Recent insights into the neural mechanisms of decision-making have come from investigations in behavioral economics. Participants typically decide between limited numbers of options differing in probability, risk, and amount of reward (1). Despite their success in explaining the choices animals make (2, 3), the optimal foraging models of ecology have had little impact on cognitive neuroscience (4) or economics (5). The key foraging choice is usually not a binary one between currently available options; instead, it is whether or not to engage with options as they are encountered (2, 3, 5). It depends not just on (i) the value of the option encountered (encounter value) but also on estimates of (ii) the environment’s average value (search value), and (iii) the cost of leaving to forage for alternatives (search cost) (2–4). We used functional magnetic resonance imaging to examine the neural mechanisms mediating foraging.