DIFFERENTIATING THE EFFECTS OF CENTRALLY ACTING DRUGS ON AROUSAL AND MEMORY - AN EVENT-RELATED POTENTIAL STUDY OF SCOPOLAMINE, LORAZEPAM AND DIPHENHYDRAMINE

The degree to which apparent amnesic effects of various centrally acti ng drugs are secondary to their effects on arousal remains a contentio us issue. The present study uses two methods to dissociate memory and arousal effects of the cholinergic antagonist, scopolamine (SP), and t he GABA-A/benzodiazepine receptor agonist, lorazepam (LZ). First, it c ompared their effects to those of an antihistamine, diphenhydramine (D Ph), to provide an active control for arousal reduction. Second, it us ed the same measure - event-related potentials (ERPs) - as as a parall el index of both the arousal and cognitive effects of the drugs. Fifty participants were allocated to one of five parallel treatment groups (0.6 mg SP; 2 mg LZ; 25, 50 mg DPh; placebo). ERPs were recorded durin g a continuous word recognition task as well as during an ''oddball'' task. SP, LZ and 50 mg DPh produced a similar profile of effects on ce rtain indices of arousal and on early components of ERPs. However, SP and LZ (but not DPh) produced marked impairments of episodic memory, a nd this pattern was similar to that on later components of ERPs. Memor y impairments by SP and LZ were highly significant on retention in the continuous recognition task and further, no drug effects were found o n response bias. Subsequent free recall was similarly very impaired by SP and LOR but not by the antihistamine. We conclude that benzodiazep ines and anticholinergic drugs both reduce arousal and induce amnesia, but these effects are not interdependent. Our findings provide strong evidence for a dissociation between the effects on episodic memory an d on arousal of these centrally acting compounds.