Lifestyle

A perennial topic in the arena of memory improvement is the question of “food for the brain”, and in particular, whether there are dietary supplements that can improve your mental abilities. While my own emphasis is improvement through development and practice of skills, I don’t dismiss the possibility of improvement through more physical means. I myself am a great fan of the “you are what you eat” principle. This is mainly because I suffer from multiple food sensitivities, so the consequences of food are very much a reality for me. That doesn’t mean I believe perfectly healthy people should obsess about their diet. There is another principle that is of great importance: we are all individuals.

For example, a year ago, I wrote of the effects of caffeine on memory, concluding that: “while caffeine may help older adults in the later part of the day, those with hypertension, diabetes, impaired glucose tolerance, or high homocysteine levels, would be wiser to avoid coffee, even if decaffeinated. In general, while caffeine may help you overcome factors that lower your cognitive performance, it does not seem that caffeine has any significant direct effect on memory, although it may well help you pay attention.”

So, caffeine is more helpful for some types of people than others, and is in fact contra-indicated for some. Moreover, the effects are different for those who are accustomed to a high caffeine intake, compared to those who only occasionally consume caffeine. And – here’s the real kicker – I also know from personal experience that the effects of caffeine are highly individual: I myself respond to caffeine not with the usual increased alertness, but in fact with decreased alertness. It makes me sleepy!

I do think there are physical factors of far greater importance than diet. Sleep is the obvious one. Individual differences don’t show up in the basic need to have enough sleep, and the right sort of sleep, to optimize brain functioning, but they do of course show up as regards how much sleep is right for us. That also, is something that changes with age, and, I imagine, health, throughout our lifespan.

Another physical factor which should be given due weight is exercise. While its effect is not as great as sleep (I don’t think anything rivals the importance of sleep!), I would give it more importance than diet because its effect is far more consistent. I don’t think anyone would fail to benefit mentally from increased physical fitness (which is not to say there isn’t a level of fitness beyond which no more mental improvement will occur).

Diet, on the other hand, depends a great deal on the individual. There is little evidence that dietary supplements or changes to the diet improve mental function in those who don’t suffer from any of the conditions which can adversely affect brain function — e.g., aging, physical disorders, depression, stress, etc.

In other words, if you are a relatively young person with no health problems, I suggest you concentrate on getting enough sleep and exercise, and learning and practicing effective memory strategies.

If you have any conditions which can adversely affect brain function I would also emphasize doing this! But, additionally, I do think there are foods and supplements you can take which may well significantly improve your brain function.

Which ones? Here we enter the area of individual difference. To find out what is effective for you, you should start with the research. What foods and supplements have been demonstrated to be effective in improving cognition?

Here we enter an area fraught with difficulty. News reports come out about foods and supplements all the time, and today’s world is filled with people hawking “health” products. How do we know what to believe?

The first thing, of course, is to ascertain whether the claims are backed up by research. But that’s not as easy as it sounds, because every seller of such products knows the importance of sounding as if research has proven the effectiveness of their product. (Actually, I automatically disavow any text which talks of research “proving” something. No researcher worth his salt would ever make such a claim.)

How do we determine the genuineness and reliability of the research? First, and most importantly, by assessing the source. For example, I only cite research from reputable academic journals, or academic conferences. I also give greater weight to research from researchers whose work I know of. Hopefully, by so doing, I also make myself a reliable source.

This is not, however, infallible, for even well-respected journals can make mistakes. For example, very topically, the truthfulness of a widely reported study of a nutritional supplement's effects on thinking and memory in the elderly has recently been cast into doubt (actually, this is a rather polite phrase for the comments now being made: “scientists who reviewed the paper had found the methods and statistical findings so unlikely that they wondered whether the study had actually been done”; "The statistics were not just implausible, they were impossible.")

Nevertheless, the very shock with which these questions are being raised demonstrates that, by and large, the system does work. We cannot expect certainty.

Having approved the source, the second thing to consider is the extent to which the research has been replicated. One study does not make an answer! It is indicative only. It is interesting.

Even a second study is little more than another support. Before we can say, “You know, I really think there’s something to this”, we need a number of studies building together from different angles.

