When you see something interesting, and you turn back to look at it again, or you hear a sound and your instinct is to tilt your head slightly towards the sound so you can listen better, it’s not coincidental. A particular part of the brain includes the superior and inferior colliculi, which allow this to happen. Do you ever wonder what the function of superior and inferior colliculi are?
The superior colliculus is the visual reflex center that allows eye movement, gaze shifts, and reactive reflexes like turning the head. The inferior colliculus is responsible for hearing and reacting to auditory input with non-auditory systems. Both vital colliculi are situated in the midbrain.
The superior and inferior colliculi are often jumbled as one in explanatory concepts because they are situated and work closely together; however, they each have distinctive characteristics and are equally essential for the brain and body to function efficiently. In this article, we will gain a detailed understanding of each structure.
What Is The Superior Colliculus?
The superior colliculus is a paired structure within the brain that is the primary visual reflex center. It receives information from environmental stimuli and coordinates gaze shifts for eye and head movements.
The Superior Colliculus In Vertebrates
The structure is known as the optic tectum or optic lobe in vertebrates. It contains a topographic map and other visual inputs from auditory and somatosensory pathways.
Where Is The Superior Colliculus Located?
The structure is located on the posterior lateral midbrain. It is caudal to the pineal glad and rostral to the inferior colliculus. Interestingly, in Latin, the superior colliculus is known as the “upper hill.” It is a structure on the roof of the mammalian midbrain and forms a significant component of that section of the brain.
The Structure Of The Superior Colliculus
The superior colliculus is a seven-layered paired structure. It is symmetrically positioned on either side of the brainstem midline and grouped into superficial, deeper, and intermediate layers.
The superficial layers include:
- The stratum zonale
- The stratum griseum superficiale
- The stratum opticum
The intermediate layers include:
- The stratum griseum intermedium
- The stratum album intermedium
The deeper layers include:
- The stratum griseum profundum
- The stratum album profundum
Function Of The Superior Colliculus
The primary function of the superior colliculus is to receive environmental stimuli directly from the retina and use that information to send signals which induce eye movements, gaze shifts, and head movements.
The superior colliculus functions through each of its layers. Here is how that works:
The Superficial Layers
They are purely sensory. The superficial layers respond to both sides of the brain's retinal input from the opposite visual stimuli.
The Intermediate Layers and Deeper Layers
These deeper layers receive input from auditory, visual, and somatosensory pathways. They are associated with sensory and motor functions.
What Does The Superior Colliculus Do?
When a strong enough signal is present, specific neurons in the layers will induce a saccadic eye movement that allows the eyes to move rapidly from one target to another. This often happens when there is no or limited head movement available.
When reading, watching a movie, laying down and the head is still and relaxed, the eyes can still move, follow texts, look for the stars, follow the visual changes in the film, or scan the room to notice a mosquito. The superior colliculus in the brain allows this to happen as it receives input stimuli from the environment through the retina.
The superior colliculus is the primary area of the brain thought to be involved in saccadic eye movements and motor functions in the generation of eye movements. It produces gaze shifts initiated by the direction of the eye movement. It will create a head shift or turn while the eyes counter-rotate to stabilize.
Superior colliculus structures assist with neck movement by sending signals to the muscles to turn and respond to visual stimuli. It works with oculomotor and head pathways.
What Is The Inferior Colliculus?
The inferior colliculus, like the superior colliculus, is a paired structure within the brain. It is the primary auditory reflex center. It receives information from environmental stimuli for auditory pathways to help localize sound and coordinate head movements.
The inferior colliculus is not studied as well as the superior, but it is an essential component of the auditory pathway. It helps fine-tune and integrate auditory sensations from various other regions. It then sends information to the thalamus and cerebral cortex.
Where Is The Inferior Colliculus Located?
The inferior colliculus is located in the lower part of the midbrain and is called “lower hill” in Latin. It is situated on either side of the brainstem midline, below the superior colliculus. They are situated on the dorsal surface of the rostral midbrain. Each inferior colliculus resembles two symmetrical bumps.
Structure Of The Inferior Colliculus
The inferior colliculus includes three regions:
- The central nucleus
- The dorsal cortex/ pericentral nucleus
- The external cortex/ lateral nucleus
The central nucleus is the largest and is encircled by the external and dorsal cortices. They are all major sites of non-auditory input to the inferior colliculus. The central nucleus sends tonotopically organized efferent fibers to the primary auditory cortex in the temporal lobe. Different neurons respond preferentially to varying frequencies of sound.
Function Of The Inferior Colliculus
The inferior colliculus’s primary function is ascending and descending auditory pathways between the brain stem and forebrain synapse.
- It localizes sound input to create more focus and better hearing.
- It provides frequency determination.
- It includes the integration of auditory with non-auditory systems.
The inferior colliculus is known for its role in hearing and is the largest nucleus of auditory systems in humans. The auditory pathways travel through this point for brain stream coverage. From this point, the auditory pathways branch out to carry auditory information onto other areas like the superior colliculus or thalamus.
The inferior colliculus neurons are specialized to respond to cues that allow for localization of sound or determination of where the sound originates from. The information is then passed to the superior colliculus involved in the movement of the head and eyes. It is how you get a response to visual and auditory cues from the environment.
