environment

I recently reported on a finding that older adults whose life-space narrowed to their immediate home were significantly more likely to have a faster rate of global cognitive decline or develop mild cognitive impairment or Alzheimer’s.

Now there are some obvious correlates of being house-bound vs feeling able to travel out of town (such as physical disability), but this relationship between cognitive decline and confined life-space remained after such factors were taken into account. The association is thought to be related to social and mental stimulation.

But I think this association also points to something more specific: the importance of distance, and difference. Different ways of thinking; different contexts. Information (in the broadest sense of the word) that stretches your mind, that gets you out of the grooves of your familiar thoughts.

Last year I reported on a study looking at creativity in problem-solving. That study found that multicultural experiences help you become more creative in solving problems. In particular, creativity was best helped by being reminded of what you’d learned about the underlying meaning or function of behaviors in the multicultural context. In other words, what was important was truly trying to understand behavior that’s very different from your own.

While travelling undoubtedly helps, you don’t need to go to a distant place to learn about different cultures. You can read about them; you can watch movies; you can listen to other people talk about what they know. And if you have those experiences, you can then think about them at any time.

A vital tool in tackling cognitive decline in old age (including the more extreme events of mild cognitive impairment and dementia) is cognitive reserve. Cognitive reserve means that your brain can take more damage before it has noticeable effects. Many people have died with advanced Alzheimer’s pathology in their brain who showed no signs of dementia in life!

Cognitive reserve is most often associated with education, but it is also associated with occupation, bilingualism, and perhaps even music. What it comes down to is this: the more redundancy in your brain, the wider and denser the networks, the more able your brain will be to find new paths for old actions, if the old paths are damaged.

The finding that life-space can affect cognitive decline is also a reminder that we are minds in bodies. I have reported on a number of examples of what is called embodied cognition (the benefits of gesture for memory are one example of this). It’s a good general principle to bear in mind — if you fake enjoyment, you may well come to feel it; if you look at the distant hills or over the sea, your mind may think distant thoughts; if you write out your worries, the weight of them on your mind may well lighten.

I made reference to bilingualism. There have been several studies now, that point to the long-term benefits of bilingualism for fighting cognitive decline and dementia. But if you are monolingual, don’t despair. You may never achieve the fluency with another language that you would have if you’d learned it earlier in life, but it’s never too late to gain some benefit! If you feel that learning a new language is beyond you, then you’re thinking of it in the wrong way.

Learning a language is not an either-or task; you don’t have to achieve near-native fluency for there to be a point. If there’s a language you’ve always yearned to know, or a culture you’ve always been interested in, dabble. There are so many resources on the Web nowadays; there has never been a better time to learn a language! You could dabble in a language because you’re interested in a culture, or you could enhance your language learning by learning a little about an associated culture.

And don’t forget that music and math are languages too. It may be too late to become a cello virtuoso, but it’s never too late to learn a musical instrument for your own pleasure. Or if that’s not to your taste, take a music appreciation class, and enrich your understanding of the language of music.

Similarly with math: there’s a thriving little world of “math for fun” out there. Go beyond Sudoku to the world of math puzzles and games and quirky facts.

Perhaps even dance should be included in this. I have heard dance described as a language, and there has been some suggestion that dancing seems to be a physical pursuit of particular cognitive benefit for older adults.

This is not simply about ‘stimulation’. It’s about making new and flexible networks. Remember my recent report on learning speed and flexible networks? The fastest learners were those whose brains showed more flexibility during learning, with different areas of the brain being linked with different regions at different times. The key to that, I suggest, is learning and thinking about things that require your brain to forge many new paths, with speed and distance being positive attributes that you should seek out (music and dance for speed, perhaps; languages and travel for distance).

Interestingly, research into brain development has found that, as a child grows to adulthood, the brain switches from an organization based on local networks based on physical proximity to long-distance networks based on functionality. It would be interesting to know if seniors with cognitive impairment show a shrinking in their networks. Research has shown that the aging brain does tend to show reduced functional connectivity in certain high-level networks, and this connectivity can be improved with regular aerobic exercise, leading to cognitive improvement.

