New Paper: Sham Protocols for tDCS

Title: Toward Development of Sham Protocols for High- Definition Transcranial Direct Current Stimulation (HD-tDCS) 

Jessica D. Richardson, Paul Fillmore, Abhishek Datta, Dennis Truong, Marom Bikson, Julius Fridriksson

NeuroRegulation Vol. 1(1):62-72 2014 doi:10.15540/nr.2014.1.1.62

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Abstract : High-definition transcranial direct current stimulation (HD-tDCS) is a noninvasive cortical
stimulation (NICS) technique that, due to the utilization of multi-electrode stimulation, may
enable development of sham conditions characterized by indistinguishable scalp sensations
compared to active conditions, with little or no cortical influence. We sought to contribute to
the development of an optimal sham electrode configuration for HD-tDCS protocols by
gathering ratings of overall sensation reported by participants during different electrode
configurations and current intensities. Twenty healthy participants completed a magnitude
estimation task during which they rated their “overall sensation” in 1-minute intervals during
five 5-minute stimulation conditions. A 5 x 5 (Time x Stimulation condition) analysis of
variance (ANOVA) was conducted to determine if sensation measurements differed over
time, and how this varied by condition. Null hypothesis significance tests and equivalence
tests were conducted to determine which sham conditions were statistically indistinguishable
from the experimental condition. The ANOVA revealed main effects for Time and Stimulation
condition. Planned comparisons, comparing each sham condition to the experimental
condition (4×1 ring configuration, 2 mA), revealed differences in sensation ratings for all but
one condition (Sham 1x1A); no sham conditions were found to be statistically equivalent to
the experimental condition. Our HD-tDCS findings build upon previous NICS reports of
differences in sensation ratings between sham versus experimental conditions when
traditional “ramping down” approaches were used. Alternative multi-electrode configurations
that manipulate electrode placement to shunt current across the scalp warrant further
investigation as valid blinding methods.

Neural Engineering