Gating of Human Theta Oscillations by a Working Memory Task

TLDR

Electrode grids on the cortical surface of epileptic patients enable high‑temporal‑spatial resolution recordings, and prior work showed intermittent large‑amplitude theta during maze navigation, but its relation to spatial versus working‑memory components was unclear. The study aimed to determine whether theta oscillations occur during a nonspatial working‑memory task. This was investigated by recording neural activity while subjects performed the Sternberg working‑memory task. The recordings revealed event‑related theta exhibiting a cognitive gating pattern—amplitude surging at trial onset, persisting through all phases including the delay, and dropping sharply at trial end—whose duration scaled with trial length and suggests theta may organize multi‑item working memory.

Abstract

Electrode grids on the cortical surface of epileptic patients provide a unique opportunity to observe brain activity with high temporal–spatial resolution and high signal-to-noise ratio during a cognitive task. Previous work showed that large-amplitude theta frequency oscillations occurred intermittently during a maze navigation task, but it was unclear whether theta related to the spatial or working memory components of the task. To determine whether theta occurs during a nonspatial task, we made recordings while subjects performed the Sternberg working memory task. Our results show event-related theta and reveal a new phenomenon, the cognitive “gating” of a brain oscillation: at many cortical sites, the amplitude of theta oscillations increased dramatically at the start of the trial, continued through all phases of the trial, including the delay period, and decreased sharply at the end. Gating could be seen in individual trials and varying the duration of the trial systematically varied the period of gating. These results suggest that theta oscillations could have an important role in organizing multi-item working memory.