Brain rhythms underlying intentional social coordination



Human social interaction depends on mutual exchange of information. Recently, we uncovered a brain rhythm --the phi complex-- located over right centro-parietal cortex that distinguished individual from social  behavior. In Tognoli et al (2007) the coordination between people was spontaneously induced when one person watched the other. Here we specifically instructed participants to coordinate or not in different ways. We simultaneously recorded the EEG from both members of a pair of subjects, each performing self-paced repetitive finger movements (N=12 subject pairs). Subjects sat face-to-face and a liquid crystal screen controlled when the other’s hand was visible. On seeing each other’s hand, subjects were instructed either to maintain their own pace (‘intrinsic’), or to coordinate with each other (‘inphase’ or ‘antiphase’).


The overall amplitude of phi rhythm was larger in the present intentional coordination task than in a previous spontaneous coordination task (Tognoli et al., 2007), including prior to visual contact. This suggests the recruitment of a system to monitor social interaction that remains active across the session. This system might be transiently engaged during spontaneous social coordination but sustained during intentional social coordination.


In our previous study, we hypothesized that phi was involved in the regulation of functional connectivity from intrinsic motor preparation and mirror neuron areas to the motor cortex. In agreement with this hypothesis, we found phi1 Event-Related Synchronization (ERS) during intentional intrinsic behavior and phi2 ERS during intentional inphase coordination.


During antiphase coordination, some subject’s  phi rhythm entirely vanished during visual contact while in another group of subjects phi persisted. In the latter group, stability of antiphase coordination was enhanced. While this needs further investigation, we speculate that it relates to differences between systems specialized for social behavior (embodied modes of coordination) and context-independent visuo-motor systems.


Finally, for all conditions, occipital alpha was suppressed during vision, but less completely during ‘intrinsic’ behavior than during coordinated conditions. Such differential suppression indexes visual attention allocated to the partner. [PDF].