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Navigating Within Space & Restoring Vision After a Stroke

Posted by Ilena Di Toro | Posted on November 21, 2023

Have you ever considered the amount of information that goes from your eyes to the brain, so that you can navigate through an area, be it in your home or a walk to the store? Also, if vision is lost as a result of stroke, can it be restored? Both deal with taking information in and processing it, so that the correct action can take place. Of course, research is taking place in these areas and here is what scientists have learned.

A Brain Region Supports Navigation
When you move from Point A to Point B, be it crossing the street to walking from the living room to the kitchen, it requires your brain to process information, which has to support navigation. The two areas of the brain that are activated when people navigate through their environment are the occipital place area (OPA) and the retrosplenial complex (RSC). Daniel Dilks, PhD of Emory University in Atlanta theorizes these areas support different kinds of navigation. The RSC supports map-based navigation, which involves finding our way from a specific place to a distant place, such as a store or restaurant. OPA supports visually guided navigation, such as moving from your living room to your kitchen without bumping into things.

Not everyone buys his theory, since the OPA doesn’t support visually guided navigation until 8 years of age. Still, kids manage to navigate around home and school before reaching that age and they do a lot of navigating while they are in the crawling stage of development. So, the question is, does OPA come on early but matures slowly, or does crawling use a different system? So, Dilks’ lab set out to find out if OPA would activate when adults crawl.

To test this, Dilks had subjects view videos that were recorded from the perspective of someone walking and someone crawling, as well as video from flying over the environment and scrambled video images in order to include a mode of navigation that is not accessible to humans. When people view videos like these, the brain works as if it were performing the activity. Researchers used functional magnetic resonance imaging (fMRI) see the activation of the brain regions in the 15 adult participants as they watched the videos.

When subjects saw the walking video, the OPA was activated. When they saw other videos, crawling, flying or scrambled, the RSC was activated. That suggests that OPA is specific to walking, not to other types of navigation. This suggests that there is a different brain system managing navigation in early as opposed to late childhood and that these parts of the navigation system come at different stages of development.

“Time is Vision”
What happens when someone experiences a traumatic brain injury, like a stroke in the occipital region of the brain? Strokes that occur in this region of the brain affect a person’s ability to see. While there may be some level of vision immediately after the stroke, over time that diminishes and eventually disappears. Yet, research done by Krystel Huxlin, PhD at the University of Rochester has shown that vision therapy can help stroke patients recover more of their lost vision, if it is administered within six months of experiencing the stroke.

Unfortunately, the “standard of care” for stroke patients with vision issues is that they received limited vision therapy that either maximizes remaining vision or teaches them to navigate with limited vision. There isn’t anything to help them get back the vision that they lost.

That’s where Huxlin’s research come in. Her lab did a study where two groups of stroke patients, one group who were more than six-month post-stroke and another group who three-month post-stroke. Both groups were trained to use a computer-based device developed by Huxlin that is a type of therapy for the visual system. It involves a set of exercises that stimulate the undamaged parts of the brain’s visual system to utilize visual information. Over time, the undamaged parts of the brain can learn to process visual information that is not “filtered” by the damaged primary visual cortex. As a result, this therapy partially restores conscious visual sensations.

There’s more. The patients who were three-month post stroke and had this therapy rediscovered global motion discrimination, which is the ability to ascertain the direction of motion in a noisy environment. These patients were also able to detect a spot of light faster and more efficiently than patients who were six-months post stroke. These finding show that persons who receive vision training after a stroke are able to both prevent vision from degrading and keep whatever perceptual ability that they have.

Vision is more than just eyes taking in images. There is the processing of the images in the brain. These research initiatives show how dynamic vision is and that there is more to learn when it comes to the neural processes involved in vision.

Sources:
https://www.nei.nih.gov/about/news-and-events/news/visually-navigating-foot-uses-unique-brain-region

https://www.rochester.edu/newscenter/regaining-vision-after-stroke-436952/

https://www.flintrehab.com/occipital-lobe-stroke/

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