Swallowing is tightly coupled with emotion–autonomic states, while olfactory pathways project to limbic and hypothalamic hubs that can enhance parasympathetic activity and reduce stress. Whether a pleasant natural-wood odor can modulate swallowing-related brain activity and behavior remains unclear. To test whether Hinoki (Japanese cypress) inhalation improves affective ratings and increases the repetitive saliva swallowing test (RSST) difference (post–pre; swallows/30 s), and whether it suppresses swallowing-related activity in the premotor cortex (Brodman area 6 (BA6)) and the hypothalamus. The effects of exploratory whole-brain and interaction between Task and Odor were also evaluated. In a randomized within-subject crossover with a one-week interval, participants inhaled Hinoki essential oil or odorless rice-oil control. We assessed brain activity during voluntary saliva swallowing using functional magnetic resonance imaging (fMRI). Outcomes included subjective ratings (odor intensity, preference, comfort, recollection) and RSST counts per 30 s; RSST difference was computed as post–pre inhalation. Hinoki improved affective ratings and increased RSST difference compared to control. The odor main effect showed reduced activation in three regions—bilateral BA6 and the hypothalamus. An interaction effect between Task (swallowing vs. rest) and Odor (Hinoki vs. control) was found in the right putamen. The pattern supports a model: odor-induced autonomic calming (lower heart rate, reduced hypothalamic activity) lowers premotor load and improves swallowing, reflected in RSST difference. These findings suggest that aromatherapy-assisted dysphagia rehabilitation using olfactory priming—particularly for patients with post-stroke sequelae or post-stroke depression with poor appetite—may help enhance training efficiency and recovery.
Koeda et al. (Tue,) studied this question.