July 3, 2013 | 1
Cognitive decline is among the most dreaded consequences of old age and disease. Few things undermine a person’s ability, opportunities, and independence more than loss of mental function. Previous research has suggested that people with higher levels of education suffer less cognitive decline after becoming afflicted by Alzheimer’s disease and other pathological insults to their brain. But why, and does studying in school also help health people resist senility in old age?
It might be that people who are blessed with more robust brains at birth are more likely to be the ones who succeed in school, so that if their brain becomes damaged there is more reserve capacity to maintain adequate cognitive function compared to people born with less powerful brains. An alternative might be that mental exercise during learning boosts brain function and rewires connections in neural circuits to enhance memory and mental performance. The same cellular processes during learning could re-route pathways in the brain to detour around damaged regions. If so, school work could help protect anyone against cognitive decline in old age or after disease even if they were not genetically gifted with bigger brains. A new study by a team of researchers in France and Spain has found that both possibilities (genetics and studying in school) are at work. The more years of schooling a person has, the more resistant people are to cognitive decline in aging because they have both more brain tissue in critical regions, and the level of metabolic function in their gray matter is elevated.
Epidemiological studies over the last decade have shown a lower incidence of dementia among individuals in the elderly population who have higher levels of education and also found that Alzheimer’s disease is delayed in this population. Brain imaging studies have reported anatomical differences in the brains of highly educated individuals that are consistent with greater cognitive performance. The volume of gray matter and the thickness of the cerebral cortex in certain regions important for cognitive function are enlarged, and there are more white matter tracts (bundles of nerve axons) connecting to these gray matter regions in more highly educated individuals. Brain scans that monitor functional activity and metabolism in specific brain regions during memory tasks have shown greater functional activity in neural networks in healthy elders with higher education compared to healthy young individuals or elders with lower mental performance. This increased functional activity is evidence that their brain is undergoing more active re-wiring during learning tests.
This collection of studies is difficult to interpret because a combination of factors could be involved. For example, does school work preserve mental activity in elderly people in general or only those coping with Alzheimer’s disease? Since structural and functional brain imaging were performed in separate studies in the past, it is also unclear whether these two brain response operate together, simultaneously increasing brain bulk and function.
This new study, led by Gaël Chételat at INSERM in France, investigated both structural differences and functional differences in the brains of healthy elderly individuals. The subjects were prescreened to detect amyloid deposits in the brain to exclude people who might have preclinical Alzheimer’s disease. This is an important advance over previous work, says Dr. Chételat. “This is the first [study] to have assessed this question in a sample of elderly with no amyloid deposition. This is important because it allows us to specifically address the relationship to education without the effect of pathology that complicates interpretation,” he says. The battery of tests included MRI to pinpoint anatomical differences in the brain, PET imaging to assess metabolic activity in brain tissue, and functional MRI, which examined neural activity and functional connectivity in the brain at rest in people between the ages of 60 and 80 who had from 7 to 20 years of school education.
The findings showed a linear increase in gray matter volume in proportion to the number of years of education the elders had. This included increases in three brain regions (right superior temporal gyrus, anterior cingulate gyrus, and left insular cortex). Brain metabolism also increased proportionately with years of education in the anterior cingulate gyrus, and functional connectivity between several brain regions that are critical for cognitive function increased linearly with the number of years of education. (For doctors and neuroscientists reading this article, this included increased connectivity with the anterior cingulate gyrus and the right hippocampus, left angular gyrus, right posterior cingulate, and left inferior frontal gyrus.)
The conclusion is that both the structure of the brain and its function in old age are increased in proportion to the number of years of education, and that these fringe benefits of classroom work benefit healthy elderly people who are free of Alzheimer’s disease. The authors conclude that while people with genetic advantages may excel in school, school work itself benefits everyone by building stronger and more active brains. “It is crucial to promote the beneficial effects of environmental factors: food, sport, mind and cognition,” Dr. Chételat says, as a complementary approach to medication in resisting cognitive decline with age.
Arenaza-Urquijo, E.M. et al., (in press) Relationships between years of education and gray matter volume, metabolism and functional connectivity in healthy elders. NeuroImage, available on-line in advance of print doi: 10.1016/j.neuroimage.2013.06.053.