A research team at the CEA’s Frédéric Joliot Hospital Service, jointly with a team at the University of Kyoto, has recently demonstrated that neurone activation can be directly and rapidly detected by measuring the movements of water molecules in the brain. This work was published in PNAS dated 23 May 2006
The method used was water diffusion magnetic resonance imaging (dMRI). It is based on the fact that molecules make random movements in all spatial directions, and that the structure of neighbouring tissues modifies those movements. Water diffusion MRI is a powerful tool for measuring the movements of water molecules at the microscopic scale, thereby visualising the fine architecture of the neurone tissue and its variations.
Measurements made using this method have shown that brain activation slightly lowers the coefficient of diffusion of water molecules due to a slight swelling of activated cells.
-Diffusion MRI thus directly reflects the modifications of neurone activity.
-It allows a more direct measurement than the classical imaging methods such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), which use the fact that blood flow increases in activated brain regions.
-It makes it possible to investigate tissue structure at the microscopic scale, much finer than the millimetric scale of MRI.
-It is much faster, the fall in the water diffusion coefficient appearing some seconds before the activation can be detected by functional MRI.
Water diffusion MRI is therefore faster, finer and more closely linked to neurone activation. It offers an interesting alternative to functional imaging of the brain.
It remains to be determined whether these changes in water diffusion behaviour during activation constitute an active component of the activation process that has been favoured by evolution. Thus water, the molecule of life, may also be the ‘molecule of the mind’.
The CEA’s NeuroSpin centre, which will be opening this year, will help to explore these issues by exploiting the potential of very high-field magnetic resonance imaging.
