When Emily Jacobs embarked on a career studying the brain in the early 2000s, a technique called functional magnetic resonance imaging, or fMRI, was having its moment. “Just like we have super-powerful telescopes that allow us to quantify the farthest reaches of the known universe, here we have this tool that could allow us to see the human brain as a whole and as a living, pulsating organ,” says Jacobs, a cognitive expert. neuroscientist at the University of California, Santa Barbara.
By measuring changes in blood flow that serve as an indicator of brain activity, neuroscientists gained new insights into how different situations stimulate conversations between brain regions and how the intensity of conversations changes over time. “I was riding that wave of emotion,” says Jacobs.
But he soon realized that there were big questions that were not being asked, important questions for half the world’s population. Do the natural hormonal changes that come with menstruation, pregnancy, and menopause affect communication in the brain? What about hormonal contraceptives, like the birth control pill, which are used by hundreds of millions of people worldwide? And what does all this mean for brain health and behavior?
The rise and fall of hormones is a big reason why women have historically been excluded from biomedical research, although hormones in men also fluctuate. The resulting gap in knowledge of female biology has led to inadequate mental, physical Y reproductive health care. “Science, and especially neuroscience, has not served the sexes equally,” says Jacobs.
Using a variety of tools — fMRI, other types of MRI and brain imaging, blood tests, neuropsychological tests, virtual reality, and more — Jacobs’ lab is trying to fill in the gaps in our basic understanding of how hormones act in the human brain. And she is studying hormones as a lens for larger questions about brain changes.
“What’s really special about Emily’s work is that she does it on so many different levels. It’s so multifaceted,” says cognitive neuroscientist Caterina Gratton of Northwestern University in Evanston, Illinois. “She has multiple different types of brain measurements, from molecular to brain systems.”
In a series of studies called 28 and Me, for the 28 days of a typical menstrual cycle, Jacobs and her colleagues closely monitored a woman’s brain for the duration of her natural menstrual cycle. Every 24 hours for 30 days, this 20-something woman’s brain was scanned, hormone levels in her blood were checked, and her mood was assessed.
As a woman’s estrogen levels peaked during ovulation, the brain regions synchronized. And the regions in a major hub called the network by default became strict talkers. What’s more, a part of this network reorganized itself to create a new and transitory communication cabal. After ovulation, when estrogen levels fell and progesterone levels rose, gray matter temporarily expanded into a brain structure linked to learning and memory.
When the same woman was examined a year later while taking the pill, which suppresses progesterone, no changes were seen.
The findings, described in 2021 in Current Opinion in Behavioral Sciencesprovide strong evidence that the ebb and flow of sex hormones it drives changes in the brain on a day-to-day basis, say Jacobs and his colleagues. They also saw links between hormonal fluctuations and brain changes. in a male participant.
The observations led cognitive neuroscientist Caitlin Taylor, a postdoc in Jacobs’s lab, to wonder how the brain responds to chronic hormone suppression from oral contraceptive use. The team is throwing a large-scale study to try to find out.
Initially, Jacobs was hesitant to greenlight the investigation. He was concerned that he might go awry to erode access to contraception. Eventually, she relented, because women “deserve to have a science that can serve us,” she says.
Another effort, which Jacobs and Taylor are building, will make the data for such large-scale studies widely available. He called the University of California Women’s Brain Initiative, aims to channel the records of the eight brain imaging research centers of the university system into an open access database. When a woman’s brain is scanned at one of the centers, her anonymous brain imaging data, medical data, and information about the use of hormonal contraceptives are entered into the database. Once all eight centers are on board, there could be around 10,000 participants annually, far more than a single lab could recruit.
The expected mountain of data should be a boon to researchers asking questions big and small about brain health, says Jacobs. And she hopes it will improve women’s health care.
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