Diffusion fMRI (DfMRI) allows to monitor brain function without BOLD vascular confounding effects. Infusion in the rat brain thalamus central median nucleus (CM) of a cell swelling inducer/blocker resulted in ADC changes confirming DfMRI sensitivity to local cell size status. ADC changes closely reflected local functional neuronal status, as evidenced from LFP recordings and electrical current thresholds required to wake-up the animals. They were also observed in remote locations connected with CM. Those results support that neural swelling is an important mechanism underlying DfMRI, and that cell size variations in neuronal networks are an important feature associated with their activity.