UNIT RESPONSES IN COCHLEAR NUCLEUS OF RAT TO PURE TONES

In a study of the response of single units in the cochlear nucleus of the white rat it was found that all the units which responded to pure tones showed a selectivity with regard to tone frequency. Responses were obtained in the tone frequency range from 200 to 34,000 Hz. Most of the units responded to pure tones with a sustained train of discharges. The threshold in these units was found to rise abruptly when the tone frequency was increased above that of the unit's characteristic frequency (CF). A much more gradual increase in threshold was noted when the tone frequency was decreased below the unit's CF. The slope of the high frequency part of the tuning curves varied between 0 and 50 Hz per dB increase in threshold, when measured 20—30 dB above the unit's threshold at its characteristic frequency. The slope measured in that way showed no apparent dependence of on the CF of the units. Many units with a high CF had tuning curves with a second peak located at a lower frequency. A few units had almost symmetrical tuning curves with a slope of the same order of magnitude as that recorded for the low frequency part of the common type units. The maximal obtainable firing rate of common type units was found to decrease rapidly when the frequency of the stimulus tone was increased above the unit's CF. Conversely the maximal discharge rate was almost constant for tones below the unit's CF. Iso‐rate functions based on stimulus response curves, were found to be similar to tuning curves when a discharge rate of about 20 per cent about the unit's spontaneous rate was used as a criterion of response. © 1969 Scandinavian Physiological Society