How Our Brain Structures Change Through the Seasons of Life

Part 2: Pregnancy, Postpartum, and Perimenopause

Last week, we discussed how our brains change during adolescence and during the menstrual cycle. Most of us know from personal experience, how differently our brains work during adolescence. However, I didn’t know until recently that the thinking and behavior changes that occur throughout the menstrual cycle weren’t “just” due to hormones, but also accompanying changes in the brain. But did you know that brain changes of a similar magnitude to adolescence are occurring during pregnancy, postpartum, and perimenopause?

In a study that tracked MRIs for one pregnant woman (from 3 weeks prior to conception to two years after giving birth), they found that grey matter volume decreased throughout pregnancy, but partially recovered after birth. This decrease is not a sign of cognitive decline, but rather “pruning” to eliminate unnecessary connections and become more efficient. The density of white matter increased during the first two trimesters of pregnancy. The volunteer’s brain changed on almost a weekly basis during pregnancy. Researchers also think some of the structural changes may increase pain tolerance in childbirth. The degree of brain changes during pregnancy also correlated with maternal-child attachment and “absence of hostility” toward the newborn.

Other studies mainly saw changes in areas involved in the default mode network. As noted last week, this network is vital to our ability to construct a “sense of self” and empathize with others. Researchers suspect these changes help mothers empathize with their babies. I’m sure that is part of it, but in my experience, motherhood had a profound and sustained impact on my sense of self and I wonder if these changes in the default mode network facilitate those changes in identity as well. In a study examining the default mode network and other brain circuits, researchers found that the default mode network was the only one that did not return to normal after childbirth, with changes in that network persisting for many years after giving birth.

Fascinatingly, women who went into labor (even if that labor ended in a C-section) were slower to return to pre-pregnancy grey matter structure than women who had a scheduled C-section. Researchers attributed this difference to the “hormonal and immune cascade” that accompanies labor.

The brain continues to change in the postpartum period. During pregnancy, hormonal changes are the main driver of brain structure changes. In the postpartum period, direct interactions with one’s baby are the main driver of these changes. Because these changes are linked to direct care for babies, fathers, adoptive parents, and grandparents also experience structural changes in their brains as well. Even NICU nurses may experience these brain changes. Unlike during pregnancy, where grey matter volumes have always been found to decrease, during postpartum, grey matter volumes increased (and none were found to decrease.) During pregnancy, there was a decrease in brain volume in areas that are mostly related to interpreting and responding to social interactions. During postpartum, there was an increase in brain volume in areas associated with motivation, bodily sensations, planning, and decision-making. The biggest changes in brain structure occur in the first 6-9 weeks postpartum, especially in areas of the brain involving emotion and stress regulation.

During perimenopause, women’s brains decrease in volume in grey matter, particularly in the prefrontal, temporal, and hippocampus areas of the brain. Volume changes impact the following structures in the brain (I have included a brief description of their function next to each:

• Superior and inferior frontal gyri: working memory, decision-making, understanding and responding to the emotions of others, impulse control, processing and regulating negative emotions, speech and language

• Lateral prefrontal cortex: sensory processing, motor control, and performance monitoring

• Anterior cingulate cortex: monitoring for conflict, social evaluation (judging others or yourself to determine the suitability of joining a group or partnership), emotional awareness, and perception of physical pain, rejection, and exclusion

• Superior temporal gyrus: Language comprehension, memory, understanding social cues

• Olfactory cortex: perceives smells and calls up memories and emotions associated with those smells

• Entorhinal cortex: memory, navigation, emotional processing

• Fusiform gyrus: facial and body recognition, emotional processing

• Superior and inferior temporal gyri: language comprehension, facial recognition, interpretation of facial and body movements

• Parahippocampus: navigation and memory

• Insula and opercula: interoception, emotion processing, and sensorimotor integration

I am struck by the recurring themes of social, emotional, and memory functions in these areas.

Women do experience many cognitive changes during perimenopause. However, both the biomedical research and the popular media focus on the deficits that occur because of these changes, particularly:

• Verbal memory

• Planning

• Organization

• Staying on task

• Depression

Just like how adolescents have more cognitive flexibility because their prefrontal cortex isn’t as connected yet, I suspect that there are gifts that come with the ways postmenopausal brains work too.

