Voice, gesture and working memory in the emergence of speech

Abstract

Language and speech depend on a relatively well defined neural circuitry, located predominantly in the left hemisphere. In this article, I discuss the origin of the speech circuit in early humans, as an expansion of an auditory-vocal articulatory network that took place after the last common ancestor with the chimpanzee. I will attempt to converge this perspective with aspects of the Mirror System Hypothesis, particularly those related to the emergence of a meaningful grammar in human communication. Basically, the strengthening of auditory-vocal connectivity via the arcuate fasciculus and related tracts generated an expansion of working memory capacity for vocalizations, that was key for learning complex utterances. This process was concomitant with the development of a robust interface with visual working memory, both in the dorsal and ventral streams of auditory and visual processing. This enabled the bidirectional translation of sequential codes into hierarchical visual representations, through the development of a multimodal interface between both systems.