Analysis of structural alterations in olfactory-related brain regions in patients with cognitive impairment and the...

To evaluate the differences in olfactory function, volumes of brain regions related to olfaction, and subregion volumes of the amygdala and hippocampus among the healthy control (HC), mild cognitive impairment (MCI), and Alzheimer's disease (AD), as well as the association of volumes and olfactory function.

Clinical data for the participants included age, gender, education level, Mini-Mental State Examination (MMSE). Participants underwent olfactory function test, including three sub-experiments as namely threshold test (TT), discrimination test (DT) and identification test (IT) and brain magnetic resonance imaging (MRI), including a three dimensions T1-weighted sequence (3D-T1WI). The brain subregions were extracted automatically by the uAI research portal.

A total of 107 participants were recruited, including 35 HC, 28 MCI and 44 AD. The volumes of hippocampal subregion (HC_Body_L and HC_Tail_L) were significant difference in HC and MCI groups while the global hippocampal volumes were not. All tested domains (TOS, TT, DT, and IT) showed statistically significant differences in olfactory function between the three groups. Furthermore, we found only IT showed significant differences across all three pairwise comparisons among the HC, MCI, and AD groups. The hippocampus and amygdala volumes showed the strongest correlation with olfactory function, followed by the PHG, PCC, lOFC and ERC, and more sub-region volumes had moderate-strength correlations with DT, IT, and TOS, according to Spearman correlation analysis.

The olfactory function and the volumes of the hippocampal subnuclei maybe good candidates as early biomarkers of preclinical AD.