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) wer e 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 1 13 SOC and in 32 of 50 ICC neurons, and resulted in an average decreas e of probe responses (1 or 2 ms after the masker) of 56.3% in SOC neur ons and 83.1% in ICC neurons. Recovery from adaptation followed expone ntial trends, with mean time constants of 106.1 ms and 226.9 ms for SO C and ICC neurons, respectively. Adaptation of inhibition was observed in the lateral superior olive, and may also affect many of the neuron s studied. Other ICC neurons (n=7) exhibited facilitation of probe ton e responses, while 6 ICC neurons exhibited more complex temporal chang es in responsiveness following a masker.