Scientists don’t yet have a complete understanding of what these structural changes mean as far as how the brain functions. In fact, there is very little they know. There is conflicting research about:

• Which areas of the brain are affected

• Which types of brain tissue (grey matter versus white matter versus cerebrospinal fluid)

• Whether the changes affect the whole brain, large segments, or small parts

• Whether these changes are beneficial or harmful

There is evidence that the hippocampus is important for remembering words and evidence that when the hippocampus shrinks during menopause there are declines in the ability to remember words. However, there is also research that shows that women were capable of remembering more words than men despite having a smaller hippocampal volume. The same study also found that individuals with the highest estrogen levels had the lowest word recall ability, which was contrary to the expectation of many that higher levels of estrogen protect against cognitive decline.

Research comparing women at different reproductive stages and men performed cognitive testing on those different populations. There have been conflicting results on these cognitive tests, with some research finding that peri- and postmenopausal women performed worse on these cognitive tests, while some found they performed better.

Recent research showed a decrease in the thickness of the grey matter in a region of the brain that regulates “high-level visual perception”. These researchers also found that the brain uses less sugar after menopause in the temporal lobe, which has many functions related to memory and perception. However, the body adapted to those changes by increasing blood flow to those areas and making more ATP (what cells use for energy). Dr. Mosconi, the primary author of this study, suspects these changes may be adaptations to maintain brain function with lower levels of estrogen.

Studies also suggest that some of these structural changes are transient and resolve over several years. One study found that decreased connections in the white matter and decreased sugar (glucose) use in the brain normalized after menopause. These resolutions were associated with improved memory and cognitive performance. The precuneus area of the brain, which is involved in memory, self-awareness, and interpreting and interacting with social environments, lost volume during perimenopause, but returned to its normal size after menopause was complete. There is no science to back this up, but these changes make me wonder if they clear the path for the necessary identity changes that come with the transition from mother to matriarch. Does this shrinking precuneus change our self-concept and how we interact socially?

Multiple studies also demonstrated smaller volumes in the amygdala, a part of the brain that is key to the experience of fear and anxiety. Interestingly, one study in adolescents and young adults found that larger amygdala volumes were correlated with social anxiety disorder. As I have asked post-menopausal women about how their brain works differently than before, this was a recurring theme. Many women said that after menopause, they “just don’t give a fuck” what people think of them. I wonder whether this structural change could play a role and whether this change in the social nervous system may be part of postmenopausal women’s unique cultural value in traditional cultures. Does this structural change allow them to speak hard truths that the necessity of maintaining peace and relationships while mothering did not allow?

In addition, research suggests that cultural views on the value of postmenopausal women have a substantial impact on the symptoms women experience during perimenopause (Hat tip to

Dr. Heidi

for sharing this study with me). A study from China compared women from the Mosuo people, China’s only matrilineal society, to women from the Yi and Han peoples, which are patriarchal societies. They found that even though their environment was very similar, menopausal symptoms were much less severe for Mosuo women. This appears to be related to lower levels of stress and anxiety, higher levels of self-efficacy, and increased social value as women age. Similarly, Mayan women “look forward to menopause because of their newfound freedom and status.”

In indigenous cultures, completing the menopause process also marks a transition within the culture to elderhood. This echoes another theme some postmenopausal women discussed. They felt that they could see to the essence of things more clearly. They were no longer distracted by the things that were not the priority. In some shamanic cultures, like the Mayan and Cree people, women must be postmenopausal to fully actualize their shamanic and healing powers. In Japan, the word for menopause is konenki. The meaning for konenki breaks down like this: ko means renewal or regeneration, nen means years, ki means season or energy. This suggests, “gradual transition where the end of periods is just one contributing feature.” I’ve also heard of the cycles of women’s lives following cycles of self orientation followed by cycles more directed toward the care of others. Maidenhood represents the first “me” cycle, followed (for many) by motherhood, a “we” cycle. Perimenopause is another time of withdrawing into the self and focusing on “me”, which can be complex for many women who are in both motherhood and perimenopause. Ideally, leaving us replenished to focus on a broader community-wide “we” in elderhood.

These transitions and cross-cultural understandings of menopause help us to see that every phase of life has its gifts and services that it can offer the community. There never comes a time in our lives where we are “past our prime” or useless, because our function continues to change. It appears that it is not only our cognitive or experiential understanding of the world that changes as we proceed through life, but that our bodies and brains change alongside those mind and soul changes. I suspect that our brains are preparing us for the next steps on our paths, and I find that fascinating and moving, this partnership of mind, body, soul and spirit that is still far beyond our comprehension.