More than half of the brain is dedicated to processing visual information. The processing of visual information isn’t as simple as it looks. Back in the 1950s, when scientist first discussed artificial intelligence, it was thought that teaching a computer to play chess would be difficult but teaching a computer to see would be easy. Well, in the 2000s, it was shown to be the opposite. There are computers that can beat humans at chess and the game show Jeopardy, but there aren’t computers that can see better than humans.
That leads to the question of how is the visual information being processed so we can tell the difference between a coffee mug and a backpack. Two research projects have studied how the brain processes visual information and this is what they learned.
Neuron Differentiation in Fruit Flies
When the brain forms in during embryonic development, there is just a small group of cells to work with. Therefore, how the do the neurons change as the embryo develops? There are neural stem cells known as neuroblasts that produce specialized neurons. How they change is not fully understood.
Scientists at the University of Illinois Urbana-Champaign learned more about this process of differentiation by studying the optic medulla of the Fruit Fly. As the neuroblasts divide and differentiate, they express transcription factors that direct the cells to the kind of neurons they are to become. These transcription factors are known as temporal transcription factors and they act as a marker that tell the researchers what stage the neuroblast is at and this helps them to put together the order of events when the neurons form.
They focused on two kinds of temporal transcription factors, eyeless and sloppy-paired. Scientists used genetics and other techniques to measure the expression pattern of genes in the optic medulla during development. They soon found that two non-coding regions near the sloppy-paired genes were necessary to ensuring that the sloppy-paired temporal transcription factors expressed at the right time and amount. When researchers removed the non-coding DNA regions, called enhancers, they found that the flies with no enhancers showed an absence of the expression of the sloppy-paired temporal transcription factors in the medulla neuroblasts.
Another thing that was found was that mechanism called Notch-signaling works together with the temporal transcription factor to trigger the expression of the next temporal transcription factor. The scientists concluded that the way the Notch-signaling regulates the temporal transcription factor expression is dependent on where the neurogenesis cascade cells are at. That means, once a specific number of neuron types have been made, the Notch-signaling regulates the transition for neuroblasts to differentiate into a different neuron type.
While this was seen in Fruit Flies, the understanding of how the temporal transcription factor and Notch-signaling works has the potential to translate to higher-order animals.
Alternating Signals
What happens in the brain when we see two objects, such as a coffee mug next to a backpack? A study at Duke University investigated that and it was found that the neurons convey visual information about two objects by alternating signals about one or the other. When two object overlap, brain cells detect them as one entity.
A subset of cells was found in the visual cortex of macaque monkeys to switch between reporting on two different images. Going back to the coffee mug and backpack example, a neuron in the visual cortex would fire 20 times a second when it sees a backpack. When it sees a coffee mug, it fires five times a second. If the neuron sees a backpack and mug next to each other, it alternates between firing 20 times a second and five times a second. Yet, if the two overlap, like having the mug in front of the backpack, the neuron fires the same way each time the eclipsing objects are presented. This implies that the neurons treat the overlapping images as a single object, as opposed to separate ones.
While real life is busier than just two side-by-side things, this gives an idea of what is going in our brains when it comes to vision. Of course, more studies are needed to better understand how our brain makes sense of all that we see. Both of these studies show that a lot is going in the brain when it comes to vision.
Sources:
https://www.rochester.edu/pr/Review/V74N4/0402_brainscience.html
https://www.igb.illinois.edu/article/researchers-investigate-neuron-differentiation-fruit-fly-brains
https://today.duke.edu/2022/11/brain-cells-use-telephone-trick-report-what-they-see