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:
When I was growing up, all the girls read Are you There God? It's Me Margaret., by Judy Blume. Its main character, Margaret, looks forward to developing breasts and getting her first menstrual period. When these finally occur she feels triumphant! More recently, Hello Flo advertisements also portray puberty as something that girls desire: they are upset if menstruation doesn't start quickly enough. Of course, fiction writing and advertisements may not reflect the full story of girls' puberty as witnessed by these memes:
Keenan, Culbert, Grimm, Hipwell, and Stepp (2014) investigated the relationship between African-American and European-American girls' pubertal timing (what age things happen), pubertal tempo (how much time passes between stages of puberty; how long puberty lasts), and depression symptoms. Their sample was part of the longitudinal Pittsburgh Girls Study, so it was large (more than 2,000 girls of diverse backgrounds), data were collected at age 10 and then each year for up to a decade, and the participants were more likely to come from low-income homes. Each year the girls completed a depression inventory; their caregivers (mostly mothers) completed the same depression inventory about their daughters. From this Keenan et al. could learn how many depression symptoms were common at each age and see how they related to the other variables of ethnicity and puberty. Overall, depression symptoms were highest at age 10 and declined at various rates after that. Even so, across the decade the girls reported that only one or two symptoms on average. The authors maintained that even "minor depression" like this can put individuals at risk for other problems. The girls provided data on pubertal timing and tempo by matching themselves to standard pictures that portrayed different stages of breast and pubic hair development, and by indicating if they had gotten their first period. One of these scales was also completed by the caregivers in reference to their daughters' development. The results replicated past research in that the earliest maturing girls (early pubertal timing for breast and pubic hair development) reported more depression symptoms at age 10 than later maturing girls (late pubertal timing). A new finding was that girls who were late to develop breasts (late pubertal timing) and also had a slow pubertal tempo (change progressed slowly) also reported more depression symptoms. There was no effect on depression related to the development of pubic hair and pubertal tempo. Similar to past research, African-American girls reported slightly higher depression symptoms. For example, at age 10 African-American girls reported one extra depression symptom compared to European-American girls. Likewise, African-American girls demonstrated earlier pubertal timing: pubic hair development occurred almost nine months earlier and breast development began about eleven months earlier than what was reported by European-American girls. Keenan et al. added to the literature by suggesting a trend: African-American girls demonstrated a little slower pubertal tempo, meaning that they took just ever so slightly longer to pass through the stages of puberty compared to the European-American girls. This trend requires further investigation in future research. New and most importantly, the relationship between depression, ethnicity, and pubertal timing was significant. The ethnic difference in depression symptoms at age 10 (their peak) was reduced up to 32% when pubertal timing was factored in. Pubertal tempo did not have a similar effect. Thus, a considerable portion of the ethnic difference in depression can be explained by African-American girls' earlier entry into puberty compared to European-American girls. In explaining their findings Keenan et al. suggested that sex hormones might be to blame for at least some of the low level depression seen in preteen girls. Girls with an earlier pubertal timing have higher levels of sex hormones like estrogen compared to girls who have not yet begun pubertal development. This biological argument would, at least in part, explain African-American girls' slightly higher rates of depression.
On the other hand, the authors predicted that a slow pubertal tempo would also predict higher levels of depression because it would mean exposure to high levels of hormones for an extended period of time. In this study, only for girls with later breast development (which implies lower hormone levels) did slow pubertal tempo predict slightly higher depression symptoms. As well, slow pubertal tempo did not explain any of the differences in depression between African- and European-American girls. So hormones cannot be the only explanation for girls' depression symptoms during puberty.
One possibility is that girls receive feedback based on their development that makes them self-conscious. Increases in estrogen cause weight gain so an early maturing girl may feel overweight compared to other girls. Breast development, a sign of puberty that is visible to others, may be desired to attract dating partners - so later maturing girls (especially those with a slow tempo) might be embarrassed by smaller breasts (but not care about lacking pubic hair, a trait that is not socially visible). Conversely, early breast development may bring with it unwanted sexual attention and comments that are uncomfortable for a young girl to navigate. It is also possible that early development of breasts and early menarche may lead parents to treat girls differently: for example, fathers may be less affectionate with their daughters once puberty begins. Parents, fearing sexual experimentation, sexually transmitted infections, teen pregnancy, or sexual assault may also impose new limits on what an early maturing girl can wear, where she can go, and whom she can be with. These sorts of social factors could also explain some of the low level depression seen in preteen girls. FURTHER READING: The Keenan et al. (2014) article is available online and through your local college library. Parents are not the only ones who may regulate girls bodies once puberty begins. Read an article in The Atlantic magazine by Li Zhou: "The Sexism of School Dress Codes." Starting at puberty, girls and women are twice as likely as boys and men to suffer from depression. This also means that depression symptoms might be missed in males because we are not expecting them to be depressed. Counselor and writer, Michael Gurian, explains some possible symptoms to look for in boys:
