A Comparison of Two Methods Designed to Rapidly Estimate Thresholds of Rewarding Brain Stimulation
Four experiments evaluated the relative merits of two procedures for rapidly estimating thresholds of rewarding brain stimulation. In the first method termed autotitration, rats earned brain stimulation by pressing a lever, and the stimulation became progressively weaker in pulse frequency with continued responding. The depression of a second Lever restored the stimulation to its original strength. In the second protocol or timed method, rats worked through the same descending sequence of frequencies and eventually quit responding but, here, they had no control over resets of stimulation; resets were automatically triggered at timed intervals by the equipment. Experiment 1 showed that autotitration consistently produced higher reset thresholds than the threshold estimates of the timed method. The second experiment showed that autotitration’s reset thresholds climbed when the stimulation sequence began at twice the customary frequency but that thresholds derived from the timed method remained at control levels with this double-frequency test. Reset thresholds from autotitration were found in Experiment 3 to be strongly influenced by changes in only the first frequency of the sequence, but this manipulation had no effect on timed-method estimates. Finally, the last experiment illustrated how autotitration might miss or seriously underestimate the effect of a pharmacological treatment. Together, these data suggest that resets made in autotitration are influenced by the value of the reinforcer made available immediately after the reset but that the alternative, timed method, is free of this problem.
KeywordsDepression Dopamine Morphine Cocaine Catecholamine
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- de Groot, J. (1959). The rat brain in stereotaxic coordinates. Amsterdam: N. V. Noord-Hollandsche Uitgevers.Google Scholar
- Gardner, E. L. (1971). An improved technique for determining brain reward thresholds in primates. Behavior Research Methods and Instrumentation, 3, 273–274.Google Scholar
- Neill, D. B., Gaar, L. A., Clark, A. S., & Britt, M. D. (1982). “Rate-free” measures of self-stimulation and microinjections: Evidence toward a new concept of dopamine and reward. In B. G. Hoebel & D. Novin (Eds.), The neural basis of feeding and reward (pp. 289–297). Brunswick, ME: Haer Institute.Google Scholar
- Neill, D. B., & Justice, J. B., Jr. (1981). An hypothesis for a behavioral function of dopaminergic transmission in nucleus accumbens. In R. B. Chronister & J. F. DeFrance (Eds.), The neurobiology of the nucleus accumbens (pp. 338–347). Brunswick, ME: Haer Institute.Google Scholar
- Stein, L. (1961). Inhibitory effects of phenothiazine compounds on self-stimulation of the brain. Diseases of the Nervous System, 22(Suppl.), 1–5.Google Scholar
- Stein, L. (1962). Effects and interactions of imipramine, chlorpromazine, reserpine, and amphetamine on self-stimulation: Possible neurophysiological basis of depression. In J. Wortis (Ed.), Recent advances in biological psychiatry (pp. 288–308). New York: Plenum Press.Google Scholar