Brain Structure as a Correlate of Odor Identification and Cognition in Type 2 Diabetes

Abstract

Background: It has been reported that type 2 diabetes (T2DM) is associated with olfactory identification (OI) impairments and cognitive decline. However, the relationship between OI impairments and cognitive decline is largely unknown in T2DM patients. Methods: Sixty-eight T2DM patients and 68 healthy controls underwent 3D-T1 MRI scans, olfactory and cognitive assessments. The cortical thickness of olfaction-related brain regions, olfactory and cognitive scores were compared between groups. Correlation analyses were carried out among cognition, olfaction, and cortical thickness of olfaction-related brain regions. Results: First, the cognitive and olfactory test scores of T2DM patients were lower than healthy subjects. Second, higher olfactory scores were associated with increased cortical thickness in the left parahippocampal gyrus and bilateral insula in T2DM. Third, higher olfactory scores were associated with higher cognitive performance in T2DM. Fourth, some cognitive performances were related to cortical thickness in the left parahippocampal gyrus and left insula in T2DM. Conclusion: These findings indicated that olfactory dysfunction may be useful for future applications that attempt to predict cognitive decline or develop tailored therapies in T2DM patients.

Keywords: cognitive function; cortical thickness; magnetic resonance imaging; olfactory function; type 2 diabetes.

Figure 1

Histogram of CSIT scores for all participants in this study. (A) The CSIT-OI scores of patients with T2DM were lower than HC (*P < 0.05). (B) There was no difference in the CSIT-self scores of the two groups (P > 0.05). T2DM, Type 2 Diabetes Mellitus; HC, Healthy Controls; CSIT, Chinese Smell Identification Test; OI, olfactory identification.

Figure 2

Scatter plots of the correlations between cognitive scores and cortical thickness of the left parahippocampus and left insula in T2DM. r, correlation coefficient (Pearson’s correlations); P, the P-value after false discovery rate (FDR) correction; P < 0.05 was considered significant. L, left; AVLT, Auditory Verbal Learning Test; MoCA, Montreal Cognitive Assessment; TMT, Trail Making Test; SDMT, Symbol Digit Modalities Test; DST, Digit Span Test; VFT, Verbal Fluency Test.