Contextually Based Conditional Discrimination of the Rabbit Eyeblink Response

Abstract

Rabbits received conditional discrimination training using contextual stimuli to set the occasion for stimulus pairings during eyelid conditioning. Specifically, animals were exposed to either the presence or the absence of an oscillating chamber light throughout the intertrial interval (50 ± 10 s). For half the animals, this light signaled paired presentations of a discrete tone conditioned stimulus (CS) and air puff unconditioned stimulus (US) while darkness signaled presentations of only the tone CS. The remaining animals experienced the opposite contextual relationship to the conditioning stimuli. These trial types occurred pseudo-randomly across a session, with all transitions between contextual settings (i.e., light or dark) taking place immediately at the CS–US offset. Under these conditions, animals successfully utilized the contextual stimuli as conditional cues for differential responding to the shared CS. Moreover, both light and dark were equally effective as discriminative stimuli. A subset of animals received further training in which the contextual contingency was removed by restricting all conditioning to the CS-alone context. Without the contingency in place, subsequent CS presentations (paired and CS-alone) evoked equivalent conditioned responding across three sessions of training. Following the reinstatement of the contextual contingencies, discriminatory responding was immediately observed and returned to previous levels within three sessions. Finally, animals appeared to use the static representation of the conditional cue, rather than the phasic transition between cues, for discriminatory responding. These findings are discussed in terms of current neurobiological models of eyelid conditioning.