Abnormal parietal cortex activation during working memory in schizophrenia: Verbal phonological coding disturbances versus domain-general executive dysfunction

Objective: The goal of this study was to determine whether the regions of the prefrontal and parietal cortices showing abnormal activation among individuals with schizophrenia during working memory tasks are associated with either 1) phonological coding processes that may be specific to verbal tasks (i.e., ventral prefrontal and parietal cortices) or 2) domain-general executive processes engaged by verbal and nonverbal tasks (i.e., dorsal prefrontal and parietal cortices). Method: The participants were 57 medicated individuals with schizophrenia and 120 healthy subjects. Functional magnetic resonance imaging was used to scan all participants during performance of verbal and nonverbal 2-back working memory tasks. Results: In the healthy subjects there was similar bilateral dorsal prefrontal and inferior parietal cortex activation for both the verbal and nonverbal working memory tasks, but greater left ventral prefrontal and parietal cortex activation during verbal compared to nonverbal working memory. Individuals with schizophrenia showed bilateral deficits in dorsal frontal and parietal activation during both verbal and nonverbal working memory tasks. They also demonstrated the typical pattern of greater activity for verbal, as compared to nonverbal, working memory in ventral prefrontal and parietal regions, although they showed less verbal superiority in a left ventral prefrontal region. Conclusions: These results support the hypothesis that working memory deficits in individuals with schizophrenia reflect deficits in activation of brain regions associated with the central executive components of working memory rather than domain-specific storage buffers.