Discharge synchronization in auditory nerve and AVCN neurons

Abstract

At suprathreshold intensities, all auditory nerve fibers and many anteroventral cochlear nucleus (AVCN) neurons exhibit discharge synchronization or phase locking to signal frequencies less than 4–5 kHz. However, the relationships between synchronization and discharge rate have not been fully described. In the present study, discharges of single auditory nerve and AVCN neurons were recorded in anesthetized cats. Signals consisted of low- and moderate-frequency pure tones. Neuronal response patterns were analyzed by techniques employing discharge rate and by Fourier transforms of period histograms synchronized to the signal frequency. A criterion number of discharges (usually in excess of 1000 spikes) was collected at each intensity in order to reduce sampling biases. In both spontaneously active and inactive neurons, the threshold for detectable phase locking is 12–18 dB below the threshold for increases in discharging rate. Once the synchronization threshold is exceeded, phase locking continues to increase with increasing signal intensity. Asymptotic phase locking is achieved prior to maximal discharge rate, but the range over which phase locking increases is somewhat greater than the range over which discharge rate increases. Mean discharge phase does not vary appreciably at intensities above the phase-locking threshold. Auditory nerve and AVCN neurons behave similarly.