Losing our minds in middle age

When negative stress affects our well-being, we sometimes feel like we are losing our minds...

But when in the lifespan does this really happen? When do we lose our brains?

Until age two we experience rapid growth of brain cells, or neurons. Around that age, rarely used neurons and unneeded connections between neurons (synapses) are reduced. Past research by Hedman, van Haren, Schnack, Kahn, and Hulshoff (2012) suggests that childhood is a time of brain growth, with more neurons being produced. Starting around age thirteen and continuing through adolescence we see brain volume loss as pruning reoccurs so that our brains can be more efficient. Most of young adulthood sees little change in brain volume, but starting at age 35, MRI scans demonstrate a yearly loss of about 0.2% of brain volume. This loss accelerates in older age: in our sixties this increases to a loss of about 0.5% of brain volume every year; this acceleration is often given as one of many explanations for other normal declines associated with aging.

To examine in detail the brain volume loss during the transition to midlife, Guo, Isohanni, Miettunen, Jääskeläinen, Kiviniemi, Nikklinen, Remes, Huhtaniska, Veijola, Jones, and Murray (2016) examined MRI scans of 43 men and 23 women as they aged from their 30s (33-35 years) to their 40s (42-44 years). The participants in this longitudinal study were part of the Northern Finland 1966 Birth Cohort so they should have had similar experiences in their lives as they grew up at the same time. The researchers' goals were to measure overall brain volume at both ages, to identify the locations of any loss as observed in the second MRI performed when the participants were in their 40s, and to clarify any sex differences that emerged.

Total brain volume decline was higher than predicted by past research: on average men lost 3.21% and women lost 4.03%. This sex difference was very small but it reached statistical significance, meaning that the difference was unlikely to be due to chance.

The location of loss also showed a sex difference. After taking into account percentage of total brain loss, Guo et al. found that men lost most of their neurons in the midline areas (specifically: bilateral precentral gyri; bilateral paracingulate gyri; and bilateral supplementary motor cortices). Most of these areas relate to motor skills and one may be involved in decoding certain emotions.

Women's loss was more spread out with most of it occurring in the outer brain (specifically: bilateral frontal parietal; temporal lobe; occipital cortex; cerebellum). These areas relate to language, motor skills, sensory interpretation, vision and visual memories, and emotion association.

Guo et al. did not make guesses beyond a quick mention of hormones as to what caused the sex differences in overall brain loss or the sex differences in loss locations. They also speculated that these differences may translate into differences in midlife men's and women's health or behavior, yet they did not offer any examples.

That leaves us all free to speculate. One bit of demographic information that caught my eye was that the researchers coded participants on "parental leave" as working full-time, because it meant that the participants usually worked full-time but were absent from that work to take care of a newborn child. This made me think about other research related to brain volume and parenting. For example, when women are pregnant their brain volumes can shrink an average 4% and not return to normal volume until about six months after birth. First, that makes the 4.03% decline found in Guo et al.'s female participants sound less ominous: this sort of decline is a normal experience for many women in young adulthood. Second, although most Finnish women in the 1980s usually started having babies at age 29, is it possible that some of the 23 women in this study gave birth just before the second MRI scan? Or is the location of brain loss during pregnancy similar to the location of women's brain loss in the transition to middle age?

Starting in the 80s, Finland offered parental leave to fathers as well as mothers. So it is possible that some of the male participants may have also identified themselves as being on parental leave. However, we know that fathers and mothers often take on different roles in parenting. For example, women are more likely to report that they get up to feed or care for babies in the middle of the night; mothers report more sleep loss than fathers even as children grow older. Poor sleep is associated with brain volume loss in the frontal, temporal, and parietal lobes. Different parental roles and related sleep loss may contribute to women's additional 1% of brain loss; brain volume loss related to poor sleep and brain volume loss related to women's transition to midlife are located in similar areas.

In the end we do not know what is causing these declines or sex differences, and even if we did, at this point we cannot know if these are related to any changes in men's and women's behavior or health as they age. The one thing you can know for sure is that if you are middle aged, pregnant, a new mother, or are sleep-deprived, you ARE losing your mind.

FURTHER READING:

The Guo et al. (2016) article can be accessed online or through your local college library.

