Rats may hold the key to unlock brain debate

Chris Richards Arizona Daily Wildcat A rat's eye view of psychology graduate student Nicholas LaMendola and lab researcher Laure Farnbauch - the two are peering over the edge of a radial arm maze designed to test the spatial learning behavior of rats.

UA Research Professor Thomas Bever used the rats to answer a long debated question -whether the left hemisphere of the brain does more computation than the right hemisphere.

Bever, a professor of cognitive science, psychology and linguistics, published his latest findings in Friday's edition of Science, a top research journal.

For a century, scientists have agreed that the brain's left hemisphere is dominant in language processing, Bever said.

"The question is whether the superiority of the left hemisphere is unique to language or whether it is a general computational superiority," Bever said.

Some researchers argue that the left hemisphere governs analytical tasks while the right hemisphere processes tasks holistically, Bever said.

"In the domain of perception for instance, the left hemisphere processes a face as parts and it assembles the parts whereas the right hemisphere creates a snapshot of the person's face," explained Nicholas LaMendola, psychology graduate student.

LaMendola is a researcher on the project.

If this is true, then the left and right hemispheres will have different strategies for carrying out tasks and different abilities to accomplish a task depending on the situation, Bever said.

Bever and LaMendola set out to see if this was indeed the case with rats navigating about a maze.

The rats were first taught to run through an eight-armed, wheel-shaped maze with food located at the end of five of the arms.

The scientists then anesthetized either the right or left side of the rats' whiskers, the rats' primary source of navigational information.

This enabled the researchers to observe the rats' behavior when guided by whiskers governed by one hemisphere of the brain.

Like humans, Bever said, rats have contralateral neurological connections. That means the left side of the rat is governed by the right hemisphere and the right side is governed by the left hemisphere, he said. By anesthetizing the whiskers of the right side the scientists could examine the rats' behavior when guided by their left whisker/right hemisphere system. Anesthetizing the rats' left whiskers would accomplish the reverse, Bever explained.

After the anesthesia was applied, the rats ran the same maze as before, only this time the maze was rotated 90 degrees inside the room. The researchers found rats guided by their left whiskers/right hemisphere system ran the maze unaffected while rats guided by their right whiskers/left hemisphere system had difficulty.

Moving the food wrecks a rat's mental map of the maze, Bever said.

Then the researchers ran the rats with the maze in its original position. However, they started the rats at a different position. Rats guided by left-whisker information were adversely affected but those guided by right whiskers had no problem. The map-like representation supplied by the right whisker/left hemisphere system was enough to guide the rats to the food.

This shows that while the right hemisphere maintains a memorized sequence of moves, the left hemisphere maintains to the food is located in space itself rather than relative to the interior of the maze, Bever said.

"Because a map representation is more complex than a memorized route this suggests that the left hemisphere may be computationally more powerful than the right as some people have suggested is true of humans," Bever said.

Thus the study offers insight as to why language is represented in the left hemisphere of the brain, Bever said.

The study addresses more than this academic question, however, LaMendola said.

By showing that brain asymmetries exist in rats, the study shows that rats may be used as a model for studying brain asymmetries in humans, LaMendola said.

"The animal model is really powerful because it allows us to test one side of the brain. Human asymmetries are difficult to study because we don't have a mechanism for turning off one side of the brain," he said.

This gives hope that in the future, rat models may help researchers better understand and devise treatments for disorders associated with brain asymmetries including dyslexia and other learning disorders, Bever said.