Effects of lorazepam on rate of forgetting, on retrieval from semantic memory and on manual dexterity.

Using a double-blind procedure, 16 out of 32 volunteer subjects (students) each took 2.5 mg of lorazepam (Ativan) orally and the remainder took a placebo. To overcome the problem of wide variation in individual tolerance to the drug, impairment on a task unrelated to memory (a manual dexterity task) was used to divide drug subjects into a group appreciably affected by the drug, subgroup 1, and a group minimally affected, subgroup 2. Only subgroup 1 showed consistent impairment of episodic memory. Both subgroups showed some impairment in a semantic memory task (generation of words from a specified category), but this was confined to the rate at which the task was carried out. The main aim of the experiment was to examine the effect of lorazepam on the rate of forgetting of word lists when drug and control subjects' initial recall levels were equalized. There was no evidence that the drug affected rate of forgetting: this suggests that it does not affect retention. There was also no evidence that it affected retrieval, since there was no impairment in the recall of material presented before administration of the drug. Hence its locus of action is attributed to input, specifically to impaired encoding of contextual information.