2 research outputs found
The time course of ineffective sham blinding during low-intensity (1mA) transcranial direct current stimulation
Studies using transcranial direct current stimulation (tDCS) typically compare an active protocol relative to a shorter sham (placebo) protocol. Both protocols are presumed to be perceptually identical on the scalp, and thus represent an effective method of delivering doubleâblinded experimental designs. However, participants often show aboveâchance accuracy when asked which condition involved active/sham retrospectively. We assessed the time course of shamâblinding during active and sham tDCS. We predicted that participants would be aware that the current is switched on for longer in the active versus sham protocol. 32 adults were tested in a preâregistered, doubleâblinded, withinâsubjects design. A forcedâchoice reaction time task was undertaken before, during and after active (10min 1mA) and sham (20s 1mA) tDCS. The anode was placed over the left primary motor cortex (C3) to target the right hand, and the cathode on the right forehead. Two probe questions were asked every 30s: âIs the stimulation on? âand âHow sure are you?â. Distinct periods of nonâoverlapping confidence intervals were identified between conditions, totalling 5min (57.1% of the total difference in stimulation time). These began immediately after sham rampâdown and lasted until the active protocol had ended. We therefore show a failure of placebo control during 1mA tDCS. These results highlight the need to develop more effective methods of shamâblinding during transcranial electrical stimulation protocols, even when delivered at lowâintensity current strengths