Odor Coding in Piriform Cortex

识别气味的能力对于避免捕食者，获得食物或寻找配偶至关重要。共同 梨状皮质（aPCx）神经元的分布式集合体的活动被认为直接导致了 然而，用于代表气味刺激的不同特征的编码策略，如 气味特性和气味强度仍然知之甚少。aPCx由以下异质群体组成： 这些神经元可能在形成气味表征和/或将这些信息传递给 下游目标区。关于它们是如何做到这一点的，我们知之甚少，因为大多数对皮质气味的研究 编码对于细胞类型或靶投射是不可知的。此外，大多数以前的研究都是在 麻醉的动物，在那里细胞的功能和随之而来的皮层代表可能会被破坏， 改变了。这里的目的是了解不同的功能气味刺激是如何代表， 在不同的aPCx神经元群体中，阐明了潜在的神经回路机制， 塑造这些形象。所使用的方法将是记录气味诱发的尖峰在大合奏 在清醒小鼠中功能性鉴定aPCx神经元。核心假设是独立的编码策略- gies被用来代表气味的身份和气味的强度，不同类型的aPCx细胞发挥不同的作用， 在塑造这些表现中的作用。这些研究的基本原理是，确定气味是如何代表的， 在清醒的行为动物的aPCx中的感觉对于理解嗅觉系统功能至关重要。本 目的1：确定梨状皮质是如何同时再现 厌恶气味特性和气味强度。初步研究表明，气味的身份是编码在分布- aPCx神经元的集合，这些集合在很大程度上是浓度不变的（即空间识别）。 气味强度由集合活动的同步性编码（即，时间强度 代码）。目的2：确定不同亚型的aPCx神经元的气味反应，遗传定义， 通过层状组织或通过不同的投射目标。体内光遗传学标记将用于鉴定 神经元亚型的反应。预测不同亚型神经元的气味反应， 反映了它们在形成不同气味刺激最相关的整体或特征中的特定作用。 目标区域。目的3：确定如何经常性电路形状皮质气味表征。输出 从主要神经元将被单侧阻断，允许同时记录控制和 “前馈”电路。初步数据表明，复发性回路极大地影响了大脑皮层的大小、时间进程和 在aPCx中获得气味响应。这一建议是创新的，因为它部署了新的工具和方法，以重新 在清醒动物的大量神经元中，脊髓气味诱发的活动， 与已识别的皮层回路元件有关。这一贡献意义重大，因为它将提供深刻的见解 通过了解潜在的回路机制，了解气味是如何在梨状皮质中表达的。

The ability to identify an odor is crucial for avoiding predators, obtaining food or finding a mate. The concerted activity of distributed ensembles of neurons in piriform cortex (aPCx) is thought to lead directly to the formation of an odor percept however the coding strategies used to represent different features of an odor stimulus, like odor identity and odor intensity, remain poorly understood. aPCx consists of a heterogeneous population of neurons that likely serve distinct roles in shaping odor representations and/or conveying this information to downstream target areas. Little is known about how they actually do so as most investigations into cortical odor coding were agnostic to cell type or target projection. Moreover, most previous studies were performed in anesthetized animals, where both the cells' functions and consequent cortical representations may be dra- matically altered. The objective here is to understand how different features of an odor stimulus are repre- sented in diverse populations of aPCx neurons, and elucidate the underlying neural circuit mechanisms that shape these representations. The approach used will be to record odor-evoked spiking in large ensembles of functionally identified aPCx neurons in awake mice. The central hypothesis is that independent coding strate- gies are used to represent odor identity and odor intensity, and that different types of aPCx cells play distinct roles in shaping these representations. The rationale for these studies is that determining how odors are repre- sented in aPCx of an awake, behaving animal is crucial for understanding olfactory system function. To this end the following three aims are proposed: Aim 1: To determine how piriform cortex simultaneously rep- resents odor identity and odor intensity. Preliminary studies suggest that odor identity is encoded in distrib- uted ensembles of aPCx neurons, and these ensembles are largely concentration-invariant (i.e. a spatial iden- tity code); and odor intensity is encoded by the synchrony of the ensembles activity (i.e. a temporal intensity code). Aim 2: To determine odor responses in diverse subtypes of aPCx neurons, defined genetically, by laminar organization or by distinct projection targets. In vivo optogenetic tagging will be used to identify responses in defined subtypes of neurons. Odor responses in different subtypes of neurons are predicted to reflect their specific roles in shaping the ensemble or the feature of the odor stimulus most relevant for different target regions. Aim 3: To determine how recurrent circuitry shapes cortical odor representations. Output from principal neurons will be unilaterally blocked, permitting simultaneous bilateral recordings of control and “feedforward” circuits. Preliminary data suggest recurrent circuits dramatically shape the size, timecourse and gain of odor responses in aPCx. This proposal is innovative because it deploys novel tools and methods to re- cord odor-evoked activity in large populations of neurons in awake animals and ascribe distinct response prop- erties to identified cortical circuit elements. This contribution is significant because it will provide deep insight into how odors are represented in piriform cortex through understanding underlying circuit mechanisms.