Reward and aversive effects of lateral hypothalamic stimulation in rats measured by a modified runway and reward summation technique.

This report presents a refinement of the reward summation technique which has seen increasing use as a measure of the reward and performance factors associated with studies of the anatomical and neurochemical mechanisms of lateral hypothalamic stimulation. The technique involves determining the vigor of reward seeking behavior at a number of stimulation levels and making calculations upon this behavior/stimulation relationship. The refinement involves separating out the behavioral consequences of aversiveness which is often mixed with hypothalamic reward, particularly at high levels of stimulation. Specifically, it is shown that total running speed, the conventional measure of reward seeking behavior in a runway, is made of two components: running the runway and latency to press the reward lever. Furthermore, the latency-to-press the lever for any brain stimulation is positively correlated with latency to escape the same stimulation in an ON-OFF apparatus. Thus, latency-to-press likely is attributable to the aversiveness of the stimulation. Measuring only the first component is a more refined measure of the reward of brain stimulation.