Objective This study aimed to investigate the relationship between insulin resistance and markers of neuronal viability and energy metabolism, as well as the additive effects of overweight or obesity, in individuals with type 2 diabetes mellitus (T2DM). Methods Using 1H‐magnetic resonance spectroscopy, prefrontal N‐acetyl aspartate (NAA) and creatine levels, markers for neuronal viability and energy metabolism, respectively, were measured in 50 adults with overweight or obesity and T2DM (T2DM‐O; aged 49.0 ± 7.4 years; 50% female), 50 adults with normal weight and T2DM (T2DM‐N), and 50 healthy adults with normal weight (healthy‐control [HC] group) matched for age and sex. The homeostatic model assessment for insulin resistance levels were calculated to assess insulin resistance. Results Prefrontal NAA levels were lower in the T2DM‐O group relative to the HC group (t = −2.51, P = 0.013). Higher insulin resistance was associated with lower prefrontal NAA levels in the T2DM‐O group (t = −2.21, P = 0.032) but not in the T2DM‐N group (t = −0.72, P = 0.48). Prefrontal creatine levels did not differ across the three groups. Conclusions Overweight and obesity might contribute to T2DM‐related neuronal viability deficits and could be the key links that connect insulin resistance to the decreased neuronal viability in the human diabetic brain.
Loss of olfaction, or anosmia, frequently accompanies emotional dysfunctions, partly due to the overlapping brain regions between the olfactory and emotional processing centers. Here, we investigated whether anosmia was associated with gray matter volume alterations at a network level, and whether these alterations were related to the olfactory-specific quality of life (QOL) and depressive symptoms. Structural brain magnetic resonance imaging was acquired in 22 individuals with postinfectious or idiopathic anosmia (the anosmia group) and 30 age-and sex-matched controls (the control group). Using independent component analysis on the gray matter volumes, we identified 10 morphometric networks. The gray matter volumes of these networks were compared between the two groups. Olfactory-specific QOL and depressive symptoms were assessed by self-report questionnaires and clinician-administered interviews, respectively. The anosmia group showed lower gray matter volumes in the hippocampus-amygdala and the precuneus networks, relative to the control group.Lower gray matter volumes in the hippocampus-amygdala network were also linearly associated with lower olfactory-specific QOL and higher depressive symptom scores.These findings suggest a close relationship between anosmia and gray matter volume alterations in the emotional brain networks, albeit without determined causal relations.
Growing evidence indicates that type 2 diabetes mellitus (T2DM)-related cognitive dysfunction may develop in the early stage of the disease and is often accompanied by hippocampal structural alterations. In the current study, we investigated volume and shape alterations of the hippocampus at a subregional level in patients with T2DM. With the use of high-resolution brain structural images that were obtained from 30 T2DM patients with less than 5 years of disease duration and 30 healthy individuals, volumetric and shape analyses were performed. We also assessed the relationship between T2DM-related hippocampal structural alterations and performance on verbal fluency. In volumetric analysis, total hippocampal volume was smaller in the T2DM group, relative to the control group. At a subregional level, T2DM patients showed significant inward deformation and volume reduction of the right dentate gyrus and cornu ammonis 2/3 subregions as compared with healthy individuals. In particular, T2DM patients with lower performance on verbal fluency had smaller right dentate gyrus volumes relative to those with higher performance. These findings suggest that the hippocampus may undergo atrophy at a subregional level even in the early stage of T2DM, and this subregion-specific atrophy may be associated with reduced performance on verbal fluency.
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