The Underlying Mechanism of Disorganized Thought in Schizophrenia
Date Issued
2012
Date
2012
Author(s)
Chen, Pin-Jane
Abstract
Purpose: Thought disorder is one of the core symptoms of schizophrenia that relates to cognitive deficits. However, the underlying neural mechanism is not well understood. The present study aimed at exploring the symptom dimension of disorganized thought in schizophrenia by investigating the spatial properties of neural correlates of thought disorder and related cognitive dysfunctions underlying semantic processing. Methods: Functional magnetic resonance imaging (fMRI) was used to investigate the underlying mechanism of disorganized thought for 25 patients with schizophrenia in Experiment 1, and for 22 patients with schizophrenia and 22 healthy controls in Experiment 2. The correlation between the symptom severity of disorganized thought and the neural activity in related brain regions was examined. Verbal measures were used to evaluate individual difference on neural correlates of thought disturbance in the patients. Results: In Experiment 1, greater activation was found in the left inferior frontal gyrus (LIFG, BA 45) and the left inferior temporal gyrus (LITG, BA 20) for the semantically related condition. Moreover, increasing disorganization scores were correlated with greater activation in these two regions for the semantically related condition. In Experiment 2, for the semantically related condition, as compared with the controls, the patients showed significant activation in LIFG and LITG, as well as reduced activation in left caudate nucleus (LCN). In addition, effective connectivity from Dynamic Causal Modeling (DCM) showed that the top-down modulatory effect from LIFG to LITG was stronger in controls while the bottom-up modulatory effect from left fusiform gyrus (LFG, BA37) to LITG was stronger in patients. Also, the modulatory effect from LCN to LIFG was weaker in patients than in controls. Furthermore, there was a trend of negative correlation between disorganized thought and connectivity strength from LCN to LIFG. Finally, there was a positive correlation between disorganized thought and significant activation in LIFG/LITG. There was a negative correlation between verbal sub-items in the WAIS verbal scale and significant activation in LITG in patients. Conclusion: In patients with schizophrenia, the severity of disorganized thought and the verbal-related cognitive deficits may be related to greater activation in the left frontal and temporal region, implying the increased demands on retrieval or selection through aberrant semantic networks. In addition, the weaker top-down modulatory effect from LIFG to LITG, the weaker inhibitory effect from LCN to LIFG, and a trend of negative correlation between disorganized thought and connectivity strength from LCN to LIFG imply a disrupted cortical-subcortical language loop for semantic processing in patients. In contrast, the stronger bottom-up modulatory effect from LFG to LITG in patients implies that they have to rely more on the direct mapping from orthography to semantics in order to counteract the deficits on the top-down connection.
Subjects
fMRI
semantic
thought disorder
disorganization
schizophrenia
Type
thesis
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