RESUMO
Objective To explore the activity of brain default mode network (DMN) in patients with mild Alzheimer's disease (AD) by resting state functional magnetic resonance imaging (fMRI) and investigate its possible neural mechanism. Methods Twenty-four patients with mild AD,admitted to our hospital from January 2009 to June 2010,and 25 normal controls (NCs) were chosen in this study.All subjects were examined by Mini Mental State Examination (MMSE), Mattis Dementia Rating Scale (DRS) and fMRI.Resting-state whole brain data were analyzed by amplitude of low frequency fluctuation (ALFF) with two-sample t test and the brain regions in mild AD patients having significantly different ALFF comparing to NCs were observed. Results As compared with that in NCs,the memory function in mild AD patients was seriously impaired (P＜0.05).As compared with NCs,mild AD patients showed significantly decreased ALFF in the posterior cingulate cortex,ventral medial prefrontal cortex and dorsal medial prefrontal cortex, which were closely relevant to the memory (P＜0.05). Conclusion AD patients show significantly decreased active intensity of some DMN nodes that relate to memory in resting state; DMN abnormalities play an important role in early memory impairment of AD patients.
RESUMO
<p><b>BACKGROUND</b>Previous studies have shown that the functional brain activity in the resting state is impaired in Alzheimer's disease (AD) patients. However, most studies focused on the relationship between different brain areas, rather than the amplitude or strength of the regional brain activity. The purpose of this study was to explore the functional brain changes in AD patients by measuring the amplitude of the blood oxygenation level dependent (BOLD) functional MRI (fMRI) signals.</p><p><b>METHODS</b>Twenty mild AD patients and twenty healthy elderly subjects participated in the fMRI scan. The amplitude of low frequency fluctuation (ALFF) was calculated using REST software.</p><p><b>RESULTS</b>Compared with the healthy elderly subjects, the mild AD patients showed decreased ALFF in the right posterior cingulate cortex, right ventral medial prefrontal cortex, and in the bilateral dorsal medial prefrontal cortex. No brain region with increased ALFF was found in the AD group compared with the control group.</p><p><b>CONCLUSIONS</b>The reduced activity in the posterior cingulate cortex and medial prefrontal cortex observed in the present study suggest that the functional abnormalities of those areas are at an early stage of AD. The ALFF analysis may provide a useful tool in fMRI study of AD.</p>