Phase/amplitude reset and theta–gamma interaction in the human medial temporal lobe during a continuous word recognition memory task

TLDR

Intracranial EEG from the medial temporal lobes of 12 epilepsy patients was recorded during a continuous word‑recognition task and analyzed with wavelet‑based methods to assess power changes, phase clustering, and mean phase relationships across frequency bands. Power changes appeared only in late ERP components (>400 ms), while early components (~190 ms) were driven by a broad‑band phase and amplitude reset involving theta, alpha, and lower beta frequencies, with stronger reset for correct rejections; additionally, gamma activity was modulated by entrained theta cycles, indicating a potential role in memory encoding and retrieval. © 2005 Wiley‑Liss, Inc.

Abstract

Abstract We analyzed intracranial electroencephalographic (EEG) recordings from the medial temporal lobes of 12 epilepsy patients during a continuous word recognition paradigm, contrasting trials of correctly recognized repeated words (hits) and correctly identified new words (correct rejections). Using a wavelet‐based analysis, we investigated how power changes and phase clustering in different frequency bands contribute to the averaged event‐related potentials (ERPs). In addition, we analyzed the actual mean phases of the different oscillations. Our analyses yielded the following results: (1) power changes contributed significantly only to the late components of the ERPs (>400 ms) (2) earlier ERP components were produced by a stimulus‐related broad‐band phase and amplitude reset of ongoing oscillatory activity about 190 ms after stimulus onset that involved not only the theta band, but also covered alpha and lower beta band frequencies (3) phase and amplitude reset occurred during an epoch of increased phase entrainment over time that lasted for about two oscillation periods for all involved frequencies and was more pronounced for correct rejections than for hits. The broad‐band phase and amplitude reset was observed for both hits and correct rejections, and therefore, did not appear to support a specific cognitive function, but rather to act as a general facilitating factor for the processes involved in this memory task. Further analyses of synchronization between oscillations and power changes in different frequency bands revealed a task‐dependent modulation of gamma activity by the entrained theta cycle, a mechanism potentially related to memory encoding and retrieval in the rhinal cortex and hippocampus, respectively. © 2005 Wiley‐Liss, Inc.