[1-14C]Octanoate (OCTO) is rapidly extracted from blood and metabolized by brain. Up to 6 min following an intravenous pulse injection the autoradiographic pattern of brain labeling reflects differences in blood flow and energy metabolism. When animals are given OCTO during visual or somatosensory stimulation the autoradiograms reveal differential labeling of activated pathways. Studies can be performed in 7-20 s allowing fast labeling of functional brain anatomy.