So, a study showing that sage can help cognitive function in healthy young adults (there is indeed such a study) is interesting. Given that sage is easy to grow, and commonly consumed (one doesn’t need to worry about toxicity), I would go so far as to say, give it a try! But I wouldn’t give a lot of weight to the research until more studies had been carried out. (I would, however, happily drink sage tea everyday on the off chance, except it turns out – I really can’t believe this! – I’m sensitive to sage, too.)

On the other hand, for a product that is expensive, or has potential side-effects, I would wait for more evidence to come in before trying it. Okay, we’ve looked at the research, we’ve found the foods and supplements of potential benefit. What next?

Next, you look at your own particular problems.

For example, my main problem is food sensitivities. The first, most dramatic, thing I did to overcome my increasing mental sluggishness was: stop eating foods which turned out to be bad for me! After concentrating on that for a year or two, with my physical and mental problems much improved (but not gone), I turned my attention to the damage done to my body over the long period during which I was unaware of my food sensitivities. I now take B12, which I am sure has had a significant effect on my brain, and have recently started taking iron (as a woman of childbearing age). I also take other mineral supplements, principally to overcome deficiencies in my environment (New Zealand’s soil is deficient in a number of minerals), and lecithin (partly because of the deficiencies in my diet as a result of having to avoid certain foods).

The final step, once you’ve established the possible foods and supplements which are worth trying, is to see whether they are effective for you. Remember me and the coffee. What works for one doesn’t necessarily work for another (and may indeed be harmful). But don’t try everything at once! One at a time, and the most likely first.

So, what foods and supplements might be of benefit to your brain?

Most of the research into the cognitive benefits of diet and supplements has been concerned with seniors, with alleviating the effects of age on the brain. This is consistent with the belief that there is little, if any, benefit to be gained by young, healthy adults. Having said that, however, the following have been shown to be of benefit in at least one study:

• creatine
• sage
• lemon balm
• a diet high in soy products

Remember my comment about the reliability of single studies! However, since three of these four are all perfectly “natural” food items, there would be little danger in trying these out.

Several substances are worth mentioning as having been of particular interest to researchers for their potential benefits to brains suffering from the effects of age:

• gingko biloba
• ginseng
• choline (lecithin)
• vitamin B12
• phosphatidylserine (PS)
• acetyl-L-carnitine (ALC)
• antioxidants (particularly vitamin E)

This article originally appeared in the May 2004 newsletter.

There is a very common form of forgetfulness that is not really a failure of memory. When we get in our car to drive to place A and find ourselves instead on the road to the more familiar place B, this is not a failure of memory. When we clear the table and find ourselves putting the margarine in the dishwasher or the dirty plate in the fridge, this is not a failure of memory. When we go into a room intending to do one thing and do something else instead, this is not, really, a failure of memory.

These are absentminded errors, and they happen to all of us. They have also been termed action slips, and this term is useful because it points more precisely to the nature of these errors. Let's look at the characteristics of action slips:

• they usually occur during the performance of tasks that are so highly practiced they are largely automatic
• they usually occur when we are preoccupied or distracted
• many involve intrusions of other habitual actions that share some characteristics with the intended action
• such habit intrusions are more likely to occur when:
  • we're departing in some way from our usual routine (for example, you decide to stop adding milk and sugar to your coffee, then finding yourself doing it automatically)
  • the situation has changed, demanding a change in our usual routine (for example, a much-visited shop moves premises, but you keep going to its old location)
  • the situation shares features with a highly familiar situation (for example, you try and open a friend's car with your own car key)

Other types of action slips are:

• place-losing errors: where you've lost your "place" in an action sequence, and so omit or repeat part of the sequence (for example, because of wheat sensitivities in my family, I make our own bread; accordingly, it is a highly practiced recipe, and I add all the ingredients in a fixed order. If something happens to distract me in the course of it, I may be unsure where I am in the sequence, and risk omitting or repeating an ingredient)
• blends: where you get confused between two active tasks (for example, you write an email while thinking about the next email you're going to write, and address the current email to the correspondent for the second email)
• reversals: where you get confused between parts of the same task (for example, you put an empty ice cube tray in the freezer, then turn to the tap to fill it)

You can see from all this that these everyday errors occur in the context of action sequences - that is, sequences of actions that we have practiced so often they have become automatic. Dressing, undressing, washing, making coffee or tea, even making quite complicated recipes - these are all common examples of action sequences.

You can see why action slip is therefore a good name for these types of error.

