认知与发展心理学研究室知识库

近来研究发现，嗅觉模态也存在知觉竞争：当向个体的鼻两侧分别呈现不 同的气味时，嗅知觉会在这两种气味间发生转换，这种内源性知觉体验的转换 涉及外周和中枢的适应。探寻伴随嗅知觉转换的大脑活动变化，将增进对嗅知 觉编码和嗅觉意识神经机制的理解。

本研究利用功能性磁共振成像技术检验被试（30 名健康女性，平均年龄±标准差=23.5 ± 2.0 岁）在鼻两侧分别暴露于苯乙醇（玫瑰气味）和乙酸异戊酯（香蕉气味）并实时按键报告嗅知觉内容时，前梨状皮质、后梨状皮质和眶额叶皮质等感兴趣区域的激活情况。

结合单变量激活分析、多体素模式分析和功能连接分析，对感兴趣区域的磁共振信号进行了分析。结果显示，所有被试知觉报告都表现出较明显的鼻双侧竞争现象。在嗅知觉切换的同时，左右侧前梨状皮质的相对激活强度也发生了交替。梨状皮质和眶额叶皮质的空间激活模式均可解码嗅知觉的内容，右侧前梨状皮质对于气味知觉的解码正确率随着知觉明确性的提高而提高。此外，梨状皮质和眶额叶皮质之间存在自下而上和自上而下的连接活动，并且后梨状 皮质到眶额叶皮质之间的连接活动受到鼻孔特异性嗅觉输入的主导侧（抑制侧）的调节。

研究结果表明，梨状皮质和眶额皮质的活动表征了嗅觉意识的内容，而不是嗅觉输入的化学特征。关于嗅觉意识的具体神经动态有待于未来的研究。

Recent studies have revealed the existence of perceptual rivalry in human olfaction. When different odors are simultaneously and separately presented to the two nostrils, perception alternates between the two odors. This endogenous alternation of olfactory percepts involves adaptation at both the peripheral and cortical levels, providing a unique window into the neural mechanisms underlying olfactory perceptual coding and olfactory awareness.

In the present study, we used functional magnetic resonance imaging to examine activities in the anterior piriform, posterior piriform and orbitofrontal cortices when participants (30 healthy females, mean age ± SD = 23.5 ± 2.0 years) were dichorhinically presented with phenylethyl alcohol (a rose-like odor) and isoamyl acetate (a banana-like odor). They reported their olfactory percepts via button presses.

BOLD signals from the regions of interest were analyzed using a combination of univariate voxel-wise analysis, multi-voxel pattern analysis, and functional connectivity analysis. The results showed apparent olfactory rivalries in the perceptual reports of all participants. The perceptual switches were accompanied by alternations of the relative activation strengths in the left and right anterior piriform cortices. The ensemble activity patterns in the piriform and orbitofrontal cortices represented the content of olfactory awareness and were spatially more correlated with those induced by the dominant odor as opposed to the suppressed odor when presented alone. In the right anterior piriform cortex, the decoding accuracy of the perceived odor object increased as the level of perceptual ambiguity decreased. Additionally, we found bidirectional functional connectivity between the piriform cortex and orbitofrontal cortex. The connectivity strength from the posterior piriform cortex to the orbitofrontal cortex was modulated by the dominance / suppression of the nostril-specific olfactory input.

Our findings suggest that activities in the piriform and orbitofrontal cortices represent the content of olfactory awareness beyond the chemical properties of the olfactory input. The exact neural dynamics underlying the computation of olfactory awareness awaits future research.