Anodal transcranial direct current stimulation (tDCS) of primary somatosensory cortex (S1) has been shown to enhance tactile spatial acuity but there is little information as to the underlying neuronal mechanisms. We examined vibrotactile perception on the distal phalanx of the middle finger before, during and after S1 tDCS (anodal, a; cathodal, c; sham, s). The experiments tested our shift-gain hypothesis which predicted that a-tDCS would decrease vibrotactile detection and discrimination thresholds (leftward shift of the stimulus-response function with increased gain/slope) relative to s-tDCS, while c-tDCS would have the opposite effects (relative to s-tDCS). The results showed that weak, a-tDCS (1 mA, 20 min) led to a reduction in both vibrotactile detection and discrimination thresholds to 73 - 76% of baseline during the application of the stimulation in subjects categorized as responders. These effects persisted after the end of a-tDCS, but were absent 30 min later. Most, but not all, subjects showed a decrease in threshold (8/12 for detection; 9/12 for discrimination). Inter-subject variability was explained by a ceiling effect in the discrimination task. Cathodal tDCS had no significant effect on either detection or discrimination threshold. Taken together, our results supported our shift-gain hypothesis for a-tDCS but not c-tDCS.
- Transcranial direct current stimulation
- SOMATOSENSORY CORTEX
- CORTICAL PLASTICITY
- Copyright © 2015, Journal of Neurophysiology