Rodriguez-Raecke Rea, Loos Helene M, Sijben Rik, Singer Marco, Beauchamp Jonathan, Buettner Andrea, Freiherr Jessica
Diagnostic and Interventional Neuroradiology, University Hospital, RWTH Aachen University, Aachen, Germany.
Sensory Analytics, Fraunhofer Institute for Process Engineering and Packaging IVV, Freising, Germany.
Front Neurosci. 2019 Nov 14;13:1219. doi: 10.3389/fnins.2019.01219. eCollection 2019.
Odor masking is a very prominent problem in our daily routines, mainly concerning unpleasant sweat or toilet odors. In the current study we explored the effectiveness of odor masking both on a behavioral and neuronal level. By definition, participants cannot differentiate a fully masked unpleasant odor from the pleasant pure odor used as a masking agent on a behavioral level. We hypothesized, however, that one can still discriminate between a fully masked odor mixture and the pure masking odor on a neuronal level and that, using a reinforcing feedback paradigm, participants could be trained to perceive this difference. A pleasant, lemon-like odor (citral) and a mixture of citral and minor amounts of an unpleasant, goat-like odor (caproic acid) were presented to participants repeatedly using a computer-controlled olfactometer and participants had to decide whether two presented stimuli were the same or different. Accuracy of this task was incentivized with a possible monetary reward. Functional imaging was used throughout the task to investigate central processing of the two stimuli. The participants rated both stimuli as isopleasant and isointense, indicating that the unpleasant odor was fully masked by the pleasant odor. The isolated caproic acid component of the mixture was rated less pleasant than the pleasant odor in a prior experimental session. Although the masked and pure stimuli were not discriminated in the forced-choice task, quality ratings on a dimensional scale differed. Further, we observed an increased activation of the insula and ventral striatum/putamen for the pure in contrast to the fully masked odor, hence revealing a difference in neuronal processing. Our hypothesis that perceptual discrimination and neuronal processing can be enhanced using a reinforcing feedback paradigm is not supported by our data.
气味掩盖是我们日常生活中一个非常突出的问题，主要涉及难闻的汗味或厕所气味。在当前的研究中，我们从行为和神经元层面探讨了气味掩盖的有效性。根据定义，在行为层面上，参与者无法区分完全被掩盖的难闻气味和用作掩盖剂的宜人纯净气味。然而，我们假设，在神经元层面上，人们仍然可以区分完全被掩盖的气味混合物和纯净的掩盖气味，并且使用强化反馈范式，参与者可以被训练来感知这种差异。使用计算机控制的嗅觉计向参与者反复呈现一种宜人的、柠檬样气味（柠檬醛）以及柠檬醛和少量难闻的、山羊样气味（己酸）的混合物，参与者必须判断两个呈现的刺激是否相同。这项任务的准确性会通过可能的金钱奖励来激励。在整个任务过程中使用功能成像来研究这两种刺激的中枢处理。参与者将两种刺激评定为同等宜人且同等强度，这表明难闻气味被宜人气味完全掩盖。在之前的实验环节中，混合物中分离出的己酸成分被评定为不如宜人气味宜人。尽管在强制选择任务中，被掩盖的刺激和纯净刺激没有被区分出来，但在维度量表上的质量评定有所不同。此外，与完全被掩盖的气味相比，我们观察到纯净气味会使脑岛和腹侧纹状体/壳核的激活增加，从而揭示了神经元处理上的差异。我们关于使用强化反馈范式可以增强感知辨别和神经元处理的假设未得到我们数据的支持。
