Reaching to the right to pick up an object is a simple task, but many stroke victims with damage to a pivotal area of their brain get their “rights” all wrong. New research by York University’s Doug Crawford has clarified the connection between sight and motion in a brain region called the parietal “reach region.”
“This area we found in the parietal cortex, the parietal “reach region,” is responsible for controlling movements. However, it doesn’t control the direction of the movement. It codes the direction you see things.”
Crawford holds the Canada Research Chair in visual-motor neuroscience. His study, published this month in Cerebral Cortex, used reversing prisms to distort subjects’ perception, swapping their left and right fields of vision. He is not the first researcher to use reversing prisms this way.
“Back in the sixties, some classic psychology experiments were done where people wore these things around for days or weeks to see what effects they had.”
The difference, Crawford explained, is that his experiment didn’t ask what would happen when a person adapted to seeing through reversing prisms, but where.
“We wanted to see where in the brain this learned vision-to-movement reversal takes place. This would tell us where the brain goes from ‘seeing’ to ‘moving,'” he said. Normally, when a subject moves left, the parietal cortex on the right side of the brain activates, and vice-versa. After adapting to the reversing prisms, subjects’ brains acted differently.
“The parietal cortex was no longer activated for reaching to objects on the opposite side, but instead on the same side of the body,” said Crawford.
Crawford’s research has led him to believe that the parietal cortex’s “reach region” “may be involved in reach, but it codes the visual direction of the object, not the reach direction.”
In other words, the “reach region” is not responsible for seeing or moving left and right, but for something in between, like setting a visual target that tells the body where to reach.
Crawford’s studies are vital to research on possible treatments for stroke patients. People with damage to their right parietal cortex have difficulty responding or reaching to the visual space on their left side.
A not-yet published study Crawford conducted at Sunnybrook Hospital’s stroke clinic explored several possibilities for treating stroke patients.
“We wanted to see if the kind of deficits [stroke victims] show reverse or stay the same with the reversing prism. We also wanted to see if learning this new behaviour [from the reversing prisms] revealed some ‘plasticity’ (capacity for change) that the patients had not yet showed, and if it helped their recovery,” said Crawford.
