The neural activity patterns of past experiences are replayed during brief pauses in waking behaviour, suggesting a role for waking replay in memory consolidation and retrieval. The paper published online this week in Nature Neuroscience differs from previous theories that suggest that only replay during sleep is important for memory.

Loren Frank and Mattias Karlsson recorded activity from groups of neurons in the hippocampus ― a brain structure important for memory formation ― while rats were running through two different environments, and while they were resting in a chamber between their bouts of activity. They found that replay of neuronal activity that occurred in each environment was just as likely to occur while the animal was in the other environment, or even in the rest box. This suggests that replay activity in the hippocampus of rats that are awake can be independent of incoming sensory information.

Replay during waking behaviour has been observed before, but always associated with the current environment. This is the first demonstration that it could occur independently, linking it to memory processing.