Background
Transcranial
direct current stimulation (tDCS) has been investigate
d as therapeutic intervention in various psychiatric an
d neurologic
disor
ders. As placebo responses to technical interventions may be pronounce
d in many clinical con
ditions, it is important to thoroughly
develop placebo con
ditions which meet the requirements for application in ran
domize
d double-blin
d controlle
d trials.
Objective
The two-part experiment reported here aims at evaluating a new sham tDCS condition in healthy subjects and device operators. Sham or active tDCS is delivered after entering a number code to the device and allows blinding of the operator before and during tDCS. The sham mode has no short stimulation period.
Methods
The experimental sequence was as follows: 1) Evaluation of successful blinding by comparing placebo to active stimulation at prefrontal sites based on the rating of subjects undergoing tDCS, 2) Evaluation of successful blinding by comparing placebo to active stimulation at prefrontal sites based on the operator/observer ratings.
Results
Subjects were not able to distinguish between active and sham tDCS for prefrontal stimulation. Overall there was no relevant discomfort and tDCS was well tolerated. Operators/observers were able to identify sham stimulation based on skin reddening after active, but not after sham tDCS.
Conclusions
The tDCS sham condition investigated here may be suitable for placebo-controlled trials keeping subjects blind to treatment conditions. However, operators can easily be aware of the condition applied and they should not get involved in rating outcome measures during the course of high standard placebo-controlled trials.
