The rewired ferrets had eyes that were hooked up to the part of the brain normally involved in hearing. So did that rewired area "see" or "hear"? The scientists taught the rewired ferrets to turn their heads right if they saw a light and left if they heard a sound. The ferrets' brains were only rewired on one side, so the normal side of the brain served as a control in the experiment. What the researchers found was that the ferrets were seeing lights with their rewired auditory cortex! So not only was the wiring different, the "hearing" cortex was working to process input from the eye. This rewired pathway did not work as well as the normal visual pathway -- it was not as sensitive -- but it was functional. The animals were "seeing" with their auditory cortex. Neuroscientists had previously thought that these specialized sensory areas were designated by birth to perform certain tasks. This work shows that these parts of the brain can adapt and change. Cells organize during development (before birth) to form these specialized structures, but input from the environment (after birth) is necessary to stabilize these areas. Before they are stabilized, different input can affect their function. This may shed light on how younger brains are better able to recover from injuries, whereas more mature brains are less capable of repair or rewiring to compensate for damaged areas. For example, some young children with severe epilepsy undergo surgery to remove half of their brain to control the spread of the seizure. Many of these children recover to develop normally if the surgery is done at an early age. Better understanding of how the brain compensates for damage (whether it be from disease or injury) will help medical researchers searching for treatments for various brain diseases.



Auditory (medial geniculate nucleus) and visual (lateral geniculate nucleus) areas of the thalamus in humans. Images courtesy of the Knowledge Weavers Project.