Segregation of stimulus phase and intensity coding in the cochlear nucleus of the barn owl

Abstract

The cochlear nucleus of the barn owl is composed of two anatomically distinct subnuclei, n. magnocellularis (the magnocellular nucleus) and n. angularis (the angular nucleus). In the magnocellular nucleus, neurons tend to respond at a particular phase of a stimulus sine wave. Phase locking was observed for frequencies up to 9.0 kHz. The intensity- spike count functions of magnocellular units are characterized by high rates of spontaneous activity, a narrow range of intensities over which spike counts changed from spontaneous to saturation levels, and a small increase in spike counts with intensity over that range. In the angular nucleus, neurons showed little or no tendency to respond at a certain sinusoidal phase, although some showed weak phase locking for frequencies below 3.5 kHz. Angular units typically had low spontaneous rates, large dynamic ranges, and large increases in spike counts with intensity, resulting in high saturation levels. The clear difference between the two nuclei in sensitivity to both phase and intensity and the reciprocity in response properties support the hypothesis that each nucleus is specialized to process one parameter (phase or intensity) and not the other.