Deterioration of cortical responses to amplitude modulations of low-frequency carriers after high-frequency cochlear lesion in guinea pigs.

Temporal modulation transfer function (TMTF) is one of the most common methods for evaluating temporal acuity in the auditory system. In this experiment, we recorded cortical responses to amplitude modulation of tone carriers from implanted electrodes in guinea pigs to generate TMTFs by calculating the response amplitude changes as a function of modulation frequencies (Mfs). High-frequency hearing loss above 8 kHz was established using tone overstimulation (12 kHz, 110 dB SPL for 30 hours). The impact of this acoustic trauma on temporal resolution in the low-frequency range (below and at 8 kHz) was evaluated with the repeated tests of TMTFs until eight weeks post trauma. Deterioration in temporal resolution was found to develop over time, especially at 2 kHz, which was indicated by the decrease in -3 dB cutoffs in TMTFs and by the overall decrease in the AM response amplitude. Potential mechanisms that may underlie this off-channel affect are discussed.