Short-term adaptation of excitation and inhibition shapes binaural processing.

The temporal dependence of neuronal responses in the superior olivary complex (SOC) and central nucleus of the inferior colliculus (ICC) were examined using modified forward masking paradigms. Masking and probe tones were at the unit's best frequency and at the same intensity (20-30 dB above threshold). Short-term adaptation was observed in 85 of 113 SOC and in 32 of 50 ICC neurons, and resulted in an average decrease of probe responses (1 or 2 ms after the masker) of 56.3% in SOC neurons and 83.1% in ICC neurons. Recovery from adaptation followed exponential trends, with mean time constants of 106.1 ms and 226.9 ms for SOC and ICC neurons, respectively. Adaptation of inhibition was observed in the lateral superior olive, and may also affect many of the neurons studied. Other ICC neurons (n = 7) exhibited facilitation of probe tone responses, while 6 ICC neurons exhibited more complex temporal changes in responsiveness following a masker.