Peripheral auditory processing in the bobtail lizard Tiliqua rugosa - I. Frequency tuning of auditory-nerve fibres

1. Primary auditory-nerve fibres of the bobtail lizard have asymmetrical, V-shaped frequency-threshold tuning curves. Fibre characteristic frequencies (CF) ranged from 0.2 to 4.5 kHz. The most sensitive fibres had a CF near 1.2 kHz and a threshold of 6 dB SPL. 2. Fibres with CFs below 0.85 kHz had simple U-shaped tuning curves; higher-CF fibres had tuning curves with obvious sharp tips around CF. These tips were up to 46 dB in depth. Several other parameters of the tuning curves, like the selectivity coefficients Q_{10 dB} and Q_{40 dB} and the course of the tuning curve flanks, also permit a separation into the same low-CF and high-CF groups. 3. The tuning sharpness and the thresholds of both low- and high-CF fibres were hypoxia-sensitive, the loss of sensitivity being greatest at CF. 4. Only the low-CF group of fibres showed two-tone rate suppression. In those fibres, two-tone rate suppression was only found with suppressor frequencies above CF, but not below CF.