Moore Brian C J, Vinay S N
Department of Experimental Psychology, University of Cambridge, Cambridge, UK.
Brain. 2009 Feb;132(Pt 2):524-36. doi: 10.1093/brain/awn308. Epub 2008 Nov 26.
Research using animals suggests that a lesion in the basal portion of the cochlea, causing a high-frequency 'dead region', leads to cortical reorganization, such that frequencies just below the edge frequency of the dead region, fe, become over-represented. We set out to determine if this reorganization has functional benefits. Two groups of subjects were tested, with and without acquired high-frequency dead regions, as assessed using the TEN(HL) test. For the ears with dead regions, the value of fe was close to 1000 or 1500 Hz. The two groups were matched in terms of audiometric thresholds for frequencies below fe and in terms of age. Three subjects with unilateral dead regions (with matched low-frequency audiometric thresholds across ears) were also tested. Three tasks were used: (i) frequency discrimination of sinusoidal tones. The level of every stimulus was roved over a 12-dB range to reduce the salience of loudness cues. The center frequencies used ranged from 250 Hz to just below fe; (ii) detection of sinusoidal amplitude modulation of a sinusoidal carrier. Carrier frequencies of 500 and 800 Hz were used with all subjects, and an additional carrier frequency of 1200 Hz was used for ears with fe close to 1500 Hz and their matched counterparts. Modulation frequencies were 4, 50 and 100 Hz; (iii) identification of consonants in nonsense syllables. The syllables were lowpass filtered at 1000 or 1500 Hz (depending on the value of fe) and complementary highpass-filtered noise was presented to prevent use of information from neurons tuned above fe. For the frequency-discrimination task, the ears with dead regions showed a significant local improvement ('enhanced' thresholds) for frequencies just below fe, as has been reported previously. For the subjects with unilateral dead regions, the enhancement occurred only for the ears with dead regions. For the amplitude-modulation detection task, thresholds were generally lower for the ears with dead regions than for the ears without, and this effect was statistically significant. For the subjects with unilateral dead regions, thresholds were lower for the ears with dead regions than for the ears without. Consonant identification was significantly better for the ears with than without dead regions, and this was true for the subjects with unilateral dead regions. We conclude that a dead region at high frequencies is associated with a better ability to process information at low frequencies. These effects may reflect cortical plasticity induced by the dead regions.
对动物的研究表明，耳蜗基部的损伤会导致高频“死区”，进而引起皮层重组，使得刚好低于死区边缘频率(fe)的频率得到过度表征。我们着手确定这种重组是否具有功能上的益处。使用TEN(HL)测试评估，对两组受试者进行了测试，一组有后天高频死区，另一组没有。对于有死区的耳朵，(fe)的值接近1000或1500赫兹。两组在低于(fe)的频率的听力阈值和年龄方面相匹配。还对三名单侧有死区的受试者（双耳低频听力阈值匹配）进行了测试。使用了三项任务：(i) 正弦音调的频率辨别。每个刺激的强度在12分贝范围内随机变化，以降低响度线索的显著性。使用的中心频率范围从250赫兹到略低于(fe)；(ii) 正弦载波的正弦幅度调制检测。所有受试者都使用了500和800赫兹的载波频率，对于(fe)接近1500赫兹的耳朵及其匹配的耳朵，还额外使用了1200赫兹的载波频率。调制频率为4、50和100赫兹；(iii) 无意义音节中辅音的识别。音节在1000或1500赫兹（取决于(fe)的值）进行低通滤波，并呈现互补的高通滤波噪声，以防止使用来自调谐到高于(fe)的神经元的信息。对于频率辨别任务，有死区的耳朵在略低于(fe)的频率处表现出显著的局部改善（“增强”阈值），正如之前所报道的那样。对于单侧有死区的受试者，增强仅发生在有死区的耳朵上。对于幅度调制检测任务，有死区的耳朵的阈值通常低于没有死区的耳朵，并且这种效应具有统计学意义。对于单侧有死区的受试者，有死区的耳朵的阈值低于没有死区的耳朵。有死区的耳朵的辅音识别明显优于没有死区的耳朵，单侧有死区的受试者也是如此。我们得出结论，高频死区与更好地处理低频信息的能力相关。这些效应可能反映了由死区诱导的皮层可塑性。
