Aging Shrinks the Brain

In most people, their brains get smaller as they age. It is not so much that neurons die but that their terminals and synaptic junctions shrivel. A known cause is the over-secretion of cortisol by stress, but perhaps there are also other age-related causes.

However, shrinkage with age is not inevitable. Certain people are "super-agers," defined as adults over 80 with memory at least as good as normal middle-aged adults. A usually reliable index for decline in memory ability is the degree of brain shrinkage, specifically cortical volume. Brain-scan studies show that super-agers have thicker layers of cortex than do others of the same age. Thus, their cortex has not shrunk as much as average elderly or they had more to start with. It is possible that something about the lifestyle of super-agers protected them from brain atrophy. It is not convenient to know how much cortical volume the elderly had in their youth. But the second option has been tested in a study that compared the rate of cortical aging in 36 adults averaging 83 years of age. The investigators recruited super-agers and normal elderly and tested them in an initial visit and again 18 months later. Before and after cognitive and memory tests and brain scans provided a basis for tracking the rate of aging.

Super-agers scored higher on cognitive and memory tests than the average group at both the beginning and end of the study period. This suggests that they may have been endowed with more mental capability when they were young. But it also indicates that super-agers are more resistant to age-induced mental decline. The two groups did not differ in any other neuropsychological measures, education, or estimated IQ.

A clear correlation occurred between the two groups and cortical volume. The average memory group had over twice as much cortical shrinkage over the 18 months as did the super-agers. Some in the average group lost as much as 3.4% of cortical volume per year. If that continued over the next 10 years, they would suffer a devastating loss of over 30% in cortical volume.

Unfortunately, the study did not examine the lifestyles in the two groups. The super-agers may have just had good genes or may have been more mentally active over their lifetime and had healthier diets, more exercise, and less stress than those in the average group. Notably, some shrinkage did occur in the super-agers, on average at a rate of 1.06% per year. They still scored as well as the average 50-year old on various cognitive and memory tests. It is possible that some shrinkage is a good thing, reflecting perhaps a pruning of neural circuitry as the brain learns and develops more efficiency. Pruning is a conspicuous phenomenon in the brains of the fetus and infants as maturation progresses. Obviously too much pruning can leave neural circuitry with insufficient resources.

These results also emphasize that age discrimination is not defensible. Each elderly person's mental competence has to be judged on its own merits, not on a negative stereotype of the elderly.

Sources:

Rogaalski,E. J. et al. (2013) Youthful memory capacity in old brains. J. Cognitive Neuroscience. 25(1), 29-36.

Cook, Amanda H. et al. (2017). Rates of cortical atrophy in adults 80 years and older with superior vs. average episodic memory. JAMA. 317(13), 1373-1375.

Thwart Stress Effects on Memory

It is well known that stress can impair memory. Everyone has had some experience of this kind. As a student suffering test anxiety, grades are likely to suffer. In high-stakes social or business interactions, the stress may well cause memory to fail us, as when Presidential candidate Rick Perry forgot the name of the agency he wanted to abolish if elected, or when we forget a friend’s name in the process of making a social introduction. How does stress do this? Is there anything we can do about it?

First, we need to know what stressful events do to the body and brain. Brain freezes, like Rick Perry's, probably occur because thinking can get so preoccupied with the stress-inducing stimuli that other thoughts cannot emerge. But other kinds of stress-induced memory impaired come from the well-known “fight or flight” response in which stress activates the release of adrenalin into the blood stream. Adrenalin has many bodily effects that support fight or flight, such as raising heart rate and blood pressure, and increasing arousal perhaps to the point of anxiety and fear. The increased attentiveness may have a fleeting beneficial effect on memory, as has been demonstrated in laboratory experiments. But the other effects of adrenalin on anxiety and distress are likely to impair memory.

The other thing that happens during stress is the activation of the anterior pituitary gland’s release of ACTH, which in turn activates another part of the adrenal gland to dump cortisol into the blood stream. In the short term, cortisol can have many beneficial effects for combatting stress, such as mobilizing white blood cells and enhancing the immune system. But cortisol binds to cells in the brain’s hippocampus, the area that converts new experiences into memory. This binding actually disrupts the memory-forming process. Ultimately, if stress continues, the synaptic regions deteriorate, making the impairment permanent.

The effects of both adrenalin and cortisol were revealed in an interesting study of mild social stress. Here, the focus was on a theory of how stress effects on memory might be thwarted by a learning technique called forced retrieval. Prior research with students, had shown, that the usual study technique of re-reading notes or text is not nearly as effective as requiring the learner to actively retrieve the information, as one might do, with flash cards, for example. Just a few months ago, I posted a blog on this forced retrieval phenomenon as a key element in “strategic studying.”

This new research was aimed at testing the possibility that forced retrieval might protect learners from the memory deficits caused by stress. In the study on the first day, 120 subjects studied a list of 30 nouns or images of nouns one at a time. Then, one half of the group restudied the items while the other half practiced retrieval by recalling as many items as they could (but without feedback telling them if they got it right). One the next day, half of each group were stressed by being required to solve hard math problems and by giving speeches in front of two judges and three peers. Then they were tested. Twenty minutes later they took a second test on items that had not been tested on the first test. The results revealed that retrieval practice yielded better results.

  

On the first test, we see that the stressed learners who just studied the items the day before had fewer of the items remembered on the first test given immediately after the stress. But there was no such effect on the stressed leaners who used retrieval practice during the initial learning. This protective effect of retrieval practice was evident on the second test 25 minutes later. In fact, the retrieval practice effect was better than on the first test, even though different items were tested. You may have noticed that the stressed study group on the second test did worse than they did on the first test. This is attributed to a mild effect of adrenalin, which as mentioned above can have some benefit on memory. Adrenalin’s action is immediate and is apparently swamped on the second test by the delayed release of cortisol, which shows up by the second test. Students might note that the magnitude of difference may appear small, but in percentage terms could equal to more than two letter grades (compare the two stressed groups on the delayed test).

To explain why forced retrieval works, the authors speculate that it provides better initial encoding. That is, the new information is registered more strongly if you make yourself try to retrieve it. This is consistent with the everyday experience that most of us have had wherein information that strongly grabs our attention is more likely to be remembered. Forced retrieval is a way to make ourselves pay better attention to what we are trying to lean.

Readers wanting to learn more about improving memory are urged to check “Memory Medic’s” books, Memory Power 101 and Better Grades, Less Effort.

               

Sources:

Klemm, W. R. (2016). Strategic studying. October 9, http://thankyoubrain.blogspot.com/2016/10/strategic-studying.html

Smith, Amy M. et al. (2016). Retrieval practice protects memory against acute stress. Science. 354 (6315), 1046-1047.