This type of water diffusion is thought to reflect the activity of the cells, but crucially, it seems it provides a more direct and quicker measure of brain activity than conventional methods.
The majority of fMRI studies use a measure of how oxygen-rich certain areas of the brain are, as it is well known that more active areas take more oxygen from the blood.
One disadvantage, is that this Brain Oxygen Level Dependent (BOLD) measure is relatively slow. It only seems to kick in 1-2 seconds after a brain area has been active and peaks up to 5 seconds later.
The new method from Le Bihan’s team has the potential to improve this process but there are still many unanswered questions, including exactly how the measure of water diffusion relates to the known activities of single neurons or synapses.