Electrophysiologic response audiometry: state of the art

Electrophysiologic response audiometry (ERA) is based upon recording neuroelectric potentials from sites extending from the cochlea to the cortex. These recordings rely on the use of averaging computers to extricate desired neuroelectric responses from the ongoing background electrical activity of the human auditory system and brain. The different neuroelectric responses are distinguished by response latency, response waveform, and probable site of origin. Responses which occur within the latency range of 1 to 5 msec originate from the cochlea and auditory nerve. Responses in the 4- to 8-msec latency range have the brain stem as their origin. Responses with latencies from about 8 to 50 msec presumably arise from the upper brain stem and primary projection areas. Responses with a fast waveform include those with latencies between 1 and 50 msec. Slow wave responses from about 50 to 300 msec originate as a secondary discharge from the primary cortical projection areas and surrounding secondary and association areas. The longest latency potentials (300 msec) are slow shifts that appear to arise from the prefrontal and secondary or association areas of the cortex. These response classes are discussed in terms of their clinical utility for threshold estimation and diagnostic value.