The following is a summary of “Association of Olfaction and Microstructural Integrity of Brain Tissue in Community-Dwelling Adults: Atherosclerosis Risk in Communities Neurocognitive Study,” published in the August 2023 issue of Neurology by Shrestha et al.
Smell and brain neuropathology could reveal brain regions linked to regular olfaction and dementia mechanisms. Researchers conducted a prospective study to uncover early brain structures impacted by reduced olfaction. Using the Atherosclerosis Risk in Communities (ARIC) Neurocognitive Study, they investigated cross-sectional links between brain microstructural integrity and olfaction.
They choose community-dwelling adults based on specific criteria: evidence of cognitive impairment, prior participation in an MRI study, and a random subset of cognitively regular participants. Utilizing diffusion tensor imaging (DTI), we assessed microstructural integrity through 2 measures: fractional anisotropy (FA) and mean diffusivity (MD). Additionally, olfaction was evaluated using a 12-item odor-identification test during the same visit. Higher FA/MD, better integrity; elevated odor-ID, improved olfaction. Brain-specific regression linked DTI metrics and olfaction, adjusting for confounders.
The results showed 1,418 participants (average age: 76±5 years, 41% men, 21% Black race, 59% with normal cognition), and the average olfaction score was 9±2.3. Higher MD in the medial temporal lobe (MTL) areas – hippocampus (β: -0.79, 95%CI: -0.94, -0.65), amygdala, entorhinal area – and related white matter (WM) tracts linked to these regions, correlated with olfaction. Associations with MD WM FA were also seen in multiple atlas regions not previously linked to olfaction. Stronger MD-olfaction links were observed in MTL regions for mild cognitive impairment (MCI) individuals compared to normal cognition (e.g., βhippocampus: -0.75, 95%CI: -1.02, -0.49 for MCI; -0.44, 95%CI: -0.63, -0.26 for normal cognition; P-interaction=0.004).
They concluded differential associations reveal MTL regions’ odor-identification ability, suggesting dementia pathogenesis.
Source: n.neurology.org/content/early/2023/08/04/WNL.0000000000207636
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