its activity, says scientist
Scans that record the brain performing certain functions may be misinterpreted if they neglect the neurotransmitter activity taking place when the brain is at rest, a study by a Yale researcher concludes.
"There is an assumption made in the use of PET scans and functional magnetic resonance imaging (fMRI) that the brain works only when you give it a task to do," says Robert Shulman, Sterling Professor of Molecular Biophysics and Biochemistry. "What I show here is that the brain works all the time. The brain at rest is doing the same sort of neuronal firing as it does when stimulated by a task. Brain activity slightly increases when a task is performed and those increases are generally assumed to measure activity."
In a study published in the January issue of The American Journal of Psychiatry, Schulman explains that if the brain's signal at rest is 100, once it undertakes a task the activity level rises by a small amount -- say, from 100 to 101. "When we look at it pixel by pixel and subtract the activity of the brain at rest from that during a task as is presently done, you would get this increment of one in certain areas of the brain," he says.
In his article, Shulman reviewed recent research done with colleagues at Yale which enabled imaging results to be interpreted in terms of a specific neuronal activity, the release of the neurotransmitter glutamate. The glutamate fluxes showed that the resting brain, in the absence of explicit external activity, was actively transmitting information.
Shulman says that his study offers hope of bridging two major divisions in psychiatry -- those scientists who have a psychiatric view of the mind and those with a neuroscientific view.
"The ability to quantitate neurotransmitter activity both in the presence and absence of stimulation highlights and provides a criticism of the psychological assumptions behind the standard interpretation of images," he says. "Instead of allowing resting activity to be disregarded, as it is when the brain is considered as a set of localized computers, it shows that resting activity is required for function and suggests ways in which more holistic theories of mind are supported by the imaging experiments."
-- By Jacqueline Weaver
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