28 DEVELOPMENT OF THE PERSON

Memory problems

We are all familiar with lapses of memory – not being able to put a name to a face; forgetting to keep an appoint-ment; and poor recall during an exam. Psychologists have learned a great deal about the process of memory in the past 100 years through both laboratory-based experiments and by studying patients with brain damage resulting in unique forms of memory loss. Although a very simplifi ed view, Figure 1 is a useful summary of a widely held basic model of memory. Items are initially held in a short-term store and whether they become permanently represented in a long-term memory (LTM) store will depend on a host of factors such as how important and interesting they are, and whether we engage in active rehearsal strategies to encode items into permanent or LTM. There are also many different divisions of LTM, in particular a distinction between declarative and pro-cedural memory (i.e. between memory for facts and autobio-graphical episodes and memory for skills and other cognitive operations).

Stages of memory

If we listen to a list of unrelated words read out to us, and then are required to recall the words immediately, items presented either fi rst or last are better remembered than those in the middle. This better recall for the more recent items is because we are retrieving them directly from the short-term memory store. If we were to delay recall of the word list by 30 seconds, then this recency effect disappears ( Fig. 2 ).

Even items which do successfully enter into LTM may not be recalled when we need them but much later are recalled. This illustrates the problem of retrieval , rather like a book which has been stored in a library: if we lose the catalogue slip, then the book is very diffi cult to fi nd. This problem of memory loss is clearly very different to being unable to locate the book because it was never stored correctly in the fi rst place. A good practical illustration of this distinction is the

difference between testing your knowledge about anatomy by recall (‘describe the structure of the brain’) and recognition (‘which of the following is part of the limbic system?’). Multiple-choice exam questions have already carried out the retrieval part of remembering, leaving only the recognition component to be necessary.

When we are consider the problems of forgetting and the poor memory of head-injured and elderly patients, and we are trying to devise methods to aid recall, we need to have clear ideas about the stage at which the process is disturbed. Is it the initial learning which is defective or do those with poor memories simply forget more quickly?

How much can we remember?

Realizing that we have seen a fi lm previously, but only about 10 minutes before its end, or revisiting a childhood home and having a fl ood of forgotten memories are powerful experiences which may tempt us into thinking that we do indeed store all events, and given the right conditions could retrieve such memories. Although there are well-documented cases of people with exceptional memories (one fascinating account, The Mind of a Mnemonist , is provided by the Russian neuropsychologist Luria (1969)), there is no scientifi c evidence to support this ‘videotape’ view of memory. To acquire permanent representation in memory we need to organize the new material and establish connections with the existing LTM store. Hence the use of mnemonic techniques which rely on devices such as learning a list of items in relation to an easily remembered rhyme, or fi rst-letter mnemonics such as Richard Of York Gave Battle In Vain for the colours of the visible spectrum. Memory tricks like this should not be scoffed at and have proved useful in helping elderly patients remember people’s names.

Helping patients to remember better

When patients have been asked to recall what they have been told during a consultation, they have been found to forget almost half. Memory for medical advice as opposed to diagnostic information can be particularly poor, especially in the case of highly anxious or elderly patients. Statements

Externalstimuli

Information thatdraws attentionand is perceived

becomes encodedinto STM

Sensorymemory

Short-termmemory

Long-termmemory

Relating informationin STM to thatin LTM helps in

chunking process

Unattended,unperceivedinformation

is lost

Unrehearsedand displacedinformation is

forgotten

Rehearsalkeeps information

in short-termmemory

Fig. 1 Memory: short-term and long-term storage. STM, short-term memory; LTM, long-term memory.

70

60

50

40

30

20

10

0151051

Serial position

Correct (%)

0-second delay

30-second delay

Fig. 2 The recency effect and short-term storage.

■ What were you doing on 15 March last year?

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29Memory problems

made early in the consultation are more likely to enter LTM (the primacy effect) and those at the end are remembered better initially but then tend to be forgotten (the recency effect). General or abstract statements are more diffi cult to remember than more specifi c concrete suggestions. Researchers have concluded that patient recall is aided by following some simple rules: ■ Give the most important information early in any set of

instructions. ■ Stress the importance of relevant items (e.g. by repetition). ■ Use explicit categorization under simple headings (e.g.

I will tell you what is wrong … what treatment you will need … what you can do to help yourself).

