Publication Date


Document Type


First Advisor

Willott, James F.

Degree Name

M.A. (Master of Arts)

Legacy Department

Department of Psychology


Startle reaction


Inbred C57BL/6J (C57) mice exhibit progressive loss of sensitivity to high frequency sounds (> 20 kHz) between 1 and 6 months of age. A previous study showed that prepulse inhibition (PPI) improved substantially in 5-month-old C57 mice when the inhibiting stimulus (SI) was a 12 or 16 kHz tone, but not when SI was 4, 8, or 24 kHz. In order to test hypotheses regarding these findings, PPI was evaluated using tones of 4, 8, 12, 16, and 24 kHz both as Sis and as startle-eliciting stimuli (S2s) in all possible combinations. Subject groups were 5-month-old C57s, 1- month-old C57s, and like-aged normal-hearing CBA mice. Sis of 12 and 16 kHz provided significantly better PPI in the 5-month-old C57s regardless of the S2 employed. CBA mice did not demonstrate age-related changes in PPI for any SI or S2 frequency. The findings support the hypothesis that enhanced PPI in 5-month-old C57 mice results from central auditory system plasticity (previously demonstrated by neurophysiological studies on C57 mice) in which middle- frequencies become "over-represented" as high frequency hearing loss develops: 12 and 16 kHz Sis exert greater inhibitory effects on the startle circuitry in the 5-month- olds. Not supported were two other hypotheses that focus on neural responses to S2. The findings indicate that central plasticity enhances the behavioral saliency of 12 and 16 kHz Sis.


Includes bibliographical references (pages [55]-62)


viii, 107 pages




Northern Illinois University

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