In a replay instance, the cells are activated as if in response to the same spatial path, but at a much faster rate than the animal actually moved in.
Subsequent studies showed that large groups of cells also demonstrated this type of increased activity during sleep.
[7] These high frequency field oscillations called ripples were observed in the sleep state and later shown to play a causal role in memory consolidation.
In 1999, ten years after the initial discovery, neural recordings in the awake state were also shown to have replay activity.
[10] It is considerably more difficult to detect this activity in the awake state and several methods including Bayesian decoding have been used to quantify replay events that occur during short wave ripples.
[13] The role of replay in memory consolidation in these different conditions and environments is still being explored and several theories attempt to answer this question.
[19] This suggests that hippocampal activation during rest may have a function not only in memory consolidation and retrieval, but also in planning: it contributes to the organization of the network for improving the encoding of future events.
This hypothesis fits well with the idea that the cortex plays an integral role in memory retrieval after consolidation occurs.
Therefore, hippocampal replay may play the role of information transfer between the hippocampus and cortex, yet this idea requires further verification.
[27] In studies done to monitor the patterns of the hippocampal replay of events happening in the minds of the rats, it was discovered that they rely heavily on long term re-playable memories for their daily lives.
The chemogenetic activating drug clozapine N-oxide (CNO), but not vehicle, reversibly impairs episodic memory replay in rats previously injected bilaterally in the hippocampus with a recombinant viral vector containing an inhibitory designer receptor exclusively activated by a designer drug (DREADD; AAV8-hSyn-hM4Di-mCherry).