Does the perception of reward magnitude of self-administered electrical brain stimulation have a circadian rhythm?

The locus of rise of the rate-frequency function was determined for rats at many times of day to ascertain whether the circadian fluctuations in the frequency of bar pressing for electrical stimulation of the medial forebrain bundle could be accounted for by alterations in the perceived magnitude of the reward. No evidence of circadian changes in the value of the locus of rise were detectable. These findings suggest that for self-stimulation, the endogenous circadian rhythm generating apparatus affects behavior through neural mechanisms similar to those through which motivational and arousal variables act. The animal's requirement for verity of memorial representations may underlie the lack of a circadian rhythm in the locus of rise.