Fig. 2.

Mean ± SEM current vocalization thresholds for 2,000-, 250-, and 5-Hz electrical stimuli for 21 mice that lived through the entire duration of the experiment. Over time, for all three electrical frequencies, 2,000, 250, and 5 Hz, and in turn, preferentially for Aβ, Aδ, and C sensory nerve fibers, average current vocalization threshold to electrical stimulus changes in an U-shaped pattern, i.e., it initially decreases and then increases (all P < 0.001). Average current vocalization threshold at young and old ages (14 and 103 weeks) are higher than those at middle ages for 250- and 5-Hz frequencies (all P < 0.05).