[Default mode network and Alzheimer's disease]

Brain functioning is mainly intrinsic, not primarily reflexive. This is supported by the high energy requirements of the resting brain (20% of all the energy consumed) which only marginally increases with changes in brain activity. Modern neuroimaging and neurophysiological techniques have led to the discovery of the so called brain default mode network (DMN), a constellation of brain regions which support brain activity at rest and whose discharges decrease during task-induced activities. Another characteristic of the DMN are the elevated levels of aerobic glycolysis (Warburg effect), that is, metabolism of glucose to lactic acid in the presence of sufficient levéis of oxygen. In Alzheimer's disease there is amyloid deposition and metabolic disruption at the DMN regions. Changes in connectivity among the different nodes of the DMN and its connections with the hippocampus have been reported. The characteristics of the DMN and its relation to Alzheimer's disease are discussed. This issue is of interest in the pathogenesis and possibly for its usefulness as a biomarker of the disease.