23/05/19
When engaging in joint actions, we need to continuously monitor our partner’s movements and to predict their possible outcomes. Recent findings from our research group showed that motor interactions requiring moment-to-moment adaptation to other’s actions elicit EEG signatures related to error monitoring (i.e. enhancement of midfrontal Theta (4-7 Hz) power (MFθ), particularly when the interaction partner is less predictable. We will present results from a sham-controlled, between-subjects study that explored the causal role of MFθ on behavioral adjustment during motor interactions by means of transcranial alternating current stimulation (tACS). After undergoing a resting-state EEG session that aimed at determining their individual frequency from their Alpha peak, participants received in two separate blocks, either Theta and Sham or Beta and Sham tACS over their centro-frontal (FCz) and centro-parietal (Pz) scalp while coordinating their movements with those of a virtual partner in a fully immersive Virtual Reality environment. The joint task required participants to control the behavior of a 1PP avatar synchronously press buttons with a Virtual Partner (VP) in order to turn on a lightbulb. Participants used a joystick with a forward motion and two buttons to make their avatar press two separate target buttons (purple or yellow) with either index or middle finger. In the Cued condition participants were instructed to press one of the two targets (e.g. the yellow button), while in the Interactive condition they had to perform an imitative (if the VP presses the purple button, the participant had to press the purple button) or complementary (if the VP presses the purple button, the participant had to press the yellow one) movements. In both conditions, the success of the task (i.e. turning on the lightbulb) depended on the ability of participants to synchronize their pressing time with respect to the ones of the VP. Importantly, in both conditions in 30% of the trials the VP suddenly changed his target halfway (i.e. from yellow to purple), thus calling for a motor adaptation only in the Interactive condition. Results indicate a frequency-specific and task-specific modulation of tACS on movement time. Specifically, Theta tACS increased (while Beta decreased) the duration of movements only in the Interactive condition and this effect was stronger in those trials were a motor adaptation after VP’s change was required. We will discuss these results along with results from exploratory analysis of EEG functional connectivity using Graph Theory parameters and their relationship with frequency-related stimulation effects.
Speaker’s Corner:
Lennie Dupont - New PhD student presentation
Prof. Matteo Candidi - Sapienza Grants for PhDs and post-docs.