PHASE-DEPENDENT ORGANIZATION OF WORKING MEMORY ITEMS IN THE PRIMATE CORTEX

Abstract

Working memory is vital for reasoning, decision-making, and many higher-order cognitive processes. How the brain represents the objects in working memory remains to be understood. Neuronal activity was recorded from the lateral prefrontal cortex (PFC) and frontal eye fields (FEF) of the macaque brain as the monkey performed a working memory task, which involved remembering a target location despite the presentation of a distractor location. We show that in the macaque lPFC, the spikes of PFC neurons contained a greater amount of stimulus information (whether target or distractor) when they occurred at specific phases of PFC local field potentials (LFPs). Within beta (26 - 30 Hz) and gamma (36 - 44 Hz) LFP oscillations, maximal encoding of target information occurred at an LFP phase that was ‘later’ in the LFP cycle than the phase that encoded maximal distractor information. This phenomenon of angular separation between optimally encoding phases for target information and distractor information was also found between FEF neurons and PFC theta LFPs (6 - 10 Hz). The phase of LFP oscillations may hence play a role in scaffolding working memory content; the observed angular separation may serve to protect encoded target information from interference by encoded distractor information.