Ma Xiaofeng, Suga Nobuo
Department of Biology, Washington University, One Brookings Dr., St. Louis, MO 63130, USA.
J Neurophysiol. 2008 Aug;100(2):1127-34. doi: 10.1152/jn.90508.2008. Epub 2008 Jul 2.
The central auditory system creates various types of neurons tuned to different acoustic parameters other than a specific frequency. The response latency of auditory neurons typically shortens with an increase in stimulus intensity. However, approximately 10% of collicular neurons of the little brown bat show a "paradoxical latency-shift (PLS)": long latencies to intense sounds but short latencies to weak sounds. These neurons presumably are involved in the processing of target distance information carried by a pair of an intense biosonar pulse and its weak echo. Our current studies show that collicular PLS neurons of the big brown bat are modulated by the corticofugal (descending) system. Electric stimulation of cortical auditory neurons evoked two types of changes in the PLS neurons, depending on the relationship in the best frequency (BF) between the stimulated cortical and recorded collicular neurons. When the BF was matched between them, the cortical stimulation did not shift the BFs of the collicular neurons and shortened their response latencies at intense sounds so that the PLS became smaller. When the BF was unmatched, however, the cortical stimulation shifted the BFs of the collicular neurons and lengthened their response latencies at intense sounds, so that the PLS became larger. Cortical electric stimulation also modulated the response latencies of non-PLS neurons. It produced an inhibitory frequency tuning curve or curves. Our findings indicate that corticofugal feedback is involved in shaping the spectrotemporal patterns of responses of subcortical auditory neurons presumably through inhibition.
中枢听觉系统产生了各种类型的神经元，这些神经元被调整到除特定频率之外的不同声学参数。听觉神经元的反应潜伏期通常会随着刺激强度的增加而缩短。然而，大约10%的棕色小蝙蝠的丘系神经元表现出“反常潜伏期偏移（PLS）”：对强声音的潜伏期长，但对弱声音的潜伏期短。这些神经元可能参与处理由一对强生物声纳脉冲及其弱回声携带的目标距离信息。我们目前的研究表明，大棕蝠的丘系PLS神经元受皮质离心（下行）系统的调节。对皮质听觉神经元的电刺激在PLS神经元中引起了两种类型的变化，这取决于受刺激的皮质神经元和记录的丘系神经元之间的最佳频率（BF）关系。当它们之间的BF匹配时，皮质刺激不会改变丘系神经元的BF，并且会缩短它们在强声音时的反应潜伏期，从而使PLS变小。然而，当BF不匹配时，皮质刺激会改变丘系神经元的BF，并延长它们在强声音时的反应潜伏期，从而使PLS变大。皮质电刺激还调节了非PLS神经元的反应潜伏期。它产生了一条或多条抑制性频率调谐曲线。我们的研究结果表明，皮质离心反馈可能通过抑制作用参与塑造皮质下听觉神经元反应的频谱时间模式。
