This week we discussed about the Visual System – which are chapter 9 (The Eye) and 10 (The Central Visual System) of the book Neurocience: Exploring the Brain.
This is a topic I particularly find very interesting. The complexity of this sphere, and everything that is behind, really fascinates me. We started by talking a bit about the anatomy of the human eye and how light affects it (the lens, specially). We briefly discussed some malfunctions of the eye, such as myopia or hyperopia.
Light must pass through many cell layers before it reaches photoreceptors at the back of the retina. These photoreceptors can be of two types: rods – that make vision possible in low light – and cones – enable us to see in the daylight. What photoreceptors do is transduce light energy into changes in membrane potential. We can perceive colours due to the contributions of short-, medium- and long-wavelength cones to the retinal signal. A curiosity on this topic: have you ever wondered if we all see colours the same way? The answer is no! Females are known to have more cones than males. That allows them to distinguish between similar colours better than men, who, in general, have more rods. Just as a conclusion to this curiosity, this happens because long time ago, men would go hunt, meaning they needed a better sense for shapes, whereas women would stay still gathering berries, for example, and needed to distinguish the colours to avoid poisonous food. Those who couldn’t do it would die, so the genes for more cones in women and more rods in men were passed onto the next generations.
About the central visual system, in this part of the lecture we explored how the information extracted by the retina is analysed by it. Our visual system provides us with a unified picture of the world around us, yet we have two eyes and therefore two visual images in our head that need to be merged. To see how the brain does that, we examine the stimuli that make different neurons in the visual cortex respond and how these response properties arise.
The left side of the retina is connected to the right side of the brain, as well as the right side of the retina is connected to the left side of the brain. This happens because the optic nerve fibers cross in the optic chiasm.
To finish the lecture we watched a movie about colour understanding and it was very informative.
Exercises Class 16.10
On this week’s exercise session, we answered some questions related to the topic. One of them was about optical illusions and how we can trick our eyes into seeing something that is different from the reality.
FOR FUN: visit https://eyewire.org/. It’s a 2012 game to map the brain that challenges players to map neurons in 3D. The goal is to identify and classify cell types as well as potentially expand the known broad classes of retinal cells.