Effects of haloperidol and amisulpride on motor and cognitive skill learning in healthy volunteers

The effects of a typical neuroleptic, haloperidol (1 and 2 mg orally), of an atypical neuroleptic, amisulpride (50 and 100 mg) and of a placebo on motor and cognitive skill learning were assessed in 60 healthy volunteers using repeated testing on the Tower of Toronto puzzle. Subjects were asked to solve three blocks of eight trials and, at distance from drug administration, a fourth block. The puzzle was connected to a computer in order to obtain a precise timing of individual moves. Two components of cognitive skill learning were assessed, the ability to learn to solve the puzzle and the acquisition of a problem-solving routine. Subjective feelings of effort and automatisation of the task were assessed using a questionnaire. Like placebo-treated subjects, neuroleptic-treated subjects were able to acquire a motor skill, to learn to solve the puzzle and to acquire a routine. However, haloperidol 2 mg-treated subjects needed significantly more moves to solve the puzzle in blocks 3 and 4, some of them having routinised a non-optimal solution. A significant cognitive slowing was observed in the haloperidol 1 mg group in block 4. The performance pattern and verbal reports suggested that haloperidol impaired the higher cognitive functions such as the ability to shift from one strategy to another and/or to assess one's performance accurately, possibly leading to the development of compensatory strategies. The only deleterious amisulpride effect was a cognitive slowing in block 4, which was observed in the lower dose group.