Subthalamic neural oscillations reveal no effect of implicit versus explicit facial emotional processing

In addition to the subthalamic nucleus’ (STN) role in motor control, STN deep brain stimulation (DBS) for Parkinson’s disease (PD) has also uncovered its involvement in cognitive and limbic processing. STN neural oscillations analyzed through local field potential (LFP) recordings have been shown to contribute to emotional (mostly in the alpha band [8-12 Hz]) and cognitive processing (theta [4-7 Hz] and beta [13-30 Hz] bands). In this study, we aimed at testing the hypothesis that STN oscillatory activity is involved in explicit and implicit processing of emotions. To achieve this objective, we used a task that presented patients with fearful emotional facial expressions and asked them to identify the emotion (explicit task) or gender associated with the face (implicit task). We evaluated emotion and task effects on STN neural oscillations power and intertrial phase consistency. Our results revealed that accuracy was lower in the implicit task. Increased STN delta power and decreased alpha and beta power were observed after stimulus presentation. However, there was no influence of emotional facial expression, i.e. neutral versus fear, nor task demands. Intertrial phase consistency in the delta and theta band increased after stimulus onset, in the same time-period as delta power increased. However, similarly to oscillatory power, no changes related to emotional fear expression or task demand were found. These findings suggest that STN oscillatory activity is not specifically involved in explicit and/or implicit processing of emotions, and that power and phase synchronization changes might be more related to overall task-execution mechanisms. These conjectures remain to be confirmed. Highlights - STN LFPs were recorded during an emotional/gender recognition task in PD patients. - STN delta power increased, and alpha and beta power decreased after stimulus onset. - Power changes were not influenced by emotional fearful expression or task demands. - Delta/theta intertrial phase consistency increased after stimulus onset. - Intertrial phase consistency was not affected by emotional valence or task demands. - The observed STN activity was likely related to general task-execution mechanisms.