Semantic processing as a neuro-cognitive endophenotype of schizophrenia
Date Issued
2015
Date
2015
Author(s)
Liu, Yun-Chung
Abstract
Introduction: Schizophrenia is characterized as a highly heritable disorder. Endophenotypes have been proposed to seek for measurable components between symptoms and genotype in schizophrenia. Disorganized speech/thought is one of the core symptoms of schizophrenia. These symptoms are related to the loosening association among concepts seen in patients with schizophrenia. However, whether semantic association is an endophenotype of schizophrenia remains unclear. We aimed to investigate the underlying neural mechanism of semantic processing in patients with schizophrenia, their unaffected siblings, and healthy controls. Methods: Functional magnetic resonance imaging (fMRI) was used to assess patients with schizophrenia (mean age = 32.9 years, SD = 5.1), their siblings (mean age = 34.0 years, SD = 6.6), and healthy controls (mean age = 33.03 years, SD = 4.9). The three groups (n = 29 each) were matched in IQ, age, and handedness (all right-handed). Participants were instructed to judge whether two Chinese characters were related in meaning while brain activation patterns were recorded. In addition, the magnitude of brain activation was correlated with scores of the WAIS-III and Positive and Negative Syndrome Scale (PANSS) to examine the relationship between brain activity and cognitive functions/symptoms of schizophrenia. Results: In the semantic judgment task, the patients showed lower accuracy rate and longer reaction time than the siblings. However, there was no difference in behavioral performance between siblings and controls. In addition, the patients showed greater activation in the left inferior frontal gyrus (IFG, BA 45) and the left middle temporal gyrus (MTG, BA 21) as compared to the siblings and controls. In contrast, the controls showed greater activation in the left inferior parietal lobule (IPL, BA 39) as compared to the other two groups. Furthermore, there was a positive correlation between the index of conceptual disorganization in the PANSS and left IFG activation in patients, as well as a negative correlation between the Digit Span score in the WAIS-III and left MTG activation in controls. Conclusions: This study reveals different biological mechanisms of semantic processing in patients and their siblings. The patients produced greater activation in left IFG/MTG, suggesting that they need more effort to retrieve semantic information and search relevant semantic representations during semantic judgments. Relative to the controls and siblings, greater activation in the patients may be treated as a state marker of schizophrenia. Moreover, the patients produced less activation in left IPL. This region is involved in higher level linguistic information integration, spatial-attentional network, and self-perception. This difference indicates that the siblings and patients may be applying a different strategy when doing the semantic judgment task. Relative to the controls, greater activation in the patients and siblings may be treated a trait marker of schizophrenia regarding semantic impairments.
Subjects
schizophrenia, semantic processing, endophenotype, fMRI
Type
thesis
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