2013年4月3日水曜日

Effort and Valuation in the Brain: The Effects of Anticipation and Execution


Irma T. Kurniawan, Marc Guitart-Masip, Peter Dayan, and Raymond J. Dolan
J. Neurosci. 2013;33 6160-6169
http://www.jneurosci.org/cgi/content/abstract/33/14/6160?etoc

Neural representations of the effort deployed in performing actions, and the valence of the outcomes they yield, form the foundation of action choice. To discover whether brain areas represent effort and outcome valence together or if they represent one but not the other, we examined these variables in an explicitly orthogonal way. We did this by asking human subjects to exert one of two levels of effort to improve their chances of either winning or avoiding the loss of money. Subjects responded faster both when exerting greater effort and when exerting effort in anticipation of winning money. Using fMRI, we inspected BOLD responses during anticipation (before any action was executed) and when the outcome was delivered. In this way, we indexed BOLD signals associated with an anticipated need to exert effort and its affective consequences, as well as the effect of executed effort on the representation of outcomes. Anterior cingulate cortex and dorsal striatum (dorsal putamen) signaled the anticipation of effort independently of the prospect of winning or losing. Activity in ventral striatum (ventral putamen) was greater for better-than-expected outcomes compared with worse-than-expected outcomes, an effect attenuated in the context of having exerted greater effort. Our findings provide evidence that neural representations of anticipated actions are sensitive to the expected demands, but not to the expected value of their consequence, whereas representations of outcome value are discounted by exertion, commensurate with an integration of cost and benefit so as to approximate net value.

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