Direct current stimulation over the human sensorimotor cortex modulates the brain's hemodynamic response to tactile stimulation

<jats:title>Abstract</jats:title><jats:p>Tactile stimuli produce afferent signals that activate specific regions of the cerebral cortex. Noninvasive transcranial direct current stimulation (<jats:styled-content style="fixed-case">tDCS</jats:styled-content>) effectively modulates cortical excitability. We therefore hypothesised that a single session of <jats:styled-content style="fixed-case">tDCS</jats:styled-content> targeting the sensory cortices would alter the cortical response to tactile stimuli. This hypothesis was tested with a block‐design functional magnetic resonance imaging protocol designed to quantify the blood oxygen level‐dependent response to controlled sinusoidal pressure stimulation applied to the right foot sole, as compared with rest, in 16 healthy young adults. Following sham <jats:styled-content style="fixed-case">tDCS</jats:styled-content>, right foot sole stimulation was associated with activation bilaterally within the precentral cortex, postcentral cortex, middle and superior frontal gyri, temporal lobe (subgyral) and cingulate gyrus. Activation was also observed in the left insula, middle temporal lobe, superior parietal lobule, supramarginal gyrus and thalamus, as well as the right inferior parietal lobule and claustrum (false discovery rate corrected, <jats:italic>P </jats:italic>< 0.05). To explore the regional effects of <jats:styled-content style="fixed-case">tDCS</jats:styled-content>, brain regions related to somatosensory processing, and cortical areas underneath each <jats:styled-content style="fixed-case">tDCS</jats:styled-content> electrode, were chosen as regions of interest. Real <jats:styled-content style="fixed-case">tDCS</jats:styled-content>, as compared with sham <jats:styled-content style="fixed-case">tDCS</jats:styled-content>, increased the percent signal change associated with foot stimulation relative to rest in the left posterior paracentral lobule. These results indicate that <jats:styled-content style="fixed-case">tDCS</jats:styled-content> acutely modulated the cortical responsiveness to controlled foot pressure stimuli in healthy adults. Further study is warranted, in both healthy individuals and patients with sensory impairments, to link <jats:styled-content style="fixed-case">tDCS</jats:styled-content>‐induced modulation of the cortical response to tactile stimuli with changes in somatosensory perception.</jats:p>