Neural mechanisms of long-term planning

DESCRIPTION (provided by applicant): To make adaptive decisions, animals require sophisticated mechanisms for tracking the desirability, magnitude and probability of an outcome. In addition, animals must integrate outcome information over multiple time scales, and must have the capacity to orient not only toward immediate but also toward delayed rewards. For humans, nearly every decision requires some form of advance planning, on time scales that can range from relatively short (going to the store in order to get an ice cream) to the exceptionally long (investing money now in order to retire in several decades). The capacity for planning is critical for normal behavior, and impairments in this faculty can have devastating consequences. Two major psychiatric disorders - attention deficit disorder and addiction - have been associated with planning deficits and with dysfunction in frontal and parietal cortical areas. However, despite the importance of long-term planning, the underlying neural mechanisms are poorly understood. Here we address this question using a sequential decision making task in conjunction with single- neuron recording in monkey lateral intra-parietal area (LIP). The task requires monkeys to choose between two alternative strategies - a suboptimal strategy oriented toward an immediate reward, and an optimal strategy oriented toward a final (delayed) reward. While prior studies have focused on ordering and timing mechanisms during sequential actions, here we focus on the underlying decisional - action evaluation - computations. How does the brain assign value to an action, based on a future (projected) reward that only arrives after multiple intervening sensory and motor events? How does the brain distinguish between actions that are and those that are not critical for obtaining a delayed reward? And finally, how does the brain resolve inter-temporal conflict, foregoing an immediate reward in order to remain focused on the final goal? While most prior studies have focused on the frontal cortex, here we record from the parietal lobe which, together with frontal areas, is likely to be critical for advance planning. Thus the proposed experiments extend our knowledge of the decision mechanisms required for long-term planning in a broader cortical network. These studies are necessary for a mechanistic understanding of long-term planning and its breakdown during mental disorders. 1 PUBLIC HEALTH RELEVANCE: The capacity for long-term planning is critical for normal decision making. Impairments in planning are thought to be part of the etiology of psychiatric disorders, including attention deficit disorders and addiction. While studies of long-term planning have been carried out in human subjects, the underlying neuronal mechanisms remain largely unknown. The present experiment probes the mechanisms by which the brain assigns action value based on delayed, rather than immediate rewards during a sequential decision making task. The goal is to provide a detailed understanding of planning mechanisms during normal behavior and mental illness. 1