Temperature Effects on Responses in the Auditory System of the Little Brown Bat Myotis l. lucifugus

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Abstract
The temperature of bats, Myotis I. lucifugus, under Nembutal anesthesia was changed within the range 10 N 40 C. Duing cooling, the evoked potential from the posterior colliculus, in response to pulsed high frequency sound, decreased reversibly in amplitude and sensitivity and increased in duration and latency. Evoked potentials could not be seen below about 12 C. With cooling, the highest effective frequency of sound and the most effective frequency both decreased. Sensitivity and amplitude of the cochlear microphonics also decreased reversibly with cooling, but at a lower rate than in the case of the neural potentials. Although the sensitivity of the evoked potential at the posterior colliculus and the auditory nerve decreased with cooling for all frequencies, the effect was greater for higher frequencies. The same was true of the cochlear microphonics but to a lesser extent. Evoked potentials from an unanesthetized bat with implanted electrodes also disappeared at temperatures below 12 C. Behavioral responses to sound were elicited with warm bats but not with cool ones. Supernormality of the response to the 2nd pulse of a pair was greater in several respects at temperatures below 25 C. Furthermore, the response to the 1st of a pair of pulses could vary in a way different from the response to the 2nd. The supernormality and difference in variation of response may provide evidence for 2 different populations of neurons, 1 specialized to respond to the 2nd pulse of a pair.

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