Theoretical emphasis tends to be placed on differentiation between the short-term memory store (STMS) and the long-term memory store (LTMS). More recently, ideas about a 'working memory' (WM) have come to the fore, this is in addition to slave systems such as the phonological store, requiring rehearsal via an articulatory loop (also used in digit-span recall); the visual sketchpad encoding mechanism; and the semantic store (where memory meets perception and language), linking attention to the temporary activation of the LTMS as used for conceptual reasoning and higher-level functioning. Additionally and of clinical importance is so-called autobiographical memory, or one's memory for personal life events, and this is thought to be located in the hippocampal and prefrontal areas of the brain.

Amnesia and other neuropsychological issues

Traditionally there has been a division between anterograde amnesia (an inability to remember events and other information since an illness) and retrograde amnesia (memory difficulties for events prior to an illness or accident). Incidentally, it is extremely rare to find retrograde amnesia without some kind of anterograde amnesia. For some neurological patients, the working memory can be intact while other memory problems may be apparent, for example in cases of global amnesia (however, thiamine levels need to be checked). Interestingly, amnesic patients have also been shown to have an intact implicit memory, which implies LTMS activation (operating independently of conscious control), although left cortical damage and right-sided damage can impair verbal (this is also the case for Alzheimer's patients with bilateral cortical atrophy) and non-verbal implicit memory, respectively. Procedural memory (involving motor movement) can also remain intact, except in cases of Huntington's or Parkinson's Disease patients who have lesions in the basal ganglia.

However, prospective memory is particularly vulnerable to impairment when frontal damage to the brain is evident. In fact, frontal dysfunction is doubly detrimental to memory because of the adverse effects it can have on working memory functioning, with the dorsal (upper) areas affecting spatial attributes and the ventral (lower) areas important for the identification of objects. Furthermore, prefrontal lesions and especially those in the dorsolateral regions, can lead to some difficulties organising and retrieving information (e.g. the order of material), yet nevertheless individuals with these problems may retain a reasonable quantity of information (It is however, important here to check for false-positives and confabulation, which may inflate scores).

An integrated model of memory

Andrewes (2001) introduces the idea of an active memory system that is seen as "a combination of what is being attended to plus the remnant of previous activations" (p. 260). New functional imaging studies indicate that it is prefrontal (associative) functioning that is particularly important for working memory (Mid-ventral areas hold information 'in mind' and control selective attention, mid-dorsolateral areas allow for further processing of material in a more abstract way, and posterior activation indicates that the information may have been retained). A component of the WM is activation of the long-term memory score, a search that is conducted by the central executive system, which does not require the consolidation system. The WM thus operates by the combined involvement of the executive system and various active LTM modules, yet "the temporary activation of the LTMS does not necessarily lead to more permanent storage unless the consolidation system is also involved" (Andrewes, 2001, p.270).

While it is possible that incremental learning of an implicit nature can occur without involving the consolidation system, new learning is aided by elaborate rehearsal and retrieval strategies using top-down processing. It is also important to remember that memory functioning has a limited-capacity (The notion of 'chunking' is thought to be limited to certain tasks and conditions, and in this sense the ability to learn will depend on the ease with which one can overcome the limited-capacity of this temporary buffer system), given that the system shares capacity with perceptual and other information-processing capabilities.

Summary

If memory functions without use of the central executive system, the system lacks direction and organisation, while the consolidation system is needed for effective learning.

Reference

Andrewes, D. (2001) Neuropsychology: From theory to practice. Hove (UK): Psychology Press.

WEBLINKS

Alzheimer's Disease Society   http://www.alzheimers.org.uk

Parkinson's Disease Society  http://www.parkinsons.org.uk

Huntington's Disease Society http://www.hda.org.uk