There is an area of the brain called the visual cortex, and it’s responsible to interpreting the signals sent to it from the eyes via the optic nerve.
Normally, the images from each eye are processed individually, but in the event of a serious injury, in which one eye is no longer able to see, the part of the visual cortex normally in charge of handling its input can adapt and begin working with the other eye. This transition was thought to be permanent, until new research published in Science showed that the neurons in this part of the brain can toggle between eyes as needed.
Serious eye injuries aren’t the only way to trick the brain into rewiring itself. Simply covering up one eye for an extended period of time is enough to alter the way that the brain processes vision, and can be used to turn what was once a non-dominant eye into a dominant one.
The switch and then the reversal in the visual cortex has been observed in mice, but its function has not been fully understood until recently.
Is there tissue within each half of the cortex dedicated to each eye, or do specific neurons rewire themselves to connect to other sources of information?
To work out the mechanism of the change, scientists used ratiometric calcium imaging, a means of observing excitatory changes in calcium concentration within the neurons, which happens when they are processing, sending, or receiving information. This way they could see exactly what was going on within a mouse’s brain as it was processing visual input.
Through rigorous experimentation, they worked out that under normal circumstances, each half of the visual cortex was solely responsible for its one eye, and that changes in the neuron-eye association only happen under rare circumstances.
Additionally, the experiments showed that the individual cells would switch between the inputs from both eyes as they were specifically triggered.
Starting from a state of binocular vision, one eye would get covered, and the neurons would then focus on the uncovered eye. Later, both eyes would be uncovered, and the neurons would return to normal function. Then, the opposite eye would become covered, and the opposite neurons would switch. This process takes time between each stage, but appeared to be infinitely repeatable.
The biggest take away of new medical information from these tests is how plastic specific areas of the brain can become after drastic changes to the sensory input it receives.
With further experimentation, and human trials, there’s hope that this may help in helping people recover from serious injuries, specifically those that affect the senses.