THE BEHAVIORAL SALIENCE OF TONES AS INDICATED BY PREPULSE INHIBITION OF THE STARTLE RESPONSE - RELATIONSHIP TO HEARING-LOSS AND CENTRAL NEURAL PLASTICITY IN C57BL 6J MICE/

Adult C57BL/6J mice exhibit high-frequency, sensorineural hearing loss accompanied by physiological changes in the upper auditory brainstem and cortex, referred to as hearing-loss induced (HLI) plasticity: as h igh-frequency sensitivity declines, many neurons come to respond bette r to still-audible, middle-frequency tones (especially 12-16 kHz). We used prepulse inhibition (PPI) to assess the relationship between the behavioral salience of tones and HLI plasticity. The ability of a tone 'prepulse' (S1), presented 100 ms before a startle-eliciting tone (S2 ), to 'inhibit' startle responses was measured in normal-hearing 1-mon th-olds and 5-month-olds with high-frequency hearing loss. Tone bursts of 4, 8, 12, 16, and 24 kHz were used as S1s and S2s in all possible combinations. PPI was significantly improved (more inhibition) in 5-mo nth-olds with 12 or 16 kHz Sis. This effect was not influenced by S2 f requency or the size of the startle evoked by S2-only stimuli (smaller for high-frequency S2s in older mice). The increased salience of 12-1 6 kHz sis in 5-month-old C57 mice parallels changes in the central rep resentation of tone frequency and implies a behavioral effect of HLI p lasticity.