Single Auditory Units in the Superior Olivary Complex: I: Responses to Sounds and Classifications Based on Physiological Properties

Abstract

Response properties to sounds were examined in single auditory units in the superior olivary complex and the ventral nucleus of the lateral lemniscus. Units were divided into ten ‘classes’; four classes were defined by single properties (spike waveshape or the timing of responses to sound bursts) and the remaining six classes were defined by which ear excited or inhibited the units. Units were also divided according to the types of poststimulus-time histograms they produced in response to sound bursts, and they were separately divided according to the shape of their inter-spike interval histograms. These latter two groupings were highly correlated with each other and with unit class, and were combined into a single classification scheme called ‘firing-pattern type’.

Units were divided into six groups based on the shapes of their tuning curves; data on the bandwidths of tuning curves are also presented. Data are presented on spontaneous firing rate, thresholds to best-frequency tones, and latency of responses to clicks. Spontaneous firing rate was found to be correlated with firing-pattern type and best frequency.

We discuss the differences between our unit categories and previously reported unit categories, and the possibility that some units may be fibers. Neural mechanisms which might bring about the correlation of firing-pattern type with spontaneous rate are also discussed. Finally, we note which unit categories appear likely to correspond to neural populations which can be distinguished anatomically.