[Effect of high frequency hearing loss on the temporal processing in the low frequency regions of guinea pigs]

To constitute the animal model of high frequency hearing loss and observer the temporal processing abilities of low frequency regions using prepulse inhibition of auditory startle response (gap-PPI).

Ten guinea pigs were randomly grouped into two groups: the high frequency hearing loss group with six guinea pigs and the control group with four guinea pigs. The former group was exposed to 12 kHz tone at 110 dB SPL for 30 hours to establish the high frequency hearing loss above 8 kHz and the latter group received no stimulations. Before and two, four, six and eight weeks after noise exposure, gap-PPI and auditory brainstem response (ABR) were recorded in both groups. In the gap-PPI experiment, three different background noises as 0.5 - 2 kHz, 0.5 - 4 kHz and 0.5 - 8 kHz were applied to test the temporal gap.

High frequency hearing loss above 8 kHz was shown two weeks after noise exposure. The averaged ABR thresholds of 16 kHz, 32 kHz and 48 kHz were elevated about 55 dB and shown statistical significance compared to those before exposure (P < 0.05). No significant difference of ABR thresholds were shown between 1 kHz, 2 kHz, 4 kHz and 8kHz before and after noise exposure (P > 0.05). In the control group, the ABR thresholds remained stable during experiment. In the gap-PPI test, two weeks after noise exposure of 8 kHz, the experiment group showed attenuated inhibition ability and recovered gradually four weeks after noise exposure. No statistical differences of inhibition ability at time points of two, four, six and eight weeks after noise exposure of 4 kHz were detected when compared with that of pre-exposure. Under the background noise of 2 kHz, the inhibition ability attenuated and reached statistical significance at 6 - 8 weeks after noise exposure.

The high frequency hearing loss might induce an impairment of the temporal processing in the low frequency region.