The differential amnesic effects of lorazepam and diazepam

There have been many attempts to classify the functions of human memory. A broad classificatory scheme that is currently in use is the division of memory into explicit and implicit memory. Explicit memory refers to the conscious retrieval of information relating to previous experiences (Schacter et al., 1993). This form of memory is assessed using tasks involving the explicit recall (immediate or delayed) of information that has been learned in an earlier study phase. Implicit memory is responsible for the retrieval of stored information without subjective awareness of the source of information (Donlon et al., 1993). One of the most common functions of implicit memory is priming. A number of experimental variables have been used to demonstrate the distinction between implicit and explicit memory. These include shifts in sensory modality between study and test phases (Berry & Dienes, 1991), changes in the surface characteristics of stimuli (Roediger & Blaxton, 1987), varied retention intervals (Tulving et al., 1982) and manipulation of the level of encoding of target items during a study phase (Roediger et al., 1992). The dissociation between explicit and implicit memory has also been demonstrated in studies involving the administration of benzodiazepines. These have found that benzodiazepines impair performance on explicit memory measures, such as recall and recognition. (Danion et al., 1989, Fang et al., 1987, File et al., 1992, Danion et al., 1992). These investigations focused primarily on the administration of either lorazepam or diazepam. When implicit memory measures are involved in benzodiazepine studies, it is generally reported that implicit memory is not affected by the drugs. Studies have found that priming remains intact after the ingestion of diazepam (Danion et al., 1989, Fang et al., 1987, Danion et al., 1992). However, priming is significantly reduced when lorazepam is administered (Knopman, 1991, Danion et al., 1992, Brown et al., 1989). This review will examine the organisation of memory, particularly the divisions and functions of explicit and implicit memory. It will also explore the current evidence of the effects of benzodiazepines on these aspects of memory.