Effects of the anxiolytic drugs diazepam and buspirone were studied on the reaction time of saccadic eye movements. The study was performed with 8 healthy volunteers in a double-blind, placebo-controlled way. The purpose was to investigate the putative drug effects on the first step of an attention shifting task: the disengagement of attention. Saccadic reaction time was measured in two conditions: the ‘gap’ and the ‘overlap’ condition. In the first condition a delay is present between the offset of a fixation spot and the onset of a target, while in the second condition the offset of the spot is overlapped by the onset of the target. Clear differences in saccadic reaction time in the expected direction were found between the two conditions, with longer reaction times of saccadic eye movements in the overlap condition. The nonsedative anxiolytic buspirone in a dose of 5 mg had no significant effects on saccadic reaction times, while clear effects of diazepam in a dose of 5 mg were established. Diazepam slowed down saccadic reaction times, reduced the number of fast sac-cades and facilitated the number of slow saccades. However, the effects induced by this drug were identical for the two conditions. The latter result implies that the disengagement of attention is not selectively disrupted by diazepam. Perhaps, the action of diazepam is expressed in other attention factors, such as in shifting attention or in the reengagement of attention. A slowing down of these processes by the vigilance-lowering properties of diazepam might be the cause of the prolonged latencies. The increased latencies of saccadic eye movements induced by a low dose of diazepam may have practical implications.

Effects of alertness and memory of a single dose of diazepam (10 mg) and the central stimulant methylphenidate (20 mg) were studied in healthy volunteers. It was questioned whether opposite effects of diazepam and methylphenidate are not only observed with respect to alertness but also with respect to memory. It was also questioned whether the two drugs equally affect the first (primacy) and last (recency) items in both the immediate and delayed recall of newly learned words. The experiment was performed in a double-blind, placebo-controlled way. 12 subjects were exposed to a subjective alertness scale and a verbal memory test: a 15-word test. Subjective alertness was found to be decreased after diazepam and increased after methylphenidate. Anterograde amnesia was found after diazepam in the memory test. More specifically, the primacy but not the recency effect was reduced during the immediate recall and both were reduced in the delayed recall. Methylphenidate had no effect on memory, however a ceiling effect might have obscured a putative drug effect. The results of a second experiment excluded this possibility. In all, the data demonstrate opposite effects of the two drugs on subjective alertness, suggesting opposite effects on vigilance. Opposite effects on memory were not established. This demonstrates that changes in alertness do not run in parallel with changes in memory. A scatter diagram, however, suggests a small effect of alertness on immediate recall. The effects of diazepam were also discussed in terms of the Atkinson and Shiffrin memory theory and it seems that diminished rehearsal processes are one of the key factors in explaining diazepam-induced amnesia.

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