Tympanal mechanics and neural responses in the ears of a noctuid moth |
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Authors: | Hannah M ter Hofstede Holger R Goerlitz Fernando Montealegre-Z Daniel Robert Marc W Holderied |
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Institution: | (1) School of Biological Sciences, University of Bristol, Woodland Road, Bristol, BS8 1UG, UK;(2) Present address: Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, UK; |
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Abstract: | Ears evolved in many groups of moths to detect the echolocation calls of predatory bats. Although the neurophysiology of bat
detection has been intensively studied in moths for decades, the relationship between sound-induced movement of the noctuid
tympanic membrane and action potentials in the auditory sensory cells (A1 and A2) has received little attention. Using laser
Doppler vibrometry, we measured the velocity and displacement of the tympanum in response to pure tone pulses for moths that
were intact or prepared for neural recording. When recording from the auditory nerve, the displacement of the tympanum at
the neural threshold remained constant across frequencies, whereas velocity varied with frequency. This suggests that the
key biophysical parameter for triggering action potentials in the sensory cells of noctuid moths is tympanum displacement,
not velocity. The validity of studies on the neurophysiology of moth hearing rests on the assumption that the dissection and
recording procedures do not affect the biomechanics of the ear. There were no consistent differences in tympanal velocity
or displacement when moths were intact or prepared for neural recordings for sound levels close to neural threshold, indicating
that this and other neurophysiological studies provide good estimates of what intact moths hear at threshold. |
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