Effects of electrical pulse polarity shape on intra cochlear neural responses in humans: Triphasic pulses with cathodic second phase

• Neurophysiological and psychophysical thresholds were measured in 5 cochlear implant recipients.
• Neural response strengths differ for various pulse shapes and polarities.
• Psychophysical threshold values differ for various pulse shapes and polarities in a similar manner.
• Therefore, pulse shape and polarity plays an important role in neural network activation.

Charge balanced pulses are used in modern cochlear implants to avoid direct current (DC) stimulation that may damage neural tissues. In this context the effect of electrical pulse shape and polarity is still a matter of debate and the most effective pulse shape needs to be determined (Bahmer et al., 2010a, Undurraga et al., 2010, Wieringen et al., 2008 and Macherey et al., 2008). Therefore, we conducted electrophysiological measurements, namely electrical compound action potentials (ECAPs) to assess response strength elicited by various pulse shapes and polarities in five cochlear implant recipients (SonataTI100/PulsarCI100 devices, MED-EL Innsbruck). ECAP response strength depending on pulse shape was compared with individual psychophysical thresholds. Results indicated the weakest response amplitude and highest thresholds for symmetric triphasic pulse shapes (with cathodic second phase), and the strongest response amplitude and lowest thresholds for biphasic pulses with anodic first phase. Biphasic pulses with cathodic first phase generated intermediate response amplitude and thresholds.