Tuesday, April 01, 2014

Evolved music specific brain reward systems.

Perhaps the most plausible suggestion for why music is universal in human societies is that it plays a central role in emotional social signaling that could have promoted group cohesion. Clark et al. comment on new work by Mas-Herrero et al. who have now documented a group of healthy people who, while responding to typical rewarding stimuli, appear to have a specific musical anhedonia, deriving no pleasure from music even though perceiving it normally. They cannot experience the intensely pleasurable shivers down the spine or ‘chills’ that are specific to and reliably triggered by particular musical features like the resolution of tonal ambiguity. These activate a distributed brain network including phylogenetically ancient limbic, stratal and midbrain structures also engaged by cocaine and sex. Clips from Clark et al.:
The musical anhedonia found by Mas-Herreo et al. is specific for musical reward assignment, rather than attributable to any deficiency in perceiving or recognising music or musical emotions. It is rooted in reduced autonomic reactivity rather than simply cognitive mislabelling. Moreover, it is not attributable to more general hedonic blunting, because musically anhedonic individuals show typical responses to other sources of biological and non-biological (monetary) reward. The most parsimonious interpretation of the new findings is that there are music-specific brain reward systems to which individuals show different levels of access….specific brain substrates for music coding … implies that these evolved in response to some biological imperative. But what might that have been?
The answer may lie in the kinds of puzzles that music helped our hominid ancestors to solve. Arguably the most complex, ambiguous and puzzling patterns we are routinely required to analyse are the mental states and motivations of other people, with clear implications for individual success in the social milieu. Music can model emotional mental states and failure to deduce such musical mental states correlates with catastrophic inter-personal disintegration in the paradigmatic acquired disorder of the human social brain, frontotemporal dementia …Furthermore, this music cognition deficit implicates cortical areas engaged in processing both musical reward and ‘theory of mind’ (our ability to infer the mental states of other people). Our hominid ancestors may have coded surrogate mental states in the socially relevant form of vocal sound patterns. By allowing social routines to be abstracted, rehearsed and potentially modified without the substantial cost of enacting the corresponding scenarios, such coding may have provided an evolutionary mechanism by which specific brain linkages assigned biological reward value to precursors of music.
These new insights into musical anhedonia raise many intriguing further questions. What is its neuroanatomical basis? The strong prediction would lie with mesolimbic dopaminergic circuitry, but functional neuroimaging support is sorely needed.
Here is the summary from the Mas-Herrero paper:
Music has been present in all human cultures since prehistory, although it is not associated with any apparent biological advantages (such as food, sex, etc.) or utility value (such as money). Nevertheless, music is ranked among the highest sources of pleasure, and its important role in our society and culture has led to the assumption that the ability of music to induce pleasure is universal. However, this assumption has never been empirically tested. In the present report, we identified a group of healthy individuals without depression or generalized anhedonia who showed reduced behavioral pleasure ratings and no autonomic responses to pleasurable music, despite having normal musical perception capacities. These persons showed preserved behavioral and physiological responses to monetary reward, indicating that the low sensitivity to music was not due to a global hypofunction of the reward network. These results point to the existence of specific musical anhedonia and suggest that there may be individual differences in access to the reward system.

1 comment:

  1. Interesting. But I have to wonder why scientists continue using the concept of the brain's "reward system" -- which is a huge misnomer -- rather than discussing things in terms of pleasurable feelings.

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