Modulation of cortical activity after anodal transcranial direct current stimulation of the lower limb motor cortex: A functional MRI study

BACKGROUND AND OBJECTIVES Functional magnetic resonance imaging (fMRI) has shown that transcranial direct current stimulation (tDCS) of the hand motor cortex modulates cortical activity of the healthy human brain. However, few studies have assessed the effects of tDCS on the leg motor cortex. We therefore used fMRI to examine the modulating effects of tDCS on lower limb motor cortex responses. METHODS In this sham-controlled case-control study, 11 subjects were exposed to active anodal (n = 6) or sham (n = 5) stimulation, with the anode being positioned on the leg motor cortex of the right hemisphere. Each tDCS was delivered for 15 minutes at 2 mA, with each subject receiving a total of four stimulatory sessions on consecutive days. Cortical activity was measured before the first and after the fourth session by fMRI, and changes in cortical activity were calculated. RESULTS Anodal tDCS increased activation of the ipsilateral supplementary motor area and lowered the extent of activation of both anterior cingulate gyri, the right middle and superior temporal gyri, the middle and superior frontal gyri, and the primary and secondary somatosensory cortices. CONCLUSIONS Anodal tDCS increased corticospinal excitability of the lower limb motor cortex in healthy subjects, suggesting that multiple brain cortical areas may be associated with leg motor performance via involvement of variable corticocortical connections.