Amygdala Represents Diverse Forms of Intangible Knowledge, That Illuminate Social Processing and Major Clinical Disorders

Abstract

Amygdala is an intensively researched brain structure involved in social processing and multiple major clinical disorders, but its functions are not well understood. The functions of a brain structure are best hypothesized on the basis of neuroanatomical connectivity findings, and of behavioral, neuroimaging, neuropsychological and physiological findings. Among the heaviest neuroanatomical interconnections of amygdala are those with perirhinal cortex (PRC), but these are little considered in the theoretical literature. PRC integrates complex, multimodal, meaningful and fine-grained distributed representations of objects and conspecifics. Consistent with this connectivity, amygdala is hypothesized to contribute meaningful and fine-grained representations of intangible knowledge for integration by PRC. Behavioral, neuroimaging, neuropsychological and physiological findings further support amygdala mediation of a diversity of such representations. These representations include subjective valence, impact, economic value, noxiousness, importance, ingroup membership, social status, popularity, trustworthiness and moral features. Further, the formation of amygdala representations is little understood, and is proposed to be often implemented through embodied cognition mechanisms. The hypothesis builds on earlier work, and makes multiple novel contributions to the literature. It highlights intangible knowledge, which is an influential but insufficiently researched factor in social and other behaviors. It contributes to understanding the heavy but neglected amygdala-PRC interconnections, and the diversity of amygdala-mediated intangible knowledge representations. Amygdala is a social brain region, but it does not represent species-typical social behaviors. A novel proposal to clarify its role is postulated. The hypothesis is also suggested to illuminate amygdala's involvement in several core symptoms of autism spectrum disorder (ASD). Specifically, novel and testable explanations are proposed for the ASD symptoms of disorganized visual scanpaths, apparent social disinterest, preference for concrete cognition, aspects of the disorder's heterogeneity, and impairment in some activities of daily living. Together, the presented hypothesis demonstrates substantial explanatory potential in the neuroscience, social and clinical domains.

Keywords: amygdala; autism spectrum disorder; embodied cognition; intangible knowledge; paradoxical functional facilitation; perirhinal cortex.

Figure 1

Summary of the hypothesis. PRC integrates complex, multimodal, meaningful and fine-grained, distributed representations. Amygdala interconnects especially heavily and reciprocally with PRC, suggesting it contributes specialized representations for integration by PRC. Consistent with this, amygala represents such forms of intangible knowledge as valence, economic value, importance, noxiousness, social status, trustworthiness and social popularity. Taken together, it is hypothesized that amygala represents diverse forms of intangiable knowledge, that participate in distributed represntations of humans, objects and other stimuli. VTC, ventral temporal cortex; PHC, parahippocampal cortex; ERC, entorhined cortex; STS, superior temporal sulcus; OFC, orbitofrontal cortex; PRC, perirhined cortex.