How some older brains decline before people realize it

August 5, 2019

Science Daily/Johns Hopkins University

Some older adults without noticeable cognitive problems have a harder time than younger people in separating irrelevant information from what they need to know at a given time, and a new Johns Hopkins University study could explain why.

The findings offer an initial snapshot of what happens in the brain as young and old people try to access long-term memories, and could shed light on why some people's cognitive abilities decline with age while others remain sharp.

"Your task performance can be impaired not just because you can't remember, but because you can't suppress other memories that are irrelevant," said senior author Susan Courtney, a cognitive neuroscientist at Johns Hopkins. "Some 'memory problems' aren't a matter of memory specifically, but a matter of retrieving the correct information at the right time to solve the problem at hand."

The findings were just posted in Neurobiology of Aging.

The researchers had 34 young adults (18 to 30) and 34 older adults (65-85) perform a mental arithmetic task while their brain activity was measured through functional magnetic resonance imaging, or fMRI. Other images were also collected to measure the integrity of the connections between brain areas called white matter tracts.

The task compared the participants' ability to inhibit irrelevant information automatically retrieved from long term memory. They were asked to indicate whether a proposed solution to an addition or multiplication problem was correct or not -- for instance 8x4=12 or 8+4=32. These examples would create interference as participants considered the right answer because although they should answer "incorrect," the proposed solution seems correct at first glance, based on long-term memories of basic math. This interference did not exist when participants were asked to answer clearly false equations like 8x4=22. Making the task even more complicated, the subjects were sometimes asked to switch to multiplication after they saw the addition symbol and vice versa.

Older people were a fraction of a second slower at answering the questions than younger participants, particularly when there was interference, but the more dramatic difference showed up in the brain scans. Older individuals who had more difficulty with interference also had more frontal brain activation than young adults.

The brain imaging demonstrated that in some aging participants, fibers connecting the front and back of the brain appear to have been damaged over the years. However other older individuals had fibers similar to much younger subjects. The greater the integrity of these fibers, the better the participant's task performance, said lead author Thomas Hinault, a postdoctoral fellow at Johns Hopkins.

"Everyone we studied had good functioning memory, but still we saw differences," Hinault said. "There are so many disruptions in the world and being able to suppress them is crucial for daily life."

The researchers were surprised to find that during parts of the task that were the trickiest, where participants had to switch between multiplication and addition and were asked to add after they saw a multiplication command or vice versa, the people with the strongest brain fiber connections counterintuitively performed even better. Something about deliberately exercising the mind in this fashion made the most agile minds even more so.

"If you have good connections between brain networks, that will help," Courtney said. "If not, you have interference."

https://www.sciencedaily.com/releases/2019/08/190805134032.htm

Women's brains appear three years younger than men's

May explain why women more likely to stay mentally sharp in later years

February 4, 2019

Science Daily/Washington University School of Medicine

Women's brains appear to be three years younger than men's of the same age, according to a new study on brain metabolism. The findings could explain why women maintain their cognitive skills longer than men.

A new study from Washington University School of Medicine in St. Louis finds that women's brains appear to be about three years younger than men's of the same chronological age, metabolically speaking. The findings, available online the week of Feb. 4 in Proceedings of the National Academy of Sciences, could be one clue to why women tend to stay mentally sharp longer than men.

"We're just starting to understand how various sex-related factors might affect the trajectory of brain aging and how that might influence the vulnerability of the brain to neurodegenerative diseases," said senior author Manu Goyal, MD, an assistant professor of radiology at the university's Mallinckrodt Institute of Radiology. "Brain metabolism might help us understand some of the differences we see between men and women as they age."

The brain runs on sugar, but how the brain uses sugar changes as people grow and age. Babies and children use some of their brain fuel in a process called aerobic glycolysis that sustains brain development and maturation. The rest of the sugar is burned to power the day-to-day tasks of thinking and doing. In adolescents and young adults, a considerable portion of brain sugar also is devoted to aerobic glycolysis, but the fraction drops steadily with age, leveling off at very low amounts by the time people are in their 60s.

But researchers have understood little about how brain metabolism differs between men and women. So Goyal and colleagues, including Marcus Raichle, MD, the Alan A. and Edith L. Wolff Distinguished Professor of Medicine and a professor of radiology, and Andrei Vlassenko, MD, PhD, an associate professor of radiology, studied 205 people to figure out how their brains use sugar.

The study participants -- 121 women and 84 men, ranging in age from 20 to 82 years -- underwent PET scans to measure the flow of oxygen and glucose in their brains. For each person, the researchers determined the fraction of sugar committed to aerobic glycolysis in various regions of the brain. They trained a machine-learning algorithm to find a relationship between age and brain metabolism by feeding it the men's ages and brain metabolism data. Then, the researchers entered women's brain metabolism data into the algorithm and directed the program to calculate each woman's brain age from its metabolism. The algorithm yielded brain ages an average of 3.8 years younger than the women's chronological ages.

The researchers also performed the analysis in reverse: They trained the algorithm on women's data and applied it to men's. This time, the algorithm reported that men's brains were 2.4 years older than their true ages.

"The average difference in calculated brain age between men and women is significant and reproducible, but it is only a fraction of the difference between any two individuals," Goyal said. "It is stronger than many sex differences that have been reported, but it's nowhere near as big a difference as some sex differences, such as height."

The relative youthfulness of women's brains was detectable even among the youngest participants, who were in their 20s.

"It's not that men's brains age faster -- they start adulthood about three years older than women, and that persists throughout life," said Goyal, who is also an assistant professor of neurology and of neuroscience. "What we don't know is what it means. I think this could mean that the reason women don't experience as much cognitive decline in later years is because their brains are effectively younger, and we're currently working on a study to confirm that."

Older women tend to score better than men of the same age on tests of reason, memory and problem solving. Goyal, Raichle, Vlassenko and colleagues are now following a cohort of adults over time to see whether people with younger-looking brains are less likely to develop cognitive problems.

https://www.sciencedaily.com/releases/2019/02/190204172217.htm