Functional neuroanatomical correlates of episodic memory impairment in early phase psychosis

Abstract

Studies have demonstrated that episodic memory (EM) is often preferentially disrupted in schizophrenia. The neural substrates that mediate EM impairment in this illness are not fully understood. Several functional magnetic resonance imaging (fMRI) studies have employed EM probe tasks to elucidate the neural underpinnings of impairment, though results have been inconsistent. The majority of EM imaging studies have been conducted in chronic forms of schizophrenia with relatively few studies in early phase patients. Early phase schizophrenia studies are important because they may provide information regarding when EM deficits occur and address potential confounds more frequently observed in chronic populations. In this study, we assessed brain activation during the performance of visual scene encoding and recognition fMRI tasks in patients with earlyphase psychosis (n = 35) and age, sex, and race matched healthy control subjects (n = 20). Patients demonstrated significantly lower activation than controls in the right hippocampus and left fusiform gyrus during scene encoding and lower activation in the posterior cingulate, precuneus, and left middle temporal cortex during recognition of target scenes. Symptom levels were not related to the imaging findings, though better cognitive performance in patients was associated with greater right hippocampal activation during encoding. These results provide evidence of altered function in neuroanatomical circuitry subserving EM early in the course of psychotic illness, which may have implications for pathophysiological models of this illness.

Keywords: Cognition; Early phase psychosis; Encoding; Episodic memory; Recognition; fMRI.

Fig 1

Activation during encoding task. The control sample had significantly greater activity (scene–control) than the patient sample in left fusiform gyrus and right hippocampus. Images depict voxels significant at p<.01 in contiguous clusters of at least 110 voxels, correcting for multiple comparisons at p<.05

Fig 2

Association of hippocampus activity with Brief Assessment of Cognition in Schizophrenia (BACS) score in patients. Mean activity during encoding (Scene – Control) extracted from the significant hippocampus cluster was significantly correlated with patients' total score from the BACS

Fig. 3

Activation during Recognition task. The control sample had significantly greater activity (target–foil) than the patient sample in precuneus, posterior cingulate, and left inferior parietal lobe. Images depict voxels significant at p<.01 in contiguous clusters of at least 110 voxels, correcting for multiple comparisons at p<.05