Impact of valence and age on olfactory induced brain activation in healthy women

The aim of the present study was to assess the effect of age on cerebral correlates of olfactory induced negative emotions. We investigated 15 healthy women (aged 21-47) in a functional MRI (fMRI) study during passive smelling of one negative odor (rotten yeast) and two control conditions presenting a neutral odor (vanilla) and odorless ambient air. Besides odor-specific differences in ratings of valence (yeast less pleasant than vanilla and air), intensity (yeast more intense than vanilla and air), and arousal (yeast more arousing than vanilla and air), self-ratings verified the intended mood induction effect: subjects experienced more disgust during yeast stimulation compared to ambient air and vanilla. Along with the superior temporal cortex, medial, and lateral orbitofrontal activations were found to discriminate between negative and neutral olfactory stimulation (yeast and vanilla) directly. Activations of the dorsolateral prefrontal cortex and the caudate were correlated with age and showed stronger valence-related responses (yeast vs. vanilla) in younger compared to older women. Stronger BOLD signals within the anterior cingulate gyrus, insula and motor areas were found during negative compared to neutral stimulation and are considered to represent an attempt to down-regulate the strong emotional experience and the organisms' preparation for withdrawal, respectively. Our results stress the role of orbitofrontal and superior temporal brain regions in odor-related valence coding and stress the necessity to consider age as a modulating factor for further studies, even in relatively young samples.