Stimulation parameters influence response involvement in reinforcing brain stimulation.

Rats pressed a lever for brain stimulation in the start box of a T-maze. Pulse trains of stimulation were available under various temporal schedules. Periods of self-stimulation (SS) alternated with intervals of experimenter-administered stimulation (EAS) during which identical stimulation was automatically delivered at the same average rate as during SS periods. Rats could terminate the on going EAS by traversing the maze and making a turn into the correct arm, thereby reinstating the availability of a SS period. Experiments 1 and 2 demonstrated that manipulations of either the intertrain interval or the train duration, which are parameters that regulate the temporal density of stimulation, influenced the latency to terminate intervals of EAS. Experiment 3 showed that omitting the stimulation during the EAS period of the standard SS-EAS cycle disrupted the resetting behaviour of the experienced rats. They required as many sessions as naive rats to learn the behaviour required to circumvent the EAS-free period. The data suggest that the behaviour patterns exhibited are dependent upon the buildup of activity that is largely influenced by the total neural activity summated across pulse train(s) of stimulation. The behaviour to terminate the EAS occurs as a consequence of an aversive effect which is concurrently produced by the rewarding stimulation. This aversive effect is attenuated by responding.