Although functional imaging studies have shown that odors activate the human piriform cortex, amygdala, entorhinal cortex and hippocampus, it remains unclear which aspects of odors — such as identity and valence — are encoded where in the brain. Kehl et al. recorded from thousands of individual neurons in these four brain areas in humans performing a task requiring them to rate (like or dislike) and identify 15 distinct odors. Each area contained a substantial number of neurons that changed their firing rate according to odor identity, and odor identity could be decoded from neuronal activity. Interestingly, neurons in the piriform cortex and hippocampus encoded the actual (chemical) and perceived odor identities, respectively. In the amygdala, odor-modulated neurons showed greater responses to ‘liked’ odors than to ‘disliked’ odors, and responses correlated with odor-valence ratings. Notably, all four areas contained neurons that changed their firing in response to visual images congruent with an odor (for example, a piece of licorice), and these populations partially overlapped with odor-modulated neurons. In the piriform cortex and amygdala, some neurons also responded to written words representing the odor (such as ‘liquorice’) and to related odors (for example, aniseed), suggesting that these early olfactory-processing areas carry out conceptual coding — an interesting notion that requires further investigation.

Original reference: Nature 634, 626–634 (2024)

尽管功能成像研究表明，气味会激活人类梨状皮层、杏仁核、内嗅皮层和海马体，但目前尚不清楚气味的哪些方面（例如身份和效价）在大脑中的哪个位置被编码。Kehl 等人记录了人类这四个大脑区域中的数千个神经元，这些神经元执行一项任务，要求他们评分（喜欢或不喜欢）并识别 15 种不同的气味。每个区域都包含大量神经元，这些神经元根据气味特性改变它们的放电速率，并且气味特性可以从神经元活动中解码。有趣的是，梨状皮层和海马体中的神经元分别编码实际（化学）和感知的气味身份。在杏仁核中，气味调节的神经元对 “喜欢 ”的气味的反应大于对 “不喜欢 ”的气味的反应，并且反应与气味效价评级相关。值得注意的是，所有四个区域都包含神经元，这些神经元响应与气味一致的视觉图像（例如，一块甘草）而改变它们的放电，并且这些群体与气味调制的神经元部分重叠。在梨状皮层和杏仁核中，一些神经元也对代表气味的书面单词（如“甘草”）和相关的气味（如茴香）做出反应，这表明这些早期的嗅觉加工区域进行概念编码——这是一个有趣的概念，需要进一步研究。

原始参考：Nature634， 626–634 （2024）