Human memory: psychology, pathology and pharmacology

Cognitive psychologists discuss human memory in terms of the encoding processes that give rise to the internal representation of the information to be learned and in terms of the functional architecture of the system in which that information is represented. Performance in short-term memory tasks is thought to depend upon a form of working memory that consists of a central executive processor of limited capacity, together with a number of dedicated subsystems. One subsystem is a phonological store that is used to retain sequences of verbal items by means of articulatory rehearsal. Another subsystem is a visuospatial sketch-pad which retains information in the form of a spatial array. Long-term memory involves the retention of both declarative knowledge about the objects and events in the world and the procedural knowledge that underlies skilled behavior. Within the domain of declarative memory, a useful descriptive distinction is between episodic memory for particular autobiographical events and experiences, and semantic memory for general knowledge about language and the world. Disorders of memory are a frequent outcome of neurological damage and disease. A few rare cases have been described with selective disorders of verbal short-term memory, sometimes despite intact articulatory skills. Conversely, patients have been described with normal digit spans despite gross disorders of overt articulation. Selective disorders of long-term memory in the form of the amnesic syndrome are more common. In such cases episodic memory is conspicuously more impaired than either semantic memory or procedural memory. In particular, amnesic patients with frontal damage are able to acquire new knowledge but have no explicit recollection of the occasion when it was learned. The normal ageing process also involves a selective impairment of long-term memory, and especially of more effortful or abstract encoding operations, but progressive degenerative dementias tend to affect a much broader range of memory functions. Many psychoactive agents also influence learning and remembering. In particular, anticholinergic drugs disrupt the encoding of new information into long-term memory in young volunteers and mimic Alzheimer's disease in normal elderly people. The benzodiazepines also have a selective effect upon long-term storage, and this resembles the pattern of impairment found in certain amnesic disorders. The catecholamines have been implicated in Parkinson's disease and in Korsakoff's syndrome, but their role in human memory seems to be a purely extrinsic or modulatory one. The same appears to be true of neuropeptides such as vasopressin and adrenocorticotrophic hormone. A considerable amount of research has been devoted to developing pharmacological agents that might enhance memory function in neurological patients. In general, however, the effects of the drugs considered to date have been too slight and too transient to be of much therapeutic value