If one eye is temporarily or permanently damaged, the visual cortex will rewire itself, devoting more resources to the remaining functional eye. This change is reversible if binocular vision is restored. But until a recent study published in Science, we didn’t know how the brain manages to reallocate its resources. This new study shows that this change happens at the level of individual cells, which can shift their attention to eyes as needed.

The visual cortex functions by integrating information from the neurons that are wired to one of an animal’s two eyes. If you cover one eye up for long enough, there’s a shift where the other eye becomes dominant, and more of the visual cortex is devoted to the working eye. This occurs in many animals, including carnivores, primates, and rodents—in mice, this shift in dominance is reversible. What we haven’t known is how it takes place. Does the visual cortex contain entire tissues devoted to different eyes that it repurposes, or do individual cells change their connections to follow different eyes?

The scientists used a technique called ratiometric calcium imaging, which allowed them to see excitatory changes in calcium concentration within the neurons, an indication that they’re busy processing signals. The team used this to follow the sight-driven activity in the binocular visual cortex of adult mice.