Olfactory testing
Olfactory testing was performed twice birhinally (before and after training) by means of the validated Sniffin’ Sticks test (Burghart Medical Technology, Wedel, Germany).14 The Sniffin’ Sticks test is divided into subtests, covering three olfactory dimensions: (i) Threshold (T), (ii) Discrimination (D), and (iii) Identification (I). Summed scores allow the categorization of olfactory performance into normosmia, hyposmia, and functional anosmia based on normative data of over 9000 healthy subjects.15 The test procedure is described in detail elsewhere.14Furthermore, Sniffin’ Sticks can also be used for follow-up testing with minimally clinically important differences defined for summed scores and each of the subtests separately.16