The auditory cortex is located in the cerebral cortex and is responsible for processing and recording acoustic stimuli. It is also called the auditory center or auditory cortex. It is found on the upper convolutions of the temporal lobe in the cerebrum. The auditory center is about the size of a thumbnail. It is also the terminus of the so-called auditory nerve pathway. There are the primary and secondary auditory cortex, which are concentric to each other.
What is the auditory cortex?
The primary auditory cortex is formed from two to four transverse convolutions of the brain. This is where recorded sounds of all kinds are processed. It is critical to the sensory quality of human hearing. Both sound pitch and loudness are verified in the primary auditory center. For example, the shrill sound of a police siren is distinguished from the muffled sound of a drum. Based on this, the secondary auditory cortex is able to record and implement more complex stimulations of what is heard. It can make sense of the words, sounds, and melodies as well as match them with already known sensory information.
Anatomy and structure
Each side of the brain has an auditory cortex associated with it. Thus, signals from the left and right ears can be processed. In each case, the sounds of adjacent frequencies are also recognized by adjacent neurons in the brain. This so-called tonotopic structure of the auditory cortex functions in principle like a keyboard. High tones are received on one side and low tones on the other. In total, the human brain is equipped with around 100 billion neurons (nerve cells). Because of its many tasks, the brain requires about 15 percent of the human body’s total energy needs. The auditory center in the brain constantly compares incoming sounds with what is already known and classifies them accordingly. In addition, previously unknown auditory stimuli are also registered continuously, for example sudden loud noises or speech signals from a conversation partner. The respective secondary auditory cortices of the two cerebral hemispheres function differently. One of the two cerebral hemispheres, usually the left, is dominant. In it, what is heard is processed rationally. In the left auditory cortex, the sensory language center (Wernicke center) is located, which enables language comprehension. In the non-dominant auditory cortex, the incoming signals are then processed holistically. This process is significant in order to be able to understand and feel music, for example. The linking of primary and secondary auditory cortex is also important for combining what is seen and heard. Both heard and read speech is processed in the Wernicke center. This information then travels to the qualitatively higher areas of the auditory center. In the motor speech center there, speech is accompanied by adequate movement.
Function and tasks
The auditory cortex comprises eleven auditory fields known so far, each responsible for different sound frequencies. That more such fields exist is not ruled out, but so far it is only a conjecture. However, the brain can also deceive itself, for example when it supplements missing information with empirical values or details that seem logical. This is where the term soul deafness comes from: Some people are able to perceive sounds, but cannot interpret and classify them. On the other hand, silent mouth movements that are only visually recognized can stimulate the auditory center and put it into heightened alertness. Looking at a speaker while he or she is speaking can also increase auditory performance considerably. Feeling or touching objects also increases activity in the auditory center. Electrical signals are the source of all hearing. They are sent from the fine hair fibers of the cochlea in the inner ear to the auditory nerves. They are then transmitted as impulses to the auditory center of the brain. There they are received by innumerable groups of nerve cells and translated for processing in the brain. In this way, very specific sounds can be consciously perceived. When what is heard reaches the brain, a reflex is first triggered, which may cause a sudden physical reaction. This depends on the intensity of the stimuli received. However, the sound is only then consciously recognized in the auditory cortex. Various other areas of the brain are involved in this process. Only the classification of the sound or sounds is followed by the corresponding so-called voluntary reaction.
Diseases
The primary auditory pathway is the crucial nerve cord of hearing, where the processing of decoded sound begins. Along this pathway, messages travel on to the temporal lobe, precisely the auditory cortex. The first station of this pathway is the brainstem, which dissects the emitted signals according to duration, strength and frequency. They are then prepared in the thalamus (the “visual mound”) for a motor response from the body. The thalamus is located at the stem of the cerebrum and is interconnected with the sensory apparatus of the human organism. The auditory center then stores the complex signal and provides it with a response (the reaction). In addition to the auditory center, the temporal lobe also contains so-called associative areas, which are important for language processing and memory formation. In addition to the primary auditory pathways, non-primary auditory pathways also receive a variety of sensory information. These first turn to that sensory message whose processing is most important. For example, when a person reads a newspaper and watches television at the same time, the non-primary auditory pathways allow them to focus on the more significant of the information received, or on the more important of the two simultaneous activities. The selected messages also arrive in the thalamus, which delivers them to sensory centers in the cortex.
