Ramping-up hippocampal ripples and their neocortical coupling support human visual short-term memory

Abstract

Emerging evidence suggests that the hippocampus contributes to visual short-term memory (VSTM). However, the neural mechanisms through which hippocampal activity supports the maintenance of VSTM representations remain largely unknown. Here, using intracranial EEG recordings from human participants performing a delayed match-to-sample task for naturalistic objects, we investigated the role of hippocampal ripple activity--brief high-frequency oscillations associated with memory replay--in VSTM maintenance and hippocampal-neocortical communication. We found that hippocampal ripple rates progressively ramped up during the maintenance period and supported successful VSTM. More critically, hippocampal ripples were temporally coupled with the ripples in the lateral temporal lobe (LTL), and these coupled ripples were associated with memory reactivation in the LTL. These findings provide direct evidence that hippocampal-neocortical interaction via coupled ripples supports VSTM, extending the role of hippocampal ripples from long-term consolidation to short-term mnemonic processes and offering new insights into the dynamic coding mechanisms of working memory. Impact StatementHippocampal ripple ramping-up and neocortical coupling support a dynamic coding mechanism for visual short-term memory maintenance