Cortical high frequency oscillations reflect encoding and retrieval of specific word concepts

High gamma and ripple frequency oscillations are engaged in encoding and recall of memory traces. Tracking specific traces with their signature neural activities across time and various tasks remains a major challenge. Using intracranial electrode recordings from epilepsy patients, we detected bursts of high-frequency oscillations in response to viewing and remembering the same common nouns in two different tasks repeated on subsequent days. We found the lowest word response selectivity of approximately 40% in the visual sensory areas and increasingly higher selectivity in the more anterior associational regions. The same word sets identified as preferred in a screening task triggered selective responses in another task during visual presentation or free recall with no sensory stimulation in the same session, and on the following day. We demonstrate that persistent reactivation of large-scale neuronal assemblies underlying particular concepts is reflected in bursts of high-frequency oscillations in the human cortex.