Functional Connectivity of the Posterior Cingulate in Mild Cognitive Impairment and Alzheimer's Disease
Fields, Julie A.
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Mild cognitive impairment (MCI) has been implicated as an early stage of Alzheimer's disease (AD) by some, while others argue this is not necessarily the case. While controversy around this issue continues, it is undisputed that MCI is a risk factor for AD. Finding a biomarker of AD would lead to early intervention that could potentially slow the progression of the disease and guide further research towards targets for a cure. Recent findings suggest that reduced connectivity between the posterior cingulate cortex (PCC) and associated brain regions may make an important contribution in this regard, as changes in the PCC/precuneus and entorhinal cortex are implicated as early biomarkers for AD. The current study used functional connectivity magnetic resonance imaging (fcMRI) to examine the posterior cingulate's connectivity with other brain regions in subjects with AD (n=10), MCI (n=9), and age-matched elderly normal controls (NC; n=10). As hypothesized, results revealed that subjects with AD showed decreased connectivity in regions of the frontal lobe, temporal lobe, and cingulate gyrus when compared to NC, and in the frontal and temporal gyri when compared to MCI. When MCI was compared to NC, decreased connectivity was observed in the cingulate gyrus and parahippocampal gyrus while increased connectivity was found in prefrontal cortex and cerebellar regions. The latter finding of increased connectivity in the MCI group in the prefrontal cortex and cerebellum was interpreted as evidence of compensatory recruitment of alternate brain regions in the face of deficient processing in parahippocampal regions in the early stage of disease. It is possible that the connectivity between the PCC and cerebello-frontal structures in MCI may be helping to sustain episodic memory and executive functions that deteriorate in AD. This study showed that fcMRI may be sensitive enough to detect subtle changes in brain structure, and while it is premature to say that fcMRI might prove to be a biomarker of AD, these preliminary findings are encouraging and may serve as an impetus for further research.