How does our brain see?
If you have ever wondered about the neurobiological correlates of vision, then this article is for you!
The primary anatomical structures that enable the reception of light stimuli from the environment are the eyeballs. They are made up of three layers of cells with distinct functions. The outermost is the sclera, which protects the eyes from damage. The middle layer is the choroid, which is responsible for the blood supply to the eyeball. The innermost layer is the retina, which is made up of light-sensitive cells - cones and rods. These are what enable us to see in colour and low-light conditions, respectively.
Fig. 1 – Layered structure of the retina
The signal from the depolarised photoreceptors is transmitted to the next layer of cells located in the retina. There are bipolar and horizontal cells, as well as amacrine cells and ganglion neurons (Fig.1). Here, the chemical signal is converted into electrical signal and an action potential is initiated, which is transmitted via the optic nerve to the optic junction (fig.2).
Fig.2 – Visual pathway
At the level of the optic junction, bundles of neurons from both eyes are mixed and the signal is then transmitted, on both the right and left sides of the brain, to an interbrain structure called the lateral colliculus (Fig.2).
In the final stage, the axons of the neurons of the lateral geniculate begin to form strands of fibres called the visual radius. This runs again on both sides of the brain to the occipital lobes of the cerebral cortex, where the analysis of the stimuli reaching our eye takes place. It is only in the primary visual cortex that light information is interpreted in terms of colour, movement or angle.
Author: Suri Stawicka
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