感觉系统的基本功能是准确地把瞬息万变的环境信息提供给大脑，而大脑的一个基本功能是在不断变化的内环境下，准确地感知外部世界。这样的正常功能，对于日常生活、生存、以及高级脑功能如在适当的情形下做出正确的判断、计划以及最终决定等至关重要。然而，感觉系统如何在不同的生理状态下完成高保真的输入，我们的了解却十分有限。
武汉物数所徐富强研究员和李安安博士等人以嗅觉系统的第一中枢嗅球作为研究对象，通过对麻醉深度的操控，使动物大脑处于不同的运行状态（高基线和低基线两种状态），利用电生理记录的方法研究动物在这两种情况下嗅球如何编码同一气味刺激的信息。研究表明，动物在处于这两种运行状态下，嗅球中的神经总活动和神经元放电频率分布，在气味刺激后与各自基线相比均发生明显改变，但气味刺激后两种状态之间相比，并无明显差别。这种对同一刺激独立于大脑状态的神经表达现象并不受所使用的麻醉剂类型，气味结构和浓度、嗅球的不同功能层、同一功能层内不同的位点、以及电信号类型（不同频段的局部场电位和多单位放电）的影响。因此，嗅球对同一气味刺激的编码是通过相对稳定的神经元组合，以绝对反应强度而不是相对反应强度来实现，同时提示嗅球中存在、但目前还不清楚的神经机制来确保在不同大脑状态下对气味准确编码，从而将外界气味信息可靠地传递到更高级的嗅觉中枢，形成相应的嗅觉感知。研究结果发表在Proceedings of the National Academy of Sciences（PNAS）上（www.pnas.org/cgi/doi/10.1073/pnas.1013814108）。
该研究得到国家自然科学基金委杰出青年基金、国家创新研究群体和中科院“百人计划”项目的支持。（生物谷Bioon.com）
生物谷推荐原文出处：
PNAS doi: 10.1073/pnas.1013814108
Brain-state–independent neural representation of peripheral stimulation in rat olfactory bulb
Anan Lia,b, Ling Gonga, and Fuqiang Xua,c,1
Abstract
It is critical for normal brains to perceive the external world precisely and accurately under ever-changing operational conditions, yet the mechanisms underlying this fundamental brain function in the sensory systems are poorly understood. To address this issue in the olfactory system, we investigated the responses of olfactory bulbs to odor stimulations under different brain states manipulated by anesthesia levels. Our results revealed that in two brain states, where the spontaneous baseline activities differed about twofold based on the local field potential (LFP) signals, the levels of neural activities reached after the same odor stimulation had no significant difference. This phenomenon was independent of anesthetics (pentobarbital or chloral hydrate), stimulating odorants (ethyl propionate, ethyl butyrate, ethyl valerate, amyl acetate, n-heptanal, or 2-heptanone), odor concentrations, and recording sites (the mitral or granular cell layers) for LFPs in three frequency bands (12–32 Hz, 33–64 Hz, and 65–90 Hz) and for multiunit activities. Furthermore, the activity patterns of the same stimulation under these two brain states were highly similar at both LFP and multiunit levels. These converging results argue the existence of mechanisms in the olfactory bulbs that ensure the delivery of peripheral olfactory information to higher olfactory centers with high fidelity under different brain states.
