Distinct brain and behavioural states are associated with organized neural population dynamics that are thought to serve specific cognitive functions^1,2,3. Memory replay events, for example, occur during synchronous population events called sharp-wave ripples in the hippocampus while mice are in an ‘offline’ behavioural state, enabling cognitive mechanisms such as memory consolidation and planning^{4,5,6,7,8,9,10,11}. But how does the brain re-engage with the external world during this behavioural state and permit access to current sensory information or promote new memory formation? Here we found that the hippocampal dentate spike, an understudied population event that frequently occurs between sharp-wave ripples¹², may underlie such a mechanism. We show that dentate spikes are associated with distinctly elevated brain-wide firing rates, primarily observed in higher order networks, and couple to brief periods of arousal. Hippocampal place coding during dentate spikes aligns to the mouse’s current spatial location, unlike the memory replay accompanying sharp-wave ripples. Furthermore, inhibiting neural activity during dentate spikes disrupts associative memory formation. Thus, dentate spikes represent a distinct brain state and support memory during non-locomotor behaviour, extending the repertoire of cognitive processes beyond the classical offline functions.

不同的大脑和行为状态与有组织的神经群体动态相关，被认为服务于特定的认知功能^1,2,3。例如，记忆重放事件发生在海马体中称为锐波波纹的同步群体事件期间，而小鼠处于“离线”行为状态，从而实现记忆巩固和规划等认知机制^{4,5,6,7,8， 9,10,11}。但是，在这种行为状态下，大脑如何重新与外部世界接触并允许访问当前的感官信息或促进新的记忆形成？在这里，我们发现海马齿状尖峰（一种经常发生在尖波波纹之间的未被充分研究的群体事件）^可能是这种机制的基础。我们表明，齿状尖峰与明显升高的全脑放电率相关，主要在高阶网络中观察到，并且与短暂的唤醒期相关。齿状尖峰期间的海马位置编码与小鼠当前的空间位置对齐，这与伴随锐波波纹的记忆重放不同。此外，抑制齿状尖峰期间的神经活动会破坏联想记忆的形成。因此，齿状尖峰代表了一种独特的大脑状态，并支持非运动行为期间的记忆，将认知过程的范围扩展到经典的离线功能之外。