Coordination of human hippocampal sharpwave-ripples during NREM sleep with cortical theta bursts, spindles, downstates and upstates

Abstract

In rodents, waking firing patterns replay in NREM sleep during hippocampal sharpwave-ripples (HC-SWR), correlated with neocortical graphoelements (NC-GE). NC-GE include theta-bursts, spindles, downstates and upstates. In humans, consolidation during sleep is correlated with scalp-recorded spindles and down-upstates, but HC-SWR cannot be recorded non-invasively. Here we show in humans of both sexes that HC-SWR are highly correlated with NC-GE during NREM, with significantly more related HC-SWR/NC-GE for downstates or upstates than theta-bursts or spindles, in N2 than N3, in posterior than anterior HC, in frontal than occipital cortex, and ipsilaterally than contralaterally. The preferences interacted, e.g. frontal spindles co-occurred frequently with posterior HC-SWR in N2. These preferred GE, stages and locations for HC-SWR/NC-GE interactions may index selective consolidation activity, although that was not tested in this study. SWR recorded in different HC regions seldom co-occurred, and were related to GE in different cortical areas, showing that HC-NC interact in multiple transient, widespread but discrete, networks. NC-GE tend to occur with consistent temporal relationships to HC-SWR, and to each other. Cortical theta-bursts usually precede HC-SWR, where they may help define cortical input triggering HC-SWR firing. HC-SWR often follow cortical downstate onsets, surrounded by locally-decreased broadband power, suggesting a mechanism synchronizing cortical, thalamic and hippocampal activities. Widespread cortical upstates and spindles follow HC-SWR, consistent with the hypothesized contribution by hippocampal firing during HC-SWR to cortical firing-patterns during upstates and spindles. Overall, our results describe how hippocampal and cortical oscillations are coordinated in humans during events that are critical for memory consolidation in rodents.\n\nSignificance StatementHippocampal sharpwave-ripples, essential for memory consolidation, mark when hippocampal neurons replay waking firing patterns. In rodents, cortical sleep waves coordinate the transfer of temporary hippocampal to permanent cortical memories, but their relationship with human HC-SWR remains unclear. We show that human hippocampal sharpwave-ripples co-occur with all varieties of cortical sleep waves, in all cortical regions, and in all stages of Non-REM sleep but with overall preferences for each of these. We found that sharpwave-ripples in different parts of the hippocampus usually occurred independently of each other, and preferentially interacted with different cortical areas. We found that sharpwave-ripples typically occur after certain types of cortical waves, and before others, suggesting how the cortico-hippocampo-cortical interaction may be organized in time and space.