Response of cat cochlear nucleus neurons to frequency and amplitude modulated tones.

Summary Extracellular recordings have been made from cochlear nucleus neurons; during stimulation with (1) static tone bursts of various frequencies and amplitudes, (2) frequency-modulated tones, and (3) amplitude-modulated tones. (1) Neurons have been classified according to the way their latencies and firing patterns depend on tone burst frequency and intensity. In most cases, the effects of frequency change can be mimicked by stimulus amplitude changes. Thus, the firing pattern of single neurons may not uniquely determine both stimulus frequency and intensity. (2) Neurons respond in various ways to amplitude-modulated tonal stimuli. These response characteristics could be correlated with firing patterns of these neurons in response to other stimuli. (3) Spike response patterns to frequency-modulated tonal stimuli fall into three symmetry classes 3 . The translation symmetry response class is shown to be the limiting case for certain stimulus parameters. Spike responses pattern envelopes are invariant as a function of stimulus frequency modulation rate and depth. Both stimulus manipulations result in trivial time scale changes of the response pattern. (4) The experimental data is interpreted in terms of transmissions and detections of properties of the auditory stimulus. The only possible stimulus properly detected by these neurons seems to be the sign of df/dt. Remaining stimulus information is variously available to higher auditory centers. It is suggested that unique determination of stimulus parameters involves at least two or three distinct populations of neurons.