Excitation and inhibition in cochlear nucleus. II. Frequency-modulated tones.

Abstract

Extracellular and intra-cellular recordings were made from neurons of the cochlear nucleus of the cat during presentation of both static and frequency modulated tonal stimuli. The firing patterns of most of these neurons in response to slow frequency modulation of the stimulus may be predicted from their response to tone bursts of fixed frequency. Three different general types of firing pattern were found in response to slow frequency modulation of the stimulus. These firing patterns may be classified according to their symmetry with regard to rising or falling tones; they may suggest different geometric arrangements of synaptic endings on the neuron under study. At higher rates of frequency modulation, the firing patterns are influenced both by df/dt and by repetition rate. The effect of df/dt was examined by using trapezoidal modulation of frequency. Several methods for examining the response of the membrane potential in relation to different portions of the stimulus cycle are shown. Frequently there is only a weak correlation between membrane potentials and firing patterns.