Reduction of latent inhibition by D-amphetamine in a conditioned suppression paradigm in humans

The sensitivity of latent inhibition (LI) to amphetamine has been tested in humans with a paradigm close to the conditioned emotional response suppres sion currently used in experimental animals. The conditioned stimulus (CS) was a tone, the unconditioned stimulus (US) a strong white noise, and the r esponse a transient delay in a regular sequence of hand movements in the re solution of the Tower of Toronto puzzle. The aim of this study was to verif y whether the previously reported, disruptive effect of CS preexposure on c onditioning really represents LI, by examining its sensitivity to amphetami ne. Three groups of healthy volunteers received placebo, 5 or 10 mg of dexa mphetamine sulphate, respectively, in a double-blind experimental design. T he preexposure, conditioning and test phases were carried out under either amphetamine or placebo. The non preexposed groups treated with amphetamine were not different from the non preexposed placebo group, indicating that a mphetamine did not affect conditioning. Among the preexposed groups, those receiving 10 mg of amphetamine showed normal rates of conditioning, whereas those treated with either 5 mg of amphetamine or placebo showed LI. Simila r results have been reported in experimental animals. This sensitivity to a mphetamine suggests that the present paradigm may be used to study LI in hu mans. (C) 2000 Elsevier Science B.V. All rights reserved.