W A S H I N G T O N, Oct. 19, 2001 -- Researchers said todaythey had shown for the first time how learning makes physicalchanges in the brain.
Rats trained to do a simple task — using one paw to dig afood pellet out of a box — had permanent brain changes thatcould be measured with electrical currents, the team at BrownUniversity in Rhode Island said.
“It’s a simple experiment, it’s a simple idea and itworked,” neuroscientist Mengia-Seraina Rioult-Pedotti, who ledthe study, said in a telephone interview.
Brain Slices Showed Activity
“I put the animal in a box and in this box is a small boxwith a hole. And the animal had to learn how to reach into thehole with the right forepaw. I trained them for five days …and they got better every day,” said Pedotti, who reported herfindings in this week’s issue of the journal Science.
“After five days I removed their brains, I cut slices, andI recorded responses.”
She ran electrical currents through the still-living slicesof brain tissue and found definite differences in regions knownto control the activity of the rats’ right front paws.
Just as in humans, the left side of a rat’s brain, ingeneral, controls the right side of its body and vice-versa.Pedotti’s team looked for changes in the left motor cortex.
“I measured activity in the area that is specific for theforelimb in the cortex,” she said. “The animals learned with asingle forelimb and the changes in the brain occurred in onlyone hemisphere.”
She could check the animals’ other hemisphere as a controland found that the synapses — the connections between neurons — were stronger in the region that controlled the new task.
Translated Into Visible Changes
“The animal is learning, I can see a change in behavior,and I can see a change in the brain,” Pedotti said.
Pedotti also wanted to prove a theory that a process calledlong-term potentiation (LTP) is responsible for strengtheningthese connections.
In a separate step, she sent high-frequency impulsesthrough the brain slices to simulate LTP. First she overloadedthe brain cells so they could conduct no more signals, then sheused a different frequency to weaken the synapses.
This gave her a range of potential for the brain cells.
“What I found was that the range, the limit, is unchangedafter learning. I have same maximum and the same minimum,” shesaid.
But there is also a baseline response, and in the trainedrats it shifted toward the upper limit, as compared tountrained rats.
Pedotti said this showed that LTP was the process thatinduced the physical changes in the brains of the rats.
Mechanism Not Known
This could explain earlier studies that have shown peoplecannot learn two similar but different physical tasks at thesame time. The brain cells, Pedotti suggests, simply becomesaturated.
She does not know the mechanism. It could the chemicalsthat carry signals between brain cells, known asneurotransmitters, become depleted. It is also possible, shesaid, that chemical doorways into the cells called receptorsget all used up.
“The link between LTP, synaptic modification and learningwas tentative,” John Donoghue, a professor of neuroscience whohelped lead the study, said in a statement.
“This latest study provides strong evidence that learningitself engages LTP in the cerebral cortex as a way tostrengthen synaptic connections.”