Bilateral amygdala damage impairs the acquisition and use of common ground in social interaction.

Abstract

The development of "common ground," or mutual knowledge of shared information, is believed to require the ability to update a mental representation of another person's thoughts and knowledge based on verbal information and nonverbal social and emotional signals, to facilitate economical communication. As in other forms of everyday social communication, the development of common ground likely requires the orchestration of multiple cognitive processes supported by various neural systems. Here, we investigate the contribution of the amygdala to these processes. SM, a patient with complete, focal, bilateral amygdala damage, and deficits in social and emotional processing, and five healthy comparison participants, each interacted with a familiar partner. We investigated the participants' ability to develop and use referential labels across 24 dynamic, collaborative interactions. Participants verbally directed their partner how to arrange a set of 12 abstract tangrams while separated by a low barrier, allowing them to see each other but hiding their tangrams. In contrast to comparison participants, SM exhibited an impaired rate of learning across trials and did not show the typical simplification in the labels generated during the interactions. Detailed analyses of SM's interactional discourse and social behavior suggested that she has impaired perspective-taking or what can be interpreted as deficient "theory of mind," manifested in abnormal "language-in-use." These results support the conclusion that the amygdala, a structure critical for social and emotional processing, plays an important role in the acquisition and use of common ground and in social communication more broadly.