May 24 2012
Maintaining our cognitive ability into old age is a top priority for some neuroscience researchers. As our population ages, cognitive decline and dementia are becoming more prevalent, requiring tremendous health care resources and having a significant impact on quality of life. Also, anyone who has had a family member suffer from dementia knows the heavy toll that this slow loss of self takes on the individual and their family.
A recent study sheds some light on the brain changes that correlate with cognitive decline in the elderly. Researchers studied 420 adults in their 70′s, using four different imaging methods to look at their brain anatomy. They found that the robustness of connections within the brain (the white matter tracts) correlated well with general intelligence.
What this study implies is that overall intelligence may be largely a factor of processing speed within the brain and the ability of the various brain regions to communicate with each other. General intelligence is less a factor of the function of any one or small number of brain regions. The white matter are the tracts in the brain where the axons that make up these connections reside.
The subjects in the study are part of the Lothian Birth Cohort of 1936, a group of 1100 people who have been followed since age 11. This is helpful because a lot of information about their overall health and intelligence has been tracked throughout their lives.
It should be noted that the current study did not look at dementia or specifically Alzheimer’s disease (AD). AD is a pathological condition that affects the brain neurons themselves, not the white matter. In AD the different parts of the brain, and the specific functions associated with them, are progressively damaged by degenerative changes. The current study was looking at the changes in brain function that happen as a consequence of aging, in some individuals, and not the effects of a specific disease.
Also, the current study found a correlation between white matter robustness and general intelligence and reaction time. It’s possible that those subjects who performed better on these tests had more robust white matter connections to begin with, rather than losing fewer of those connections as they aged. Longitudinal follow up of the current study will be helpful to sort out the relative contribution of these two factors. In other words – is loss of white matter connections causing cognitive decline in the elderly? This study suggests that it is, but again would benefit from confirmation.
The next question, of course, is how to prevent the loss of white matter connections. Not everyone suffers such a decline as they age. Are the lucky ones who stay sharp into very old age just benefiting from having the right genes, or are there lifestyle changes that can improve our odds? This study did not address that issue, but does provide an excellent tool for studying that question.
There are a number of studies that do look at the risk of dementia and cognitive decline in the elderly. A recent review of this research concludes that the usual lifestyle risk factors you would guess to be associated are in fact risk factors for cognitive decline. These risk factors include hypertension, obesity, smoking, a high saturated fat diet, and social isolation. Protective factors include physical activity, staying mentally active and socially engaged, moderate alcohol consumption, and vegetable and fish consumption.
In short – good overall physical health contributes to overall cognitive health. It is also important to keep mentally engaged, and research suggests that the best way to do this is to keep challenging yourself with new types of activity.
I am not sure I buy the moderate alcohol consumption factor. This research has gone back and forth over the years, depending upon how factors are accounted for. For example, if the non-drinker category is contaminated with ex-alcoholics this tends to worsen the overall outcome of that group. Moderate alcohol consumption may also just be a marker for some other factor, such as social engagement. It’s possible moderate amounts of alcohol, or perhaps certain kinds of alcohol, like red wine, have a vascular protective effect, but I don’t think the final word is in on this yet.
I agree that research into cognitive decline with aging, what causes it, what changes occur within the brain, and how to prevent or minimize it – is a very high priority. Since we essentially are our brains, preserving them in good health and function throughout life is very important. Loss of brain function represents a literal loss of self.
And yes, I am deliberately making a reference to the debate on consciousness that has been raging on this blog over the last week. This kind of neuroscience research, in my opinion, establishes a clear direction of cause and effects. Systemic disease and illness causes changes to the brain and concomitant loss of cognitive function. The brain is a biological organ. Biological factors affect its function. That function is our cognition – our consciousness. The conclusion is ineluctable.
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