Haloperidol enhances latent inhibition in visual tasks in healthy people.

We have previously shown that 0.5 mg haloperidol (i.v.) increased latent inhibition in one of two visual tasks. The present study analysed the effects of a higher dose of haloperidol (1.0 mg, i.v.) on latent inhibition in these two visual tasks in healthy volunteers in a randomised controlled trial. In the task where 0.5 mg haloperidol had enhanced latent inhibition, 1.0 mg had the same effect, thus replicating the previous result. In the task where 0.5 mg haloperidol had been ineffective, 1.0 mg haloperidol enhanced latent inhibition in high schizotypal subjects only. This indicates that subjects with higher schizotypy scores are more sensitive to dopamine blockade. A comparison of the results from the studies at the two different doses suggests a dose dependence of haloperidol's effects on latent inhibition that parallels results from animal work.