Contrast the lifestyles of people in their seventies who do and do not suffer from Alzheimer’s disease and clues about how to keep your brain ticking over nicely, well into old age, jump right out at you. Those who do not suffer with this dreaded disease tend to have been more committed to a regular exercise regime throughout their later years; hitting it as hard as their inevitable physical infirmities would allow (TOP TIP: Tai Chi is an excellent example of a low impact physical exercise which improves strength and flexibility at any age. It requires no equipment and can be practiced wherever you happen to be). They tend to have been more engaged in a wider array of social activities. They tend to have been careful with their diet in the long term, favouring a healthy Meditteranean-style diet (see below for more) over a typical modern Western diet (often high in saturated fats and sugars). They also tend to have been more proactively involved with their local community and more motivated to seek regular mental stimulation. People are now being advised to adopt a variety of brain-healthy habits if they wish to reduce the likelihood of developing cognitive deficits that the progression of Alzheimer’s disease can, but does not always, induce.
Alzheimer’s disease is the most common of the many different types of dementia, affecting 10% of those over 65 and almost 50% of people over the age of 85 (Evans et al, 1989). Dementia describes a syndrome that involves progressive cognitive decline occurring at an accelerated pace compared to the very gradual loss of mental faculties associated with normal aging. Dementia can involve the deterioration of reasoning, judgement, thinking, mood control, language, understanding and, most famously of all, memory. Colloquially-speaking, Alzheimer’s disease is an almighty metabolic cock-up: a brain protein (beta-amyloid) is not constructed properly due to a misprint in the genetic recipe, causing it to form tiny sticky clumps (plaques) that develop between brain cells, preventing them from communicating with each other properly and eventually killing them off entirely. To make matters worse neurofibrillary tangles accumulate within brain cells, which also ultimately leads to cell death.
Depending upon which brain structures these plaques form in, different mental functions can be disturbed. For instance, a brain structure that typically gets more than its fair share of amyloid plaques and neurofibrillary tangles in Alzheimer’s is the hippocampus. As I’ve described in a previous brainpost this brain structure is critical for the formation of memories and so when its function is compromised by the plaques and tangles of Alzheimer’s, people can become extremely forgetful.
To date, scientific research has yet to come up with a treatment to stop the formation of these amyloid plaques and neurofibrillary tangles, but there is evidence that drug treatments designed to boost the cholinergic neurotransmitter system can make symptoms less severe. Furthermore and extensive body of studies has gradually accumulated over the past 20 years to indicate that some people are able to tolerate the disruption caused by these plaques better than others (e.g. Katzman et al, 1988). The Katzman study described individuals who had shown no cognitive impairment whatsoever in life, yet post-mortem examination of their brains revealed that telltale signs of Alzheimer’s disease (the plaques and tangles) which had progressed to a considerable degree. This disparity begs the question: if two people’s brains are affected by the same degree of plaque damage, why does one continue to enjoy normal mental faculties, whilst the other suffers severe impairments to their memory, thinking and mood? The concept of “cognitive reserve” was introduced to describe brains which seemed to be able to compensate for the damage done by Alzheimer’s, presumably by using other brain networks not affected by the metabolic damage to take over certain cognitive tasks.
A separate study, this time involving 593 individuals in New York over the age of 60 and on an “at risk of dementia” register, concluded that “increased educational and occupational attainment may reduce the risk” of developing Alzheimer’s disease. A more recent study conducted in the UK concluded that cognitive reserve is almost entirely mediated by childhood cognitive ability and educational attainment, whilst whether people had successful careers or not had very little influence. So does this mean that the only way to “plaque-proof” yourself is to study hard at school and stay in education for as long as possible? Well, yes and no. Yes – in the sense that this certainly seems to protect you from the ravages of amyloid plaque buildup. No – because there ARE things you can do to build up your cognitive reserve in later life, they just have nothing to do with what you do for a living and how good you are at it.
Diet may well influence the rate at which Alzheimer’s disease progresses, probably due to the negative influence of a modern Western diet on the brain’s blood vessels. In a recent article, prominent Alzheimer’s researcher Dr Scarmeas describes a study providing evidence that a traditional Meditteranean diet – characterised by lots of fish, unsaturated fats, vegetables, fruit and cereals – seems to protect against the development of Alzheimer’s disease. In a different study which used a mouse model of the disease it was suggested that coffee may help to slow the progress of Alzheimer’s disease by preventing build up of amyloid plaques.
