Brain mechanisms in aromatherapy: fMRI and mood changes in response to odors in females with functional abdominal pain

Women with irritable bowel syndrome (IBS) have shown increased perceptual responses to visceral, somatic and auditory stimuli, but perceptual and brain responses to olfactory stimuli has not been studied. Functional magnetic resonance imaging (fMRI) was used to determine the impact of odor on mood and brain activations in women with IBS (IBS: N=8; healthy controls, HC: N=9). A validated emotional faces protocol was used to evoke emotional arousal (Match Emotions) and emotional modulation (Identify Gender). Although there were no significant group differences, compared to HCs, the IBS group was more accurate in rating odors, better able to perceive odors, and gave (by %) higher ratings for odor hedonics (pleasant: 35%; unpleasant: 29.76%), intensity (pleasant 6.81%; unpleasant 11.11%), and familiarity (pleasant 13.69%; unpleasant 12.30%). While HCs did not demonstrate any evidence for mood changes in response to any odor, patients responded to both pleasant and unpleasant odors with more negative emotions (PANAS-X; guilt, sadness, hostility; [group difference; ANOVA: pleasant p=.05; unpleasant p=.02]). Significant activations occurred in the insula, the interoceptive cortex involved in processing and modulation of interoceptive information and emotion regulation. Right anterior insula activations occurred for both IBS and HCs during the pleasant odor condition, consistent with conscious perception of both odors; posterior insula activations occurred for IBS patients, but not for HCs during the unpleasant odors. During the faces paradigm, similar regions were engaged in both groups: Activations for both groups were most consistent with activity in the homeostatic afferent processing network. During the emotional modulation task both groups showed activations of the lateral PFC (HCs in the dorsolateral prefrontal cortex (dIPFC) and ventrolateral prefrontal cortex (v1PFC) in the HC's, and the dIPFC in the IBS group). Both PFC subregions have been implicated in corticolimbic inhibition. During the emotional arousal task of the faces paradigm, patients showed significant brain activations while exposed to both odors; but only to the unpleasant odor during the emotional modulation task. Findings suggest enhanced odor sensitivity in the IBS group most evident during the emotional task, with a preferential response of negative affect to either odor condition.