Analogue signal representation in the medial superior olive of the cat

Abstract

Temporal sound processing is likely to depend upon a delay line at a low level in the auditory pathways. We searched for such a delay line in the medial superior olivary nucleus of anesthetized cats. A remarkably pure sinusoidal neurophonic field potential could be recorded in the center of the MSO which was localized electrophysiologically as the point of the field potential polarity reversal and histologically by microinjection WGA-HRP through the recording microelectrode. Fourier analysis of the neurophonic potentials revealed increasing degradation by distortion products with distance from the MSO center. Neurophonic tuning curves indicated a similar frequency selectivity for individual recording sites as predicted by cochlear filter functions. Cross correlation of neurophonics recorded at different positions along the medio-lateral axis demonstrated the presence of a delay line, extending to over 0.6 ms. It is concluded that delay lines required for directional hearing and complex tone identification exist in the MSO.