A novel method for quantifying the amplitude of the N1 peak of the human compound action potential

Abstract

Human auditory nerve (AN) activity is commonly estimated via the compound action potential (CAP), a population response generated by the AN and measured using tympanic-membrane (TM) electrodes. The amplitude of the CAP’s first prominent negative peak (N1) is typically quantified by calculating the voltage difference between the N1 and the maximum voltage of the surrounding positive peaks (“peak-to-peak amplitude”). Despite the widespread use of this method, these peaks have different neural generators, potentially confounding the interpretation of N1 amplitudes. Variability in the amplitudes of these surrounding peaks may also introduce variability to the N1 response, further obscuring findings and reducing reliability. An alternate method is measuring N1 amplitude relative to a time-averaged baseline (“absolute amplitude”), a practice ubiquitous throughout cortical electroencephalography (EEG) studies. The current study recorded CAPs from younger adults with normal hearing to either clicks or tone bursts using TM electrodes placed on the tympanum and measured both peak-to-peak and absolute amplitudes of the N1. For absolute amplitudes, two baseline windows were evaluated, a pre-stimulus window and a whole-trial window. Advantages of measuring absolute N1 amplitudes and implications for assessing AN function will be discussed. [Work supported by NIH/NIDCD.]