The external cortex receives input from auditory areas and information regarding body sensations. It plays a role in representing body positions in response to environmental sounds. When the inferior colliculus identifies the location of the sound in space, it orients the body towards the sound.
Do the Superior And Inferior Colliculi Function Together?
Both colliculi can interact together if they receive input simultaneously. They help orient the eyes and head toward stimuli you see and hear. They work together, if necessary, like when you watch a movie, you look and listen. If someone calls out to you, you will turn to look where the voice is coming from and look for the person while localizing the sound of their voice to listen further.
What Happens If The Superior And Inferior Colliculi Gets Damaged?
The effect of a damaged superior and inferior colliculi colliculus is detrimental. It can affect the entire concept of your ability to pick up visual and auditory input and send information to the eyes, ears, and head for response in movement.
Here are some effects of a damaged superior colliculus:
- Difficulty when scanning, detecting movement, and processing visual data.
- Difficulty noticing objects within the peripheral visual field.
- Inability to track the target (common with animals).
- Your planned movement will be inaccurate.
- Experience of increased latency and decreased velocity of saccades.
- Increased distractibility.
- Increased intracranial pressure
- Long-term morbidities.
- Chronic headaches
- Deficits in attention and vigilance
If the inferior colliculus is Damaged alone, it will possibly only affect the correct functioning of your auditory pathways. If the superior colliculus is damaged, it will affect your visual functions and some auditory functions.
The inferior colliculus has neurons that send signals to the superior colliculus. The superior is in charge of sending sensory signals to the body for movement. They work together to ensure your motor functions run smoothly, and when they are damaged, they can be detrimental to your health mentally and physically.
Problems With The Brainstem
The superior and inferior colliculi are situated in the midbrain. The midbrain is located in the brainstem in the most superior region.
Any damage or impairment of the brainstem affects the midbrain, thus causing issues with any function related to the superior and inferior colliculi. The superior and inferior colliculi are part of the tectum function in the midbrain.
Several factors could affect the midbrain. Any pathological processes, like strokes, tumors, demyelinating processes, infections, or neurodegenerative diseases, play a role. Some specific conditions include:
- Oculomotor (third) nerve palsy is a midbrain lesion due to a stroke, tumor, inflammation, or infection. It can damage the oculomotor nerve resulting in an inaccurate positioned eye, dilated pupil, droopy eyelids, and double vision.
- Trochlear (fourth) nerve palsy – a lesion with an oculomotor nerve palsy that results in upward deviation of the eye and blurry vision. Diplopia, tilting the head to accommodate visual changes.
Effects Of A Damaged Midbrain On Superior And Inferior Colliculi
The midbrain is the small portion of the brain between the forebrain and hindbrain, where the superior and inferior colliculi are located. When the midbrain is damaged or affected, it can hinder the proper function of the superior and inferior colliculi. The role of the midbrain is all about motor function and receiving and integrating sensory information.
The auditory and visual functions are significant parts of the midbrain, and any damage can cause problems with hearing, vision, and related movement. It can also create trouble with memory. The midbrain also houses the hypothalamus, which is vital for automatic body functions.
How To Improve The Midbrain Function
You can improve your midbrain, which results in better functioning of the superior and inferior colliculi. The left and right sides of the midbrain also need to be balanced for improved well-being and a better lifestyle. Here is how you can achieve that:
- Meditating regularly
- Playing memory games or testing your memory
- Reading and engaging in literature
- Building puzzles and playing word games
- Ensuring you get enough sleep
- Socializing and interacting with people who are good for you
- Exercising and staying fit
- Drinking enough water daily
- Eating healthy, nutritious, wholesome food
What Happens When The Midbrain Functions Efficiently?
If you take care of your health and mind by doing the above activities and trying to live a healthy balanced life, your midbrain will also remain healthy and can improve if it is weak. Here is what will happen if you have improved your midbrain:
- You will have better focus
- You will have a better memory
- You will experience less stress
- Your health will be good
- You will experience improved sleep
- Your motor skills will be better
- You will have a better sense of imagination and creativity
- You will notice super sensory perception
- You will have greater emotional control
- Your self-confidence will be leveled up
Activating the midbrain will bring balance between the right and left sides, resulting in balancing the rest of the body. Your superior and inferior colliculi will improve significantly, giving you more clarity and efficiency in your visual and auditory pathways and improving memory.
Once you achieve that, you will focus better, be more alert, and have more energy without feeling worn out and overstimulated too quickly. In situations where your vision and hearing functions are triggered, for example, in social interactions or where there are large crowds, loud noises, bright lights, or overstimulation, you will be much less sensitive.
Your inferior and superior colliculi will be able to absorb, accept, process, and send information quicker and more efficiently through their pathways. This allows you to have better reflexes, and your body will respond accordingly.
The superior and inferior colliculi are vital structures in the midbrain for the efficient functioning of the auditory and visual pathways and associated sensory movements of the eyes, head, and sometimes the body.
Both colliculi respond to environmental stimuli through the retina and ears and send input to the brain, giving signals to the eyes for saccadic movement, ears for localization and sound frequency, and the spine to allow neck movement for the head to turn.