FORAGING FOR BRAIN-STIMULATION - TOWARD A NEUROBIOLOGY OF COMPUTATION

The self-stimulating rat performs foraging tasks mediated by simple co mputations that use interreward intervals and subjective reward magnit udes to determine stay durations. This is a simplified preparation in which to study the neurobiology of the elementary computational operat ions that make cognition possible, because the neural signal specifyin g the value of a computationally relevant variable is produced by dire ct electrical stimulation of a neural pathway. Newly developed measure ment methods yield functions relating the subjective reward magnitude to the parameters of the neural signal. These measurements also show t hat the decision process that governs foraging behavior divides the su bjective reward magnitude by the most recent interreward interval to d etermine the preferability of an option (a foraging patch). The decisi on process sets the parameters that determine stay durations (duration s of visits to foraging patches) so that the ratios of the stay durati ons match the ratios of the preferabilities.