Differences in the central-nervous processing of olfactory stimuli according to their hedonic and arousal characteristics

• Neuropsychological studies seldom investigate the arousal properties of odors.
• We evaluated brain activation caused by odors differing in pleasantness and arousal through fMRI.
• We confirmed the previous findings of activation related to pleasantness dimension.
• Arousing stimuli activated the thalamic relay and influenced magnitude of cerebral activation.

Given the strong relationship between human olfaction and emotion, it is not surprising that numerous studies have investigated human response to hedonic and arousing qualities of odors. However, neuropsychological research addressed rather the pleasant–unpleasant, and not the arousing–calming dimension of emotional states generated by odorants. The purpose of the presented fMRI study was to evaluate the differences in cerebral processing of olfactory stimuli, focusing on both of these dimensions of emotional experiences, i.e., pleasantness and arousal. We investigated the patterns of activation generated by odors differing in hedonic tone and generated arousal while controlling the stimuli intensity. This design allowed for a new insight to the emotional odor processing with imaging techniques. The pleasantness was related to activation in the cingulate gyrus, the insula, the hippocampal area, the amygdala, and the superior temporal gyrus, whereas arousal affected activation in the thalamic relay. The present study showed also that the emotional states generated by arousing qualities of odorants are an important determinant of magnitude of cerebral activation.