EVALUATING THE IMPACT OF ELECTRODE PLACEMENT ON AUDITORY BRAINSTEM RESPONSE WAVEFORMS

The auditory brainstem response (ABR) test measures the electrical activity in the brainstem in response to sound stimuli. The resulting ABR traces consist of a series of waves, each representing activity in the successive nuclei of the ascending auditory pathway. The amplitudes and latencies of these waves reflect the degree of synchronous neural firing in the nuclei and the axonal conduction between them, respectively. When ABRs are recorded from animals, three sub-dermal electrodes are placed to record electrical activity evoked by the acoustic stimulus: an active, a reference, and a ground electrode. However, where the electrodes are positioned relative to the ear could impact the amplitudes and latencies of the resulting ABR waveforms. This can in turn affect the reported thresholds. Here we tested different electrode arrangements to investigate the effect of recording electrode placement at different anatomical sites on the resulting ABR waveforms. We conducted ABR recordings on domestic cats (Felis catus) and presented broadband click stimuli to each subject (n=5) at intensities ranging from 20-80dB. We changed the locations of the active and reference electrodes while keeping the location of the ground electrode constant. We compared wave amplitudes and latencies following the click stimuli between electrode placement sites. Our findings highlight the best electrode sites for obtaining strong ABR recordings, which is essential for reliably detecting ABR waves from background noise and for noticing small changes in hearing thresholds.