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The Journal of Neuroscience, April 5, 2006, 26(14):3731-3744; doi:10.1523/JNEUROSCI.5159-05.2006

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Behavioral/Systems/Cognitive
A Biophysically Based Neural Model of Matching Law Behavior: Melioration by Stochastic Synapses

Alireza Soltani and Xiao-Jing Wang

Volen Center for Complex Systems and Department of Physics, Brandeis University, Waltham, Massachusetts 02454

Correspondence should be addressed to Xiao-Jing Wang at the above address. Email: xjwang{at}brandeis.edu

In experiments designed to uncover the neural basis of adaptive decision making in a foraging environment, neuroscientists have reported single-cell activities in the lateral intraparietal cortex (LIP) that are correlated with choice options and their subjective values. To investigate the underlying synaptic mechanism, we considered a spiking neuron model of decision making endowed with synaptic plasticity that follows a reward-dependent stochastic Hebbian learning rule. This general model is tested in a matching task in which rewards on two targets are scheduled randomly with different rates. Our main results are threefold. First, we show that plastic synapses provide a natural way to integrate past rewards and estimate the local (in time) "return" of a choice. Second, our model reproduces the matching behavior (i.e., the proportional allocation of choices matches the relative reinforcement obtained on those choices, which is achieved through melioration in individual trials). Our model also explains the observed "undermatching" phenomenon and points to biophysical constraints (such as finite learning rate and stochastic neuronal firing) that set the limits to matching behavior. Third, although our decision model is an attractor network exhibiting winner-take-all competition, it captures graded neural spiking activities observed in LIP, when the latter were sorted according to the choices and the difference in the returns for the two targets. These results suggest that neurons in LIP are involved in selecting the oculomotor responses, whereas rewards are integrated and stored elsewhere, possibly by plastic synapses and in the form of the return rather than income of choice options.

Key words: matching behavior; reward-dependent stochastic Hebbian learning; lateral intraparietal cortex; melioration; decision making; dopamine

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Received Dec. 3, 2005; revised Jan. 26, 2006; accepted Feb. 17, 2006.

Correspondence should be addressed to Xiao-Jing Wang at the above address. Email: xjwang{at}brandeis.edu

This article has been cited by other articles:

				H. Seo, D. J. Barraclough, and D. Lee Dynamic Signals Related to Choices and Outcomes in the Dorsolateral Prefrontal Cortex Cereb Cortex, September 1, 2007; 17(suppl_1): i110 - i117. [Abstract] [Full Text] [PDF]

				Y. Loewenstein and H. S. Seung Operant matching is a generic outcome of synaptic plasticity based on the covariance between reward and neural activity PNAS, October 10, 2006; 103(41): 15224 - 15229. [Abstract] [Full Text] [PDF]

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