Akshita Joshi

Neural associations between well-being and odor perception

PhD Thesis, TU Dresden

Objective

 In healthy subjects using functional magnetic imaging (fMRI) technique we investigated (1) if odors influence individual’s state of well-being (WB) (2) if state of WB affects the way odors are processed.

Method

The experiment consisted of two parts: Pre-testing followed by fMRI scans. Hundred subjects were recruited in the pre-testing. Pre-testing session was done for the selection of two odors that would strongly associate to well-being and two odors that were weakly associated to well-being. All the subjects rated intensity (scale 0-10), pleasantness or unpleasantness (-5 to +5; with 0 being neutral) and WB (scale 1-10) for the 14 pleasant odors. These odors were: lavender, apple strudel, forest, flower, peppermint, lilac, orange, rose, vanilla, chocolate, coffee, grass, cedarwood oil and leather. Pre-testing resulted in selection of flower and orange odor that were strongly associated to WB and grass and coffee that were weakly associated to WB. In addition, all the subjects filled up a general habitual well-being questionnaire that would reflect their state of well-being. Based on the questionnaire scores, subjects were divided into two groups that is, people with high and low WB state. From a total of hundred subjects, 44 subjects that had similar preferences for strongly and weakly associated odors to WB were scanned. All these 4 odors including flower, orange, coffee and grass odors were presented to the subjects lying in the MRI scanner using a computer based olfactometer which is a portable odor delivery system. Each odor was presented in 12 ON+OFF repeats with ON session of 8 seconds followed by OFF session of 12 seconds. After each odor presentation subjects were again asked to rate intensity, valence and WB associations.

Results

Odor ratings during pre-testing did not differ significantly when compared to ratings asked during scans. Neuroimaging results showed that in presence of odors strongly associated to WB (flower + orange); people that have a low WB state lead to increased activations in the high-cognitive brain regions including conscious perception of stimuli, attention processing, memory retrieval linking information from different modalities and sub-systems (angular gyrus, inferior frontal gyrus, insula). Whereas in presence of weakly associated odors (coffee + grass) subjects having low WB state showed major activations in the olfactory processing area (orbitofrontal cortex) with comparatively less involvement of cognitive and emotional processing area (inferior frontal gyrus). When we compared subjects with high vs low WB state, only low WB subjects showed stronger activity in the right angular gyrus in presence of strongly WB odors whereas no voxel survived for weakly odors.

Conclusion

The present results support the idea of an association between WB state and the cortical processing of odors. People having low WB state showed a preferential neural engagement for strongly associated WB odors, possibly linking them to their experiences thus activating higher order cognitive and emotional brain areas. In other words, odors may play an important role in lifting mood or altering emotional state especially in people with low WB.