gms | German Medical Science

Objective: In primary auditory cortex (A1), frequency tuning curves characterize the response strength and timing of sensory neurons. As patients with hearing loss have difficulties understanding speech in noise, we sought to determine how the response timing of neural responses in A1 changes with different Signal-to-Noise-Ratios (SNRs) in normal hearing and hearing impaired animals.

Material and Method: Measurements were performed on normal hearing and hearing impaired rats (rattus norvegicus, strain: Sprague Dawley). Mild to moderate hearing impairment was induced by unilateral tonal exposure (9 kHz, 110 dB, 75 min). After mapping the location of A1, we calculated mean latencies and response durations for different SNR conditions (7–47 dB) from tuning curves for responses to 25ms tones in the range of 50–40000 Hz and 15–85 dB SPL.

Results: With decreasing SNR, the mean peak latency was more delayed in normal animals. The onset and the offset-latencies were more delayed as well and the range of response durations across tuning curves was generally wider for lower SNRs. In hearing-impaired animals the trends were similar, however, latencies were generally shorter than in control animals.

Conclusion: The effect of different SNRs on response timing did reveal a change of response timing in hearing impaired animals. Latencies were actually slightly shorter than in normal controls suggesting that timing effects may not be solely responsible for the reduced processing abilities in background noise observed in patients with hearing loss.

Unterstützt durch: Unterstützt durch die Deutsche Forschungsgemeinschaft; GZ: TE 845/1-1

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