Evaluating the Neurocomputational Mechanisms of Explore-Exploit Decision Making in Older Adults

The full experiment involves participants coming into the lab on five separate occasions for neuropsychological testing, a decision making battery, functional and structural MRI, and two TMS sessions for stimulation of the target or control stimulation site. The clinical trial component concerns only the last two sessions where subjects will be randomly assigned to different groups to receive different TMS interventions. In particular, the TMS experiments will ask two main questions: 1. What is the causal role of frontal pole in explore-exploit behavior in younger and older adults? 2. What is the causal role of IFG in explore-exploit behavior in younger and older adults? The investigators will use continuous theta-burst transcranial magnetic stimulation (cTBS, Huang et al. 2005) to inhibit neural activity in each region for approximately 50 minutes (Wischnewski \& Schutter, 2015) and measure the downstream effects on behavior in younger and older adults. Consistent with their respective roles in the explore-exploit circuit (Figure 5 in Research Strategy), the investigators predict that inhibition of frontal pole will lead to a selective reduction in directed, but not random, exploration, while inhibition of IFG will decrease exploitation and lead to increases in both types of exploration. Participants in each age group will be pseudo-randomly assigned to either the frontal pole group or IFG group such that the study will have 42 participants (21 males, 21 females) in each group. Thus there will be four distinct groups of subjects older frontal pole, younger frontal pole, older IFG, younger IFG. Each participant will take part in two TMS sessions, one target and one control session. The order of sessions will be counterbalanced across subjects. The primary endpoints of the study are to determine whether: 1. cTBS applied to frontal pole inhibits directed exploration within the younger and older groups 2. cTBS applied to IFG promotes both directed and random exploration within the younger and older groups The study is powered to answer these questions with 80% power at a threshold of p \< 0.05.