Laminar differences in taste coding: a circuit perspective

 描述（由申请人提供）：味觉信息如何在皮层中表示？这个问题的答案一直是味觉神经科学领域最激烈争论的话题之一1 -3。在过去的几十年里，人们提出并讨论了两种理论。根据标记线理论，味觉刺激的生理化学特性是由特定的神经元子集编码的，每个神经元子集都被严格地调整到单一的味觉质量（即咸、甜、酸、苦或鲜味）4-7。另一种理论，跨神经元模式理论，假设味觉编码依赖于大量皮层神经元的联合活动。根据这一理论，神经元不需要对特定的味道质量进行选择，相反，每个神经元可以通过编码多种质量来密集地表示信息。 这两种理论都得到了实验证据的支持。最近的一项双光子钙成像研究表明，麻醉小鼠GC中仅存在窄调谐神经元7;麻醉和警觉啮齿动物多年的电生理记录表明GC中存在窄调谐和密集编码神经元10 -13。尽管有证据表明GC中存在使用不同编码策略的神经元，但争论仍然是两极分化的，并且没有出现皮层中味觉编码的统一观点。 这个提议的首要目标是检验这样一个假设，即窄调谐和密集编码的神经元反映了皮层处理的不同阶段。具体地说，我们提出编码方案根据皮质层而变化，表层（即，层2/3）特征在于经调谐的神经元和深层（即，层4和5）含有密集编码神经元。此外，在这个建议中的实验旨在提供一个机制解释这些差异，连接编码特性与抑制驱动的层依赖性变化。这些实验将依赖于复杂的电生理方法的组合，以直接关联编码特性，兴奋和抑制之间的平衡，以及局部微电路的特性。 这项资助的框架是牢固地建立在关于感觉信息皮层编码的文献14 -17，并得到我们的初步结果的支持，显示了味觉反应特性和局部连接的层特异性差异。这项研究将有助于该领域超越过时的争论，并将把关于味觉编码的讨论推向更面向电路的角度。如果成功的话，这项研究将第一次提供一个关于警觉啮齿动物皮层回路中味觉编码的统一观点。

 DESCRIPTION (provided by applicant): How is gustatory information represented in the cortex? The answer to this question has been one of the mostly intensely debated topics in the field of gustatory neuroscience1-3. Two theories have been proposed and discussed over the past decades. According to the labeled-line theory the physiochemical identity of a gustatory stimulus is encoded by specific subsets of neurons, each of which is narrowly tuned to a single taste quality (i.e. salty, sweet, sour, bitter or umami)4-7. An alternative theory, the across-neuron pattern theory, postulates that taste coding relies on the combined activity of large ensembles of cortical neurons8. According to this theory, neurons do not need to be selective for specific taste qualities, instead each neuron can densely represent information by encoding multiple qualities3,9. Both theories are supported by experimental evidence. While a recent 2-photon calcium imaging study suggested the exclusive presence of narrowly tuned neurons in GC of anesthetized mice7; years of electrophysiological recordings in anesthetized and alert rodents demonstrate the presence of both narrowly tuned and densely coding neurons in GC10-13. Despite evidence that neurons using different coding strategies exist in GC, the debate is still polarized and no unifying view of taste coding in the cortex has emerged. The overarching goal of this proposal is to test the hypothesis that narrowly tuned and densely coding neurons reflect different stages of cortical processing. Specifically, we propose that the coding scheme varies depending on the cortical layers, with superficial layers (i.e., layers 2/3) featuring narroly tuned neurons and deep layers (i.e., layers 4 and 5) containing densely coding neurons. In addition, the experiments in this proposal aim at providing a mechanistic explanation for these differences, linking coding properties with laminar-dependent variations in inhibitory drive. The experiments will rely on a combination of sophisticated electrophysiological approaches to directly relate coding properties, balance between excitation and inhibition, and properties of local microcircuits. The framework of this grant is firmly grounded in the literature on cortical coding of sensory information14-17, and supported by our preliminary results, showing layer-specific differences in taste response properties and local connectivity. This research will help the field go beyond a dated debate and will move the discussion on taste coding toward a more circuit-oriented perspective. If successful this research will provide, for the first time, a unifid view of taste coding in cortical circuits of alert rodents.