Proc. Natl Acad. Sci. USA 106, 18390–18395 (2009)

Functional magnetic resonance imaging (fMRI) maps brain activity by measuring changes in local blood flow and oxygen levels. Neuroscientists have long thought that most changes in these signals were due to neurons becoming active and requiring more oxygen.

A study in October by Aniruddha Das and his colleagues at Columbia University in New York challenged this idea. They used intrinsic signal optical imaging, a technique similar to fMRI, to measure changes in blood volume and oxygenation in the brains of two macaques while the monkeys performed a visual task. The researchers simultaneously recorded local neuronal activity.

They showed that the initial part of the imaging signal is marked by changes in blood volume, not in blood oxygen levels. The authors concluded that blood volume is more tightly linked to neuronal activity and is thus a better measure to use in brain imaging. They say that boosting blood volume is the brain's way of 'anticipating' neuronal activity to meet the cells' impending need for more oxygen.