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This one is about: ABR - Hearing Test Explained


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Can anybody tell me what ABR is? What it does? How it does it? What it's like? Sedating my baby makes me very nervous. Thanks.

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ABR stands for Auditory-evoked Brainstem Response. It is the same as the BEHR (Brainstem Evoked Hearing Response) and BAER (brainstem auditory evoked response?) that have been referred to in the list before.

It is a sort of electroencephalogram (EEG) that measures the brainstem's response to hearing the test sound.

When the brain hears a sound its nerve cells fire off in a set pattern to tell the owner of the brain there was a sound. (The brainstem is just a part of the brain just above the spinal cord at the base of the skull). The nerve cells firing off naturally produce a small electrical signal that can be picked up by sensitive electrodes stuck onto the scalp, much like electrodes on the chest pick up the natural electrical signal of the heart muscle firing off in an electrocardiogram (ECG or EKG). The signal is measured over many repetitions of the test sound and averaged by computer to remove the influence of electrical interference and artefact.

The baby has to be asleep so you are just getting the brain's response to the sound, rather than the brain's response to looking around the room, crying, gooing at the audiologist and so on, not to mention the interference from the movement of the scalp and facial muscles (which produce a much stronger electrical signal than the brain cells do from the other side of the skull bones!)

As Joanne has said before, this is the only accurate way of measuring hearing in babies because they can't tell us when they can hear something or not. This test lets their brain tell us directly. I think it's pretty neat! It can also tell right from left because you can play the sound into the right and then the left ear and see if there is a difference in the volume needed to produce a brainstem response.

Emma has had two of these tests. We didn't have to sedate her. The advice was to wake her early that day, not allow her to have her normal nap, and to delay her feeding until we got to the clinic. Then we fed her and she fell right off to sleep.

It required two people to get her there though - one to drive and the other to keep her awake in the car seat! It felt so mean to keep her awake like that. Once I gave her a blast with the car stereo to wake her up. Hope that didn't affect the results of the test! :> I know this method didn't work with all the babies though.

The audiologist said we were very lucky to have Emma go off to sleep so easily. Other mothers had waited for hours at the clinic, and had even had to come back another day to have another try! Anyway, I don't think you should have to sedate him.

This might even effect the result of the test, I don't know (just speculating there).

There is another article on hearing tests. Go to WS-182.html

Good luck!


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