[Self-stimulation of phylogenetically new and ancient hypothalamic structures when reinforcement schedules are changed].

The following two types of reaction are exhibited by self-stimulating rats following a transition from the regimen of preference (free) to that of fixed series of stimuli: I. increased frequency of pressings with simultaneous shortening of their duration, approaching the duration of fixed series; II. reduced frequency of pressings with their longer duration. Of the two studied hypothalamic areas, the former type of reaction is exhibited predominantly in the self-stimulation points located in the lateral hypothalamic area, while the latter type - in the lateral preoptic area. Different strategy of the animals' behaviour observed during the change of reinforcement routines is discussed with regard to different levels of integration of emotionally-positive mechanisms of brain structures of phylogenetically different age.