■ Make advice specifi c, detailed and concrete rather than general and abstract.

Memory after traumatic brain injury

Memory problems often follow accidental trauma from a closed head injury. In their most dramatic form, the patient may be unable to recall not only the events leading up to the accident, but for many years prior to that. This memory loss extending backwards in time is known as retrograde amnesia, as distinct from the inability to form new memories, which is known as anterograde amnesia. Such patients may well report themselves as 10 years younger than they are, and be unable to recall all the events of those 10 years, such as marriage, birth of children and employment. At the same time, they will repeatedly need to be told why they are in hospital and the names of the nurses and doctors caring for them. Eventually these years of memory loss will be recovered, indicating that the problem was diffi culty of retrieval, but they may be left with enduring defi cits of memory which may be secondary to attentional or concentration diffi culties. The exact nature of the defi cit will require extensive testing by a neuropsychologist. A collection of essays dealing with the effects of brain damage is Oliver Sacks’ book The Man who Mistook his Wife for a Hat (1986).

Organic amnesia

Permanent memory loss is a serious problem necessitating continuous care of such patients. These instances of organic amnesia may be due to long-term alcohol abuse and development of Korsakoff’s syndrome; to the brain damage from viral encephalitis; or to other surgical interventions. In cases where the memory loss is primary and not secondary to other cognitive defi cits, patients are likely to have suffered damage to components of the limbic system, with the hippocampus being a key structure (see Case study).

Brain imaging

Brain imaging techniques such as functional magnetic resonance imaging allow researchers to examine directly the parts of the brain involved in cognitive processes. In the last decade there have been several important discoveries relevant to understanding memory mechanisms, and which also demonstrate the considerable plasticity of the brain with

respect to function. Animal studies have long implicated the hippocampus as playing a particular role in spatial memory, and this has also been shown to apply to humans in a particularly interesting study of London taxi drivers performed by Maguire et al. (1998). The researchers studied taxi drivers qualifi ed in the ‘knowledge’ – a 2-year acquisition of street locations and one-way systems in London. Comparing taxi drivers and a control group of casual drivers they found differences in the cellular density of the left and right hippocampus, with the posterior hippocampus having a larger volume on both sides for the taxi drivers whereas in the control group the anterior hippocampus was larger. The researchers found a positive correlation between years of experience in the job and volume of the right posterior hippocampus and a negative correlation for the anterior hippocampus. This strongly suggests the changes are acquired as a result of the experience of taxi driving and the spatial maps formed as a result. There are clear implications here for rehabilitation suggesting that a similar environment-related plasticity is possible in other regions of the brain.

■ How would you set about establishing the extent of retrograde amnesia in a patient for whom you have no autobiographical infor-mation?

■ Can you recall the moment you fi rst en-countered a younger sibling? Your fi rst day at school? Why do such memories endure?

Case study HM is an engineering worker who, in 1953, in his late 20s was

operated upon in an experimental procedure intended to relieve

his epileptic seizures. The operation involved a radical bilateral

medial temporal lobe resection, destroying the anterior two-thirds

of the hippocampus, as well as the uncus and amygdala. It was

successful in alleviating the epileptic symptoms, but left HM with

profound memory impairment. Although he can remember events

and facts he acquired up to 2 years before his operation, he can

remember essentially nothing that has occurred since. He does not

know what he had for lunch an hour ago, how he came to be where

he is now, where he has left objects used recently or that he has

used them. He reads the same magazines over and over again. He

has learned neither the names of doctors and psychologists who

have worked with him for decades nor the route to the house he

moved to a few years after his surgery. Yet despite such diffi culties

he is not intellectually impaired. His language comprehension

and production and conversational skills are normal, he can

reason competently and do mental arithmetic. His IQ measured in

1962 was an above-average 117 – higher than the 104 measured

presurgery in 1953. This neurological dissociation supports the idea

that the temporary retention of information in working memory

and the permanent storage of new information depend on different

brain mechanisms (for a lengthier account of HM’s problems, see

Hilts, 1995).

Memory problems

■ The distinction between registration, retrieval, recall and recogni-tion processes in memory is clear.

■ Different kinds of memory mechanisms underlie short-term memory and LTM, as shown by the serial position effect and the nature of the amnesic syndrome in brain-damaged patients.

■ Improving memory recall by means of mnemonic aids is especially useful for unconnected items and events.

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