Response of cochlear nucleus neurons in the unanesthetized cat to slowly repeated tones

Abstract

Extracellular unit recordings were made in the cochlear nucleus of adult decerebrate cats. The responses of 43 units were studied during 206 repetitive tone sequences; each sequence consisted of 25 trials with tone durations and intertone intervals from 1 to 9 s. Control responses were obtained before and after the tone sequences. Many sequences produced response decrements of 25 to 35%; decrements of more than 40% developed during continuous tone stimulation. Decrements were most marked during the initial 5 to 10 trials and approached asymptote thereafter. Spontaneous recovery occurred within the first 10 s and was generally complete by 30 to 40 s. The rate of recovery was not influenced by stimulation beyond asymptote. Significant positive correlations existed between magnitude of decrement and response latency and interspike intervals of the initial four spikes of the response. A weak negative correlation existed between magnitude of decrement and spontaneous activity. Constant-latency units (0.2 ms standard deviation in 10 control trials) did not show onset response decrements but did show decrements in the remainder of their response. Units with more variable latencies showed decrements in both early and late response components.