On the mechanism of prepulse inhibition

Prepulse inhibition of the acoustic startle response in rats was studied in normal or sham-operated animals or animals with bilateral lesions in the frontal poles, dorsal hippocampus and overlying parietal cortex, parietal cortex alone, or bilateral electrolytic lesions in the motor nuclei of the fifth and seventh cranial nerves which control the activity of the middle ear muscles (m. tensor tympani and m. stapedius). Lesions in the frontal poles had no effect on prepulse inhibition. Lesions of parietal cortex produced some impairment of prepulse inhibition at short interstimulus intervals (1 and 2 sec) while lesions of the motor nuclei of the fifth and seventh cranial nerves markedly reduced prepulse inhibition at all intervals tested. The hypothesis is suggested that reflexive contraction of the middle ear muscles may produce prepulse inhibition of the acoustic startle response.