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The role of mental stimulation in aiding memory

Does mental stimulation protect you from Alzheimer's and other dementias?

A number of studies in the past few years have supported the theory that engaging in mentally stimulating activities can help keep your mind sharp. Most of these studies have, understandably, been concerned with the effect of stimulation on the aging mind, and in particular on the question of whether it helps protect against dementia:

• one study found that participation in leisure activities of all kinds was associated with a risk in dementia risk, although intellectual activities had the most beneficial effect. (Scarmeas et al. 2001)
• a large-scale study of seniors aged 65 years and older found that participation in various cognitive activities (such as reading a newspaper) was positively associated with a decreased risk of developing Alzheimer’s. This effect remained even after education and occupation (both associated with Alzheimer's risk) had been taken into account. Physical activity had no effect. (Wilson et al. 2002b)
• a large-scale study of seniors found that more frequent participation in cognitively stimulating activities (such as reading books, newspapers or magazines, engaging in crosswords, puzzles, board or card games, going to museums) was significantly associated with a reduced risk of Alzheimer’s disease. (Wilson et al. 2002c)
• a study involving seniors aged 75 or older found those who participated at least twice weekly in reading, playing games (chess, checkers, backgammon or cards), playing musical instruments, and dancing were significantly less likely to develop dementia. Although the evidence on crossword puzzles was not quite statistically significant, those who did crossword puzzles four days a week had a much lower risk of dementia than those who did one puzzle a week. Only one physical activity had any significant impact — ballroom dancing — possibly because of the mental demands of remembering dance steps, responding to music and coordinating with a partner.(Verghese et al. 2003)

Does mental stimulation protect you from general age-related cognitive decline?

General cognitive decline has been found to be less among those seniors who did more cognitively stimulating activities. In particular, working memory, perceptual speed, and episodic memory (all processes particularly affected by aging) were all helped. (Wilson et al. 2002b)

Another study followed a large group of seniors, aged 70-93 at the beginning of the study, over a seven-year period. Most participants, unsurprisingly, reduced their level of activity over the period. The rate at which individuals reduced their activity level was substantially correlated with changes in cognitive and health measures, although some decline in cognitive performance was evident even in those who maintained their activity levels. (Mackinnon et al. 2003)

In a recent large-scale British study of civil servants aged between 35 and 55, participation in various leisure activities was associated with level of cognitive ability. Specifically, regular cultural visits to theatres, art galleries and stately homes, were associated with the highest level of cognitive ability, closely followed by reading and listening to music, then by involvement in clubs and voluntary organizations, and participation in courses and evening classes. (Singh-Manoux et al. 2003)

Interestingly, this particular study found that the association between the selected 13 leisure activities and cognitive ability was slightly stronger for men than for women. One reason for this may be that women are more likely to engage in activities other than those selected.

In particular, it has been speculated that women are more likely to engage in more social interaction, which may be beneficial. There is some evidence that social interactions benefit cognitive functioning.

Just talking may help prevent cognitive decline

"Social engagement" can be measured by how often people talk on the phone with friends, neighbors and relatives, how often they get together with them, how many people they can share their most private feelings and concerns with. A series of studies by Dr Oscar Ybarra (as yet unpublished) have found that, across all age groups, the more socially engaged people are, the lower their level of cognitive impairment and the better their working memory performance.

This does not necessarily mean that more social contact leads to a sharper mind. People in better shape mentally are probably more inclined to be social in the first place.

However, the studies do build on earlier research. One study found that seniors who reported more demands from social relationships had better cognitive functioning. This may reflect the benefit of complex social interaction (or of course, it may simply reflect the fact that those with better cognitive function are more likely to have demands made on them). (Seeman et al. 2001)

Social engagement also appears to have an effect on health. A study growing out of the Seattle Longitudinal Study found low levels of social networks were associated with more hospital and doctor visits, and higher health costs. Those with greater health problems were more likely to be socially isolated, and also had lower levels of education and income. (Bosworth & Schaie, 1997)

Personality variables also play a role

The association between all these factors is assuredly complex. One aspect to it may be that people with low self-worth may be less likely to engage in stimulating activities (social, intellectual, and physical). Recent research has found that age-related cognitive decline is more likely in those with low self-worth, and that the brains of those with less self-worth were significantly smaller than those of people who felt good about themselves. So perhaps those with low self-worth don’t bother to do much, and their brains shrink, reflecting this lack of use, in the same way that our stomachs shrink when we feed them less. (Lupien, 2003)

Self-worth is also associated with anxiety and depression, and these factors have been shown to be associated with an increased risk of developing Alzheimer's in several studies:

• a seven-year study found that those with the greatest number of depressive symptoms at the start of the study were more likely to develop Alzheimer's disease and also showed more rapid cognitive decline.(Wilson et al. 2002a)
• a longitudinal study found that those who most often experience negative emotions like depression and anxiety were twice as likely to develop Alzheimer's disease as those who were least prone to experience negative emotions. (Wilson et al. 2003)
• a study of Alzheimer’s patients found that their level of impairment in episodic memory on initial evaluation was related to their tendency to experience psychological distress (as assessed by a knowledgeable informant) prior to developing Alzheimer’s. This was not, however, a factor in the rate at which cognitive function declined over the course of the disease. (Wilson et al. 2004)

A person’s tendency to experience psychological distress has been shown to be a stable personality trait throughout adulthood. In the second study, proneness to stress was specifically associated with a decline in episodic memory (measured by asking participants to recall a list of words or a story) — an area particularly problematic for those with Alzheimer's. Episodic memory ability declined 10 times faster in those high in proneness to distress than in those low in this response.

