June 27, 2014 |
In a new study by UC San Francisco scientists, running, when accompanied by visual stimuli, restored brain function to normal levels in mice that had been deprived of visual experience in early life.
In addition to suggesting a novel therapeutic strategy for humans with blindness in one eye caused by a congenital cataract, droopy eyelid, or misaligned eye, the new research—the latest in a series of UCSF studies exploring effects of locomotion on brain function—suggests that the adult brain may be far more capable of rewiring and repairing itself than previously thought.
In 2010, Michael P. Stryker, PhD, the W.F. Ganong Professor of Physiology, and postdoctoral fellow Cris Niell, PhD, now at the University of Oregon, made the surprising discovery that neurons in the visual area of the mouse brain fired much more robustly whenever the mice walked or ran.
Earlier this year, postdoctoral fellow Yu Fu, PhD, Stryker and a number of colleagues built on these findings, identifying and describing the neural circuit responsible for this locomotion-induced “high-gain state” in the visual cortex of the mouse brain.
Neither of these studies made clear, however, whether this circuit might have broader functional or clinical significance.
It has been known since the 1960s that visual areas of the brain do not develop normally if deprived of visual input during a “critical period” of brain development early in life. For example, in humans, if amblyopia (“lazy eye”) or other major eye problems are not surgically corrected in infancy, vision will never be normal in the affected eye—if such individuals lose sight in their “good” eye in later life, they are blind.
In the new research, published June 26, 2014 in the online journal eLife, Stryker and UCSF postdoctoral fellow Megumi Kaneko, MD, PhD, closed one eyelid of mouse pups at about 20 days after birth, and that eye was kept closed until the mice reached about five months of age.
As expected, the mice in which one eye had been closed during the critical developmental period showed sharply reduced neural activity in the part of the brain responsible for vision in that eye.
As in the previous UCSF experiments in this area, some mice were allowed to run freely on Styrofoam balls suspended on a cushion of air while recordings were made from their brains.
Little improvement was seen in the mice that had been deprived of visual input either when they were simply allowed to run or when they received visual training with the deprived eye not accompanied by walking or running.
But when the mice were exposed to the visual stimuli while they were running or walking, the results were dramatic: within a week the brain responses to those stimuli from the deprived eye were nearly identical to those from the normal eye, indicating that the circuits in the visual area of the brain representing the deprived eye had undergone a rapid reorganization, known in neuroscience as “plasticity.”
Interestingly, this recovery was stimulus-specific: if the brain activity of the mice was tested using a stimulus other than that they had seen while running, little or no recovery of function was apparent.
“We have no idea yet whether running puts the human cortex into a high-gain state that enhances plasticity, as it does the visual cortex of the mouse,” Stryker said, “but we are designing experiments to find out.”