Neural correlates of acoustic behavior in the Australian bullfrog Limnodynastes dorsalis (Anura: Leptodactylidae)

Summary

• 1. The responses of single units in the midbrain auditory nuclei of Limnodynastes dorsalis to sound stimuli differing in frequency and intensity were examined. On the basis of best frequency, the units could be divided into three groups: units with best frequency below 300 Hz; units with best frequency between 300 and 1000 Hz (Fig. 1A, B); and units with two best frequencies, one above and one below 300 Hz (Fig. 1 A). It is suggested that units of the first two groups are derived respectively from the amphibian papilla and basilar papilla of the inner ear, and those of the third group are derived from convergence of units from both papillae. The range of spectral sensitivity of units of the second group matches the spectral characteristics of the male mating call (Fig. 1A-C).

• 2. A behavioral response (the evoked vocal response) was also used to study auditory function. Intensity thresholds at which the vocal response could be evoked were lowest between 500 and 900 Hz and increased sharply both above and below this range (Fig. 3); these behavioral thresholds were at least 20 dB higher than the lowest thresholds obtained from auditory units. It is suggested that the evoked vocal response results from sufficient stimulation of the basilar papilla. The general lack of specificity of this response is discussed in terms of its likely function.