OT: Getting Older Thread

Men have a daily hormone cycle — and it's synced to their brains shrinking from morning to night
News
By Nicoletta Lanese published 2 days ago
A month-long study of a man's brain revealed that its volume consistently shrunk over the course of each day and then reset overnight.

The daily ebb and flow of hormones in the male body may play a role in shrinking the brain throughout the day, a study hints. After losing volume between morning and evening, the brain resets overnight, starting the cycle again, the research shows.

The study involved scanning a 26-year-old's brain 40 times in 30 days. Each magnetic resonance imaging (MRI) scan was collected at either 7 a.m. or 8 p.m., which is when levels of steroid hormones — namely, testosterone, cortisol and estradiol — are at their highest and lowest, respectively.

"Males show this 70% decrease from morning to night in steroid hormones," said study co-author Laura Pritschet, who's now a postdoctoral scholar in psychiatry at the University of Pennsylvania Perelman School of Medicine. The degree of change between morning and night narrows with age, but that general pattern persists throughout life.

"You can think of it almost like a pulsating rhythm from morning to night," Pritschet told Live Science. Females also experience a daily flux in hormones, but it's not as pronounced, she noted, because the menstrual cycle is simultaneously driving longer-term shifts in hormones.

The new study revealed that, throughout the day, the subject's overall brain volume decreased, as did the thickness of the cortex, the brain's outer layer. The volume of gray matter, which contains the cell bodies of neurons and the connections between them, fell by an average of about 0.6%.

Two regions of the cortex, known as the occipital and parietal cortices, shrank the most. Changes were also seen in deeper brain structures, including the cerebellum, brainstem and parts of the hippocampus. These parts of the brain are respectively involved in coordinating movement; relaying information between the brain and body; and storing memories.

The decline in brain volume parallels the daily decline in hormones. However, it's not yet clear whether the hormones drive the brain changes, the study authors wrote in a report published Wednesday (Sept. 18) in The Journal of Neuroscience.

  --
I like the counterpoint that we are now highlighting the ways in which men's endocrine systems are variable.

Pavel Shapturenka, the study's subject
  --

"I think that's an open question," study co-author Elle Murata, a doctoral student in psychology and brain sciences at University of California, Santa Barbara (UCSB), told Live Science. But nonetheless, "this is, I think, another example debunking the myth that hormones are only relevant for females."

Past research suggests that steroid hormones shape the brain. The menstrual cycle has been linked to volume changes across the whole brain, and studies suggest those changes don't happen when the hormonal cycle is altered — for example, by birth control. Decades of animal studies also suggest that steroid hormones shape brain structure on short timescales.

"I'm convinced that hormones impact the brain and brain structure," Murata said. "But in this study, we can't say that it's directly causing it."

Could males' hormonal circadian rhythm be affecting brain function? For now, it's unclear exactly how it might be doing so. That said, a different study by the team suggests there are changes in the brain's connectivity that follow a 24-hour cycle.

In that other study, the team probed the same individual but looked at the patterns of communication between different parts of the brain, rather than taking snapshots of its structure. The researchers found that "coherence" — a measure of synchronization — across the brain rose and fell along with the levels of steroid hormones.

Interestingly, brain regions that process visual information cropped up in both studies, Murata noted. These brain areas showed both a loss of volume and a loss of coherence throughout the day.

Pregnancy shrinks parts of the brain, leaving 'permanent etchings' postpartum
News
By Nicoletta Lanese published September 16, 2024
A study tracks how the structure of the brain changes during pregnancy, drawing on brain scans gathered before, during and just after one person's pregnancy.


Pregnancy may cause more than 80% of the brain's gray matter to shrink, leaving "permanent etchings."

That's what researchers found when a pregnant neuroscientist underwent more than two dozen brain scans throughout her pregnancy and for two years postpartum. After pregnancy, the new mom regained some gray matter, which includes both the cell bodies of neurons and the connections between them. But much seemed to be gone for good.

On average, there was a 4% decrease in gray-matter volume within the affected brain areas, said Emily Jacobs, an associate professor of psychological and brain sciences at the University of California, Santa Barbara (UCSB) and co-senior author of the study.

"That's similar to the amount of reduction in puberty," Jacobs noted at a news conference Thursday (Sept. 12). Hormone surges in puberty come with a dip in gray-matter volume, as the brain prunes excess tissue so it can run more efficiently. Something similar may happen in pregnancy, Jacobs suggested.

"Sometimes people bristle when they hear that gray-matter volume decreases during pregnancy — like, 'That can't be a good thing,'" she said. However, "this change probably reflects the fine-tuning of neural circuits, not unlike the cortical thinning that happens during puberty."

That fine-tuning may forever change the brain. "Many of these changes seem to be what you might think of as permanent etchings in the brain," Jacobs said