Abstract
Numerous studies have shown that the lateral prefrontal cortex (LPFC) plays a major role in both visual perception and working memory. While neurons in LPFC have been shown to encode perceived and memorized visual stimulus attributes, it remains unclear whether these two functions are carried out by the same or different neurons and population activity patterns. To systematically address this, we recorded the activity of LPFC neurons in macaque monkeys performing two similar motion direction match-to-sample tasks: a perceptual task, in which the sample moving stimulus remained perceptually available during the entire trial, and a memory task, in which the sample disappeared and was memorized during a delay. We found neurons with a wide variety of combinations of coding strength for perceived and memorized directions: some neurons preferentially or exclusively encoded perceived or memorized directions, whereas others encoded directions invariant to the representational nature. Using population decoding analysis, we show that this form of mixed selectivity allows the population codes representing perceived and memorized directions to be both sufficiently distinct to determine whether a given direction was perceived or memorized, and sufficiently overlapping to generalize across tasks. We further show that such population codes represent visual feature space in a parametric manner, show more temporal dynamics for memorized than perceived features, and are more closely linked to behavioral performance in the memory than the perceptual task. Our results indicate that a functionally diverse population of LPFC neurons provides a substrate for discriminating between perceptual and mnemonic representations of visual features.