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Hippocampal replay is a phenomenon observed in rats, mice, cats, rabbits, songbirds and monkeys. During sleep or awake rest, replay refers to the re-occurrence of a sequence of cell activations that also occurred during activity, but the replay has a much faster time scale. It may be in the same order, or in reverse. Cases were also found where a sequence of activations occurs before the actual activity, but it is still the same sequence. This is called preplay. The phenomenon has mostly been observed in the hippocampus, a brain region associated with memory and spatial navigation. Specifically, the cells that exhibit this behavior are place cells, characterized by reliably increasing their activity when the animal is in a certain location in space. During navigation, the place cells fire in a sequence according to the path of the animal. 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. == Background == Place cell activity was already well established when the first study explored this phenomenon in 1989. They showed that neural activity of single place cells during sleep resembled the activity during the awake state. This activity was greater than that of other cells and this study was only the first step towards understanding replay. Subsequent studies showed that large groups of cells also demonstrated this type of increased activity during sleep. In addition, it was discovered that the order of activity of place cells was also replicated during sleep. High frequency field oscillations called ripples were observed in the sleep state and later shown to play a causal role in memory consolidation. The next step was the discovery of replay during the awake state. In 1999, ten years after the initial discovery, neural recordings in the awake state were also shown to have replay activity. 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. Recent advances include finding that replay can occur in reverse and that it has also been found to occur in different environments. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hippocampal replay」の詳細全文を読む スポンサード リンク
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