TEMPORAL PRECISION AND DYNAMICAL CODING IN THE OLFACTORY BULB

识别由神经元活动代表的刺激特征，并理解这种表征的保真度，是理解大脑如何处理感觉世界的核心。在哺乳动物嗅球中，二尖瓣/簇状(M/T)细胞都接受来自感觉神经元的突触输入，并作为中央脑结构的主要输出。由于身体的限制，脊椎动物气味感受器上的气味强度(浓度)的变化可能比其他感官方式(如视觉或听觉)的刺激强度变化慢得多。由于这种速度限制，动作电位(AP)的精确计时将不会像其他感觉系统那样跟踪刺激特性的快速、毫秒级的变化。相反，准确的AP计时提供的额外“带宽”可以编码其他嗅觉刺激特征，如身份或背景。如果气味识别是在刺激反应的早期AP计时中编码的，并且这种计时在相同的刺激中是可靠的，那么行为反应潜伏期可以被最小化。在呼吸周期中，相同的AP组合反应可以用来确认气味身份。或者，在不同的呼吸周期中，这种反应的定向变化可能会在每个呼吸周期中传达关于复杂刺激的新信息。在这里，我建议测试的假设是，集合AP计时编码小鼠嗅球气味刺激的特征，并在呼吸周期中以动态方式进行编码。

Identification of the stimulus features represented by neuronal activity, and understanding the fidelity of this representation, are central to understanding how the brain processes the sensory world. In the mammalian olfactory bulb, mitral/tufted (M/T) cells both receive synaptic input from sensory neurons, and serve as the principal output to central brain structures. Due to physical constraints, odor intensity (concentration) at odorant receptors in vertebrates is likely to vary much more slowly than stimulus intensity in other sensory modalities such as vision or audition. Because of this speed limit, the precise timing of action potentials (APs) will not track rapid, millisecond-timescale changes in stimulus properties as in other sensory systems. Rather, the extra "bandwidth" afforded by precise AP timing could encode other olfactory stimulus features, such as identity or context. If odor identity is encoded in AP timing early during a stimulus response, and this timing is reliable across identical stimuli, behavioral response latencies could be minimized11. Across respiratory cycles, an identical ensemble AP response could serve to confirm odor identity. Alternatively, directed changes in this response across cycles could convey novel information in each respiratory cycle about a complex stimulus. Here I propose to test the hypotheses that ensemble AP timing encodes features of odor stimuli in the mouse olfactory bulb, and does so in a dynamic fashion across respiratory cycles.