SENSORY INTEGRATION & WORKING MEMORY

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To produce meaningful behavior, the brain must link information represented in sensory cortex to motor circuitry involved in the planning and execution of behavior. We have discovered that neurons in the association cortex of the parietal and frontal lobes respond during a complex visual task in a manner that suggests they play a role in establishing the linkage between sensory information and behavioral intention. These same neurons are known to contribute to short-term memory and the guidance of spatial attention. We have discovered that these neurons represent the conversion of visual motion information toward a perceptual decision and plan of action. We have trained monkeys to judge the direction of moving dots viewed on a video monitor. By controlling the difficulty of the task we can induce errors and thereby dissociate sensory information from a perceptual decision. We have found neurons in association cortex whose response predicts the monkey's decision abou t di rection. In the past year, we have discovered that the neural response evolves in a time frame that accompanies formation of the decision, and predicts the moment of commitment to a judgment. These insights have inspired a computer model of the decision process. If successful, the model will account for neural computations from visual processing to behavior. We have hypothesized that the link between sensory input and behavior might depend on the expectation of reward. Results from two monkeys indicate that neurons in the frontal lobe are affected by the anticipated size of a reward. The experiments have begun to reveal the computations performed by neurons in association cortex, lending novel insight into the neurobiology of cognition and its disorders. We are optimistic that our results will lead to new understanding and treatment of such pernicious disorders as Alzheimer's disease, encephalopathy, and stroke. FUNDING NIH grants RR00166 and EY11378 and a grant from the McKnight Foundation. Shadlen, M.N. and Newsome, W.T. The variable discharge of cortical neurons implications for connectivity, computation and information coding. J Neurosci 18, 3870-3896, 1998. Leon, M.I. and Shadlen, M.N. Exploring the neurophysiology of decisions. Neuron 21, 669-672, 1998. Leon, M.I. and Shadlen, M.N. Modulation of dorsolateral prefrontal cortex neurons by varying expectations of reward magnitude. Soc. Neurosci. Abstr. 24, 1425, 1998. Mazurek, M.E. and Shadlen, M.N. Statistical properties of weakly-correlated neural ensembles. Soc. Neurosci. Abstr. 24, 2095, 1998. Roitman, J.D. and Shadlen, M.N. Response of neurons in area LIP during a reaction-time direction discrimination task. Soc. Neurosci. Abstr. 24, 262, 1998.