Olfactory training: effects of multisensory integration, attention towards odors and physical activity

Olfactory training (OT) has been shown to be of value in the treatment of olfactory dysfunction. The present study aimed to investigate whether the efficacy of OT could be modulated with multisensory integration, attention towards odors, odor complexity, or physical activity assessed with a questionnaire. One hundred healthy participants were recruited and divided into 4 groups. Except for controls (n = 26, mean age +/- SD = 36 +/- 15 years) all participants performed OT 4 times a day. In the "video" group (n = 26, age 39 +/- 19 years) OT was performed while watching specific and congruent video sequences. In the "counter" group (n = 24, 38 +/- 17 years) participants additionally counted the number of odors 1 day per week, and in the "training only" group no additional measures were taken in addition to OT (n = 24, 38 +/- 20 years). "Single-molecule" odorants or "complex mixtures" were distributed randomly for training stimulation. Sniffin' sticks tests (odor identification, odor discrimination, and odor threshold), cognitive tests, and a series of scales were measured at both baseline and after 3 months of OT. The degree of physical activity was recorded with a questionnaire. Olfactory function improved in the video and counter groups after OT, especially for odor threshold and discrimination. Yet, odor complexity and the degree of physical activity had limited effects on olfactory improvement after OT. Both multisensory interaction and attention towards odors plus OT appeared to facilitate improvement of olfactory function in healthy individuals compared with OT alone and controls, which could provide new promising treatments for clinical applications.