Regional modulation of BOLD MRI responses to human sensorimotor activationby transcranial direct current stimulation

Blood oxygenation level dependent (BOLD) MRI was used to monitor modulation s of human sensorimotor activity by prior transcranial direct current stimu lation (tDCS), Activation maps for a right hand sequential finger oppositio n task were obtained for six subjects before as well as 0-5 min and 15-20 m in after a 5-min period of 1 mA cathodal and, in a separate session, anodal tDCS of the left-hemispheric motor cortex, Cathodal tDCS resulted in a glo bal decrease of the mean number of activated pixels by 38% (P < 0.01) 0-5 m in after stimulation, which reduced to 28% (P < 0.05) 15-20 min after stimu lation, A region-of-interest analysis revealed a 57% decrease of activated pixels (P < 0.001) in the supplementary motor area, but no change in the ha nd area of the primary motor cortex. Anodal tDCS yielded a nonsignificant 5 % increase of activated pixels with no regional differences, These findings support the view that reduced neuroaxonal excitability after cathodal tDCS causes reduced brain activity, However, rather than affecting the primary sensorimotor input of an active task, the process appears to dampen those r esponses that rely on cortico-cortical connections and related processing. Magn Reson Med 45: 196-201, 2001. (C) 2001 Wiley-Liss, Inc.