Aizawa Naotaka, Eggermont Jos J
Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada.
J Assoc Res Otolaryngol. 2006 Mar;7(1):71-81. doi: 10.1007/s10162-005-0026-3. Epub 2006 Jan 12.
Here we show that mild hearing loss induced by noise exposure in early age causes a decrease in neural temporal resolution when measured in adulthood. We investigated the effect of this chronic hearing loss on the representation of a voice onset time (VOT) and a gap-duration continuum in primary auditory cortex (AI) in cats, which were exposed at the age of 6 weeks to a 120-dB SPL, 5-kHz 1/3 octave noise band for 2 h. The resulting hearing loss measured using auditory brainstem responses and cortical multiunit thresholds at 4-6 months of age was 20-40 dB between 1 and 32 kHz. Multiple single-unit activity was recorded in seven noise-exposed cats and nine control cats related to the presentation of a/ba/-/pa/ continuum in which VOT was varied in 5-ms step from 0 to 70 ms. We also obtained data for noise bursts with gaps, of duration equal to the VOT, embedded in noise 5 ms after the onset. Both stimuli were presented at 65 dB SPL. Minimum VOT and early-gap duration were defined as the lowest value in which an on-response, significantly above the spontaneous activity, to both the leading and trailing noise bursts or vowel was obtained. The mild chronic noise-induced hearing loss increased the minimum detectable VOT and gap duration by 10 ms. We also analyzed the maximum firing rate (FRmax) and the latency of the responses as a function of VOT and gap duration and found a significant reduction in the FRmax to the trailing noise burst for gap durations above 50 ms. This suggests that mild hearing loss acquired in early age may affect cortical temporal processing in adulthood.
我们在此表明，幼年时噪声暴露所致的轻度听力损失在成年期测量时会导致神经时间分辨率下降。我们研究了这种慢性听力损失对猫初级听觉皮层（AI）中语音起始时间（VOT）和间隙持续时间连续体表征的影响，这些猫在6周龄时暴露于120分贝声压级、5千赫1/3倍频程噪声带中2小时。在4至6月龄时使用听觉脑干反应和皮层多单位阈值测量的结果听力损失在1至32千赫之间为20至40分贝。在七只噪声暴露猫和九只对照猫中记录了多个单单位活动，这些活动与/a/ba/-/pa/连续体的呈现有关，其中VOT以5毫秒步长从0变化到70毫秒。我们还获得了在噪声起始后5毫秒嵌入噪声中的、持续时间等于VOT的带间隙噪声脉冲的数据。两种刺激均以65分贝声压级呈现。最小VOT和早期间隙持续时间被定义为对领先和尾随噪声脉冲或元音获得明显高于自发活动的开启反应的最低值。轻度慢性噪声诱发的听力损失使最小可检测VOT和间隙持续时间增加了10毫秒。我们还分析了最大放电率（FRmax）和反应潜伏期作为VOT和间隙持续时间的函数，发现对于间隙持续时间超过50毫秒的尾随噪声脉冲，FRmax显著降低。这表明幼年获得的轻度听力损失可能会影响成年期的皮层时间处理。
