Electrical and acoustical activation of the middle ear muscle in a songbird

Summary

The effect of electrically-elicited middle ear muscle (MEM) contractions on cochlear microphonic potentials (CM) was studied in anesthetized starlings. In addition, the presence or absence of acoustic MEM reflexes was explored in awake starlings and one tawny owl, using the CM for detecting MEM contractions. The most commonly observed effect of electrically-elicited contractions in the anesthetized starlings was a frequency-dependent decrease in CM-amplitude (Fig. 2a) and a shift of the CM input-output functions towards higher SPL's (Fig. 3). It is concluded that the MEM might act as a bandpass filter exerting a (limited) protective effect against acoustic overstimulation of the ear and be capable of extending the ear's dynamic range to higher SPL's. A further physiological significance is discussed. Characteristic CM amplitude modulations, which have previously been shown to result from acoustic reflex contractions of the MEM, were observed in the awake tawny owl, but not in the starlings (Fig. 4).