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 high-frequency sensitivity declines, many neurons come to respond better 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-month-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-month-olds with 12 or 16 kHz S1s. This effect was not influenced by S2 frequency or the size of the startle evoked by S2-only stimuli (smaller for high-frequency S2s in older mice). The increased salience of 12-16 kHz S1s in 5-month-old C57 mice parallels changes in the central representation of tone frequency and implies a behavioral effect of HLI plasticity.