Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, Boston, MA, USA.
J Neurophysiol. 2012 Dec;108(12):3172-95. doi: 10.1152/jn.00160.2012. Epub 2012 Sep 12.
The spatio-temporal pattern of auditory nerve (AN) activity, representing the relative timing of spikes across the tonotopic axis, contains cues to perceptual features of sounds such as pitch, loudness, timbre, and spatial location. These spatio-temporal cues may be extracted by neurons in the cochlear nucleus (CN) that are sensitive to relative timing of inputs from AN fibers innervating different cochlear regions. One possible mechanism for this extraction is "cross-frequency" coincidence detection (CD), in which a central neuron converts the degree of coincidence across the tonotopic axis into a rate code by preferentially firing when its AN inputs discharge in synchrony. We used Huffman stimuli (Carney LH. J Neurophysiol 64: 437-456, 1990), which have a flat power spectrum but differ in their phase spectra, to systematically manipulate relative timing of spikes across tonotopically neighboring AN fibers without changing overall firing rates. We compared responses of CN units to Huffman stimuli with responses of model CD cells operating on spatio-temporal patterns of AN activity derived from measured responses of AN fibers with the principle of cochlear scaling invariance. We used the maximum likelihood method to determine the CD model cell parameters most likely to produce the measured CN unit responses, and thereby could distinguish units behaving like cross-frequency CD cells from those consistent with same-frequency CD (in which all inputs would originate from the same tonotopic location). We find that certain CN unit types, especially those associated with globular bushy cells, have responses consistent with cross-frequency CD cells. A possible functional role of a cross-frequency CD mechanism in these CN units is to increase the dynamic range of binaural neurons that process cues for sound localization.
听觉神经（AN）活动的时空模式，代表了沿音调轴的尖峰的相对时间，包含了声音的感知特征的线索，如音高、响度、音色和空间位置。这些时空线索可能是由耳蜗核（CN）中的神经元提取的，这些神经元对来自不同耳蜗区域的 AN 纤维输入的相对时间敏感。这种提取的一种可能机制是“交叉频率”吻合检测（CD），其中一个中央神经元通过优先在其 AN 输入同步放电时放电，将沿音调轴的吻合程度转换为一个率码。我们使用了 Huffman 刺激（Carney LH。J Neurophysiol 64: 437-456, 1990），它们具有平坦的功率谱，但相位谱不同，从而可以在不改变总放电率的情况下系统地改变沿音调相邻 AN 纤维的尖峰的相对时间。我们将 CN 单元对 Huffman 刺激的反应与模型 CD 细胞的反应进行了比较，这些模型 CD 细胞的反应是基于从具有耳蜗缩放不变性原理的 AN 纤维的测量反应中得出的 AN 活动的时空模式。我们使用最大似然法来确定最有可能产生测量的 CN 单元反应的 CD 模型细胞参数，从而可以将表现出交叉频率 CD 细胞行为的单元与那些与同频 CD 一致的单元（其中所有输入都将来自同一音调位置）区分开来。我们发现，某些 CN 单元类型，特别是与球状布什细胞相关的单元，其反应与交叉频率 CD 细胞一致。这种交叉频率 CD 机制在这些 CN 单元中的一个可能的功能作用是增加处理声音定位线索的双耳神经元的动态范围。
