Discharge properties of primary auditory fibres in Caiman crocodilus: comparisons and contrasts to the mammalian auditory nerve.

Single fibre recordings were performed from the auditory nerve of the caiman, Caiman crocodilus. All neurones were spontaneously active (1-80 imp/s). Clicks evoked multiple peaks in the post stimulus time histogram spaced at 1/CF. At high intensities irregularities were observed. The latencies of the first peak observable were intensity-dependent and related to CF. The number of peaks was correlated with tuning properties of the fibre. Frequency threshold curves were asymmetrical, with low frequency slopes less steep than high frequency slopes. Q10 dB was between 1.5 and 7 with best tuning at high CF. CF ranged from 30 Hz to 2.8 kHz, lowest thresholds down to 5 dB SPL. Intensity functions were nonmonotonic. In isointensity contours the best frequency shifted downwards with increasing stimulus level. At highest levels a response dip was observed above CF. Phase locking, two tone suppression and excitability by combination tones were observed. In comparison to the mammalian cochlea similarities and differences were found.