(Medical Xpress)—Pioneering experiments back in 1982 by Tasaki and Iwasa at the NIH revealed that action potentials in neurons are more than just the electrical blips that physiologists readily amplify and record. These so-called "spikes" are in fact multi-modal signalling packages that include mechanical and thermal disturbances propagating down the axon at their own rates. Nobel Laureate Francis Crick published a paper that same year, in which he postulated potential mechanisms that would explain twitching in dendritic spines, adding to an emerging picture of a brain more vibrant and motile than had been previously imagined. More recently, researchers have developed diffusion-based MRI methods, like diffusion tensor imaging (DTI), to trace the trajectories of axons, and perhaps more intriguingly, determine their directional polarity. Working at the EPFL in Switzerland, Denis Le Bihan and his co-workers have been using diffusional MRI in slightly different way. They now appear to be able to directly measure neuronal activity from the subtle movements of membranes, the water within them, and in the extracellular space around them. Their work, just published in PNAS, provides a much needed conceptual shift away from currently established, but typically nebulous, ideas regarding neurovascular coupling of brain activity to blood flow.
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