Hearing and the brain

Much is known about the deterioration of hearing caused by noise exposure, toxicity and the aging process. Inner-ear or “sensory” hearing loss accounts for the majority of cases seen in hearing centers and reflects the risk factors of the population. Hearing, however, relies on more than the ear. There are brain and nerve relays and processing centers that work constantly to help us make sense of the sounds our ears take in. When faced with patients whose hearing abilities in quiet greatly outpaces their ability in noisy environments, one realizes there may be problems beyond the ears that affect the ability to listen effectively in poor acoustical surroundings. There are major connections between the elements of hearing and the brain.

Research has found that in patients with significant hearing loss, the aging of the brain may be accelerated by at least six years, and hearing loss is associated with reduction in brain volume exceeding that which would be expected for the patient’s age. Researchers estimate the brain’s aging process can be accelerated by more than six years in patients whose hearing loss affects listening to speech.

Central presbycusis is a term used to describe a limitation the brain has imposed on hearing beyond what one would expect from inner ear damage alone, based on standard audiometric testing.

Presbycusis (or “presbyacusis”) means “elder hearing” and describes hearing that has been affected by the aging process. The most typical consequences are poor high-frequency hearing for sounds such as alarms, phones and electronic beeps, difficulty hearing consonant sounds such as /s/, /f/ and /th/, and reduced clarity of speech and music. Most often this is due to gradual deterioration of the sensory cells in the inner ear.

“Central” refers to the central nervous system, the brain and nerve network involved in hearing. The nervous system/brain processing of sound allows us to take the signals our ears detect and “decode” nerve impulse patterns that tell us: what kind of sound we’re hearing, the identity of a speaker, what words mean, how loud or soft sounds are, whether music sounds “musical”, the direction(s) sounds originate from, and other aspects that give meaning to sound. Another function of the brain in listening is to “filter out” and ignore background noise, a typical property of younger ears. This brain function may fade over time irrespective of hearing levels. Overall, many brain regions operate in concert, providing us with all the information we extract from the sounds we hear.

There are tests beyond the traditional hearing diagnostic evaluation that can help assess the ability to hear in the presence of background noise, learn sequences of sounds or repeat complex patterns. Often we need to use additional assessment tools, in order to learn the nature of the problems a patient complains about. Not surprisingly, a five minute free screening at a retail hearing aid center yields very little useful information about the true state of a person’s hearing system. The options we select for rehabilitation and counseling depend on more than just numbers on one sheet of paper. Choose professionals wisely when you suspect a problem. When the time comes we will be there for you and will do our best to keep you on a Clear Path to good hearing!