NEURAL DELAYS SHAPE SELECTIVITY TO INTERAURAL INTENSITY DIFFERENCES IN THE LATERAL SUPERIOR OLIVE

Neurons in the lateral superior olive (LSO) respond selectively to int eraural intensity differences (IIDs), one of the chief cues used to lo calize sounds in space. LSO cells are innervated in a characteristic p attern: they receive an excitatory input from the ipsilateral ear and an inhibitory input from the contralateral ear. Consistent with this p attern, LSO cells generally are excited by sounds that are more intens e at the ipsilateral ear and inhibited by sounds that are more intense at the contralateral ear. Despite their relatively homogeneous patter n of innervation, IID selectivity varies substantially from cell to ce ll, such that selectivities are distributed over the range of IIDs tha t would be encountered in nature. For some time, researchers have spec ulated that the relative timing of the excitatory and inhibitory input s to an LSO cell might shape IID selectivity. To test this presenting stimuli that varied in interaural intensity and in interaural time of arrival. The results suggest that, or more than half of the cells, the latency of inhibition was several hundred microseconds longer than th e latency of excitation. Increasing the intensity to the inhibitory ea r shortened the latency of inhibition and brought the timing of the in puts from the two ears into register. Thus, a neural delay of the inhi bition helped to define the IID selectivity of these cells, accounting for a significant part of the variation in selectivity among LSO cell s.