By Susan Scott
Many clients that we work with experience some type of auditory processing problem. The effect of this on a person’s life can be very disruptive, whether the symptom is auditory inattentiveness, hypersensitivity to sound, or inability to decode what is being heard. The following article will outline some of the neurological dysfunctions that can interfere with our ability to understand and incorporate what we hear.
Before we begin it is necessary to clarify that this article will not be dealing with deafness resulting form injury to the ear itself, but with injury or dysfunction of the brain as it affects the way we hear. If the eardrum is damaged or the bones of the inner ear fused, neurological reorganization will not be an effective solution.
A good place to start when talking about the role of the brain in how we hear is to trace the nerves that leave the ear as they travel up through the brain. Briefly, our ear works in this way: sound waves captured by the auricle (the cartilage formation on the side of the head) are funneled down the outer ear canal and vibrate the eardrum. Behind the eardrum three tiny bones transmit the vibrations to a membrane on the side of the cochlea (the hearing organ in the inner ear). The cochlea is innovated by the VIIIth cranial nerve. The cranial nerves are those nerves that do not exit/enter the brain through the spinal cord. They are responsible for the muscle movement and sensation of the head, face, mouth, throat, and some of the vital organs in our body.
When the nerve leaves the cochlea it travels into the cerebellum. Here it forms synapses with a new nerve fiber, which exits the cerebellum and crosses to the opposite side of the brain in the pons. From the pons this nerve fiber, with a pit stop for another synapse travels up to the thalamus in the midbrain. Nerve fibers leaving the thalamus then carry information about what we hear to its final destination in a specific part of our cortex. This roadmap of the nerves from the ear to the cortex is very simplified but it provides a good base for understanding some of the dysfunctions that can interfere with auditory processing.
The cerebellum acts as a time sequencer for incoming and outgoing nerve impulses. Consequently, dysfunction in the cerebellum may cause the nerve impulses coming from the ear to get “out of order” before they are sent on their way to higher brain centers. To make an analogy about what this might be like, imagine not hearing all of the sounds in a word in the correct order. Suppose that on one occasion you heard the word animal as aminal, on another occasion you heard it as nominal. If on some rare occasion you heard it as animal you would have no way to know that that word was any more meaningful than aminal. Without the cerebellum maintaining the order of the signals coming in from the ear it would not be possible to reasonably interpret the words and sounds that we hear.
As the auditory messages travel through the pons one of the things that it is responsible for is deciding whether or not the sound that has been heard represents a threat (such as the sound of a dog barking fiercely or a person yelling), our pons should instantly signal our body to be on guard for danger. If there is a dysfunction in the pons, a person may become auditorily inattentive. Such a person may fail to react to noises in his or her environment. For example, a child may seem to pay no attention when his mother calls him angrily to have him clean up a mess that he left, or fail to get out of the street even when a car horn has been honked. In extreme cases of auditory inattention a person may seem to be hard of hearing although a hearing test shows normal hearing.
Moving up the nerve pathway we come to the thalamus, which is the traffic director for most of the incoming sensory information that we receive. If dysfunction exists in this part of the brain a person may experience a problem nearly opposite to that related to a pons dysfunction. Instead of being inattentive to auditory stimulation, a person with dysfunction in the thalamus (part of the midbrain) may have difficulty filtering out extraneous sounds and focusing on a primary incoming message. In other words, he may have difficulty ignoring background noise and paying attention to what his parents or teacher are saying. Under normal circumstances our thalamus evaluates all incoming stimuli, prioritizes them, and sends the most important to our cortex for our conscious attention. When our thalamus is not functioning effectively all the incoming stimuli flood up to our cortex without being sorted or prioritized, making it necessary for the cortex to take responsibility for this function. However, our cortex is not well equipped for this job and does not do it as efficiently as our thalamus can. The result is that a person with this dysfunction will probably find it very difficult to focus his attention on a single primary auditory message.
At the end of this nerve pathway some incoming auditory stimuli end up in an area of our cortex assigned to process auditory messages. We might make the analogy that if the messages conducted up our nerve pathway are in Morse code; it is our cortex that transcribes the Morse code into verbal language. It decodes the messages so that we can use the information. If a dysfunction exists in this part of the cortex, a person might have difficulty decoding messages. This would pertain to understanding the meaning of the words that he hears. His native language may sound to him little different than a foreign language. He may have difficulty understanding what is meant by those speaking to him.
As with all neurological dysfunction, there is a continuum of degrees of severity from mild to severe. It is clear that auditory processing disorders may be the result of a variety of different neurological dysfunction; there is a continuum of degrees of severity from mild to severe.
When trying to address such disorders it is critically important to evaluate what is the underlying dysfunction. Once that is known, an appropriate program of neurological reorganization can be assigned. Dysfunctions in different areas of the brain need to be addressed in different ways, using developmental activities appropriate to the particular area that is dysfunctional. Attempting to address all auditory processing disorders in the same manner will not effectively address the underlying neurological dysfunction.
Contact Developmental Movement Consultants if you would like more information about auditory processing disorders or how neurological reorganization may help to address them. Go to the Contact page at neurologicalreorganization.org