F46. USING TRANSCRANIAL DIRECT CURRENT STIMULATION TO REDUCE INTERNAL NOISE AND IMPROVE VISUAL PERCEPTION IN SCHIZOPHRENIA

Abstract

Background: Prior work suggests that poor visuoperceptual discrimination and visual working memory (WM) in individuals with schizophrenia (SZ) is characterized by higher levels of model‐derived estimates of internal neural noise relative to controls (CO). However, the neural origin of internal noise remains unclear. We compared frontal versus posterior cortical involvement in the generation of internal noise during visual perception with a transcranial direct current stimulation (tDCS) paradigm. Specifically, we sought to determine whether application of anodal tDCS over posterior parietal cortex or medial frontal cortex could reduce levels of model‐estimated internal noise during visual perception and improve visual discrimination in individuals with SZ. Methods: Individuals with SZ completed three sessions of tDCS (anodal medial frontal, anodal posterior parietal, sham) on different days, with at least 48 hours between sessions. Participants were blinded to the stimulation type, and session order was randomized across participants. Each session consisted of 20‐minutes of active or sham tDCS, followed by a visual perceptual discrimination task. The perceptual discrimination task involved distinguishing orientations of briefly presented gratings (1 cycle/°; tilted ±45° from vertical) embedded in varying levels of external noise (0‐21%). Contrast thresholds were estimated, and levels of internal noise were modeled from task performance with the perceptual template model. Results: Anodal tDCS over medial frontal, but not posterior‐parietal cortex, reduces PTM‐estimated levels of internal noise during visuospatial discrimination in SZ. There was no difference in estimated internal noise levels between tDCS over posterior‐parietal cortex and sham tDCS. Preliminary analyses suggest that individuals with higher baseline contrast thresholds (sham condition) exhibit greater improvement with tDCS. Discussion: We found evidence that 20‐minutes of anodal tDCS over medial frontal cortex reduced internal noise levels during visual perception and improved visual discrimination performance in SZ. These findings suggest that heightened internal noise during visual perception in those with SZ may be partly driven by impairments in top‐down, frontally‐mediated processes that enable efficient perceptual learning. Results also suggest that anodal tDCS over posterior parietal cortex may not sufficiently reduce internal noise levels during visual perception. While future work must identify the specific mechanism of enhanced visual processing by tDCS, the current findings point to a promising, simple, and noninvasive method for improving visuoperceptual discrimination in those with SZ.