Do monkeys dream about food while sleeping?

Abstract

Can we tell what animals are dreaming about from their brain activity? This fascinating question has been explored extensively using the rodent hippocampus, where place cells are sequentially reactivated during sleep, consistent with replay of paths explored while awake. However, dreams involve vivid visual experiences, and whether analogous replays occur in the visual cortex has not been explored, that too in primates. To address this gap, we performed wireless neural recordings from the high-level visual (IT) and motor regions (PMv, PFC) in two monkeys while they viewed food images on a screen while awake, and afterwards while they slept in their natural setting. Decoders trained on sleep/wake neural activity in each region were able to accurately predict the ongoing sleep/wake state, as well as upcoming transitions between states. Interestingly, decoders trained to categorize neural responses to food (but not faces/objects) showed increased probability during REM-like sleep compared to NREM or awake states. Thus, behaviorally relevant visual stimuli seen while awake are reactivated during REM-like sleep. In other words, these monkeys saw food, faces and objects while awake, and dreamt selectively about food while sleeping.