Coding of odorous stimuli has been mostly studied using single isolated stimuli. However, a single sniff of air in a natural environment is likely to introduce airborne chemicals emitted by multiple objects into the nose. The olfactory system is therefore faced with the task of segmenting odor mixtures to identify objects in the presence of rich and often unpredictable backgrounds. The piriform cortex is thought to be the site of object recognition and scene segmentation, yet the nature of its responses to odorant mixtures is largely unknown. In this study, we asked two related questions. (1) How are mixtures represented in the piriform cortex? And (2) Can the identity of individual mixture components be read out from mixture representations in the piriform cortex? To answer these questions, we recorded single unit activity in the piriform cortex of naïve mice while sequentially presenting single odorants and their mixtures. We find that a normalization model explains mixture responses well, both at the single neuron, and at the population level. Additionally, we show that mixture components can be identified from piriform cortical activity by pooling responses of a small population of neurons—in many cases a single neuron is sufficient. These results indicate that piriform cortical representations are well suited to perform figure-background segmentation without the need for learning.

中文翻译：

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前梨状皮层的混合编码和分割


气味刺激的编码主要是使用单个孤立的刺激来研究的。然而，在自然环境中吸一口空气可能会将多个物体散发的空气中的化学物质引入鼻子。因此，嗅觉系统面临着分割气味混合物的任务，以识别存在丰富且通常不可预测的背景的物体。梨状皮层被认为是物体识别和场景分割的场所，但其对气味混合物的反应性质在很大程度上尚不清楚。在这项研究中，我们提出了两个相关问题。 (1) 混合物在梨状皮层中是如何表现的？ (2) 能否从梨状皮层的混合物表征中读出各个混合物成分的身份？为了回答这些问题，我们记录了幼稚小鼠梨状皮层的单个单位活动，同时顺序呈现单一气味剂及其混合物。我们发现归一化模型可以很好地解释单个神经元和群体水平上的混合反应。此外，我们还表明，通过汇集一小群神经元的反应，可以从梨状皮层活动中识别出混合物成分——在许多情况下，单个神经元就足够了。这些结果表明，梨状皮层表示非常适合执行图形背景分割，而无需学习。