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105 - AUDITORY BRAINSTEM RESPONSE (ABR) TESTING
Whenever a sound wave is detected by the ear, it triggers a number of neuro-physiological responses along the auditory pathway. An action potential is conducted along the eighth nerve, the brainstem, and finally to the brain.
About one third of a second after initial stimulation, the signal evokes a response in the area of the brain where sounds are interpreted. These response signals are so small that they are frequently masked by the "background noise" of electrical activity in the brain. This interference is random with respect to the initial stimulation.
If you find an average of this interference signal, it will approach zero. However, since the evoked response is dependent on the stimulus, it should occur at the same time relative to the stimulus when the process is repeated. Therefore, if you repeat this stimulus-response process many times the "background noise" will disappear and what will be left is the neuro-physiological response of principal interest.