Is there anything we can do to minimize action slips? Well, the standard advice is to pay attention to what you're doing, but of course the whole point of action sequences is that they free our mind from needing to pay attention, so this is not a strategy I particularly recommend. However, if there are some action slips that you are particularly prone to, you might want to try this.

The most useful thing you can do is simply be aware of the circumstances that set you up for such errors. Then you can either:

• make a sterling effort to pay attention when it's important to you (for example, both my partner and I are careful when we are driving and need to depart from familiar routes, to remind ourselves - or each other - of our destination at key points), or
• use an object to signal that you have done something, or remind you where you are in a sequence (to take the recipe example again, you could move used ingredients to a particular part of the kitchen bench), or
• decide it's not important!

This article originally appeared in the December 2003 newsletter.

The effects of exercise on cognitive function in older adults

A number of studies in the past few years have provided evidence that physical exercise can ameliorate the effects of aging on the brain, in terms both of preventing or postponing dementia, and reducing the more normal age-related decline in cognitive function. The reasons for the effect are almost certainly multiple, for example:

• Exercise has clear effects on cardiovascular fitness, and many recent studies have provided converging evidence that there is an association between cardiovascular fitness and mental fitness — "what's good for the heart is good for the brain".
• Exercise helps control blood sugar levels, and a recent study has found that those with impaired glucose tolerance tend to have a smaller hippocampus.
• Exercise may increase the flow of oxygen-rich blood to the brain.
• Exercise may increase self-confidence, and may reduce anxiety and depression.

Interestingly, while exercise benefits both genders, there is some evidence that it may be of greater benefit to women (at older ages). This may be related to estrogen status. There is some evidence that, in females, the benefits of exercise depend on the presence of estrogen. Levels of voluntary physical activity also seem to depend on estrogen status. This may be behind some of the benefit hormone therapy can have on older women's cognitive functioning.

But the undoubted benefits of physical activity for seniors do not imply that exercise has any effect on memory and learning in younger people. That is quite a different question. In seniors, the hope is that exercise will counteract some of the biological wear and tear caused by aging. Does physical fitness matter at younger age levels?

The effects of exercise on cognitive function in children and young adults

Unfortunately, there have been far fewer studies involving young people. However, one study [1] found that, following a 12 week regimen of jogging for 30 minutes two to three times a week, young adults significantly improved their performance on a number of cognitive tests. The scores fell again if participants stopped their running routine.

In this particular case, it does not seem that level of fitness is the primary cause — otherwise, you'd expect test performance not to be so quickly affected by the cessation of physical activity. The researchers suggested that increased oxygen flow to the brain might have been behind the improvement in mental sharpness. Oxygen intake did rise with the joggers' test scores. Supplemental oxygen administration has been found to significantly improve memory formation in healthy young adults, as well as improving reaction time [2].

On the other hand, preliminary results from a series of studies undertaken with elementary school children do indicate a strong relationship between academic achievement and fitness scores. One study found that physically fit children identified visual stimuli faster. Brain activation patterns provided evidence that the fit children allocated more cognitive resources towards the task, as well as processing information faster. [3]

What studies with non-humans tell us

Rodent studies have a big advantage over human studies - many subjects ready to hand, complete control of their environment - and accordingly, it is easier to receive more direct answers. These studies tell us not simply that exercise can be beneficial for learning, but why it might be so.

Studies with mice have made it clear that exercise can:

• increase levels of BDNF (brain-derived neurotrophic factor; BDNF helps support and strengthen the synapses in the brain (the connections between neurons), as well as helping protect and grow new neurons),
• stimulate neurogenesis (the creation of new neurons),
• increase resistance to brain insult, and
• perhaps promote brain plasticity. [4]

However, while there is no doubt that exercise increases levels of BDNF in the hippocampus, we can’t take it for granted that this is entirely a good thing. Mice bred for 30 generations to be more active (indeed, exercise “addicts”), showed high levels of BDNF and grew more neurons in the hippocampus, and yet performed terribly when attempting to navigate around a maze. Researchers suggested that too much exercise may cause the brain to “max out” in the production of BDNF and neurons, and this may prevent learning. Alternatively, the highly active mice may simply have been too focused on running to concentrate on anything else! [5]

The point is that at the moment, we don’t know for sure what the significance of the exercise-induced increase in BDNF and neurogenesis is. It may be that high levels of exercise place stress on the hippocampus, damaging or killing neurons. The increased levels of BDNF and neuron production may simply be attempts to counteract the damage done. All that's certain is that exercise provokes a lot of activity in the hippocampus, in particular in that particular region of the hippocampus called the dentate gyrus.

