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Saturday, October 16, 2021

Making memories in a brain-scanner

Deep in the fleshly, pink center of the human brain is an odd structure. It’s a sort of bent-over “Y” shape that fires into action to form new memories. The structure is called a hippocampus, and without it, you’d have amnesia.

Scientists used to think the hippocampus stopped developing in early childhood. Another memory-forming area, called the prefrontal cortex, developed over time, but the hippocampus never changed.

A recent study by UC Davis scientists challenges this assumption. Simona Ghetti, associate professor of psychology at UC Davis, looked at brain scans taken as children and adults formed new memories, and her team found that different areas of the hippocampus lit up when subjects of different ages formed memories.

“The basic function of the hippocampus seems to change throughout childhood,” Ghetti said.

Ghetti’s team tested eight-year-olds, 10-to-11 year-olds, 14-year-olds, and college-age adults. The subjects were put into a brain-scanner, shown a series of pictures in red ink and asked whether the items in the pictures belonged in a house. Then they were shown pictures in green ink and asked whether those items were living things. Outside the scanner, they were shown the same pictures – mixed with new ones – and asked whether they’d seen the pictures before. Had the pictures been red or green?

Taking the scans during memory formation and then testing those memories showed the researchers how the hippocampus functioned. There are different regions of the hippocampus, and the brain scans showed that adults were more selective in which region they recruited when forming new memories.

“The way in which the eight to 10-year-olds used the hippocampus to do the tasks is different from the way 14-to-15 year-olds and adults use the hippocampus,” Ghetti said.

The hippocampus helps a person form episodic memories. It packs the setting, characters and details of a memory into a tidy little package that can be retrieved later. Your brain stores not just the memory of your first kiss, but whether your fellow kisser had braces and garlic-breath.

“All the features are bound together by the hippocampus,” Ghetti said.

While Ghetti’s study shows that humans use the hippocampus differently as they age, scientists still don’t know how that change happens. Brain scans and memory-tests are useful tools for neuroscientists, but dissecting a brain also reveals a lot about how it develops. Of course, no one is going around dissecting the hippocampi of eight-year-olds.

Larry Harper, professor of human and community development at UC Davis, said scientists studying animals have learned a lot by studying the brains of dead animals. As the brain develops, there are changes in the production and inhibition of signal receptors and signaling molecules. Train an animal to do a new task, kill it, then dissect its brain, and you’ll see an accumulation of certain signaling molecules.

“In animals, you can see it happen,” said Harper. “You’ve got to get in there and look at the brain, but you obviously can’t do that in little children.”

Neuroscientists already know that childhood is a critical time for brain development. The connections between the two hemispheres of the brain become more elaborate during middle childhood, and signaling pathways develop that help children learn language and reasoning.

“The wiring of the nervous system changes with age,” Harper said.

Brain-scanners, like those used in Ghetti’s study, have been a blessing for neuroscientists who want to see inside a living, synapse-firing brain.

Other scientists have had luck analyzing the brain through behavioral studies and eye-movement tracking.

Zhe Chen, professor of human and community development at UC Davis, studies children’s thinking and learning processes. To test a child’s problem-solving skills, his team uses a test to see how children will balance weights on a scale.

“We observe the kinds of strategies they use,” said Chen. “It’s just like playing a game.”

While wrangling squirrelly kids into brain-scanners and laboratories may not be a scientist’s favorite job, it can reveal a lot about the way our minds work. Ghetti’s ongoing research will continue to examine the hippocampus and what happens when a moment becomes a memory.

MADELINE McCURRY-SCHMIDT can be reached at science@theaggie.org.

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