Differential effects of microinjections of d-amphetamine into the nucleus accumbens or the caudate putamen on the rat's ability to ignore an irrelevant stimulus.

Latent inhibition is an attentional process by which animals learn to ignore an irrelevant stimulus. Rats received either 0 or 30 preexposures to a tone which was later used as a conditioned stimulus (CS) in a two-way avoidance task. Tone preexposure resulted in retarded conditioning (i.e., latent inhibition) in animals which received microinjections of saline or amphetamine in the caudate-putamen and for those which received microinjections of saline in the nucleus accumbens. This latent inhibition effect, however, was not present in animals which received d-amphetamine microinjections in the nucleus accumbens. The failure of CS preexposure to retard conditioning in these animals was not due to drug-induced changes in either tone or shock sensitivity. The results are discussed in terms of the role of the mesolimbic dopamine system in learning to ignore an irrelevant stimulus and the use of LI as a possible animal model of the attentional deficit that seems to characterize some subpopulations of schizophrenic humans.