophrenia subjects during episodic memory tests. We used fMRI to examine activation in fifteen chronic, medicated schizophrenia subjects and eighteen control subjects in two different recognition memory tests. The item recognition memory test required subjects to make old/new judgments, and the associative recognition memory test required them to make intact/rearranged judgments. We examined brain connectivity separately, with a structural equation modeling, based on anatomical links found in the literature. During associative recognition memory, subjects with schizophrenia failed to demonstrate the significant connectivity bilaterally between different areas of PFC and posterior MTL/fusiform regions that was observed in control subjects. However, during recognition memory of individual items, subjects with schizophrenia demonstrated significant connectivity between the anterior part of the MTL and medial PFC similar to control subjects. These findings provide evidence of a lack of proper integration between PFC and fusiform/MTL areas underlying episodic memory deficits of visual objects in schizophrenia, particularly during associative recognition memory