MS Defense: Nathaniel Greene

Response Properties of Single Units in the Lateral Superior Olive of the Decerebrate Cat

Abstract

Neurons in the central nucleus of the inferior colliculus (ICC) of decerebrate cats show three major response patterns when tones of different frequencies and sound pressure levels (i.e. a response map) are presented to the contralateral ear. The frequency response maps of type I units are uniquely defined by a narrow V-shaped excitatory area at best frequency (BF) with flanking inhibition at higher and lower frequencies. Units that produce type I maps typically have a high BF (>3 kHz), a high rate of spontaneous activity (~10 spikes/s), and monotonic rate-level curves for BF-tones and noise. These units receive ipsilateral inhibition, and display binaural excitatory/inhibitory (EI) interactions. Given this constellation of properties, it has been hypothesized that the contralateral lateral superior olive (LSO) provides the dominant excitatory input to type I units. All previous quantitative studies of the LSO have been made in anesthetized preparations; here, we report on the monaural, binaural, and temporal response properties of single units in the LSO of decerebrate cats. The results reveal that LSO units form a relatively homogeneous population. Monaural responses were classified in the response map scheme, binaural classification was based on sensitivity to interaural level differences (ILDs) at multiple levels, and temporal responses are classified based on responses to 200 ms peri-stimulus time (PST) histograms presented 20 dB above threshold. The response maps of LSO units show relatively narrow V-shaped excitatory tuning, with flanking inhibition in units with spontaneous activity. LSO units generally have high BFs, low spontaneous rates (