When accompanied by visual stimuli, running can help restore brain function in mice who have been deprived of sensory experiences early on. These new experiments suggests that the adult brain is way more capable of rewiring and repairing itself that we previously assumed. 

Scientists have known since the 1960s that the brain doesn’t develop normally if it’s deprived of visual input from one eye during a critical period early in life. If people with amblyopia (known as “lazy eye”), don’t have corrective surgery as infants, their vision will never be normal in the affected eye. The new work hints at novel strategies for restoring vision to people who are blind in one eye from a congenital cataract, droopy eyelid, or misaligned eye. 

Recent work revealed how neurons in the visual cortex of the mouse brain fire more robustly whenever the rodent walks or runs. In fact, running more than doubles the response of mouse’s visual cortex neurons to visual stimulation, Nature explains. This is referred to as locomotion-induced “high-gain state.” 

In new research published in eLIFE last week, Megumi Kaneko and Michael Stryker from the University of California, San Francisco, closed one eyelid of mouse pups 20 days after they were born. The eye was kept shut until the mice were five months old. Then, as expected, these mice showed reduced neural activity in the part of the brain that’s responsible for vision in that particular eye. 

The team recorded brain activity as the mice ran freely on Styrofoam balls suspended on a cushion of air and also when they received visual training with the deprived eye. The training involved looking at a pattern designed to activate most cells in the primary visual cortex. The researchers saw little improvement in mice who were only allowed to do one: run freely or get visual training. Neither by themselves promoted recovery. 

However, when the mice were exposed to the visual stimuli while they were running or walking, the brain responses from the deprived eye were nearly identical to those from the “good eye” within a week. The brain circuits had apparently undergone rapid reorganization -- called plasticity, which neuroscientists believe is the basis of learning. 

It’s probably more important, and taxing, to keep track of the environment when navigating it at speed, Stryker explains to Nature, and lower responsiveness at rest may have evolved to conserve energy in less-demanding situations. “It makes sense to put the visual system in a high-gain state when you’re moving through the environment, because vision tells you about far away things, whereas touch only tells you about things that are close,” he adds. 

The researchers don't know yet if running puts the human cortex into a high-gain state that enhances plasticity like in rodents: “We have no idea yet," Stryker says in a news release, “but we are designing experiments to find out.”