Don’t disdain the benefits of simply daydreaming in your armchair! Daydreaming has been found to activate areas of the brain associated with complex problem-solving, and it’s been speculated that mind wandering evokes a unique mental state that allows otherwise opposing networks to work in cooperation. Daydreaming about a more distant place has also been found to impair memory for recently learned words more than if the daydreaming concerned a closer place — a context effect that demonstrates that you can create distance effects in the privacy of your own mind, without having to venture to distant lands.

I’m not saying that such daydreaming has all the benefits of actually going forth and meeting people, seeing new sights. Watching someone practice helps you learn a skill, but it’s not as good as practicing yourself. But the point is, whatever your circumstances, there is plenty you can do to stretch your mind. Why not find yourself a travel book, and get started!

Because it holds some personal resonance for me, my recent round-up of genetic news called to mind food allergies. Now food allergies can be tricky beasts to diagnose, and the reason is, they’re interactive. Maybe you can eat a food one day and everything’s fine; another day, you break out in hives. This is not simply a matter of the amount you have eaten, the situation is more complex than that. It’s a function of what we might call total allergic load — all the things you might be sensitive to (some of which you may not realize, because on their own, in the quantities you normally consume, they’re no or little problem). And then there are other factors which make you more sensitive, such as time of month (for women), and time of day. Perhaps, in light of the recent findings about the effects of environmental temperature on multiple sclerosis, temperature is another of those factors. And so on.

Now, I am not a medical doctor, nor a neuroscientist. I’m a cognitive psychologist who has spent the last 20 years reading and writing about memory. But I have taken a very broad interest in memory and cognition, and the picture I see developing is that age-related cognitive decline, mild cognitive impairment, late-onset Alzheimer’s, and early-onset Alzheimer’s, represent places on a continuum. The situation does not seem as simple as saying that these all have the same cause, because it now seems evident that there are multiple causes of dementia and cognitive impairment. I think we should start talking about Total Cognitive Burden.

Total Cognitive Burden would include genetics, lifestyle and environmental factors, childhood experience, and prenatal factors.

First, genetics.

It is estimated that around a quarter of Alzheimer’s cases are familial, that is, they are directly linked to the possession of specific gene mutations. For the other 75%, genes are likely to be a factor but so are lifestyle and environmental factors. Having said that, the most recent findings suggest that the distinction between familial and sporadic is somewhat fuzzy, so perhaps it would be fairer to say we term it familial when genetics are the principal cause, and sporadic when lifestyle and environmental factors are at least as important.

While three genes have been clearly linked to early-onset Alzheimer’s, only one gene is an established factor in late-onset Alzheimer’s — the so-called Alzheimer’s gene, the e4 allele on the APOE gene (at 19q13.2). It’s estimated that 40-65% of Alzheimer’s patients have at least one copy of this allele, and those with two copies have up to 20 times the risk of developing Alzheimer’s. Nevertheless, it is perfectly possible to have this allele, even two copies of it, and not develop the disease. It is also quite possible — and indeed a third of Alzheimer’s patients have managed it — to develop Alzheimer’s in the absence of this risky gene variant.

A recent review selected 15 genes for which there is sufficient evidence to associate them with Alzheimer’s: APOE, CLU, PICALM, EXOC3L2, BIN1, CR1, SORL1, TNK1, IL8, LDLR, CST3, CHRNB2, SORCS1, TNF, and CCR2. Most of these are directly implicated in cholesterol metabolism, intracellular transport of beta-amyloid precursor, and autophagy of damaged organelles, and indirectly in inflammatory response.

For example, five of these genes (APOE; LDLR; SORL1; CLU; TNF) are implicated in lipid metabolism (four in cholesterol metabolism). This is consistent with evidence that high cholesterol levels in midlife is a risk factor for developing Alzheimer’s. Cholesterol plays a key role in regulating amyloid-beta and its development into toxic oligomers.

