An old craftsman is shown in the doorway of his shop.

Keeping Our Wits

Airplanes are required to carry more than the minimum weight of fuel that could insure a safe flight. In seeming analogy, humans overproduce neurons in preparation for the journey that starts in early development, then discard the unneeded surplus. Tiny microglia remove excess neurons soon after birth and, later, the unnecessary connections that would otherwise unite neurons into networks. Adjustments in the number of neurons and their interconnections are possible by neurogenesis throughout most of life, although the evidence for neurogenesis has been contested since it was first reported by Joseph Altman in 1962.

At the other end of life, aging brains undergo shrinkage and atrophy in most people. The cerebral cortex tends to show the changes most strikingly, losing the surface area and therefore the sulci that give the highest functional region its wrinkled appearance.

To carry an analogy to its breaking point: Just as pilots try not to overuse their fuel supply, people are concerned about preventing loss of brain function through aging, drug use, stress, and disease. Fortunately we cannot use up our brains through overuse. There is evidence that aging in the brain can be postponed by exercise and meditation, among other practices that support general health. There are even ways to slow the aging of the brain while the rest of the body continues into senescence.

In fact there is a name for the postponement of brain aging, the cognitive reserve. So in some people there is prolonged brain fitness, and the cause that sets such people apart is presumed to be their cognitive reserve.

This presumption can lead people astray, when the cognitive reserve is taken to be a “thing”, or reified, for naming is not explaining, nor does it signify understanding. Consider the fate of the term “addiction”, which was a label for substance abuse that became a disorder and then a brain process without ever gaining clarity or concreteness.

Cognitive reserve likely lacks a location in the brain. It’s getting more popular to map behavioral differences to brain connections (research here) even for the famous Phineas, Tan and H.M. It seems likely to me that cognitive reserve is more a matter of connectivity than a fountain of youth tucked away at a spot in the brain. Important connectivity may extend outside the brain. Measures of EEG coherence that assess the extent of neuronal interconnectivity appear to estimate the magnitude of cognitive reserve. Admittedly, this view destroys any analogy involving thirsty airplanes. There is evidence that cognitive reserve counteracts some of the genetically programmed attacks on brain connectivity that contribute to dementia.

Problems of construct validity, for that is the problem we face with reification, are often thorny. They call on a degree of statistical expertise that isn’t a feature of undergraduate psychology classes and I won’t lead a discussion here, except to cite an article.

A woman is shown seated at a spinning wheel.

BIO: Aging affects the brain in a number of ways (watch for cognitive reserve to appear at 38 minutes). Research on the biological foundation of the cognitive reserve is dwarfed by work on resilience, which is a similar concept. Such research has clarified the effects of stress on the brain, which is what a cognitive reserve offers protection against. Resilience is easier to explain on an evolutionary basis, since it operates to increase reproductive fitness in each individual, while a cognitive reserve is seen mostly in old people who have completed all the reproduction they are likely to accomplish. However, Allen, Bruss and Damasio have pointed out that old people have long been known to support the inclusive fitness of a community by caring for and educating the young of other parents.

Quoting from those earlier topics, research has shown that “microglia nibble at some synapses, performing a kind of synaptic pruning that makes weak synapses harder to retrieve.”

Under “chronic stress the work of the microglia turns harmful. They “turn rogue” and destroy  synaptic connections.” The cognitive reserve is the kind of resilience that we rely on to prevent such changes. The link between stress and mental decline is strengthening with recent research.

A biological measure of dementia might simplify the task of quantifying the cognitive reserve. There are too many varieties of dementia and too many causes of cognitive decline to make latency measures of reaching a criterion of cognitive impairment very useful.

PSYCHO: Unlike some bodily changes—lens cataracts, say—the mental hesitations that accompany aging are fairly obvious. We cover them with references to “brain fog” or “senior moments”. The Global Council on Brain Health recommends taking up stimulating activities, but it is not specifically prescriptive: Does that mean video games? Brain foods? Crossword puzzles? This website says that activity means physical activity. Will that explain the greater value of visiting a museum than a movie theater? The gut bacteria mentioned in the discussion of moods may help to link physical and cognitive health.

The fuzziness of the concept prevents finding a convincing remedy. For now, despite the temptation to lump brain reserve and other antidementia “reserves” together, let’s conservatively keep them  distinct.

Cognitive reserve can be loosely but operationally defined as brain fitness. It appears as the postponement of dementia. More positively, the fitness link suggests that “You can think of cognitive reserve as your brain’s ability to improvise and find alternative ways of getting a job done.” (However, the same paragraph insists that cognitive reserve is “developed by a lifetime of education”, a belief that has inflamed controversy that we will examine in a moment. Furthermore, it recommends a Guide to Cognitive Fitness that does not specifically mention education in the advertisement, though it does wave the flag for brain food. 😊 )

Cognitive reserve, which seems helpful in cases of Alzheimer’s disease and multiple sclerosis and may help with TBI, has been claimed to develop from education and mental effort before an injury or old age occurs.

Education, particularly higher education and late-life education, have offered a plausible explanation for individual differences in responses to traumatic brain injury. However, such loose associations call for further research to avoid reminders that correlation is not causation. For one thing, education comprises a multitude of experiences, and it’s possible that openness to new experience, rather than book learning, provides the effective defense. In addition to personality, lifestyle could be important. However, neuropsychologist Robert Wilson has argued that education is irrelevant to the magnitude of a cognitive reserve.

SOCIAL: Social isolation is associated with memory declines in old age, and a diminished cognitive reserve has been hypothesized to be responsible. However the positive correlation between social isolation and cognitive decline is uneven. For people who are already victims of depression or anxiety, social isolation does not weaken, nor does social support strengthen, the advantages of a cognitive reserve.

Social activity, on the other hand, is part of the lifestyle factor that may promote a cognitive reserve.

SOCIAL: Giving directions definitely varies from person to another. Culture is one factor: Giving directions in Nicaragua or Japan is no picnic, though technique helps (research here).

Our sense of direction varies among individuals, sexes and cultures. It is hard for a Westerner to grasp the subtle navigational skills of Pacific Islanders in past centuries, for example, or for anyone to find their way across some places.

Does using a GPS threaten these abilities? Will using high-tech direction finders weaken our native abilities to navigate? The first effect of GPS systems may be to “medicalize” poor navigation. Just as clocks have put a premium on good timekeeping and cut us off from relying on the sun alone, GPS systems not only help us but make us expect perfection in arriving where we want to be. One thing leads to another: Without clocks we would not have the GPS, and without the GPS, where would we be?

Like a clock, a GPS has no regard for our health or our proneness to errors in specifying exactly where we want to go. Unlike cognitive maps, the GPS has not evolved to keep us alive. Even worse, there is speculation and some evidence that relying on a GPS may rob us of some of our navigational ability through disuse, by destroying our need to explore.

In other words, there may be costs to balance the obvious benefits of GPS.

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