N-methyl-D-aspartate receptors and information processing: human choice reaction time under a subanaesthetic dose of ketamine

Ketamine is an N-methyl-D-aspartate antagonist that induces cognitive dysfu nctions. The purpose of the present study was to investigate the effects of a subanesthetic dose of ketamine on human information processing, using th e additive factor method. During perfusion of a subanesthetic dose of ketam ine (0.5 mg/kg over 60 min) or a placebo (randomized double-blind, cross-ov er design), eight adults (aged 22-33, mean = 27) performed a two-choice vis ual reaction time (RT) task. Signal intensity, stimulus-response mapping, a nd foreperiod duration wens manipulated. The effects of these three variabl es were found to be additive on RT, indicating that three independent stage s - namely, stimulus preprocessing, response selection and motor selection- were manipulated. Ketamine altered RT performance in a specific way: it in teracted with foreperiod duration but its effect was additive with those of signal intensity and stimulus-response mapping. These results show that ke tamine specifically affects the stage of motor adjustment, which suggests t hat the glutamatergic system plays an important role in motor processes. (C ) 2001 Published by Elsevier Science Ireland Ltd.