Human Subthalamic Nucleus Beta and Theta Oscillations Are Involved in Gating the Encoding of Memories

Introduction: Basal ganglia beta oscillations are thought to play an inhibitory role in action selection. However, whether they play a similar role in gating actions that do not involve movement remains poorly understood. We hypothesized that the same mechanisms that gate whether a movement is executed may also be involved in gating the formation of a memory.

Methods: We recorded local field potentials from the subthalamic nucleus (STN) of six Parkinson’s Disease patients (n=12 STNs) chronically implanted with the Percept battery. Our task involved two types of trials: “Target” trials in which subjects memorized a displayed letter and “Non-Target” trials, where subjects were not required to memorize the displayed letter. Crucially, subjects were informed whether the current trial was a “Target” or a “Non-Target” trial at three possible time points: Before the letter was displayed (“Proactive” trials), at the same time the letter was displayed (“Reactive” trials), and after the letter had already been displayed (“Retroactive” trials).

Results: Similar to the decrease in STN beta power that occurs when movements are executed, we observed a beta power decrease during the “Target” trials when a memory was encoded. This decrease occurred at separate time points for the “Proactive”, “Reactive”, and “Retroactive” trials, which suggests beta oscillations may act as a gate for memory encoding. We also observed a novel theta power increase when subjects were told if the current trial was a “Target” or “Non-Target” trial. This increase was significantly higher for “Target” trials and suggests theta oscillations are involved in gating the higher-level rules of the current trial.

Conclusion : We have shown that STN theta and beta oscillations are not only involved in gating motor actions, but also higher-level cognitive tasks. Future work will aim to determine whether manipulating basal ganglia activity with DBS can modulate performance on cognitive tasks.