Low-frequency subthalamic neural oscillations are involved in explicit and implicit facial emotional processing - a local field potential study

In addition to the subthalamic nucleus (STN) role in motricity, STN deep brain stimulation (DBS) for Parkinson9s 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. We used a task that presented the patients with emotional facial expressions and manipulated the cognitive demand by either asking them to identify the emotion (explicit task) or the gender of the face (implicit task). We evaluated emotion and task effects on STN neural oscillations power and inter-trial phase consistency. Our results revealed that STN delta power was influenced by emotional valence, but only in the implicit task. Interestingly, the strongest results were found for inter-trial phase consistency: we found an increased consistency for delta oscillations in the implicit task as compared to the explicit task. Furthermore, increased delta and theta consistency were associated with better task performance. These low-frequency effects are similar to the oscillatory dynamics described during cognitive control. We interpret these findings as reflecting a greater need for cognitive control. Overall, our study suggests that low-frequency STN neural oscillations, especially their functional organization, are involved in implicit emotional processing.