Abstract

Animals will work vigorously for electrical stimulation delivered to the medial forebrain bundle. The activity thus elicited is believed to mimic the effects of naturally rewarding stimuli, such as food and sex. This thesis tests a model of performance for this rewarding electrical stimulation. The proportion of time allocated to self-stimulation activities is evaluated with respect to the subjective intensity and opportunity cost of rewards. The 3D surface that comes from assessing self-stimulation performance based on the pulse frequency and stimulation price of a rewarding train of brain stimulation can then be used to determine the stage at which a given manipulation contributes its effects to reward processing. The pulse frequency determines the intensity of the rewarding effect of the stimulation; the amount of time an animal must invest in harvesting each reward controls the price. Previous attempts to validate a model of performance for rewarding brain stimulation relied on the assumption that an animal's preference for self-stimulation activities is revealed by the testing situation. The present thesis provides evidence that rat preferences are constructed by the testing situation much like human beings' preferences. Presenting animals with randomized test trials of varying price-frequency pairs provides a solution that minimizes the systematic biases to which the testing situation contributes. This improved methodology was used to validate that the model can correctly detect the effect of manipulations that act prior to the output of the spatio-temporal integrator that summates the activity elicited in primary reward neurons by the electrical stimulation.