Our brains adapt after retinal damage

The brains of macular degeneration (MD) patients have shown distinctive adjustments to the disease, thickening in peripheral-vision areas and thinning in central-vision regions.

The observations, discovered by University of Alabama at Birmingham and Pennsylvania State University researchers, were made in adult brains – highlighting just how flexible and responsive the nervous system can be.

The research team compared the brains of 10 MD patients with 10 normal-sighted people closely matched in age, gender and education. The areas of the brain associated with central vision, which is most commonly affected in MD, were compared with the areas associated with peripheral vision.

The researchers found that MD patients had a significantly thinner central-vision cortex compared to people with normal sight. 

The MD patients also had a peripheral-vision cortex that was demonstrably thicker. The team speculates that, by using their peripheral vision to compensate for their central vision loss, patients are contributing to the cortical thickening seen in the study.

Research co-author, Dr Kristina Visscher, told OT that, even though the team had hypothesised such thinning and thickening occurring, the results were still exciting.

Dr Visscher explained: “The result intuitively makes sense using the analogy of muscles. When you use certain muscles more over time, they tend to get bigger. However, if you use those same muscles much less over time, you would expect those muscles to decrease in size.

“We are observing these brain changes in individuals who acquired their vision loss during adulthood. This means that we’re observing pretty profound brain changes in people who are well past the ‘critical period’ during which we often think brain plasticity slows down or stops,” she emphasised.

Graduate student and the paper’s first author, Wes Burge, said the findings could also be of interest for patients who in future might be cured of MD. He hypothesised that an imaginary patient receiving a ‘miracle’ cure might not initially have the same central vision of someone with permanently healthy vision.

“Speculatively, our data also suggests that this hypothetical patient, with a now-perfect retina, would initially have somewhat decreased central vision ability, related to their thinned cortex. Over time, however, we would expect this effect to go away as the patient experiences central vision, as the cortex corresponding to central vision became thicker,” he told OT.

Mr Burge said that the overall scientific findings on the brain would be noteworthy for researchers testing MD cures for effectiveness in the short and long term, as well. “This idea that there is use-dependent brain plasticity has been shown in many domains, and clinicians should, I think, keep it in mind,” he concluded.

Image credit: Bob Jacobs