How Learning Changes the Brain

by Maggie Fox, Health and Science Correspondent

10/19/2000

WASHINGTON, Oct 19 (Reuters) - Researchers said on Thursday they had shown for the first time how learning makes physical changes in the brain. Rats trained to do a simple task -- using one paw to dig a food pellet out of a box -- had permanent brain changes that could be measured with electrical currents, the team at Brown University in Rhode Island said.

"It's a simple experiment, it's a simple idea and it worked," neuroscientist Mengia-Seraina Rioult-Pedotti, who led the study, said in a telephone interview. "I put the animal in a box and in this box is a small box with a hole. And the animal had to learn how to reach into the hole with the right forepaw. I trained them for five days ... and they got better every day," said Pedotti, who reported her findings in this week's issue of the journal Science. "After five days I removed their brains, I cut slices, and I recorded responses." She ran electrical currents through the still-living slices of brain tissue and found definite differences in regions known to control the activity of the rats' right front paws.

Just as in humans, the left side of a rat's brain, in general, 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 the forelimb in the cortex," she said. "The animals learned with a single forelimb and the changes in the brain occurred in only one hemisphere."

She could check the animals' other hemisphere as a control and found that the synapses -- the connections between neurons -- were stronger in the region that controlled the new task.

LEARNING TRANSLATES INTO VISIBLE CHANGES

"The animal is learning, I can see a change in behaviour, and I can see a change in the brain," Pedotti said. Pedotti also wanted to prove a theory that a process called long-term potentiation (LTP) is responsible for strengthening these connections.

In a separate step, she sent high-frequency impulses through the brain slices to simulate LTP. First she overloaded the brain cells so they could conduct no more signals, then she used 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 unchanged after learning. I have same maximum and the same minimum," she said.

But there is also a baseline response, and in the trained rats it shifted toward the upper limit, as compared to untrained rats. Pedotti said this showed that LTP was the process that induced the physical changes in the brains of the rats. This could explain earlier studies that have shown people cannot learn two similar but different physical tasks at the same time. The brain cells, Pedotti suggests, simply become saturated.

She does not know the mechanism. It could the chemicals that carry signals between brain cells, known as neurotransmitters, become depleted. It is also possible, she said, that chemical doorways into the cells called receptors get all used up.

"The link between LTP, synaptic modification and learning was tentative," John Donoghue, a professor of neuroscience who helped lead the study, said in a statement. "This latest study provides strong evidence that learning itself engages LTP in the cerebral cortex as a way to strengthen synaptic connections."