There Appears to be More to a Particular Ancient Structure in the Brain Than Meets the Eye

Researchers say that an ancient structure of the brain, known as the superior colliculus, might play a more important sensory role than first thought.

superior colliculus in the midbrain
The superior colliculus of the midbrain is quite small in humans, but in fish and birds, it is quite a dominant structure. Credit: Britannica

Researchers from the Netherlands Institute for Neuroscience unveil that the function(s) of the superior colliculus may be far more crucial to visual processing and responding to stimuli in the environment than at first thought.

An intriguing structure in the brain

The superior colliculus is a small, symmetrical structure comprised of two superior colliculi, each abutting the other on the midline of the brain stem.

The structure pervades the vertebrate group, existing in a wide range of organisms, from birds, fish, amphibians, and reptiles, to mammals. In humans, the visual cortex is much more developed, while in organisms like birds and fish, the superior colliculus appears larger and more critical to everyday activities.

When light travels through the retina and hits the light-receiving (photoreceptor) cells at the back of the eye, a signal is produced, which travels via the optic nerve to different regions of the brain. The signal travels to the visual cortex where it is processed, enabling us to gauge motion and understand what it is we are perceiving. The signal also travels to the superior colliculus.

Function

It is thought that the superior colliculus guides our attention to objects in our environment and facilitates prompt responses. Furthermore, the superior colliculus coordinates head movements to bring the most relevant part of the scene into sharper focus.

In situations demanding swift action, this structure can initiate rapid reflexes, like flinching or reaching, without the need for full cortical processing. Although we have some knowledge of the superior colliculus and its functions, science has yet to discover more.

youtube video id=NsWukc8G6wE

Like humans, mice also use the two visual pathways: the visual cortex and the superior colliculus. This is why the team of researchers behind the present study, chose this animal model.

The mice were taught to distinguish between left and right images by licking them. Previous studies proposed a parallel mechanism for visual recognition of objects in mice. By deactivating the superior colliculus in this investigation, the researchers saw a decrease in the mice's object detection abilities. This highlights the critical function of the superior colliculus in the process.

Additionally, measurements showed that the superior colliculus contains information regarding the visual task, and dissipates when an error is made during object detection. This points toward a relationship between the ability to achieve a task and measured information.

Although it is known that the superior colliculus is not as well developed as the visual cortex in humans, we know that it mediates our gaze as we see someone throw a ball to us or wave. We also know that people who cannot see because of a double lesion in the visual cortex, are still able to move around within their environment and avoid objects. This indicates that there is more going on with the superior colliculus than meets the eye.