Ripple contributions to human memory: making the spiking content count.

Memories shape our sense of self and enable adaptive behaviour based on prior experiences, yet the neural mechanisms underlying memory formation and retrieval are not fully understood. Building on work in animal models and the unique opportunities afforded by intracranial recordings, a growing number of studies have focused on the contributions of awake ripples (transient neural oscillations 20-100 ms long in the 80-150 Hz range) to human memory. Here, we review the body of evidence linking awake ripples to human memory and highlight relevant insights as well as unresolved discrepancies between studies. On the basis of previous evidence from work in animals that ripples may provide a biomarker for bursts of underlying population spiking activity, we suggest that examining the underlying spike content of ripples may help clarify their role in human memory and resolve these discrepancies. Recent support for this notion comes from human studies that, similarly to the prior animal work, relate patterns of neuronal spiking activity to ripples. Thus, our ability to understand the role of ripples in human memory may benefit from fully understanding these spiking events.