The effects of ventromedial prefrontal cortex damage on interpersonal coordination in social interaction

Conversation is a highly interactive and coordinated effort between interactants. For example, interactants often mimic the behaviors and speech of one another and coordinate the timing of behaviors, or interactional synchrony. Despite being affected in certain neurological and psychiatric disorders, the neural mechanisms underlying these processes are not understood. The goal of this study is to understand the role of the ventromedial prefrontal cortex (vmPFC), an area of the brain involved in social and emotional behavior, for interpersonal coordination, including mimicry and interactional synchrony. To test the role of the vmPFC for mimicry, normal comparison (NC), brain damaged comparison (BDC), and participants with vmPFC damage interacted in two sessions with a research assistant (RA) who was performing a target behavior (1st session: nodding, 2nd session: face touching). The amount of time the participants spent nodding or touching their face in each session was recorded. NC and BDC participants tended to mimic the partner and nodded slightly more in the session in which the RA was nodding, and touched their face slightly more in the session in which the RA was touching their face. In contrast, vmPFC patients showed no difference in their behaviors in either session, suggesting that they were not influenced by the partner's behaviors and did not mimic them. In a second experiment, all of the above participant groups had a naturalistic conversation with an unfamiliar interactional partner. The conversational data were analyzed for numerous aspects of interpersonal coordination, including convergence of number of words, words per turn and backchannels, reciprocity of self-disclosures, the use of questions, interactional synchrony, and a time series analysis of response latency and speech rate. The vmPFC participants performed consistently worse than NC participants on convergence of words and words per turn, self-disclosures and asking questions. All brain-damaged participants were impaired on aspects of interactional synchrony, and no conclusive results were found for the time series analysis of response latency and speech rate. This study provides support for the hypothesis that the vmPFC is important for interpersonal coordination as the vmPFC group differed significantly from the NC group on the majority of the analyses. The final goal of this study was to understand the effects of traumatic brain injury (TBI) on interpersonal coordination. TBI patients participated in all of the experiments described above and preliminary results showed that they also seemed to be impaired on the mimicry task, and they performed slightly worse than NC participants on many of the interpersonal coordination analyses of the conversational data. This suggests that TBI also does seem to affect certain aspects of interpersonal coordination.