A recent NYT article describes research into bilingual people who seem to develop the symptoms of Alzheimer’s on average 5 or 6 years later than those who speak only one language. This suggests that the cognitive demands of regularly switching between two or more languages may delay the onset of Alzheimer’s. Although this has yet to be proven, it is thought that speaking two languages may increase cognitive reserve by improving the function of prefrontal brain areas involved in executive control. Executive control involves mental functions like holding relevant information in working memory whilst ignoring irrelevant distractions, as well as other faculties relating to problem solving, planning and decision making.
In the not-so-distant future it may be possible to replace brain cells damaged by the abberent metabolic processes of Alzheimer’s with fresh ones created from a person’s own skin cells. Other recent research has suggested that the amyloid plaques might cause memory problems by attaching to certain important neurotransmitters, and that drugs preventing this from happening may help to ease the symptoms of memory loss associated with Alzheimer’s disease. In light of the importance of early intervention to catch the disease before it causes too much damage new scanning techniques have already been developed to spot the disease before it induces any clinical deficits.
A variety of lifestyle changes can build up cognitive reserve, helping to keep dementia at bay and improving quality of life to boot!
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From adolescence onwards we all begin to lose brain cells. As a consequence our brains gradually and inexorably shrink (compare the “old” brain on the left to the “young” brain on the right). In fact by the age of 80 your brain will occupy 15% less of the space within your skull than in the prime of life. Yet over the course of adulthood, as our brains are losing more and more cells, our knowledge and repertoire of skills nonetheless continues to grow as we accumulate more and more experience. How is this possible? Well, despite the incremental decrease in quantity of brain cells over the years connections between neuronal networks that are in regular and intensive communication with each other are selectively reinforced. This enables increased efficiency in execution of the mental processes that those networks support. Hence we can do more with less as we age. Sadly, for all of us, there will always come a time when the degree of brain cell loss is such that mental function begins to decline. In other words, if we all could live forever, dementia will inevitably strike at some point in time.
Although we cannot halt the process of grey matter loss completely, the good news is that we can slow down its progression. This month a study conducted at the University of Pittsburgh and published in the journal “Neurology” describes the influence of regular exercise on the rate of reduction of brain volume and cognitive function in 299 elderly individuals.
It was observed that those individuals of this group of average age 78 who walked in excess of 6 miles per week had a significantly reduced rate of grey matter loss and consequently a lesser degree of cognitive decline. The greater the distance walked each week, the smaller the reduction in volume over a 9 year period within their frontal lobe, occipital lobe, entorhinal cortex and critically, in the hippocampus. My post last month described the vital role that the hippocampus plays in the creation and recall of long term memories.
This begs the question – how and why does exercise slow down the rate at which grey matter shrinks? An exciting possibility is that all that walking might actually increase the rate at which new brain cells are created; a process known as neurogenesis. This boost in the creation of new brain cells might help to compensate for the loss of old brain cells. Evidence to support this hypothesis comes from research conducted over a decade ago suggesting, in the mouse brain at least, that exercise does indeed increase the rate of neurogenesis.
Exactly why this happens is unclear, but I would propose that, given the hippocampus is heavily involved in navigation, particularly when it comes to flexibility in finding the best route from A to B, it would make sense for physical activity to trigger production of new cells in this brain area. A greater number of hippocampal neurons would presumably support a greater capacity to memorise routes and landmarks encountered whilst exploring the environment. This could feasibly convey a critical survival advantage by helping to prevent people from getting lost. Over the thousands of years of our species evolultion, getting lost was probably an excellent way of deleting oneself from the gene pool and so those with movement-triggered hippocampal neurogenesis may have been more likely to survive.
This seems a plausible (but by no means concrete) account of why older individuals who take regular exercise appear to have more grey matter and superior cognitive function than those who do not. Whatever the true explanation, it seems clear if you want to hang onto your marbles in the long term then it’s probably a good idea to take a regular stroll for the rest of your life.
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