Coding of Amplitude and Frequency Modulated Sounds in the Cochlear Nucleus of the Rat

Abstract

Abstract The responses of single units in the cochlear nucleus of the rat to sinusoidally amplitude‐ and frequency‐modulated tones and amplitude‐modulated broadband noise were studied. The distribution of discharges within a cycle of modulation was determined from cycle histograms locked to the modulation wave. In response to amplitude‐modulated tones and broadband noise, all units investigated showed a peak in the degree of modulation of the spike frequency within the modulation frequency range from 50 to 200 Hz. In many units the relationship between the degree of modulation of the stimulus sound and of the modulation of the resulting spike train was almost unchanged over a wide range of sound intensities. In other units, enhancement of modulation within a certain range of modulation frequency became more pronounced when the sound intensity was increased. This was mainly due to a suppression of modulation at lower modulation frequencies. The shape of the histograms was nearly sinusoidal even at modulation depths which resulted in nearly 100% modulation of the neural discharge frequency. The amount of modulation of the discharge frequency in response to frequency‐modulated tones was dependent on the frequency of the tone in relation to the CF of the unit.