Development of the acoustic startle response in the rat: ontogenetic changes in the magnitude of inhibition by prepulse stimulation.

Three experiments examined the development of the acoustic startle reflex and its modification by a preliminary stimulus in the infant rat during the 2nd and 3rd postnatal weeks. The 1st experiment employed a white noise S1 (20 msec, 70 dB), the 2nd a cutaneous S1 (.5 msec, .5 mA and 1.0 mA shock), and the 3rd identical S1-S2 pairs (20 msec, 10 kHz, 110 dB tones). The results demonstrate a similar maturation of the prepulse modification pattern over days in the 3 experiments, evidenced mainly in the growth of inhibition. The findings indicate peripheral and central mechanisms that are maturing during the period of life under observation and that contribute to the developmental patterns of modification.