当人的嗅觉被阻断时,相应的大脑活动也会发生变化,不过这种变化会随着嗅觉的恢复很快地逆转复原。先前的研究认为嗅觉系统对气味丧失之后的感知变化具有一定的抵抗性,但是本周《自然—神经科学》杂志上的一项研究认为嗅觉感知的稳定性其实是因为大脑中存在快速补偿变化。
Keng Nei Wu等人通过完全堵住受试者的鼻孔来限制对其气味的感知,并让受试者连续一个星期呆在医院的低气味监护室中。结果发现在试验前后,受试者对气味的感受很大程度上并未发生改变。但是,与气味相关的大脑活动却有所变化。在气味感知受限后,受试者大脑眶额皮层的活动便有所增加,而初级嗅觉皮层的活动则马上减少。研究人员表示,这种组合变化可能维持着嗅觉感知的稳定性。
在气味感知受限一个星期后,大脑对气味的反应恢复到试验前的水平,这表示这种以气味受限的方式引发的变化已经快速逆转了。嗅觉系统的这种快速逆转与其他感知系统有很大不同,比如视觉系统,对于无光的环境会产生持续时间较长的反应。科学家认为之所以嗅觉系统会产生这种不同于其他感知系统的现象,是因为嗅觉的丧失一般是由病毒感染或过敏症引起的。(生物谷Bioon.com)
doi:10.1038/nn.3186
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Olfactory input is critical for sustaining odor quality codes in human orbitofrontal cortex
Keng Nei Wu, Bruce K Tan, James D Howard, David B Conley & Jay A Gottfried
Ongoing sensory input is critical for shaping internal representations of the external world. Conversely, a lack of sensory input can profoundly perturb the formation of these representations. The olfactory system is particularly vulnerable to sensory deprivation, owing to the widespread prevalence of allergic, viral and chronic rhinosinusitis, but how the brain encodes and maintains odor information under such circumstances remains poorly understood. Here we combined functional magnetic resonance imaging (fMRI) with multivariate (pattern-based) analyses and psychophysical approaches to show that a 7-d period of olfactory deprivation induces reversible changes in odor-evoked fMRI activity in piriform cortex and orbitofrontal cortex (OFC). Notably, multivoxel ensemble codes of odor quality in OFC became decorrelated after deprivation, and the magnitude of these changes predicted subsequent olfactory perceptual plasticity. Our findings suggest that transient changes in these key olfactory brain regions are instrumental in sustaining odor perception integrity in the wake of disrupted sensory input.