Behavioral and Neural Mechanisms of Patch Foraging

Abstract

Serial stay-or-search decisions, in which one must choose to stick with a current resource or to search for a new, potentially better one, are ubiquitous across many domains. These decisions have been studied extensively in patch-foraging paradigms, in which animals, including humans, decide to stick with a depleting reward within a ”patch,” or to leave the current ”patch” to search for a new one yielding greater rewards, but that comes at the cost of time and effort spent traveling to the new ”patch.” A variety of animals, ranging from invertebrates to birds to mammals, generally follow predictions of the optimal foraging theory, particularly the Marginal Value Theorem (MVT; Charnov, 1976), but animals have the tendency to overharvest, or stick with the depleting reward longer than is predicted by MVT. Common biases in intertemporal choice, such as decreasing marginal utility for larger rewards or discounting of future reward, have been hypothesized as the cause of overharvesting, but there have been few direct tests of whether these biases influence foraging behavior. From a neural perspective, multiple brain regions that contribute to stay-or-search decisions have been identified, including the anterior cingulate cortex (ACC), which is hypothesized to monitor the difficulty in deciding to stay vs. search, and the locus coeruleus (LC), which is hypothesized to regulate the decision process. This thesis extends knowledge of the behavioral and neural mechanisms of stay-or-search decisions. In Chapter 2, I describe a novel, operant chamber based patch foraging for rats. Similar to other animals, rats follow qualitative predictions of MVT: they stay longer in patches that yield greater rewards, and longer in all patches when the cost of traveling to a new patch is greater, but overharvest, staying patches longer than is predicted by MVT. In Chapter 3, I thoroughly characterized rat foraging behavior across a series of experiments: these revealed that in the context of foraging, rats exhibit time preferences similar to delay discounting paradigms, and that suboptimal decision making in foraging and delay discounting tasks is best explained by hyperbolic discounting. In Chapter 4, I begin to examine the neural mechanism of foraging decisions, investigating the role of the LC. Stimulation of LC-NE neurons impaired rats ability to focus on salient information in the task and impaired their ability to perform the task in general. In Chapter 5, I examine the function of the anterior cingulate. Rat ACC neurons increased in activity as rewards in a patch depleted and animals were more likely to leave patches. However, manipulation of ACC activity revealed that ACC was neither necessary for adaptive foraging decisions nor sufficient to drive decisions to leave patches. Altogether, these studies contribute to our knowledge of how animals make foraging decisions from a behavioral and neural perspective.