People are used to living with sound. Hearing everything around us is something we have so internalized that we don’t even stop to think about how this information enters our ears and becomes experienced by us.
In this article we will talk about the auditory areas of the brain , which, together with the auditory system, is in charge of collecting these signals sent by the auditory nerves and sending the already processed information to the rest of the nervous system.
What are the auditory areas of the brain?
The auditory areas of our brain include both the auditory pathways, which consist of bundles of fibers that carry information from the ear to the brain and vice versa, and the areas of the brain dedicated to hearing .
These brain areas are the brainstem along with the upper olive complex, the lemniscic and the colliculus; the thalamus and the primary auditory cortex.
In addition, it is necessary to point out the importance of the function of the auditory nerve. This nerve is essential for our hearing. Composed of more than 30,000 neurons, it is responsible, along with the auditory pathways, for transporting information to the brain by means of electrical impulses.
Function of the auditory pathways
Like all other sensory modalities, the auditory system is composed of a series of primary brain pathways and centers whose function is to process and transport auditory information.
In the case of the auditory pathways we find the primary auditory pathway whose only purpose is to transport auditory information, and the non-primary pathway which also integrates other sensory modalities.
Primary hearing pathway
The primary auditory pathway is a short neural circuit with the ability to transport information very quickly, since it is formed by thick myelinic fibres.
Its only task is to transport the information that is collected by the cochlea, performing decoding and interpretation tasks at each level. This information is transferred from one level to another until it reaches the auditory cortex.
However, before the information reaches the auditory cortex, the thalamus integrates the information and prepares to emit a response or reaction to the auditory stimulus.
After the first level, which integrates both auditory pathways as one, a part of this pathway known as the non-primary pathway is diverted by joining the ascending reticular pathway, which integrates sensory information of all types.
The main function of this route is to bring together several different sensory messages, but they are being given at the same time, to select those that need to be processed most urgently.
Parts of the brain stem involved in hearing
The brain stem is the structure through which almost all sensory pathways pass and its function is to communicate the spinal cord, cerebellum and brain. In it we can locate the nuclei corresponding to the auditory system in the brain . These are the following.
1. Cochlear nuclei
The cochlear nuclei are located on the surface of the brain stem , and their main function is to examine the intensity of the sound, as well as its beginning, duration and end. In addition, they also provide the brain with information about the frequency of sound, i.e. whether it is a low or high sound.
2. Upper olive grove complex
One of the most complex systems of the auditory brain is the upper olive complex. Its dense neural network is designed to analyze and filter all acoustic information that is directed to the cerebral cortex.
3. Lateral lemniscs and colliculi
The nucleus of the lateral lemniscate is involved in encoding the duration of the most complex sounds.
On the other hand, the colliculus is divided into the dorsal and external cortex and the central nucleus , which is composed of a large number of neurons.
The dorsal and external cortex is dedicated to examining acoustic information and recognizing complex sounds. While the central core analyzes the frequency of the sound and divides it into bass or treble.
The thalamus and auditory cortex
Other areas of the brain involved in hearing are the thalamus and the auditory cortex. Let’s see how they work.
The auditory thalamus, also known as the Medial Genetic Body (MGB) , receives fibers from both the dorsal and external cortex of the collicle and the central nucleus of the collicle. This part of the thalamus is divided into three specialized function zones. These zones are: the dorsal zone, the middle zone and the ventral zone.
Neurons in the dorsal area send projections to the secondary auditory cortex. These neurons tend to respond to various different sensory stimuli.
Its neurons travel to the primary auditory cortex and are also involved in the analysis of sound frequency , maintaining the latency between communications.
Primary auditory cortex
In people, the auditory cortex covers 8% of the entire surface of the cerebral cortex .
This primary auditory cortex consists of more than twelve different auditory fields which are located in the upper area of the temporal lobe , where they extend through the angular gyrus towards the Silvio’s fissure; there they meet the transverse gyres of Heschl.
This brain area can be divided into two regions differentiated by the organization of their neurons and their functions. These areas are the following.
- The AI area is composed of neurons that determine the spatial representation of the stimulus .
- The AII area is dedicated to locating sound in external space, examining complex sounds and is closely related to auditory memory.
Finally, the area surrounding these two areas is in charge of analyzing and integrating the auditory information with the other sensory information perceived by the person.