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Robert O. Deaner, Michael L. Platt; Social expectations modulate neuronal activity in parital cortex. Journal of Vision 2004;4(8):625. doi: 10.1167/4.8.625.
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Behavioral decisions reflect the expected value of available options. Recent studies suggest that neuronal activity in several brain areas also reflects the expected value of fluid reinforcement associated with eye movements. These observations raise the question of whether neuronal signals of eye movement value are specific to particular reinforcers or are more abstract. To address this issue, we first used a choice task to measure the value of orienting towards social images. On each trial, a monkey subject fixated a central yellow square. After a delay, two peripheral targets (T1, T2) were illuminated and, following the offset of the central stimulus, the monkey was free to shift gaze to either target. Gaze shifts to T1 were followed by juice delivery and gaze shifts to T2 were followed by juice delivery and the display of a social image. Across blocks of 30 trials the amount of juice delivered for shifting gaze to T1 and T2 was varied, while every 150 trials a different pool of social images was displayed at T2. Social image pools consisted of 20 frontal images of each of 12 familiar individuals or 20 posterior images of several familiar individuals. Varying the outcomes for orienting to T1 and T2 permitted us to estimate the value, in fluid units, of orienting to particular social image pools. We found that subjects consistently sacrificed large juice rewards in order to view some image pools, particularly of dominant individuals or female perineums, but required overpayment to view other image pools. Next, we studied the activity of single neurons in intraparietal cortex and found that firing rate was modulated by both the amount of juice and the social image pool that could be expected for T2 choices. Across the neuronal population, correlations between firing rate and social value mirrored correlations between firing rate and fluid value. These findings suggest that parietal cortex carries an abstract representation of orienting value.
R03-MH-66259 (MLP) and F32-MH-068128 (ROD)
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