EFFECTS OF FLUNITRAZEPAM ON RESPONSES TO LATERALIZED VISUAL-STIMULI -EVIDENCE FOR CEREBRAL ASYMMETRY OF EXECUTION OF MANUAL MOVEMENTS TO TARGETS IN CONTRALATERAL AND IPSILATERAL VISUAL SPACE

In order to examine the effects of benzodiazepines on response executi on by the left and right hemisphere, flunitrazepam (1 mg) or placebo w as administered to healthy, right handed volunteers in two separate ex periments. In experiment 1, drug was administered daily during a treat ment period of 8 days, and subjects were instructed to fixate vision c entrally and to execute laterally directed manual responses correspond ing to the position of visual stimuli presented in either the right or left hemifield. Experiment 2 was performed with a single dose and cro ss-over design, and subjects responded to the laterally presented visu al stimuli by key press of a centrally positioned response device, i.e . neither detection of position of the stimulus in space nor response selection was required before initiation of the response. In experimen t 1, intake of flunitrazepam generally increased reaction time more du ring response execution by the left as compared to the right hemispher e, and the most pronounced effect was observed on responses with the r ight hand, directed across the body axis, to visual stimuli presented in the left visual field. In contrast to these observations, in experi ment 2, flunitrazepam impaired responses with the right and left hand practically to the same extent. Together, the results indicate that be nzodiazepines may affect manual responses executed by left and right h emisphere differently, and that this asymmetry may be related to a sti mulus-response compatibility effect in tasks that require response sel ection.