Brain correlates of social cognition and interaction

Abstract

Although humans spend a considerable amount of their time in interaction with other people, brain activity has mostly been studied in artificial and simplified settings without real social interaction. However, such conditions are not optimal for understanding how the brain really processes complex and often non-recurring information that arises during interaction with other people. This Thesis probes the brain basis of social observation and live interaction by studying how subtle facial movements (eye blinks) affect the brain activity of the viewer, and how brain rhythms, especially the rolandic mu rhythm, behave during natural conversation. Magnetoencephalography (MEG) was used to track the brain activity of the healthy adults. The results showed that the brain of the viewer responds to observed eye blinks, even if the blinks are embedded in other auditory and visual information (e.g. while watching someone telling a story). Brain responses to eye blinks remained equally fast and strong even when the blink video was considerably slowed down to 38% of the original speed. Moreover, the strength of the brain responses to eye blinks correlated positively with the empathy of the viewers. These findings indicate that even facial movements that often go unnoticed are relevant social cues and affect the brain activity of the viewers in an empathy-related manner. For studies of live social interaction, we developed a dual-MEG system. Using this new setup, we recorded MEG from 9 pairs of healthy adults during natural conversation. The sensorimotor cortex was activated in a left-hemisphere-dominant manner when the subjects were speaking, indicated by the suppression of rolandic mu-rhythm both in 10- and 20-Hz frequency bands. The power of the 10-Hz mu rhythm increased transiently 1–3 s before the end of previous speaker's turn, suggesting that the subjects predicted the turn changes to prepare for their own turns. The results of this Thesis broaden the knowledge about how different aspects of social interaction, ranging from perceiving trivial facial movements to turn changes in conversation, modulate the brain activity of the interacting participants.