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Proc Natl Acad Sci U S A. 2006 May 23;103(21):8263-8. Epub 2006 May 15.

Direct and fast detection of neuronal activation in the human brain with diffusion MRI.

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Human Brain Research Center, Kyoto University Graduate School of Medicine, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.


Using MRI, we found that a slowly diffusing water pool was expanding (1.7 +/- 0.3%) upon activation on the human visual cortex at the detriment of a faster diffusing pool. The time course of this water phase transition preceded the activation-triggered vascular response detected by usual functional MRI by several seconds. The observed changes in water diffusion likely reflect early biophysical events that take place in the activated cells, such as cell swelling and membrane expansion. Although the exact mechanisms remain to clarify, access to such an early and direct physiological marker of cortical activation with MRI will provide opportunities for functional neuroimaging of the human brain.

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