Electrical brain stimulation as a Pavlovian conditioned inhibitor

Abstract

Rabbits received differential conditioning in a Pavlovian conditioned inhibition pardigm utilizing electrical brain stimulation (ESB) as CS-. The reference response was the nictitating membrane reflex elicited by electric shock to the infraorbital region of the eye. A 1200 Hz tone served as the reinforced CS, and a compound consisting of the same tone plus ESB was the nonreinforced CS. The major findings from a series of three experiments were as follows: (a) ESB served as a true conditioned inhibitor when inhibitory potential was assessed in summation and retardation tests and contrasted with pseudoconditioned inhibition controls; (b) the effectiveness of ESB as a conditioned inhibitor was not related to locus (hypothalamus, lateral geniculate, medial geniculate nucleus) of stimulation; and (c) tests of stimulus generalization following conditioned inhibition training indicated that concurrent ESB lowered the (concave downward) generalization gradient along the audiofrequency dimension. The fact that concurrent ESB did not eliminate or invert the gradient suggests that the 1200 Hz tone retained its excitatory potential in the presence of the inhibitory CS. These findings were related to a hierarchial neuronal model of inhibitory stimulus control.