Cochlear Events and Whole-Nerve Action Potentials

Abstract

For proper interpretation of electrocochleographic recordings, it is essential to know how the activity of primary auditory neurons is reflected by the whole-nerve action potential (AP). It is easy to show theoretically that for stimulation with tone bursts the latency of the AP decreases with increasing stimulus intensity as a result of cochlear frequency selectivity. It is less easy to show that the phenomenon of saturation as shown by primary auditory neurons is almost equally important in this respect. The proof centers around a peculiar property: theoretically, latency effects will be absent when the input-output relation of auditory neurons can be described by a power law. APs evoked by clicks also show latency changes as a result of variations in stimulus level. These changes can also be interpreted as the result of frequency selectivity and saturation. Here the main factor is that the whole-nerve AP reflects the activity of neurons sensitive to high frequencies far better than those sensitive to low frequencies.

Key Words:

• Cochlea
• Action potential
• Electrocochleography