Galazyuk A V, Feng A S
Department of Molecular and Integrative Physiology, and the Beckman Institute, University of Illinois, Urbana, Illinois 61801, USA.
J Neurosci. 2001 Jun 1;21(11):RC147. doi: 10.1523/JNEUROSCI.21-11-j0001.2001.
To study how sound intensity altered the temporal response pattern of a unit, we recorded from 92 single neurons in the inferior colliculus (IC) of the little brown bat and investigated their firing patterns in response to brief tone pulses (2 msec duration) at the characteristic frequency of the unit over a wide dynamic range (10-90 dB sound pressure level). We found two unusual response characteristics at high sound levels in approximately one-third of the IC neurons investigated. For 16 IC neurons (17%), an increase in sound level not only elicited a shorter response latency and an increase in spike count but also transformed the firing pattern of the unit from phasic to periodic; this pattern was more pronounced at higher sound levels. The firing periodicity was unit specific, ranging from 1.3 to 6.7 msec. Twenty-seven IC neurons (29%) exhibited a longer response latency at higher sound levels compared with lower sound levels [i.e., paradoxical latency shift (PLS)]. The majority of this population showed a one or more quantum increase in latency when sound level was elevated. The quantum shift was also unit specific, ranging from 1.2 to 8.2 msec. We further investigated the firing patterns of 14 IC neurons showing PLS before, during, and after iontophoretic application of bicuculline. For 12 of these neurons, drug application abolished the PLS and transformed the firing patterns of the unit at high sound levels from phasic into sustained periodic discharges. Our results suggest that neural oscillation in combination with ordinary inhibition may be responsible for the creation of PLSs shown previously to be important for temporal information processing.
为了研究声音强度如何改变一个神经元的时间响应模式，我们从小棕蝠下丘（IC）的92个单神经元进行记录，并在一个宽动态范围（10 - 90分贝声压级）内，以该神经元的特征频率，研究它们对短暂音调脉冲（持续时间2毫秒）的放电模式。我们在大约三分之一被研究的IC神经元中发现了在高声级下的两种异常响应特征。对于16个IC神经元（17%），声级增加不仅引发了更短的响应潜伏期和放电计数增加，还将该神经元的放电模式从相位型转变为周期型；这种模式在更高声级下更明显。放电周期性是神经元特异性的，范围从1.3到6.7毫秒。27个IC神经元（29%）在高声级下与低声级相比表现出更长的响应潜伏期[即矛盾潜伏期 shift（PLS）]。这群神经元中的大多数在声级升高时潜伏期有一个或多个量子增加。量子偏移也是神经元特异性的，范围从1.2到8.2毫秒。我们进一步研究了14个显示PLS的IC神经元在离子电泳应用荷包牡丹碱之前、期间和之后的放电模式。对于其中12个神经元，药物应用消除了PLS，并将高声级下神经元的放电模式从相位型转变为持续的周期放电。我们的结果表明，神经振荡与普通抑制相结合可能是产生PLS的原因，PLS先前已被证明对时间信息处理很重要。
