The temporal structure of motivation II: Determinants of reinforcement patterns in the local organization of intracranial reward.

When rats and other animals are permitted chronic and continuous access to intracranial reinforcement (intracranial self-stimulation (ICS)) they typically display episodic response patterns (bursts). The motivational determinants of response bursts are not known; however, previous studies have pointed to the importance of priming effects in ICS. To further investigate the role of priming in ICS bursts adult male Sprague-Dawley rats were allowed chronic (minimally 2-week) access to ICS, with bursts collected for a subsequent 10-day period. Analysis of burst patterns indicated (a) relatively higher initial response rates were associated with longer bursts, (b) rates of response generally increased within individual response bursts, and (c) higher initial rates were associated with bursts that persisted in contrast to those which did not. In addition, a tonic reinforcement effect was found in the analysis of overnight records. Several burst parameters were increased in the final vs the initial 2 hr of responding. The first three findings support a role for priming as one determinant of burst patterns. The final effect may point to a second mechanism involved in incentive seeking.