The brain has a way of repurposing unused real estate. When a sense like sight is missing, corresponding brain regions can adapt to process new input, including sound or touch. Now, a study of blind people who use echolocation—making clicks with their mouths to judge the location of objects when sound bounces back—reveals a degree of neural repurposing never before documented. The research shows that a brain area normally devoted to the earliest stages of visual processing can use the same organizing principles to interpret echoes as it would to interpret signals from the eye.
In sighted people, messages from the retina are relayed to a region at the back of the brain called the primary visual cortex. We know the layout of this brain region corresponds to the layout of physical space around us: Points that are next to each other in our environment project onto neighboring points on the retina and activate neighboring points in the primary visual cortex. In the new study, researchers wanted to know whether blind echolocators used this same type of spatial mapping in the primary visual cortex to process echoes.
The researchers asked blind and sighted people to listen to recordings of a clicking sound bouncing off an object placed at different locations in a room while they lay in a functional magnetic resonance imaging scanner. The researchers found that expert echolocators—unlike sighted people and blind people who don’t use echolocation—showed activation in the primary visual cortex similar to that of sighted people looking at visual stimuli.
That means, the “visual” cortex seems to have applied its spatial mapping ability to a different sense, the researchers report today in the Proceedings of the Royal Society B. And the more a participant’s brain activity aligned with this spatial map during listening, the better they were at guessing the location of the object in the recording from its echo. The finding reveals unrecognized neural flexibility, the authors say, and suggests the brain can be trained to make expert use of spatial information, even if it doesn’t come through the eyes.