Chemosensory ERP Suggest Peripherally Driven Olfactory-Trigeminal Interactions in Healthy Older Adults

The olfactory and intranasal trigeminal systems interact closely, influencing chemosensory perception, yet the mechanisms underlying their interaction remain poorly understood and have been studied mainly in young adults. We aimed to characterize olfactory-trigeminal interactions in aging by comparing electrophysiological and behavioral responses under ipsilateral and contralateral olfactory-trigeminal co-stimulation, to determine the relative contributions of peripheral and central mechanisms. Using chemosensory event-related potentials and a localization task, 44 healthy older adults (66.3 ± 4.6 years; 29 women) were tested under four conditions: pure trigeminal (carbon dioxide; CO₂), pure olfactory (2-phenylethanol; PEA), ipsilateral co-stimulation (PEA+CO₂ in the same nostril), and contralateral co-stimulation (PEA+CO₂ in opposite nostrils). Ipsilateral, but not contralateral olfactory-trigeminal co-stimulation, improved trigeminal localization performance and induced larger late positive component amplitudes. Together, these findings suggest that olfactory-trigeminal interactions are driven primarily by peripheral rather than central mechanisms. This study also provides normative CSERP data for healthy older adults.