The acoustic cricothyroid response in the rat

Contraction of the cricothyroid muscle (CTM) in the bat is known to raise vocal pitch. An electrode was placed on the CTM of 12 adult lightly-anesthetized rats and electromyograms obtained in response to 5-sec pure tones from 2-80 kc/s at 100 db SPL. Response patterns (rate-of-firing by frequency) were obtained for each rat, being greatest at frequencies below 15 kc/s. This is not the region of greatest audibility, which in the rat is thought to be 30-40 kc/s. Response latencies were determined to be 830 msec at each rat's best frequency. Evidently in rats, as in bats, the CTM is acoustically responsive, but its precise ethological role in controlling vocal pitch is not as yet understood.