Abstract
The value of an object acquired by a particular action often determines the motivation to produce that action. Previous studies found neural signals related to the values of different objects or goods in the orbitofrontal cortex, while the values of outcomes expected from different actions are broadly represented in multiple brain areas implicated in movement planning. However, how the brain combines the values associated with various objects and the information about their locations is not known. In this study, we tested whether the neurons in the dorsolateral prefrontal cortex (DLPFC) and striatum in rhesus monkeys might contribute to translating the value signals between multiple frames of reference. Monkeys were trained to perform an oculomotor intertemporal choice in which the color of a saccade target and the number of its surrounding dots signaled the magnitude of reward and its delay, respectively. In both DLPFC and striatum, temporally discounted values (DVs) associated with specific target colors and locations were encoded by partially overlapping populations of neurons. In the DLPFC, the information about reward delays and DVs of rewards available from specific target locations emerged earlier than the corresponding signals for target colors. Similar results were reproduced by a simple network model built to compute DVs of rewards in different locations. Therefore, DLPFC might play an important role in estimating the values of different actions by combining the previously learned values of objects and their present locations.
Highlights
During decision making, outcomes expected from different actions are evaluated along multiple dimensions, including various properties of the object targeted by each action and the cost of acquiring it
We have shown that such behaviors were relatively well accounted for by a temporal discounting model, in which the value of the reward from each target is determined by the product of the reward magnitude and a temporal discount function (Kim et al, 2008; Hwang et al, 2009)
We found that the signals related to the difference in the discounted values (DVs) for left and right targets tended to appear in the dorsolateral prefrontal cortex (DLPFC) before the signals related to the position (C) and color (C∗) of the target chosen by the animal, and before the signals related to the difference in the DVs of the reward chosen by the animal and the other reward (Figure 6A; Kolmogorov– Smirnov test, p < 0.05, in all cases)
Summary
Outcomes expected from different actions are evaluated along multiple dimensions, including various properties of the object targeted by each action and the cost of acquiring it. We tested whether the activity of each neuron was modulated by the difference in the DVs for left and right targets or by their difference for red (large reward) and green (small reward) targets, using the following model, S = a0 + a1∆DVLR + a2∆DV LRG + a3∆DVCU + a4DVsum + a5C + a6C ∗, (model 1)
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