Anatomical and Functional Deficits in Patients with Amnestic Mild Cognitive Impairment

BACKGROUND Anatomical and functional deficits have been studied in patients with amnestic mild cognitive impairment (MCI). However, it is unclear whether and how the anatomical deficits are related to the functional alterations. Present study aims to characterize the association between anatomical and functional deficits in MCI patients. METHODS Seventeen amnestic MCI patients and 18 healthy aging controls were scanned using a T1 Weighted MPRAGE sequence and a gradient-echo echo-planar imaging sequence. Clinical severity of MCI patients was evaluated by using Clinical Dementia Rating, Mini Mental State Examination (MMSE), Clock Drawing Test, Auditory Verbal Learning Test and Activities of Daily Living. VBM with DARTEL was used to characterize the gray matter deficits in MCI. Regional amplitude of low-frequency (0.01-0.08 Hz) fluctuations (ALFF) was used to evaluate regional functional alteration in MCI and fractional ALFF(fALFF) in slow 4 (0.027-0.073 Hz) and slow 5 (0.01-0.027 Hz) were also calculated. RESULTS Significantly decreased gray matter volume (GMV) was observed in amnestic MCI group mainly in bilateral prefrontal, left temporal and posterior cingulate cortex. Significant positive correlation was observed between the GMV in left inferior frontal gyrus and MMSE scores. Interestingly, decreased ALFF/fALFF was revealed in MCI group compared to controls mainly in prefrontal, left parietal regions and right fusiform gyrus, while the increased ALFF/fALFF was found in limbic and midbrain. Furthermore, the changes of fALFF in MCI in the slow-5 band were greater than those in the slow-4. No significant correlation was found between the morphometric and functional results. CONCLUSIONS Findings from the study document that wide spread brain volume reduction accompanied with decreased and increased regional function in MCI, while the anatomical and functional changes were independently. Therefore, the combination of structural and functional MRI methods would provide complementary information and together advance our understanding of the pathophysiology underlying the symptoms of MCI.