Cortical activation during a cognitive task may also be an important biomarker of future dementia in older people and in those with type 2 diabetes. In recent resting state fMRI studies, patients with type 2 diabetes displayed reduced functional connectivity and white matter integrity in the default mode network compared with controls. Functional magnetic resonance imaging (fMRI) studies demonstrate alterations in the activity of distributed neural networks serving memory function in patients with early AD and its precursor state of mild cognitive impairment (MCI) and even in otherwise asymptomatic individuals at risk for AD.
Dementia, particularly Alzheimer’s dementia (AD), is associated with changes in brain function that may precede overt structural brain abnormalities or cognitive deficits by several years. People with onset of type 2 diabetes in middle age have a greater risk of a future dementia than those with late onset disease possibly because of longer exposure. Type 2 diabetes mellitus is associated with an increased incidence of dementia in late life. They support the search for modifiable later-life environmental factors or epigenetic mechanisms linking type 2 diabetes and cognitive decline. These results provide evidence for preclinical memory-related neuronal dysfunction in type 2 diabetes. Differences in activation were more pronounced among monozygotic (MZ) pairs, with MZ individuals with diabetes also displaying greater frontal activation. These findings were present in the absence of within-pair differences in standard cognitive test scores, brain volumes, or vascular lesion load.
Type 2 diabetes was associated with significantly reduced activation in left hemisphere temporoparietal regions including angular gyrus, supramarginal gyrus, and middle temporal gyrus and significantly increased activation in bilateral posteriorly distributed regions. Twenty-two twin pairs discordant for type 2 diabetes mellitus (mean age 60.9 years) without neurological disease were recruited from the Australian Twin Registry (ATR) and underwent functional magnetic resonance imaging (fMRI) during a memory encoding task, cognitive tests, and structural MRI. We aimed to study the impact of type 2 diabetes on brain activation during memory encoding in middle-aged people, controlling for age, sex, genes, and early-shared environment. Type 2 diabetes mellitus increases the risk of dementia and neuronal dysfunction may occur years before perceptible cognitive decline.
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