An introduction to the biophysics of the electrically evoked compound action potential

A computational model of the electrically evoked compound action potential (ECAP) has been developed. In addition to being a useful research tool, it serves as an excellent introduction to the basic biophysics of ECAP recording techniques. ECAPs are modeled as a sum of single-fiber action potentials (SFAPs) in response to an electrical stimulus. Each SFAP is calculated from the potential induced at the recording site by the membrane currents arising on an axon as a spike propagates along it. The factors that alter SFAP and ECAP morphology and latency are discussed, as are the mechanisms of stimulus artefact and the advantages and limitations of different artefact-suppression techniques. The assumptions of the model are presented, as are potential ways of improving the physiologic data available from clinical recordings. Potential applications of this technology in the investigation of the biophysical mechanisms of the implanted cochlea are suggested.