Neural Correlates of Vocal Repertoire in Primates.

Jacob C Dunn,Jeroen B Smaers

doi:10.3389/fnins.2018.00534

Abstract

Understanding the nature of the relationship between vocal complexity and brain architecture across non-human primates may help elucidate some of the key elements underlying the evolution of human speech. Here, we report a positive correlation between vocal repertoire size and the relative size of cortical association areas (governing voluntary control over behavioural output) in non-human primates. We further demonstrate that a hominid grade shift in the relative volume of cortical association areas coincides with a similar grade shift in the hypoglossal nucleus (which is associated with the cranial nerve that innervates the muscles of the tongue). Our results support a qualitative continuity in the neural correlates of vocal repertoire, but a quantitative discontinuity in the extent to which the neural system supporting speech is innervated by cortical association areas in great apes and humans.

Highlights

Relative to humans, non-human primates produce a very limited range of vocalisations
The basic layout of the larynx and vocal tract is highly conservative and homologous in both form and function among virtually all terrestrial mammals, including humans (Fitch, 2000, 2006, 2010; Fitch and Zuberbuhler, 2013; Fitch et al, 2016). This strongly suggests that differences in vocal repertoire among primate species do not result from differences in vocal tract morphology (Fitch et al, 2016; Boë et al, 2017)
We used phylogenetic analysis of covariance (Smaers and Rohlf, 2016; Smaers and Mongle, 2018) to assess the occurrence of grade shifts among primate clades in the relative volumes of brain regions and phylogenetic generalised least squares regression analysis [pGLS; Rohlf et al (2001)] with a likelihood-fitted lambda parameter (Pagel, 1999) to test for correlations between vocal repertoire size and the relative size of brain regions

Summary

Introduction

Non-human primates (hereinafter “primates”) produce a very limited range of vocalisations. The basic layout of the larynx and vocal tract is highly conservative and homologous in both form and function among virtually all terrestrial mammals, including humans (Fitch, 2000, 2006, 2010; Fitch and Zuberbuhler, 2013; Fitch et al, 2016). This strongly suggests that differences in vocal repertoire among primate species do not result from differences in vocal tract morphology (Fitch et al, 2016; Boë et al, 2017). Despite many attempts, no non-human primate has ever been trained to produce speech sounds

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Results

Conclusion