Consciousness Blog 13 February 2016


It is scarcely news by now that the appreciation of music as expressed in dance and song was a very early capacity of the human brain, possibly or even probably predating semantic speech, and that comparable capacities exist in other animals, but it has been difficult to pin down musical appreciation to distinct regions of the brain in humans, let alone in other animals. The relationship of musical understanding and expression to consciousness is obscure, while language is a tool that is intricately bound up with consciousness. Arguably, self-aware consciousness as experienced by humans would not be possible without linguistic capability.

Recent research has however begun to elucidate the neural processes that are involved in human appreciation of music. Published in Neuron, Volume 88, Issue 6, p1281–1296, 16 December 2015, an article 'Distinct Cortical Pathways for Music and Speech Revealed by Hypothesis-Free Voxel Decomposition', by Sam Norman-Haigner, Nancy G. Kanwisher and Josh H. McDermott, of the Massachusetts Institute of Technology, reports on the identification of distinct cortical pathways for speech and music in the auditory cortex. Previous work by the same team reported in The Journal of Neuroscience in 2013, also using fMRI scanning, had identified specific regions of the auditory cortex that respond exclusively to clearly pitched harmonic tones, known as 'resolved' tones, as distinct from pure frequency-based 'noise'. In a normal human, the process of harmonic resolution is carried out within the cochlea, so that input to the auditory cortex is 'resolved' where that is neurally feasible.

Through a crowd-based survey, the researchers identified 165 sound clips of two seconds each, representing a thorough overview of types of sound input, including speech and music, and observed the fMRI response to this range of sounds in human subjects. The experiment resulted in the identification of clearly distinct regions of the auditory cortex for speech and music. "This analysis revealed six components," say the researchers, "each with interpretable response characteristics despite being unconstrained by prior functional hypotheses. Four components embodied selectivity for particular acoustic features (frequency, spectrotemporal modulation, pitch). Two others exhibited pronounced selectivity for music and speech, respectively, and were not explainable by standard acoustic features."

The research supports the idea, obvious to many commentators, that music and rhythm had a role in socialization from very early on in evolution: you have only to think of bird-song or whale-song, and mating rituals in numerous animal species. Darwin wrote in The Descent of Man and Selection in Relation to Sex: "the males sometimes pay their court by dancing, or by fantastic antics performed either on the ground or in the air. With birds of paradise a dozen or more full-plumaged males congregate in a tree to hold a dancing-party, as it is called by the natives: and here they fly about, raise their wings, elevate their exquisite plumes, and make them vibrate, and the whole tree seems, as Mr. [Alfred] Wallace remarks, to be filled with waving plumes…One observer, who kept several pairs alive, did not doubt that the display of the male was intended to please the female."

Musical harmonies and rhythm are two different things, of course, and it is not clear that many or any pre-human species combined them into dance as we understand it, although some bird species seem to come close to it; but what is clear is that when groupish behaviour came along, it enlisted music and dance as means of strengthening the bonds between group members. One stream of research would have it that the combination of musical and motor skills that is required for dancing arose in human and bird species because both are 'vocal learners', whereas pre-human primates had relatively unsophisticated vocal skills. However that theory does not sit well with plentiful research showing an abundance of 'CV's (conspecific vocalizations) in non-human primates, see e.g. Pascal Belin, Voice processing in human and non-human primates, Philos Trans R Soc Lond B Biol Sci. 2006.

So while the jury is still out as regards the 'chicken-and-egg' problem of whether groupishness drove the emergence of dancing among humans, or whether it pre-existed among primates, there is at least no doubt that music-specific circuitry in the auditory cortex is of very ancient origin.


Read more in Chapter Three of Agent Human by Michael Bell,
The Evolution of Social Consciousness in Humans.


 

The material contained on this site is the intellectual property of M G Bell and may not be reproduced, transmitted or copied by any means including photocopying or electronic transmission, without his express written permission.