Training with Odors Impacts Hippocampal Thickness in Patients with Mild Cognitive Impairment

Article type: Research Article

Authors: Haehner, Antje^{a; 1; *} | Chen, Ben^{b; a; 1; *} | Espin, Melanie^a | Haussmann, Robert^c | Matthes, Claudia^c | Desser, Dmitriy^a | Loessner, Lorenz^c | Brandt, Moritz D.^{d; e} | Donix, Markus^{c; e} | Hummel, Thomas^a

Affiliations: [a] Smell & Taste Clinic, Department of Otorhinolaryngology, TU Dresden, Dresden, Germany | [b] Center for Geriatric Neuroscience, The Affiliated Brain Hospital of Guangzhou Medical University, Guangzhou, Guangdong Province, China | [c] Department of Psychiatry, TU Dresden, Dresden, Germany | [d] Department of Neurology, TU Dresden, Dresden, Germany | [e] German Center for Neurodegenerative Diseases (DZNE), Dresden, Germany

Correspondence: [*] Correspondence to: Ben Chen, PhD, Center for Geriatric Neuroscience, The Affiliated Brain Hospital of Guangzhou Medical University, Guangzhou, Guangdong Province, China; Smell & Taste Clinic, Department of Otorhinolaryngology, TU Dresden, Fetscherstrasse. 74, 01307 Dresden, Germany. Tel.: +49 351 458 4189; E-mail: [email protected]; Antje Haehner, PhD, Smell & Taste Clinic, Department of Otorhinolaryngology, TU Dresden, Fetscherstrasse. 74, 01307 Dresden, Germany. Tel.: +49 351 458 4189; E-mail: [email protected].

Note: [1] These authors contributed equally to this work.

Abstract: Background:The olfactory system is affected early in Alzheimer’s disease and olfactory loss can already be observed in patients with mild cognitive impairment (MCI). Olfactory training is effective for improving olfactory and cognitive function by stimulating the olfactory pathway, but its effect on patients with MCI remains unclear. Objective:The aim of this randomized, prospective, controlled, blinded study was to assess whether a 4-month period of olfactory training (frequent short-term sniffing various odors) may have an effect on olfactory function, cognitive function, and morphology of medial temporal lobe (MTL) subregions and olfactory bulb in MCI patients. Methods:A total of thirty-seven MCI patients were randomly assigned to the training group or a placebo group, which were performed twice a day for 4 months. Olfactory assessments, cognitive tests and magnetic resonance imaging were performed at the baseline and follow-up period. Results:After the training, there was an increase in odor discrimination, and increased cortical thickness of bilateral hippocampus (CA23DG and CA1) and mean MTL. Additionally, the change of olfactory score was positively associated with change of volume of olfactory bulb and hippocampus; the change of global cognition was positively associated with change of cortical thickness of hippocampus, entorhinal cortex and mean MTL; the change of cortical thickness of entorhinal cortex was positively associated with change of executive function. Conclusion:Olfactory training was associated with an increase in cortical thickness of the hippocampus but not olfactory bulb volume in patients with MCI. Olfactory training may serve as an early intervention of preventing hippocampal atrophy.

Keywords: Cortical thickness, hippocampus, mild cognitive impairment, olfactory bulb, olfactory training

DOI: 10.3233/JAD-220248

Journal: Journal of Alzheimer's Disease, vol. 88, no. 2, pp. 743-755, 2022