Brain stimulation as a cue for event-related potentials in rat cortex: amphetamine effects.

Slow potential (SP) responses were recorded bilaterally from the frontal cortex of rats with permanently implanted silver-silver chloride electrodes. Trials were presented at variable intervals from 15 to 50 sec and the interval between the pulse cue and onset of the rewarding train was 2 sec. The cue stimulus was a single 0.5 msec monophasic square wave pulse of the same current intensity as rewarding stimulation (100 Hz, 500 msec train). Appropriate current strength was determined by prior testing for self-stimulation. The single pulse by itself failed to evoke an SP response but after repeated pairings, large negative SP responses developed which were bilaterally equal. These responses extinguished rapidly when rewarding stimulation was discontinued. d-Amphetamine (0.125, 0.25 and 0.5 mg/kg, SC) produced a dose-related depression of the SP response to the pulse cue, an effect comparable to that observed using an auditory cue with either food or MFB stimulation reinforcement. The results indicate that frontal cortex SP responses which develop in anticipation of a meaningful event do not require a peripheral sensory cue. Furthermore, amphetamine suppression of these SP responses is not produced via a disruption of the auditory system.