Hippocampal contributions to value-guided foraging

Abstract

The work in this thesis tested the contribution of the hippocampus to value-guided decision making in rats. A novel paradigm for testing intertemporal decision making in rats with sensitivity to the topology of choices that animals might face in natural settings was developed and validated. Rats made sequences of accept or reject decisions between feeder sites that offered an equal amount of food after differing amounts of delay. Exponential and hyperbolic delay discounting models were inconsistent with rats' behavior on the task. However, rats performing the foraging task approached maximization of long-term food intake rates, consistent with behavioral ecology models of foraging decision making. Tetrode recordings were taken from the dorsal CA1 region of hippocampus as rats engaged in the foraging task. As rats ran trajectories between feeder locations, the spiking of place-selective hippocampal neurons was organized into temporally-structured sequences bounded by the ongoing theta frequency (6-12 Hz) local field potential oscillation. Spatial representations traced out by spiking sequences were related to animals' behavior on the task, with longer sequence representations occurring as rats ran longer trajectories through the environment, suggesting that the content of hippocampal representations depended on rats' current spatial goals. At the level of single place cells, goal-dependent modulation of sequence representations manifested as an earlier activation of place fields on long trajectories. Together, these data suggest that as behavior is executed, hippocampal ensemble representations multiplex both information about the animal's current location in space and information related to current goals.