Electrically-evoked compound action potential (ECAP) telemetry

Modern implants can record the neural response to their own stimulation: an electrically-evoked compound action potential (ECAP) is the synchronous firing of auditory-nerve fibers to a stimulus pulse, measured on a non-stimulating intracochlear electrode via the device's back-telemetry (NRT/NRI/AutoNRT and related). ECAPs are the workhorse objective measure in the clinic — used to confirm nerve responsiveness intraoperatively, set approximate stimulation levels in infants who cannot report loudness, and probe channel interaction through spread-of-excitation and refractory-recovery paradigms.

As a marker they are coarse: ECAP amplitude and thresholds correlate only weakly with speech outcomes and do not cleanly index spiral-ganglion count or health. Research directions include panoramic/electrode-scanning ECAP imaging of neural excitation profiles, ECAP-derived cochlear-health metrics to guide site-specific programming, and using intracochlear electrocochleography (recording residual hair-cell/neural responses to acoustic stimuli) to monitor and protect residual hearing during and after insertion.