Seki Satoshi, Eggermont Jos J
Department of Physiology and Biophysics, University of Calgary, 2500 University Drive N.W., AB, Canada T2N 1N4.
Hear Res. 2002 Nov;173(1-2):172-86. doi: 10.1016/s0378-5955(02)00518-x.
In this paper we present findings in the primary auditory cortex of cats exposed for 2 h to a 115 dB SPL, 6 kHz tone at 36 days, 56 days or 118 days after birth. We evaluate the effects of age at exposure, amount of hearing loss, and time after induction of trauma on the functional reorganization of the cortical tonotopic map. We found a fairly sharp demarcation in the amount of hearing loss (20-25 dB) that caused cortical reorganization. For localized hearing losses, unmasking of excitatory contributions of neighboring frequency regions was found. For cats showing reorganization of the tonotopic map, the frequency-tuning curve bandwidth at 20 dB above threshold at CF (BW(20dB)) increased with increasing threshold at CF. Threshold at CF, and BW(20dB) increased with time after exposure. Minimum spike latency was initially increased, but subsequently decreased with time after exposure at a rate that was two times faster in cats with reorganized cortex than in cats with normal tonotopic maps, to reach the same asymptotic value. Thresholds at CF were correlated with the peripheral hearing loss at near CF frequencies as estimated from ABR measurements. The correlation between BW(20dB) and CF threshold suggests that part of the reorganization could be due to 'residual' sensitivity of the high frequency neurons to not-affected lower or higher frequencies. However, for CFs above 6 kHz, the BW(20dB) for cats with reorganization of the tonotopic map was significantly lower (on average 0.3 octave, P<0.05) than for cats with normal tonotopic maps. This is not what one would expect in cases of pseudo-plasticity characterized by concurrent shifts in BW(20dB) and CF as a result of residual sensitivity to lower frequencies.
在本文中，我们呈现了出生后36天、56天或118天的猫暴露于115 dB SPL、6 kHz纯音2小时后，其初级听觉皮层的研究结果。我们评估了暴露时的年龄、听力损失程度以及创伤诱发后时间对皮层音调拓扑图功能重组的影响。我们发现导致皮层重组的听力损失量（20 - 25 dB）存在相当明显的界限。对于局部听力损失，发现相邻频率区域的兴奋性贡献被揭示。对于显示音调拓扑图重组的猫，在CF阈值以上20 dB处的频率调谐曲线带宽（BW(20dB)）随CF阈值的增加而增加。CF阈值和BW(20dB)随暴露后时间增加。最小尖峰潜伏期最初增加，但随后随暴露后时间减少，在皮层重组的猫中减少速度比具有正常音调拓扑图的猫快两倍，以达到相同的渐近值。CF处的阈值与根据ABR测量估计的CF附近频率的外周听力损失相关。BW(20dB)与CF阈值之间的相关性表明，部分重组可能是由于高频神经元对未受影响的较低或较高频率的“残余”敏感性。然而，对于高于6 kHz的CF，音调拓扑图重组的猫的BW(20dB)显著低于（平均0.3倍频程，P<0.05）具有正常音调拓扑图的猫。这与因对较低频率的残余敏感性导致BW(20dB)和CF同时变化的假可塑性情况所预期的结果不同。
