Platt, M. L., & Glimcher, P. W. (1999). Neural correlates of decision variables in parietal cortex. Nature, 400(6741), 233-238. http://www.nature.com/nature/journal/v400/n6741/full/400233a0.html #empirical #rate4 - [[value-based decision making]] - [[choice models]] - [[sensory-motor process]] # Idea The authors described a mathematical approach for the physiological study of the [[sensory-motor process]] and showed how the lateral [[intraparietal area]] of the macaque brain implements this model. Problem: Neurobiological models of decision making that connect sensation and action almost never propose the explicit representation of decision variables by the nervous system. They ignore the fact that neural signals can encode more than just sensory and motor signals. **The authors proposed that decision theory (decision-theoretic approach) might provide a powerful alternative framework for studying the sensory-motor process in parietal cortex (i.e., lateral [[intraparietal area]]).** Their model has two classes of inputs: * current sensory data * reflect the agent's best estimate of the current state of the salient elements of the environment * influenced by stored information that could improve the efficiency of sensory processing through selective attention * a stored representation of environmental contingencies * represent the agent's assumptions about current environmental contingencies (e.g., a class of inputs that detail how an action affects the agent) > p237. Experiment 1 indicates that both the gain expected from a particular response and the probability that a particular response will be required systematically increase the activation of neurons in posterior parietal cortex. > p237. Experiment 2 shows that when an animal is free to choose between alternative responses, the gain expected from each possible action exerts a correlated infuence on both the choice behaviour of the animal and the activation of posterior parietal neurons... These fndings support the hypothesis that the variables that have been identifed by economists, psychologists and ecologists as important in decision-making are represented in the nervous system. ## Expected gain/value modulates LIP firing rate Lateral [[intraparietal area]] (LIP) neurons fire more when more juice was delivered (black line; vs less juice, grey line). ![[Pasted image 78.png]] Expected gain (juice) correlated with LIP firing rate during early visual, late visual, and early cue periods, but not later on, suggesting a temporal shift in the information encoding—from expected value earlier on to movement made at the end of the trial. About 62.5% of neurons in the LIP were modulated by expected gain early on during a trial when decision variables are especially important for planning movement. ![[Pasted image 79.png]] ![[Pasted image 80.png]] ![[Pasted image 81.png]] ## Outcome probability modulates LIP firing rate LIP neurons fire more when outcome probability was higher (black line; vs lower, grey line). 75% of LIP neurons encoded probability information at some point during the trial. ![[Pasted image 82.png]] ## Expected gain modulates LIP activity in a free choice task ![[Pasted image 83.png]] ## Expected value (gain x probability) modulates LIP activity The authors used choice frequencies as an estimate of the subject's relative valuation of the two reinforced responses. They computed a behavioral estimate of the subjective value of a movement into the response field, based on Herrnstein's melioration theory, by computing the difference in rate of reinforcement the animal had obtained from each of the two possible choices over the preceding 10 trials. > p236. Thus, when an animal is presented with a choice between two possible saccadic gaze shifts, the animal's estimate of the relative value of these two movements is correlated with the activation of intraparietal neurons. The activation of intraparietal cortex therefore appears to reflect the decision processes animals use to guide behaviour. ![[Pasted image 84.png]] # References