Having said that, let's note that this is the first study to demonstrate a case of neurogenesis that is not associated with learning improvement. In general, the production of new neurons is associated with improvement in learning and memory. It would be unwise, therefore, to take these findings as indicating the reverse. What they do suggest is that we cannot assume that such an association always occurs, and that in the case of exercise, it may well be that you can have too much of a good thing! It does seem clear, from this and other studies, that there is a direct association between amount of exercise and BDNF level.

On the subject of whether you can have too much exercise, it's worth noting that a human study found that, while moderate aerobic exercise for up to an hour improved performance on particular cognitive tasks, too much exercise had a deleterious effect. [6]

Brain regions affected by exercise

Notwithstanding the (understandable) emphasis placed on the hippocampus, a critical region for learning and memory, human studies have implicated many parts of the brain. Specifically, one study of seniors found that executive functions were particularly improved by exercise - executive functions are primarily located in the prefrontal cortex. Another study of seniors found reduced grey and white matter in the frontal, temporal, and parietal cortices of those who were less physically fit. In similar vein, another study of seniors found differences in the middle-frontal and superior parietal regions of the brain as a function of aerobic fitness.

Interestingly, in the possibly first study to look at higher cognitive function during exercise (sustained, moderate), it was found that functions dependent on the prefrontal cortex were impaired, but not those requiring little prefrontal activity. [7]

Exercise and diet

Exercise should not, of course, be considered entirely without reference to diet. The effect of exercise on cardiovascular fitness and blood glucose levels is a counterweight to the effect diet has had in inducing impaired glucose tolerance and cardiovascular problems. A number of rodent studies* have found that a high-fat diet impairs learning and memory. Rodent experiments have also found that exercise can reverse the decrease in BDNF levels in the hippocampus resulting from a high-fat diet, and prevent the deficit in spatial learning induced by such a diet. [8]

The question might therefore arise, if the diet has been healthy, is exercise beneficial? Interestingly, a very recent study involving older beagles found that both a diet enriched with antioxidants and a stimulating environment were helpful in preventing or reducing age-related cognitive decline. That is, each were good, but both was best. This doesn't directly answer the question, of course, but it does seem likely that both diet and exercise are important factors in physical and mental health.

Physical exercise and mental exercise

The beagle study used what is termed an "enriched" environment — typically this involves opportunities for social interaction and mental stimulation, as well as physical activity. A mouse study endeavored to separate the components of such an enriched environment, in order to see whether all were necessary to achieve the observed increased neuron production in the dentate gyrus. Interestingly, they found that voluntary wheel running was in itself sufficient to achieve the level of neurogenesis achieved in typical enrichment conditions. [9]

This is intriguing, but as much as anything else it points to the limitations of rodent studies as models for human behavior. A number of human studies, again, mainly with older adults, point to the value of mental stimulation in protecting against cognitive decline. Interestingly, one such study found ballroom dancing was apparently of (surprising) value in protecting against age-related cognitive decline — it was suggested that there was an intellectual component to it lacking in other physical activities. But perhaps, if I may speculate, we should consider more seriously that activities that combine intellectual and physical (and perhaps social) attributes might be best of all.

It does seem clear that, while both mental stimulation and physical exercise might both help cognitive function, they do so in quite different ways, for different reasons.

Recommendations

An analysis of 18 studies [10] on the effects of exercise on cognitive function in older adults concluded that:

• exercise programs involving both aerobic exercise and strength training produced better results on cognitive abilities than either one alone
• more than 30 minutes of exercise per session produce the greatest benefit

Caveat: Not everyone benefits equally from exercise

It does seem clear that older adults benefit more from exercise than younger people, as far as cognitive function is concerned. It also seems that older women, especially those on hormone-replacement therapy, receive greater cognitive benefits from exercise than men.

Generalizations aside, it is as well to remember the findings of a very recent study showing that, while most people benefit (physically) from exercise, the degree of benefit is hugely variable between individuals, and some people don’t benefit at all! [11]

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