Five genes (PICALM; SORL1; APOE; BIN1; LDLR) appear to be involved in the intracellular transport of APP, directly influencing whether the precursor proteins develop properly.

Seven genes (TNF; IL8; CR1; CLU; CCR2; PICALM; CHRNB2) were found to interfere with the immune system, increasing inflammation in the brain.

If you’re interested you can read more each of these genes in that review, but the point I want to make is that genes can’t be considered alone. They interact with each other, and they interact with other factors (for example, there is some evidence that SORL1 is a risk factor for women only; if you have always kept your cholesterol levels low, through diet and/or drugs, having genes that poorly manage cholesterol will not be so much of an issue). It seems reasonable to assume that the particular nature of an individual’s pathway to Alzheimer’s will be determined by the precise collection of variants on several genes; this will also help determine how soon and how fast the Alzheimer’s develops.

[I say ‘Alzheimer’s’, but Alzheimer’s is not, of course, the only path to dementia, and vascular dementia in particular is closely associated. Moreover, my focus on Alzheimer’s isn’t meant to limit the discussion. When I talk about the pathway to dementia, I am thinking about all these points on the continuum: age-related cognitive decline, mild cognitive impairment, senile dementia, and early dementia.]

It also seems plausible to suggest that the precise collection of relevant genes will determine not only which drug and neurological treatments might be most effective, but also which lifestyle and environmental factors are most important in preventing the development of the disease.

I have reported often on lifestyle factors that affect cognitive decline and dementia — factors such as diet, exercise, intellectual and social engagement — factors that may mediate risk through their effects on cardiovascular health, diabetes, inflammation, and cognitive reserve. We are only beginning to understand how childhood and prenatal environment might also have effects on cognitive health many decades later — for example, through their effects on head size and brain development.

You cannot do anything about your genes, but genes are not destiny. You cannot, now, do anything about your prenatal environment or your early years (but you may be able to do something about your children’s or your grandchildren’s). But you can, perhaps, be aware of whether you have vulnerabilities in these areas — vulnerabilities which will add to your Total Cognitive Burden. More easily, you can assess your lifestyle — over the course of your life — in these terms. Here are the sorts of questions you might ask yourself:

Do you have any health issues such as diabetes, cardiovascular disease, multiple sclerosis, positive HIV status?

Do you have a sleep disorder?

Have you, at any point in your life, been exposed to toxic elements (such as lead or severe air pollution) for a significant length of time?

Did you experience a lot of stress in childhood? Stress might come from a dangerous living environment (such as a violent neighborhood), warring parents, a dysfunctional parent, or a personally traumatic event (to take some examples).

Did you do a lot of drugs, or indulge in binge drinking, in college?

Have you spent many years eating an unhealthy diet — one heavy in fats and sugars?

Do you drink heavily?

Do you have ongoing stress in your life, or have experienced significant amounts of stress at some period during middle-age?

Do you rarely engage in exercise?

Do you spend most evenings blobbed out in front of the TV?

Do you experience little in the way of mental stimulation from your occupation or hobbies?

These questions are just off the top of my head, the ones that came most readily to mind. But they give you, I hope, some idea of the range of factors that might go to make up your TCB. The next step from there is to see what factors you can do something about. While you can’t do anything about your past, the good news is that, at any age, some benefit accrues from engaging in preventative strategies (such as improving your sleeping, reducing your stress, eating healthily, exercising regularly, engaging in mentally and socially stimulating activities). How much benefit will depend on how much effort you put into these preventative strategies, and on which and how many TCB factors are pushing you and how far you are along on the path. But it’s never too late to do something.

On the up-side, you might be relieved by such an exercise, realizing that your risk of dementia is smaller than you feared! If so, you might use this knowledge to motivate you to aspire to an excellent old age — with no cognitive decline. We tend to assume that declining faculties are an inevitable consequence of getting older, but this doesn’t have to be true. Some ‘super-agers’ have shown us that it is possible to grow very old and still perform as well as those decades younger. If your TCB is low, why don’t you make it even lower, and aspire to be one of those!