Mitigating cutaneous sensation differences during tDCS: comparing sham versus low intensity control conditions.

BACKGROUND Cutaneous sensations at electrode sites during the administration of direct current brain stimulation may inadvertently influence participants' subjective experience and task performance. OBJECTIVE The present study evaluated the utility of a methodological variation that substitutes sham administration with very low intensity (0.5 mA) current delivery. METHODS We used a 4 × 1 high-definition ring electrode transcranial direct current (HD-tDCS) system to target the left dorsolateral prefrontal cortex (Brodmann's Area 9). Four stimulation conditions were compared in a repeated-measures design: sham 2.0 mA and 0.5 mA intensity, versus active 2.0 mA and 0.5 mA intensity. During stimulation participants performed a cognitive interference task that activates the cingulo-frontal-parietal network, and periodically provided perceived sensation ratings. RESULTS We demonstrate that a relatively low intensity control condition attenuates otherwise large differences in perceived sensation between active and sham conditions. Critically, behavioral task differences maintained between the two active conditions. CONCLUSION A low intensity control stimulation condition may prove a viable methodological alternative to conventional sham techniques used in repeated-measures designs, though important limitations are discussed.