Department of Physiology, Aerospace Medical Research Unit, McGill University, Montréal, Québec, Canada.
J Neurophysiol. 2011 Apr;105(4):1798-814. doi: 10.1152/jn.00910.2010. Epub 2011 Feb 9.
Understanding how sensory neurons transmit information about relevant stimuli remains a major goal in neuroscience. Of particular relevance are the roles of neural variability and spike timing in neural coding. Peripheral vestibular afferents display differential variability that is correlated with the importance of spike timing; regular afferents display little variability and use a timing code to transmit information about sensory input. Irregular afferents, conversely, display greater variability and instead use a rate code. We studied how central neurons within the vestibular nuclei integrate information from both afferent classes by recording from a group of neurons termed vestibular only (VO) that are known to make contributions to vestibulospinal reflexes and project to higher-order centers. We found that, although individual central neurons had sensitivities that were greater than or equal to those of individual afferents, they transmitted less information. In addition, their velocity detection thresholds were significantly greater than those of individual afferents. This is because VO neurons display greater variability, which is detrimental to information transmission and signal detection. Combining activities from multiple VO neurons increased information transmission. However, the information rates were still much lower than those of equivalent afferent populations. Furthermore, combining responses from multiple VO neurons led to lower velocity detection threshold values approaching those measured from behavior (∼ 2.5 vs. 0.5-1°/s). Our results suggest that the detailed time course of vestibular stimuli encoded by afferents is not transmitted by VO neurons. Instead, they suggest that higher vestibular pathways must integrate information from central vestibular neuron populations to give rise to behaviorally observed detection thresholds.
理解感觉神经元如何传递有关相关刺激的信息仍然是神经科学的主要目标。神经变异性和尖峰时间在神经编码中的作用尤为重要。外周前庭传入显示出与尖峰时间重要性相关的差异变异性；规则传入显示出很小的变异性，并使用定时码来传递有关感觉输入的信息。相反，不规则传入显示出更大的变异性，而是使用速率码。我们通过记录一组称为前庭唯一（VO）的神经元来研究前庭核内的中枢神经元如何整合来自两种传入类别的信息，这些神经元已知对前庭脊髓反射有贡献，并投射到高级中枢。我们发现，尽管单个中枢神经元的敏感性大于或等于单个传入的敏感性，但它们传递的信息较少。此外，它们的速度检测阈值明显大于单个传入的阈值。这是因为 VO 神经元显示出更大的变异性，这不利于信息传输和信号检测。从多个 VO 神经元的活动中进行组合增加了信息传输。然而，信息率仍然远低于等效传入群体的信息率。此外，将来自多个 VO 神经元的响应结合起来会导致更低的速度检测阈值值接近从行为测量的值（∼2.5 与 0.5-1°/s）。我们的研究结果表明，传入神经编码的前庭刺激的详细时间过程不会通过 VO 神经元传递。相反，它们表明，较高的前庭途径必须整合来自中枢前庭神经元群体的信息，以产生行为观察到的检测阈值。
