Working memory performance is tied to stimulus complexity

Abstract

1.SummaryWorking memory is the cognitive capability to maintain and process information over short periods. Recent behavioral and computational studies have shown that increased visual information of the presented stimulus material is associated with enhanced working memory performance. However, the underlying neural correlates of this association are unknown. To identify how stimuli of different visual information levels affect working memory performance, we conducted behavioral experiments and single unit recordings in the avian analog of the prefrontal cortex, the nidopallium caudolaterale (NCL). On the behavioral level, we confirmed that feature-rich complex stimuli demonstrated higher working memory performance compared to feature-poor simple stimuli. This difference was reflected by distinct neural coding patterns at the single unit level. For complex stimuli, we found a highly multiplexed neuronal code. During the sample presentation, NCL neurons initially reflected both visual and value-related features of the presented stimuli that switched to a representation of the upcoming choice during a delay period. When processing simple stimuli, NCL neurons did not multiplex and represented the upcoming choice already during stimulus presentation and throughout the delay period. It is conceivable that the maintenance of the upcoming choice in working memory was prolonged for simple stimuli due to the early choice representation. This possibly resulted in increased decay of the working memory trace ultimately leading to a decrease in performance. In conclusion, we found that increases in stimulus complexity are associated with increased neuronal multiplexing of the working memory representation. This could possibly allow for a facilitated read-out of the neural code resulting in further enhancements of working memory performance.