What is going on in the cellular space and the neurological space that allows us to see? As you can guess scientists have studied these things and here are what they have found.
Stem Cells
There have been great advancements in the development of lab-grown photoreceptors. The problem lies in implanting them. Once they are implanted, they need to grow axons to connect with existing neurons in order for the light that they detect to be transmitted to the brain. Researchers from the University of Wisconsin School of Medicine demonstrated that photoreceptors derived from stem cells are able to grow axons and connect to other cells. The problem is that they lose this ability within 40 to 80 days. Still, all is not lost since they found mobile helper cells that assist the photoreceptors that aren’t able to grow on their own by pulling and stretching parts of the photoreceptor.
Researchers used time-lapse imaging of the cells to see the axons extend from the photoreceptors to their target cells. The ends of newly generated cone photoreceptor axon could stretch but only up to date 80 of their existence. As for rod photoreceptors, they didn’t have the ability to extend axon on their own. They soon learned that the older lab grown photoreceptor cells could make the connections if they were grown along with retinal cells that had motility. That’s not all, the axons of these photoreceptors could attach themselves to the cells and be pulled along for the ride. Learning about how the photoreceptors make these connections brings researchers closer to being able to transplant stem-cell derived photoreceptors as a means to cure blindness.
Vision via the Brain
Now what’s happening in the brain that leads to vision. Scientists at New York University’s Center for Neural Science and Department of Psychology, studied the size of primary visual cortex. Like most parts of the brain, has its share of bumps and grooves and, like a fingerprint, every person’s visual cortex has its own pattern of bumps and grooves. It’s not known how significant these bumps and grooves are, especially when it comes to our ability to see.
Researchers wanted to learn more about the relevance of these traits, as it relates to how we see. The primary visual cortex arranges images like a map and like many maps, some parts are enlarged as compared to other parts. This is due to the fact that the primary visual cortex enlarges the center of the image that we see, since that is where our eye is focused. The reason for that is because it has more tissue dedicated to the center of our field of vision. The primary visual cortex also enlarges locations to the left and right of where our eyes are focusing on relative to locations above or below and it does so because of differences in the arrangement of the tissue.
Scientists mapped the primary visual cortex of 24 people, using functional magnetic resonance (fMRI). They also measured the quantity of the primary visual cortex tissue these persons have that are dedicated to the processing of visual information from locations such as to the left or right in the field of view. The subjects also did tasks that assessed the quality of their vision at the same locations in their field of view as the primary visual cortex measurements. They categorized among the orientation of patterns shown on a computer screen. These images were used to gauge the ability to make distinctions among images, also known as contrast sensitivity.
The results showed that the differences in the surface area of the primary visual cortex could predict the measurements of the subjects’ contrast sensitivity. For example, those with a large primary visual cortex had better contrast sensitivity than those with a small primary visual cortex.
All of that means that the more surface area the primary visual cortex has dedicated to a specific location, the better the vision in that location. So, the differences in perception are related to the differences in the structure of the primary visual cortex.
Of course, research in these areas is ongoing. Still, all of this shows that there is more to the neurological response to vision than meets the eye.
Sources:
https://www.med.wisc.edu/news-and-events/2022/june/uw-eye-research-stem-cell-photoreceptors/