Loss of brain cells does not always relate to loss of cognitive functioning. Read an APA Monitor on Psychology article by Melissa Phillips on the strengths of the middle-aged mind.

Childhood trauma can also reduce brain volume. Read a report on trauma's effects on brain development from the Child Welfare Information Gateway (U.S. Dept. of Health and Human Services).

BONUS:

Watch a video from Brown University on Synaptic Pruning:

In defense of Kristen Stewart

There are many memes mocking Kristen Stewart for not smiling. This week's meme is one of them:

 
However, if you type her name into a Google Images search, and then do a second search for her Twilight co-star Robert Pattinson you will see that the two actors are both pictured smiling and not smiling. When I did this (albeit unscientific) search and compared the first 25 images for both actors, I found that both of them were shown smiling 11 times and not smiling 14 times. So why the shade for Kristen while Robert's image remains sparkling?

Part of it is due to gender expectations in our culture: women smile more than men and are punished more for not smiling. The most recent review of this phenomenon occurred in 2003 when LaFrance, Hecht, and Paluck published a meta-analysis of 162 studies. A meta-analysis allows researchers to statistically combine the results of many studies to determine if a difference exists and how big (or meaningful) that difference may be. The overall results from LaFrance et al. confirm that across these studies there is a small to moderate, or noticeable in the real world, effect of men smiling less. Fans are used to seeing women smiling so they notice and react poorly when Kristen Stewart bucks that gender expectation. Likewise, fans are used to men not smiling so the same facial expressions from Robert Pattinson go unnoticed as if they were invisible.

The researchers also used statistics to examine the different contingencies of the studies to see what is associated with this difference getting smaller or larger. In some cases it would come out smaller than the overall difference: in these situations women and men were closer to smiling at similar rates. Many of these effects were very small or even close to zero, which means that in the real world these contexts would likely be associated with very few observable differences between women and men:
*when people are not aware of being observed
*when they are in a group of four or more people (so the focus is not on one person)
*when they are not interacting with the people around them
*when they are very familiar with each other
*if they are comfortable because there is low pressure to impress
*when they are talking to a younger person or an older person
*when they are paired with a woman
*when they are interacting with somebody of the opposite sex
*when they share equal power with the other person
*if they are asked to play a role that requires caretaking, like taking care of a baby
*if they are forced to argue against the other person
*if people are from England
*if people are African-American
*if people are middle aged or senior citizens

In other cases this gender difference would come out larger than the overall difference: in these situations women were even more likely to smile than men. These range from moderate to almost high effects, which means that in the real world these contexts would likely be associated with actual observable differences between women and men:
*when people are alone (and presumably self-conscious about being observed)
*when people are alone but asked to imagine another person being with them
*when they are paired with a man
*if they are asked to persuade somebody
*if they have to reveal personal information about themselves
*if they are made to feel embarrassed
*if people are Canadian
*if people are teenagers (a time of gender intensification)

Looking at the results LaFrance et al. note that,"...the extent of sex differences in smiling is highly contingent on social groups and social factors" (p. 326). In simpler language, men tend to smile less than women, but when this happens and how obvious it is depends on the characteristics of the situation. For example, there are personal and cultural factors like age, race, and culture. There is also the question of what is required in this situation: do they have to persuade; argue; or be in charge of the care of another being? Who are they interacting with - do they share the same age, sex, or level of power in the situation?

Notably for Kristen Stewart the results also demonstrate that people are more likely to show this gender difference when they know that they are being watched, when they imagine that they are being watched, and when they feel like they need to make a good impression (or instead are facing embarrassment). So another reason that fans may be critical is that, by being an actor and a public figure, she is constantly in these contexts yet she does not do what most women would do in those situations, she does not smile. On the other hand, if Robert Pattinson reacts the same way on the red carpet he is actually doing what we expect men to do in those situations, so once again he escapes criticism. And that really bites.

Further Reading:

A pdf of the LaFrance et al. (2003) article can be accessed on Dr. Elizabeth (Betsy) Paluck's website.

 Kristen Stewart may wish to work on her smile - not for the fans - but for how smiling, even fake smiling, might help her deal with stress. Read the Association for Psychological Science (APS) coverage of research done by Kraft and Pressman (2012).

Kristen Stewart is not alone. Read Emily Matchar's article, "Memoirs of an Un-Smiling Woman," from The Atlantic.