PROJECT SUMMARYWhether it's choosing between dinner locations health plans or investment vehicles for our savings manydecisions involve a tradeoff between exploring options that are unknown and exploiting options we know well.Making such explore-exploit decisions correctly i.e. in such a way as to maximize long-term gain issurprisingly difficult and mathematically optimal solutions are intractable in most cases. Despite this difficultywe have recently shown that young people make remarkably effective explore-exploit decisions using amixture of two strategies: directed exploration in which information seeking drives exploration by choice andrandom exploration in which adaptive behavioral variability drives exploration by chance. Despite thisprogress little is known about how directed and random exploration are implemented in the brain and almostnothing is known about how these strategies change with age. Given the ubiquity of these decisions in dailylife this is a critical omission if we are to understand decision making in aging and cognitive decline.The objective of this proposal is to develop and test a neurocomputational model that describes explore-exploitdecision making throughout the lifespan. In this model we propose that the overall balance betweenexploration and exploitation is set by activity in a specific set of brain areas. Our central hypothesis is that age-related changes in explore-exploit behavior can be accounted for by age-related changes in this circuit. To testthis hypothesis we will pursue three Specific Aims that test key predictions of this neurocomputational modelas it applies to healthy aging. Aim 1 will test the behavioral predictions of this model by characterizing theexplore-exploit behavior of a large sample of healthy older and younger adults. Aim 2 will map the brain areasinvolved in directed and random exploration using functional and structural magnetic resonance imaging.Finally in Aim 3 we will manipulate directed and random exploration using transcranial magnetic stimulation toperturb neural firing in key areas of the explore-exploit network.The proposed research is innovative as the first to study directed and random exploration in older adults thefirst to probe the neural correlates of these strategies and the first to manipulate explore-exploit behavior inolder adults with transcranial magnetic stimulation. In addition by testing the predictions of the circuit modelthis work will build towards a neurocomputational account of explore-exploit behavior. This model will havesignificant impact on our understanding of decision making in old age and provide a framework forunderstanding how these decisions change with cognitive decline and Alzheimer's disease. Finally if oursingle-session TMS manipulations are successful we will open the possibility of using multi-session neuralstimulation to enhance explore-exploit decision making in cases where it is impaired.