Evidence of Activity-Silent Working Memory in Prefrontal Cortex

The lateral prefrontal cortex encodes working memory and motor preparation information, but the underlying neural mechanisms are debated. Recurrent neural network models relying on persistent neural activity have been challenged by the observation of periods of absent activity and information during memory maintenance, implying the existence of activity-silent mechanisms. To assess whether activity-silent mechanisms are needed for working memory maintenance, we recorded neural activity in macaque prefrontal cortex during a delayed-saccade task. We replicated the observation of periods of absent activity and decreased information between bursts of gamma power, but we show that these results are consistent with models that rely exclusively on persistent activity. However, an assessment of the length of periods with absent selective activity across the population revealed that activity-silent mechanisms are indeed needed to maintain memory information, although this is only evidenced in a small fraction of trials.