A magnetic resonance (MR) imaging brain mapping method was used to localize an activated volume of brain tissue in chloralose-anesthetized rats during electrical stimulation of the forepaw. Physiologically-induced changes are characterized by alterations of the magnetic properties of blood as determined by the oxygenation state of hemoglobin. Stimulation of the left forepaw led to an increase in MR signal intensity of the contralateral frontal and parietal cortices, which corresponded to forelimb motor and somatosensory areas. The activation was contiguous in coronal planes between +5 and +2 mm anterior to the bregma, and its volume was calculated to be 20-30 mm3. Each activated region was revealed using a paired t-test statistical analysis method and the activated volume was calculated from regions exposed by thresholding at p < 0.005. Physiologically-induced fractional signal changes, delta S/S, in the motor and somatosensory areas were 0.06 +/- 0.04 and 0.17 +/- 0.06, respectively.