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Jeff T. Klein, Robert O. Deaner, Michael L. Platt; LIP neurons encode both social and fluid value for visual orienting. Journal of Vision 2006;6(6):743. doi: 10.1167/6.6.743.
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Recent studies suggest that neuronal activity in several brain areas reflects the expected value of fluid reinforcement associated with saccades. We sought to address the question of whether this activity is specific to particular reinforcers, or is more abstract. Monkey subjects therefore performed a choice task, in which saccades to one target (T1) were rewarded with juice, while saccades to the other target (T2) were rewarded with both juice and an image of the face or perineum of a familiar monkey. Varying the outcomes for orienting to T1 and T2 permitted us to estimate the value of orienting to social images in fluid units. We found that male subjects paid a fluid premium to view images of female perineums and the faces of dominant individuals, but were indifferent to images of subordinates. Moreover, social value was highly consistent across subjects and independent of particular images displayed. Next, we studied the activity of single neurons in area LIP and found that firing rate was modulated by both the juice value and the social value associated with T2 choices. Population analysis revealed correlations between firing rate and social value that mirrored correlations between firing rate and fluid value. We also permitted monkeys to perform single target trial blocks where social and fluid value varied independently. During single target blocks, LIP firing rate was not systematically correlated with juice or social value. These findings collectively suggest that parietal cortex carries an abstract representation of relative orienting value.
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