Auditory nerve fibre activity in the Tokay gecko

Summary

We have recorded from single auditory nerve fibres in the lizard,Gekko gecko, while changing the animal's temperature within the range 19–30 °C. Small steps of 0.5–2 °C (as measured next to the otic capsule or within the contralateral inner ear) cause a small but reliable and reversible change in the tuning characteristics of a fibre: its tuning curve (frequency-threshold curve) shifts to higher frequencies with warming and lower frequencies with cooling (Figs. 1, 2 and 3). The sharpness of tuning and overall sensitivity of the fibres are relatively unaffected by these procedures. The mean shift in characteristic frequency (CF) for 34 fibres was 0.06 octaves per °C (Fig. 4A). A more accurate estimate is given by the mean shift in ‘centre frequency’: a point midway between the low-frequency and high-frequency sides of the tuning curve at 10 dB above CF threshold. This shift was 0.05 octaves per °C (Fig. 4B), which is equivalent to a thermalQ ₁₀ of approximately 1.4 for the frequency change with temperature. Comparison of these results and analogous frequency shifts with temperature reported for other auditory organs suggests that tuning in the mammalian cochlea is less temperature-dependent than it is in nonmammalian inner ears; this may reflect a basic difference in how tuning is achieved. The observed temperature sensitivities are discussed in terms of what might be expected for tuning by basilar and/or tectorial membranes and for tuning of conductances within the hair cell membrane.