Neural Hearing Loss

When speaking of hearing loss, references usually make the distinction into three categories: conductive hearing loss, sensorineural hearing loss and mixed hearing loss. Sensorineural hearing loss is characterized by some problem in the sensory components of hearing, i.e. the nerve receptors in the cochlea or even the auditory nerve that sends sound messages to the brain. Many scientists, however, further breakdown this category into sensory hearing loss and neural hearing loss.

While sensory hearing loss involves damage to the sensory cells, or receptors, found in the inner ear, neural sensory loss involves damage to the auditory nerve or to the nerve pathway that connects the inner ear to the brain. Even if signals reach your ear loud and clear, they cannot be properly passed on to the brain and so they cannot be properly heard.

This type of hearing loss is relatively rare, but quite serious because it is not often reversible. Neither hearing aids nor cochlear implants can improve hearing in cases where there is no auditory nerve function because both rely on creating or amplifying signals to then be transported to the brain via the auditory nerve. Neural hearing loss may also be due to problems in the brain; a common cause of the malfunction of brain hearing centers is the presence of a tumor, which can be life-threatening. Other serious causes of neural hearing loss, which is also called retrocochlear hearing loss, are multiple sclerosis and stroke.

In certain cases, something called an auditory brainstem implant, or ABI, can be of help to people suffering from neural hearing loss. The ABI is a tiny electrode that is designed to bypass the inner ear and the auditory nerve and so send sound signals directly to the brain. This device is surgically placed directly over the brainstem’s nerve center for the detection of sounds and electrically stimulates the acoustic nerves.

The electrode works with other components in order to achieve its goal. There is a microphone on the outer ear, which picks up sound signals and transmits them via digital technology to a decoding chip implanted beneath the skin. The decoding chip sends the sounds to the electrode via a wire that attaches the two; the electrode will then differentially stimulate the brainstem depending on the sounds received.

Once the surgery to implant the device is complete, patients work with doctors and audiologists to fine-tune their devices and learn how to deal with the new sounds that they will be able to hear. While the ABI cannot fully restore normal hearing, it allows people who would otherwise be completely deaf to have some hearing sensation and it makes lip-reading much easier. It is the only device that is capable of allowing people with no auditory nerve function to avoid complete sound isolation.