INHIBITION SENSITIVE TO INTERAURAL TIME DIFFERENCE IN THE BARN OWLS INFERIOR COLLICULUS

In spontaneously active neurons in the external nucleus of the inferio r colliculus of the barn owl, a stimulus-driven discharge was followed by a quiescent period lasting tens of milliseconds before the spontan eous activity resumed. The more favorable the interaural time differen ce, the longer the quiet period. The duration of the quiescent period also depended on stimulus frequency. Frequencies different from the ne uron's best frequency induced shorter quiescent periods, although they could elicit similar rates of impulses. Also, the duration of the qui escent period was independent of interaural intensity difference. Thus , the quiet period is not due to an after-hyperpolarization but was an inhibitory effect that depended on the activity of other neurons. In some neurons, discharge continued after the stimulus without a quiesce nt period and gradually decayed over a period of 50-100 ms past the st imulus offset. The similarity between the quiescent period of the neur ons mentioned above and the time course of the poststimulus discharge in these neurons suggests that these neurons serve as inhibitory inter neurons.