Dopamine manipulations limited to preexposure are sufficient to modulate latent inhibition.

Four experiments are reported that demonstrated that dopamine (DA) transmission is involved in the acquisition of latent inhibition (LI) of a conditioned taste aversion. LI refers to weaker conditioning as a consequence of nonreinforced preexposure (PE) of the future conditioned stimulus. Although it is known to depend on DA transmission during the conditioning phase, it is usually thought that the cognitive processes involved in the establishment of LI (during the PE phase) are DA independent. Either amphetamine (AMPH; 0.5 or 1.0 mg/kg) or haloperidol (HAL; 0.1 mg/kg) were injected before 1 or all of the 3 PE sessions. AMPH blocked the acquisition of LI if it was injected before each or before only the last PE session and HAL potentiated LI.