Why Do We Lose Learning Ability?

Any mom who's struggled to ski as her children whizzed by on the bunny hill, or any dad who's had his kid figure out a new remote in 30 seconds flat can attest: adult brains don't learn as quickly as children's brains.

Last week researchers at the State University of New York (SUNY) figured out a small piece of the puzzle explaining why our learning ability declines. They also -- at least in mouse models -- pointed to a temporary antidote to the learning decline that starts in adolescence.

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"Clearly there are major differences between mice and humans in terms of motivation and how we behave, but very simple processes still stay true," said Sheryl Smith, lead author on the paper explaining the findings published Friday in the journal Science. "We know that we all have the same kinds of brain chemicals."

"I hope people recognize that the teenage brain is quite different than a child's brain or an adult brain," she said.

Smith and her team at SUNY found a change in the part of the brain called the hippocampus during puberty. Before puberty, the hippocampus has very few GABA receptors, then the numbers swell during puberty. Smith said the number of GABA receptors diminishes again in adulthood, but never falls to pre-pubescent levels.

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A GABA (gamma aminobutyric acid receptor) receptor works in complex lock and key system within the brain. The GABA receptor sits in a brain cell called a neuron, and when it sees a neurotransmitter called GABA, it puts a brake on brain activity.

For some reason, and Smith could only guess why, the presence of the GABA receptors in the teenage brain blocks a specific learning ability.

"It's special kind of learning," said Smith, who gave the example of learning how to spot openings in a moving basketball game, or memorizing a location of a shop when driving around town.

"But it could be something as simple as remembering where you put the keys when you set them down," said Smith. "For a mouse, it might be something as simple-minded as your parents teaching you how to remember to find the nest."

Smith tested the mice's learning ability by putting them on a round, movable surface which had a specific section designed to give an uncomfortable jolt should the mouse set foot there. She found the young mice easily learned where the jolt was coming from and how avoid it in one or two tries, but the mice going through puberty never learned how to avoid the jolt on the moving surface.

Stress Can Help or Hurt Learning

Smith then documented another unique property of the GABA receptors in puberty -- the reaction to a stress steroid called THP. In young mice, and presumably young humans, the THP steroid acts as a calming tranquilizer, which also temporarily impedes our ability to learn.

"THP is released later on … about 20-30 minutes after the stress," said Smith, who gave an example of giving a presentation as a stress. "Its role is to relax you. It acts like a subtle tranquilizer."

"In general, the drugs that relax you impair learning -- In fact doctors who sometimes administer tranquilizers along with a procedure do so so that you don't remember everything," said Smith.

But while adults and children are relaxed by THP (and learn less); adolescents have an opposite reaction because of the increased GABA receptors. The adolescent mice learn more.

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