SPREADING WAVES OF DECREASED DIFFUSION-COEFFICIENT AFTER CORTICAL STIMULATION IN THE RAT-BRAIN

A method is demonstrated for the noninvasive detection and study of sp reading cortical depression. Spreading depression (SD) was elicited in rats by topical application of potassium chloride to the exposed cort ex. The apparent diffusion coefficient (D-app) of water in a region of the cortex, measured using a PFG-NMR spin echo sequence with an obser vation time of 40 ms, declines 35% within 30 s and recovers to the nor mal value within the next 30 s. The region of decreased D-app was show n to be 2 mm in size and to move in the cortex, away from the point of application, with a uniform velocity of 3.3 +/- 0.5 mm/min. The behav ior of the affected region is consistent with other reports of the beh avior of SD as monitored by electrophysiological means. The technique can be implemented on currently available MRI equipment and makes poss ible the noninvasive study of SD in animal models of neurological diso rders, their therapeutic intervention, and possibly the study of SD in humans.