Investigations of Operant Conditioning of Single Unit Activity in the Rat Brain

Year: 1972

DOI: 10.7907/FQEA-6371

The aim of these studies was to show that the capacity for operant responses is distributed differentially in the brain and that such capacity is maintained in the absence of feedback from movement in specific parts of the brain. The experimental subjects were rats chronically implanted with microelectrodes for single unit recording from several different brain structures. There were three experimental paradigms. In Experiments I and II positive reinforcement was applied following bursts of activity of an arbitrarily selected unit during periods indicated by a discriminative stimulus. All such units in cerebellum and brain stem displayed significant conditioned rate increases while only about half those in hippocampus, midbrain and superior colliculus did so indicating that operant conditioning is more a property of "motor" units. Experiment II was a direct continuation of Experiment I with some of the rats which had conditioned units. The contribution of the bodily movement which seemed inevitably correlated with the conditioned unit response was determined by inducing skeletal muscle paralysis with Flaxedil. Conditioned responses were maintained under paralysis in all 5 rats with an experimental unit in the brain stem but in only one of the 6 rats with an experimental unit in the cerebellum, and none in the other 7 rats with experimental units divided among hippocampus, midbrain and superior colliculus. This indicated that the conditioned responses of most of the units were fed-back from movement which the conditioned activity of the brain stem units probably preceded. A control experiment with non-contingent reinforcement showed that these conditioned responses were probably not entirely due to operant conditioning. This ambiguity was absent in Experiment III which showed clearly operant activity. The rate of units, predominantly in the cerebellum, was increased or decreased depending upon the contingency of reinforcement. However, Experiment III used active animals and tested no units in the brain stem. A final experiment demonstrated clearly operant activity of a brain stem unit under paralysis. Reinforcement was made contingent upon rapid alternation between activity and inactivity of the unit. After acquisition, this behavior was brought under the control of a discriminative stimulus, and then maintained under paralysis, which eliminated the alternation of stereotyped movements that had been correlated with the unit activity.

(Photographic materials on pages 18, 22, 66, 68, 144, 146, and 148 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered.)