Neural activation patterns indicate robust auditory nerve synchrony generated with octave-band chirps

Abstract

Recent research has suggested that the amplitude of high-intensity compound action potentials (CAPs) can detect auditory nerve damage that is missed by traditional threshold measurements. The use of octave-band chirps may enhance neural synchrony and provide clinicians and researchers a precise tool for identifying changes in auditory nerve integrity. A group of Mongolian gerbils (N = 12) was used to compare the difference in amplitude-intensity functions and neural activation patterns generated by octave-band chirps and tonebursts at octave frequencies between 2 and 16 kHz at 40, 60, and 80 dB SPL. Amplitude-intensity functions revealed larger absolute CAP amplitudes for octave-band chirps than for tonebursts. Neural activation patterns were constructed by plotting the derivative of CAP amplitude across multiple conditions of simultaneous broadband noise that was high passed in 1/3 octave intervals. Neural activation patterns for octave-band chirps and tonebursts showed that the frequency location of peak activation was generally equivalent while the height of peak activation was greater for octave-band chirps than for tonebursts. This suggests that octave-band chirps elicit more synchronous neural firing, thereby indicating that they could be an optimal stimulus for detecting regional damage in auditory neurons that encode supra-threshold stimuli.