Figure 1.

Stages of memory processing inferred from the results of neuropharmacological experiments. Depicted are two trials of any standard learning paradigm: (a) acquisition training and (b) retention testing. Pharmacological interventions before acquisition can potentially affect a range of sensory, perceptual, attentional, motivational and motor performance factors, in addition to learning and memory processes. To rule out the nonspecific factors that affect learning and memory per se, it is usually necessary to compare the effects on performance that is previously established (e.g. after a single trial of training as in the retention test). A lack of effect on retention indicates a specific effect on learning or memory-related processes such as encoding or memory consolidation. A lack of effect on initial training in acquisition accompanied by an effect on retention usually indicates a specific effect on memory consolidation or retrieval. The post-trial manipulations administered after the acquisition trial (e.g. in the home cage) cannot affect simple performance factors during the acquistion trial but do affect the hypothetical processes of memory consolidation. The time-limited nature of consolidation means that post-trial treatments soon after the first trial will affect memory consolidation, indicated by performance in the retention test, typically 1–7 days later. However, ineffective post-trial treatments at later time-points than immediate post-trial indicate the temporally limited nature of the consolidation process and rule out proactive effects of post-trial treatments themselves on the retention test. Working memory is an active process of memory that is usually engaged soon after perceptual processing to encode memory traces into passive storage. However, memories that are re-activated by memory cues also place retrieval memory traces into an active form in working memory for the guidance of behaviour (see [8,28] for further details).