Fontaine Bertrand, MacLeod Katrina M, Lubejko Susan T, Steinberg Louisa J, Köppl Christine, Peña Jose L
Dominick Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York;
Department of Biology, Neuroscience and Cognitive Science Program, University of Maryland, College Park, Maryland; and.
J Neurophysiol. 2014 Jul 15;112(2):430-45. doi: 10.1152/jn.00132.2014. Epub 2014 Apr 30.
In the visual, auditory, and electrosensory modalities, stimuli are defined by first- and second-order attributes. The fast time-pressure signal of a sound, a first-order attribute, is important, for instance, in sound localization and pitch perception, while its slow amplitude-modulated envelope, a second-order attribute, can be used for sound recognition. Ascending the auditory pathway from ear to midbrain, neurons increasingly show a preference for the envelope and are most sensitive to particular envelope modulation frequencies, a tuning considered important for encoding sound identity. The level at which this tuning property emerges along the pathway varies across species, and the mechanism of how this occurs is a matter of debate. In this paper, we target the transition between auditory nerve fibers and the cochlear nucleus angularis (NA). While the owl's auditory nerve fibers simultaneously encode the fast and slow attributes of a sound, one synapse further, NA neurons encode the envelope more efficiently than the auditory nerve. Using in vivo and in vitro electrophysiology and computational analysis, we show that a single-cell mechanism inducing spike threshold adaptation can explain the difference in neural filtering between the two areas. We show that spike threshold adaptation can explain the increased selectivity to modulation frequency, as input level increases in NA. These results demonstrate that a spike generation nonlinearity can modulate the tuning to second-order stimulus features, without invoking network or synaptic mechanisms.
在视觉、听觉和电感觉模态中，刺激由一阶和二阶属性定义。例如，声音的快速时间压力信号作为一阶属性，在声音定位和音高感知中很重要，而其缓慢的幅度调制包络作为二阶属性，可用于声音识别。从耳朵到中脑的听觉通路中，神经元对包络的偏好越来越明显，并且对特定的包络调制频率最为敏感，这种调谐被认为对编码声音身份很重要。这种调谐特性在通路中出现的水平因物种而异，其发生机制存在争议。在本文中，我们针对听觉神经纤维与耳蜗核角状核（NA）之间的过渡。猫头鹰的听觉神经纤维同时编码声音的快速和缓慢属性，而在一个突触之后，NA神经元比听觉神经更有效地编码包络。通过体内和体外电生理学以及计算分析，我们表明一种诱导动作电位阈值适应的单细胞机制可以解释这两个区域之间神经滤波的差异。我们表明，随着NA中输入水平的增加，动作电位阈值适应可以解释对调制频率选择性的增加。这些结果表明，动作电位产生的非线性可以调节对二阶刺激特征的调谐，而无需调用网络或突触机制。
