A close link between metabolic activity and functional connectivity in the resting human brain

Abstract

Default-mode network (DMN) functional connectivity and its task-dependent downregulation have attracted a lot of attention in the field of neuroscience. Nevertheless, the exact underlying mechanisms of DMN functional connectivity, or more specifically, the blood oxygen level-dependent (BOLD) signal, are still not completely understood. To investigate more directly the association between local glucose consumption, local glutamatergic neurotransmission and DMN functional connectivity during rest, the present study combined for the first time 2-Deoxy-2-[18F]fluoroglucose positron emission tomography (FDG-PET), proton magnetic resonance spectroscopy (1H-MRS), and resting-state functional magnetic resonance imaging (rs-fMRI). Seed-based correlation analyses, using a key region of the DMN i.e. the dorsal posterior cingulate cortex as seed, revealed overall striking spatial similarities between fluctuations in FDG-uptake and the BOLD signal. More specifically, a conjunction analysis across both modalities showed that DMN areas as the inferior parietal lobe, angular gyrus, precuneus, middle and medial frontal gyrus were positively correlated with the dorsal posterior cingulate cortex. Furthermore, we could demonstrate that local glucose consumption in the medial frontal gyrus, posterior cingulate cortex and left angular gyrus was associated with functional connectivity within the DMN. We did not find a relationship between glutamatergic neurotransmission and functional connectivity. In line with very recent findings, our results provide further evidence for a close association between local metabolic activity and functional connectivity and enable further insights towards a better understanding of the underlying mechanisms of the BOLD signal.

Gray Matter Hypertrophy and Thickening with Obstructive Sleep Apnea in Middle-aged and Older Adults

“…In addition, our results showed that hypoxemia was associated with core constituents of the default mode network, namely the parietal and posterior cingulate regions of the cortex. The metabolic activity of these highly connected regions fluctuates together (46) and their elevated oxygen demand could make them more vulnerable to hypoxemia (47). Finally, we found that amygdala volume was linked to respiratory disturbances, which is consistent with its altered activity during a respiratory challenge in OSA subjects (48).…”

Structural Plasticity, Effectual Connectivity, and Memory in Cortex

“…Recall that we have introduced “effectual connectivity” as a measure of memory related synaptic connectivity (Figure 2C ) that shares with other definitions of connectivity (such as anatomical and potential connectivity) the idea that any “connectivity” measure should correspond to the chance of finding a connection element (such as an actual or potential synapse) between two cells. By contrast, in brain imaging and connectome analysis (Friston, 1994 ; Sporns, 2007 ) the term “connectivity” has a more heterogeneous meaning ranging from patterns of synaptic connections (anatomical connectivity) and correlations between neural activity (functional connectivity) to causal interactions between brain areas. The latter is also referred to as “effective connectivity” although usually measured in information theoretic terms (bits) such as delayed mutual information or transfer entropy (Schreiber, 2000 ).…”

Evaluation of the default-mode network by quantitative 15O-PET: comparative study between cerebral blood flow and oxygen consumption

“…In this study, we attempted to estimate the functional correlations in the DMN by means of quantitative 15 O-labeled gases and water PET, and to compare the contribution of CBF and CMRO 2 to the DMN. While a similar study has been conducted previously using FDG-PET [ 5 ], there is still no report of analysis of the CBF and CMRO 2 to identify DMN correlations. The purpose of this study was to evaluate the functional correlations in the DMN by means of quantitative 15 O-labeled gases and water PET, and to compare the contribution of the CBF and CMRO 2 to the DMN.…”