fMRI GOES WITH THE FLOW
This week, in a technical tour de force, Nikos Logothetis and colleagues at the Max Planck Institute for Biological Cybernetics at Tübingen in Germany report that functional magnetic resonance imaging (fMRI) shows brain cells (neurons) receiving and processing electrical signals (Nature, Vol. 412, No. 6843, 12 Jul 2001). Previously, no one knew whether the bright areas in fMRI images were due to this or to some other aspect of neuron function, such as their production of electrical pulses when stimulated by other neurons.
Logothetis’ team prove for the first time that what the fMRI technique really measures are changes to the flow of blood in the brain. When a group of neurons in the brain becomes active, it needs more blood, and so it generates a signal in an fMRI scan.
Using a completely new technique, Logothetis and colleagues measured the fMRI signal in the primary visual cortex of monkeys at the same time as the electrical activity of the neurons. They found that the fMRI signal was most strongly related to the input and processing of signals, rather than the production of output pulses. This, they say, makes sense: processing inputs is the most energy-consuming part of a neuron’s job, and so needs more fuel. This fuel is glucose, burnt up by oxygen — both of which are carried in the bloodstream.
In an accompanying News and Views article Marcus E. Raichle of the Washington University Medical Center in St Louis describes the work as "a major step forward" that "portends even more exciting advances in the future".
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(C) Nature press release.
Message posted by: Trevor M. D'Souza
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