Assessing the effects of smell training on the brains of patients with an impaired sense of smell after surgery

INTERVENTION: All participants undergo an olfactory measurement test to diagnose olfactory dysfunction and assess severity. Also, they are examined by an ENT specialist's including a complete physical exam and nasofibroscopy, to exclude other conditions that could be causing smell impairment. For the scanning sessions, an odour infusion system is attached to a single air‐line, to perform the sniffing paradigm, which is characterized by an odour intake of eucalyptus essential oil through a nasal cannula. Also, a trigeminal activation paradigm is performed to assess the indemnity of the trigeminal system, characterized by the intake of odourless CO2 through a nasal cannula. After the first fMRI and olfactory performance assessment, the smell‐impaired cohort is randomized into two groups. Participants are randomized by simple randomization using computer‐generated random numbers. The allocation is concealed from the research team. No masking is used. Intervention: Olfactory training for 12 weeks Control: No treatment Olfactory training is performed using four essential oils: lemon (limonene 67.08% and b‐pinen 12.52%), eucalyptus glovus (1‐8‐cineole 60%), clove (eugenol 75.49% and eugenol acetate 13.59%) and lavender (linalool 36.53% and linalyl acetate 32.80%). Patients are instructed to expose themselves twice a day to each odour taking deep sniffs for 30 seconds and resting 10 seconds between each oil. Additionally, they are instructed to evoke a memory or feeling during the odour exposure that is associated with the smell of the essential oil. Patients are contacted monthly to maintain compliance and motivation during the training period. At the end of the 12‐week training period, b CONDITION: Post‐surgical olfactory dysfunction ; Ear, Nose and Throat PRIMARY OUTCOME: Activation areas and functional connectivity during olfactory stimulation measured using functional MRI images before olfactory training and 12 weeks after the intervention SECONDARY OUTCOME: Olfactory function assessed using olfactometric measurements before olfactory training and 12 weeks after the intervention INCLUSION CRITERIA: 1. Referred post‐surgical olfactory dysfunction lasting for at least 1 year 2. Only patients with a definite diagnosis of olfactory dysfunction were finally included 3. No history of psychiatric or neurodegenerative diseases