My father has been recommended to take the BAER test for hearing loss. What is the BAER test, and what will the results tell him?

Ellen

BAER stands for Brainstem Auditory Evoked Response. It is used to detect "retrocochlear pathology." Take a moment or two to overcome the urge to slap me. Now, here's the explanation:

Hearing is, ultimately, a collection of electrochemical signals relayed from the cochlea (an inner-ear organ that enables you to hear) to the brain via the auditory nerve. It is important to picture this as electrical charges moving through space. (Actually, they're moving through white matter, but you get the idea.)

Whenever a charge is in motion, electromagnetic radiation is emitted. If this happens within the brain's neurons (the cells of the nervous system), then the emitted electromagnetic radiation is known (commonly) as "brain waves." Place electrodes on the face and scalp, connect them to appropriate recording equipment, and you can detect these brain waves. The recorded signals are known as an EEG (electroencephalogram).

As you might imagine, an EEG is a mishmash that reflects the business of the brain at that instant. It is impossible to look at an EEG and say, "Oh, my, that little blip corresponds to the itch in my left big toe, and that one corresponds to my brain's efforts to keep me breathing," and so forth. One might as well stand in the middle of a crowded football stadium and try to hear one particular conversation among thousands.

But ... imagine the following experiment. You are still standing in the middle of a crowded football stadium, but now you have a bit of equipment: a microphone, a computer (with appropriate software) and a cigarette lighter. Someone in the stadium has been instructed to blurt the word, "Plastics!" whenever he sees you light the cigarette lighter. Your computer/microphone setup will record the general noise for a five-second interval each time you light the lighter. You perform this little task 1,000 times; each time, the microphone receives all of the incoming noise, and the computer records it.

Now for the gimmick: Instead of recording each of the 1,000 five-second blocks in a back-to-back string, the computer "sums" or overlays the recordings. When this is done, the noise will remain noise, but the signal "Plastics!" will be present with each recording. Initially, this signal will be imperceptible, but by the 1,000th recording, it will boom through loud and clear.

That's how a BAER works. Electrodes will be pasted to your father's head. A signal (a click or tone) will be played repeatedly, and his brain waves will be recorded (and summed) for a brief instant after each signal. The rest of the brain's activity will remain as noise, but the brain waves specific to the auditory system will become more and more evident with each repetition.

What's it good for? BAERs indirectly measure the electrical activity between the cochlea and the brain. Your father's doctor may think there is a chance (usually a very small chance) that he has a tumor on or near the auditory nerve. Such tumors slow the transmission of nerve impulses through the cochlear nerve, and this delay is detectable using BAER. Thus, BAER is used to detect "retrocochlear pathology." (Anything behind the cochlea is considered "retrocochlear." "Pathology" merely means "something's wrong.")

BAER is also indispensable for testing hearing in newborns and young infants, or anyone who is unable to cooperate with an audiologist. BAERs can also be useful if the audiologist thinks the patient is faking a hearing loss. After all, brain waves just happen -- they don't require the patient's cooperation, and they can't be faked.