Single auditory neuron response during acute acoustic trauma.

By recording from single auditory neurons in the spiral ganglion of the guinea pig cochlea it was possible to monitor threshold changes to acoustic stimuli in the same neuron during acute exposures to continuous pure tones (100 dB SPL) delivered for periods of up to 180 min. Initial changes in the tuning curve were sensitivity losses at and above the characteristic frequency (CF). This asymmetric loss resulted in a shift in the CF to lower frequencies. Further exposure (up to 20 min) produced a complete loss of the sharply tuned portion of the tuning curve and the most sensitive area moved to lower frequencies by up to 0.75 of an actave when compared to the original CF. Sensitization of the low frequency section of the tuning curve could take place for short exposures (up to 20 min) but disappeared with further exposure, whether continuous or interrupted. Long term exposures (60--80 min) produced losses in the low frequency portion of the tuning curve until a point was reached when the unit no longer responded to stimuli at 110 dB SPL.