Shofner W P
Parmly Hearing Institute, Loyola University Chicago, Chicago, Illinois 60626, USA.
J Neurophysiol. 1999 Jun;81(6):2662-74. doi: 10.1152/jn.1999.81.6.2662.
Temporal encoding of stimulus features related to the pitch of iterated rippled noises was studied for single units in the chinchilla cochlear nucleus. Unlike other periodic complex sounds that produce pitch, iterated rippled noises have neither periodic waveforms nor highly modulated envelopes. Infinitely iterated rippled noise (IIRN) is generated when wideband noise (WBN) is delayed (tau), attenuated, and then added to (+) or subtracted from (-) the undelayed WBN through positive feedback. The pitch of IIRN[+, tau, -1 dB] is at 1/tau, whereas the pitch of IIRN[-, tau, -1 dB] is at 1/2tau. Temporal responses of cochlear nucleus units were measured using neural autocorrelograms. Synchronous responses as shown by peaks in neural autocorrelograms that occur at time lags corresponding to the IIRN tau can be observed for both primarylike and chopper unit types. Comparison of the neural autocorrelograms in response to IIRN[+, tau, -1 dB] and IIRN[-, tau, -1 dB] indicates that the temporal discharge of primarylike units reflects the stimulus waveform fine structure, whereas the temporal discharge patterns of chopper units reflect the stimulus envelope. The pitch of IIRN[+/-, tau, -1 dB] can be accounted for by the temporal discharge patterns of primarylike units but not by the temporal discharge of chopper units. To quantify the temporal responses, the height of the peak in the neural autocorrelogram at a given time lag was measured as normalized rate. Although it is well documented that chopper units give larger synchronous responses than primarylike units to the fundamental frequency of periodic complex stimuli, the largest normalized rates in response to IIRN[+, tau, -1 dB] were obtained for primarylike units, not chopper units. The results suggest that if temporal encoding is important in pitch processing, then primarylike units are likely to be an important cochlear nucleus subsystem that carries the pitch-related information to higher auditory centers.
针对灰鼠耳蜗核中的单个神经元，研究了与重复波纹噪声音高相关的刺激特征的时间编码。与其他产生音高的周期性复合声音不同，重复波纹噪声既没有周期性波形，也没有高度调制的包络。当宽带噪声（WBN）被延迟（τ）、衰减，然后通过正反馈与未延迟的WBN相加（+）或相减（-）时，就会产生无限重复波纹噪声（IIRN）。IIRN[+，τ，-1dB]的音高为1/τ，而IIRN[-，τ，-1dB]的音高为1/2τ。使用神经自相关图测量耳蜗核神经元的时间响应。对于初级样神经元和切迹神经元类型，都可以观察到神经自相关图中在与IIRN τ相对应的时间滞后处出现的峰值所显示的同步响应。对响应IIRN[+，τ，-1dB]和IIRN[-，τ，-1dB]的神经自相关图进行比较表明，初级样神经元的时间放电反映了刺激波形的精细结构，而切迹神经元的时间放电模式反映了刺激包络。IIRN[+/-，τ，-1dB]的音高可以由初级样神经元的时间放电模式来解释，而不能由切迹神经元的时间放电来解释。为了量化时间响应，将神经自相关图中给定时间滞后处峰值的高度测量为归一化速率。尽管有充分的文献记载，切迹神经元对周期性复合刺激的基频的同步响应比初级样神经元大，但对IIRN[+，τ，-1dB]的响应中，最大的归一化速率是在初级样神经元中获得的，而不是切迹神经元。结果表明，如果时间编码在音高处理中很重要，那么初级样神经元可能是一个重要的耳蜗核子系统，它将与音高相关的信息传递到更高的听觉中枢。
