Improved identification and differentiation from epileptiform activity of human hippocampal sharpwave-ripples during NREM sleep

In rodents, pyramidal cell firing patterns from waking may be replayed in NREM sleep during hippocampal sharpwave-ripples (HC-SWR). In humans, HC-SWR have only been recorded with electrodes implanted to localize epileptogenesis. Here, we characterize human HC-SWR with rigorous rejection of epileptiform activity, requiring multiple oscillations and coordinated sharpwaves. We demonstrated typical SWR in those rare HC recordings which lack interictal epileptiform spikes (IIS), and with no or minimal seizure involvement. These HC-SWR have a similar rate (~12/min) and apparent intra-HC topography (ripple maximum in putative stratum pyramidale, slow wave in radiatum) as rodents, though with lower frequency (~85Hz compared to ~140Hz in rodents). Similar SWR are found in HC with IIS, but no significant seizure involvement. These SWR were modulated by behavior, being largely absent (<2/min) except during NREM sleep in both stage 2 (~9/min) and stage 3 (~15/min), distinguishing them from IIS. This study quantifies the basic characteristics of a strictly selected sample of SWR recorded in relatively healthy human hippocampi.