Effects of physostigmine on stimulus encoding in a memory-scanning task.

Previous studies of the effects of physostigmine on memory have involved other drugs, a memory that has already been impaired, or both, often with contradictory results. Also, traditional memory tests do not differentiate memory from other task components such as perception and response, and drug effects on these could be mistaken for effects on memory. The present study was designed to investigate the effects of physostigmine alone on normal memory using Sternberg's additive-factor, memory-scanning task, with additional variables to isolate effects on stimulus encoding and response stages. Sixteen volunteers participated, the design was between-groups, and physostigmine or normal saline was given, double-blind, by intravenous infusion for 70 min. The drug had no effect on the memory component of the task, but significantly improved stimulus encoding (P < 0.001). Thus, it is possible that physostigmine improves performance on memory tests by improving perception as well as, or instead of, memory.