This result was not altered when participants’ engagement in cognitively stimulating activities was taken into account, suggesting that this personality factor is independent of activity level.

The way in which we respond to stress may also change as we get older, and this may contribute to poorer memory performance in old age. A study involving 14 healthy seniors compared memory performance on two tasks, one of them assumed to be stressful (a public speaking task) and one not (an attentional task). It was found that declarative memory (conscious recollection of learned information) was impaired on the stressful task, but not on the nonstressful task. Nondeclarative memory (information retrieved without conscious or explicit effort) was not affected by stress. Measurement of cortisol levels suggested that it was the anticipation of stress rather than the stress itself that affected memory. It is speculated that an altered cortisol responsivity to acute and/or chronic stress may be partly responsible for age-related cognitive decline. (Lupien et al. 1997)

But what do all these studies really mean? It must always be remembered that correlation doesn't mean causation. The fact that depressed people are more likely to develop Alzheimer's doesn't mean depression causes Alzheimer's. Physical changes in the brain that occur long before symptoms appear may also make it more likely that the individual will suffer depression, for example. The fact that people who lead busier, more active and involved lives, tend to perform better on memory and cognitive tasks, doesn't mean that it is their activities that keep their minds sharp. It may be that those whose minds are sharp are more likely to engage in such activities.

Is higher mental ability protective against cognitive impairment?

The main problem with determining the relationship between cognitive activities and cognitive performance is that we don’t usually know the previous history of cognitive performance. Level of education, occupation, socio-economic class, these are all indicators, but to know whether a person engages in more cognitive activities because he is intellectually able, or whether he has retained more mental ability because he has kept himself mentally active, we really need to know his cognitive abilities at an earlier age.

A recent longitudinal study bears on this question (unfortunately, only preliminary results are as yet available). The Scottish Mental Survey assessed 87,498 eleven-year-olds in 1932, and another 70,805 in 1947. In a fascinating follow-up to this study, over 1000 of these students were contacted and re-assessed, on the exact same tests. It was found that, first of all, the seniors did rather better than they had at age 11, and more importantly, that differences in mental ability remained fairly stable with age — “with some interesting exceptions, the high scorers did well and the modest remained so.” (Deary, 2003)

A study of 215 seniors aged 66-75 found that those with a larger head size had significantly higher scores on intelligence tests, and also showed less decline in memory performance over the 3 ½ year follow-up period. Those with the smallest heads had a fivefold increased risk of cognitive decline compared to those with the largest. However, there was no correlation with head size at birth, indicating that it is brain development in the early years that is important. During the first year of life, babies' brains double in size, and by the time they are six, their brain weight has tripled. These, it appears, are the crucial years for laying down brain cells and neural connections (pointing to the importance of providing both proper nourishment and intellectual stimulation in these early years). (Gale et al. 2003)

There is also evidence that the more formal education you have, and the greater your head size (reflecting brain size), the more you are protected from the effects of Alzheimer’s. That is, these factors don’t reduce your likelihood of developing Alzheimer’s, but, by providing reserve brain capacity — a “cognitive reserve” — normal function can be retained for longer. (Mortimer et al. 2003; Bennett et al. 2003)

Interestingly, a longitudinal study found that those who wrote more densely (packed more ideas into the sentences) of autobiographical essays written when they were young were less likely to get Alzheimer's disease six decades later. (Early language ability may be linked to lower risk of Alzheimer's )

However, it must also be remembered that the effects of education and occupation on Alzheimer's risk seem to be greatly reduced when you take into account mentally stimulating activities (Wilson, 2002b). That is, those with higher levels of education and higher income are more likely to engage in mentally stimulating activities, and this accounts for much (though not all) of the effects of education and occupation.

Clearly all these factors impact on each other: physical health, cognitive function, social engagement, depression, self-worth, income, education.It does seem most plausible, however, that stimulation is a critical factor. Stimulation in the early years grows complex brains (builds more neurons and richer networks of connections between them). Education may be presumed to provide stimulation - thus, more years of formal education would correlate with more years of stimulation, as well as providing training that encourages the individual to continue to find mental stimulation rewarding. Occupation similarly, can also readily be seen to be correlated with level of stimulation.

Why should mental stimulation help prevent cognitive decline?

Stimulation clearly helps the growing brain. But why should stimulating activities help the aging brain? One reason may be that stimulation helps older brains retain sufficient flexibility to compensate for difficulties it experiences by finding different ways of doing things. Keeping the brain active with a variety of cognitive tasks may be one way to retain flexibility. Imaging studies have provided evidence that better-performing seniors show different patterns of brain activity compared to both younger adults and poorer performing seniors, implying that those who perform well in old age are those who have found new ways of processing information. (Cabeza et al. 2002)

Activities such as reading, doing crosswords, indeed anything that uses language and keeps you meeting new words, have also been suggested as helping reduce the occurrence of those occasions when you feel you know something, “on the tip of your tongue”, but can’t quite recall it. Participation in such activities is thought to help by keeping your memory links strong. (James & Burke, 2001)

Conclusion

My own opinion is that mental stimulation is absolutely critical at all stages of one's life - in infancy and childhood, in early adulthood and middle life, and in old age. While the whole question of neurogenesis (the making of new nerve cells) in adult brains is still unclear, there is no question that connections between neurons continue to be made throughout one's life. We know that connections are stronger when they are used, and grow weak when they have not been used for a long while. We know that the more connections there are, the more possible paths to a memory there are. How could it not be, that the more you use existing connections, and the more connections you make, the easier it will be to remember and think?

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