Improvement of spatial tactile acuity by transcranial direct current stimulation

Objective: Non-invasive brain stimulation such as transcranial direct current stimulation (tDCS) has been successfully used to induce polarity-specific excitability changes in the brain. However, it is still unknown if anodal tDCS (tDCS_anodal) applied to the primary somatosensory cortex (S1) can lead to behavioral changes in performance of tactile discriminative tasks. Methods: Using an accurate tactile discrimination task (grating orientation task: GOT) we tested the hypothesis that application of 1 mA of tDCS_anodal (current density at the electrodes of 0.04 mA/cm²) over the left S1 can lead to an improved tactile spatial acuity in the contralateral index-finger (IF). Results: Performance in the GOT task with the contralateral IF but not with the ipsilateral IF was enhanced for about 40 min after a 20 min application of tDCS_anodal in the absence of changes with sham stimulation. Conclusions: These results provide the first evidence that tDCS_anodal over S1 improves performance in a complex somatosensory task beyond the period of stimulation. Significance: The ability to induce performance improvement in the somatosensory domain with tDCS applied over S1 could be used to promote functional recovery in patients with diminished tactile perception.