Task-dependent properties of brain stimulation reward

Lawful relationships established between lever-pressing and parameters of brian stimulation reward (BSR) were examined for several tasks. Task-contingent BSR was given to the same rats at identical sites using identical stimulation parameters. Lengthening stimulation duration from 100 to 300 msec increased lever-press rates. Subsequent lengthening from 400 to 800 msec decreased lever-press rates. Wheel-turning rates increased linearly with lengthening duration. The form of the response-duration function depended on current for lever-pressing but not for wheel-turning. As duration lengthened, time between responses increased systematically for the lever and was invariant for the wheel. Stimulation of the substantia nigra, posterior medial forebrain bundle, and anterior hypothalamus produced similar relations. To further examine the generality of these findings, licking and barrier-jumping were tested. Licking decreased monotonically as stimulation duration lengthened. Barrier-jumping increased from 100 to 500 msec and subsequently remained stable despite lengthening duration to 900 msec. In all tasks examined BSR was rewarding, but the form of the response-duration function depended on task characteristics. Since identical sites were stimulated, task differences cannot be attributed to neurochemical substrates. Results provide evidence for behavioral constraints on BSR.