Electric Stimuli for Auditory Brainstem Responses

The electrical stimuli used to examine the animals’ electrically evoked auditory brainstem responses (eABRs), and the behavioral ITD sensitivity were generated using a Tucker-Davis Technology (TDT, Alachua, FL) IZ2MH programmable constant current stimulator at a sample rate of 48,828.125 Hz. The most apical ring of the CI electrode served as stimulating electrode, the next ring as ground electrode. All electrical intracochlear stimulation used biphasic current pulses similar to those used in clinical devices (duty cycle: 40.96 µs positive, 40.96 µs at zero, 40.96 µs negative), with peak amplitudes of up to 300 μA, depending on eABR thresholds and informally assessed behavioral comfort levels (rats will scratch their ears frequently, startle or show other signs of discomfort if stimuli are too intense). For behavioral training, we stimulated all neonatally deafened, cochlear implanted (NDCI) rats 2–6 dB above these thresholds depending on the pulse rate. Behavioral stimuli from the TDT IZ2MH were delivered directly to the animal through a custom built head connector that was connected and disconnected before and after each training session. As before, animals received binaurally synchronized input from the first stimulation. For full details on the electric stimuli and stimulation setup see^{11 (link)}.