Changes in local brain function in mild cognitive impairment due to semantic dementia

Area of Science:

• Neuroscience
• Cognitive Neurology
• Medical Imaging

Background:

• Mild cognitive impairment due to semantic dementia (MCI-SD) is the preclinical stage of semantic dementia.
• Identifying preclinical changes is crucial for early intervention before dementia progression.
• Local functional activity changes in preclinical semantic dementia are not well understood.

Purpose of the Study:

• To investigate local functional activity changes in patients with MCI-SD.
• To identify potential brain changes preceding the onset of semantic dementia.
• To explore the utility of resting-state functional MRI in detecting preclinical semantic changes.

Main Methods:

• Recruited 22 patients with MCI-SD and 19 healthy controls (HC).
• Administered comprehensive neuropsychological tests to assess cognitive function.
• Utilized structural MRI for gray matter volume comparison and resting-state functional MRI (rs-fMRI) with multiple sub-bands to evaluate functional activity.

Main Results:

• MCI-SD patients showed significant semantic performance decline but intact other cognitive domains.
• rs-fMRI revealed widespread local functional changes in MCI-SD across various frequency sub-bands and indicators.
• Functional changes were observed both within and outside atrophic gray matter areas, with the left precuneus showing significant correlations with semantic tasks.

Conclusions:

• Local functional alterations occur in MCI-SD, extending beyond areas of gray matter atrophy.
• The left precuneus, influenced by functional connectivity, may be a key region in preclinical semantic dementia.
• Frequency-dependent analysis, particularly slow-2 and slow-3 sub-bands, is valuable for detecting these subtle functional changes.