Spatiotemporal patterns of neocortical activity around hippocampal sharp-wave ripples

Abstract

Keywords 19Hippocampus, neocortex, hippocampal-cortical interaction, memory consolidation, sharp-wave 20 ripple, multi-unit activity, wide-field mesoscale optical imaging, local field potential, head-21 restrained sleep 22 23 24 25Abstract 26A prevalent model is that sharp-wave ripples (SWR) arise 'spontaneously' in CA3 and 27 propagate recent memory traces outward to the neocortex to facilitate memory consolidation 28 there. Using voltage and extracellular glutamate transient recording over widespread regions of 29 mice dorsal neocortex in relation to CA1 multiunit activity (MUA) and SWR, we find that the 30 largest SWR-related modulation occurs in retrosplenial cortex; however, contrary to the 31 unidirectional hypothesis, neocortical activation exhibited a continuum of activation timings 32 relative to SWRs, varying from leading to lagging. Thus, contrary to the model in which SWRs 33 arise 'spontaneously' in the hippocampus, neocortical activation often precedes SWRs and may 34 thus constitute a trigger event in which neocortical information seeds associative reactivation of 35

Multiple memories can be simultaneously reactivated during sleep as effectively as a single memory

“…However, studies exploring the timescale for reactivation in TMR suggest that at least some aspects of reactivation occur seconds after cue onset (e.g., EEG activity seconds after onset encompasses stimulus-related information and predicts memory benefits 35,41 ; cuing benefits are eliminated if reactivation is disrupted <~1 s after onset 42,43 ). These results are complemented by evidence from animal studies showing a cortico-hippocampal-cortical loop for spontaneous (i.e., not cuedriven) reactivation lasting several hundreds of milliseconds 44,45 . Taken together, these findings suggest that the full cycle of reactivation may last substantially longer than replay expressed by the hippocampal neuronal ensemble.…”

Miniaturized head-mounted microscope for whole-cortex mesoscale imaging in freely behaving mice

“…As a final demonstration, we used the mini-mScope to measure dynamic changes in extracellular glutamate release in the cortex during transition from wakefulness to natural sleep. Much of the previous work studying extracellular glutamate release has been done using fixed-potential amperometry 27 , or optical imaging in head-fixed mice 28 . Inducing sleep in head-fixed mice is challenging and typically requires sleep deprivation which can alter the overall sleep structure and patterns of rapid eye-movement (REM) and non-REM (NREM) sleep 29 , 30 .…”

Learning offline: memory replay in biological and artificial reinforcement learning

“…Techniques have been developed to penalise, limit, or freeze weight changes in the network that were important for one task when learning a new additional task. For example, with elastic weight consolidation, the learnt connections that are important for one task but not another can be restricted to limit weight changes, ensuring that new learning is encoded by a different set of connections in the same network [84]. To some degree this resembles the largely non-overlapping cortical neuronal representations that are enforced when successive tasks are learnt in quick succession, which has been shown to prevent interference [85], although this is not characteristic of hippocampus [86], and over longer timescales and larger spatial scales 'representational drift' achieves a similar effect by different mechanisms [80].…”