Off-responses in the auditory system in relation to the signal end phase and neuronal characteristic frequency

Off-responses of single neurons from the inferior colliculus (IC) as well as summed off-responses (evoked potentials) from the IC, cochlear nucleus and auditory nerve were studied while varying the end phase of tonal signals. It was found that with tonal signals higher than the characteristic frequency, off-responses at all the auditory levels studied were greatest at the end phases near 0 and 180 degrees and were of minimal value at the end phases near 90 and 270 degrees. On the contrary, with tonal signals lower than the characteristic frequency, the greatest off-responses corresponded to the end phases near 90 and 270 degrees, and responses of the lowest value were registered at the end phases near 0 and 180 degrees. The observed phenomena did not result from transient 'off'-responses of the acoustic system. It is suggested that they reflect certain cochlear processes connected with different effectiveness of oscillation phases at frequencies below and above the resonance.