An early sign of the progress of old age is when you have to hang onto something to safely get into your underpants. Is this a signal of wider physiological changes in the brain? Are struggles to get into underpants warnings of fading intelligence?
Australian investigator, Kaaren Anstey and her collaborators have convincingly shown that among groups of people aged from 60 to 90 years lower scores on tests of vision, hearing and balance predict lower scores on intelligence and memory tests1-3, but these documentations of discouraging news are not straightforward to interpret.
I visit Harcourt Arboretum most years to check on some favourite trees. Each time I gladly find that the trees have flourished but reflect that, since my last visit, my brain has shrunk and my intelligence has correspondingly declined. Just because tree burgeoning and wit-withering happen over the same period of time they will be correlated. But savage tree pruning would not check my decline because the trees and my brain are independent clocks measuring the same intervals. Similarly the amounts of changes in my eyes and ears and knees and vestibular system may strongly correlate with the amounts of changes in each other, and also in my brain, memory and intelligence just because they all, quite independently, progress over the same periods. In ageing studies, it is crucial to remember that most bits of us degrade over the same periods of our lifespan but not necessarily for the same reasons or at the same rates.
To resolve this we need a direct measure of how much our brains have changed as we have aged that we can add into computations of relationships between sensory and mental abilities. The number of white matter lesions in the brain (WMLs) increases throughout life and so is a convenient, index of global brain changes with ageing. Many studies show that WMLs correlate negatively with scores on tests of speed of decisions, intelligence and memory. In one of our studies, volunteers’ WML scores were entered into regression equations with their ages, and scores on intelligence and balance tests4. As expected, the more WMLs they had the worse were their scores on intelligence and balance tests. As in some Australian studies, balance also correlated with intelligence but this association vanished when densities of WMLs was also taken into account. This strongly suggests that the relationships between age-related declines in balance and in intelligence are not accidental temporal synchronicity of independent processes but are functionally connected because age-related brain changes, marked by increases in WMLs, drive changes in both.
If tottering is a sign of decline in intelligence can we preserve our brains and wits by improving our balance? Yes, up to a useful point. Further analyses find that amounts of declines in balance, intelligence and memory are effective markers for general health. As health declines, so do our brains and intelligence test scores. Declines of health are inevitable in old age but are slowed by good habits such as eating less and exercising more. Among many other benefits this improves brain blood supply and so slows brain ageing, reduces numbers of WMLs and so maintains both balance and intelligence. We should not take changes in balance as omens of inevitably imminent brain-rot but as warnings to pay more attention to the whole of our bodies and begin, in the most literal sense, to take as many steps as we can steps to minimise and to slow changes that, in the long run, we all have to put up with as best as we can.
1. Anstey, K. J., & Smith, G. A. (1999). Interrelationships among biological markers of aging, health, activity, acculturation, and cognitive performance in late adulthood. Psychology and aging, 14(4), 605.
2. Anstey, K. J., Hofer, S. M., & Luszcz, M. A. (2003). Cross-sectional and longitudinal patterns of dedifferentiation in late-life cognitive and sensory function: the effects of age, ability, attrition, and occasion of measurement. Journal of Experimental Psychology: General, 132(3), 470.
3. Anstey, K. J., Dear, K., Christensen, H., & Jorm, A. F. (2005). Biomarkers, health, lifestyle, and demographic variables as correlates of reaction time performance in early, middle, and late adulthood. The Quarterly Journal of Experimental Psychology Section A, 58(1), 5-21.
4. Rabbitt, P. M., Scott, M., Thacker, N., Lowe, C., Horan, M., Pendleton, N., … & Jackson, A. (2006). Balance marks cognitive changes in old age because it reflects global brain atrophy and cerebro-arterial blood-flow. Neuropsychologia,44(10), 1978-1983.