The effects of intravenous diazepam and hyoscine upon recognition memory

Diazepam and hyoscine are known to have amnesic effects when administered intravenously. Nevertheless, they achieve these effects by entirely different neurochemical mechanisms, and so the question arises whether they can be differentiated in terms of their effects upon different categories of encoding operations. Sixteen normal volunteers received intravenous administrations of diazepam, hyoscine, and saline following a double-blind procedure. Both drugs completely eliminated the subjects' ability to discriminate between successive lists of words in a test of recognition memory. Moreover, both drugs also impaired the subjects' ability to reject homophones or synonyms of presented words. Thus, both diazepam and hyoscine appeared to impair the use of list tags, phonemic coding, and semantic coding in storing individual stimulus items in long-term memory.