A novel tDCS sham approach based on model-driven controlled shunting

Area of Science:

• Neuroscience
• Neurology
• Psychiatry

Background:

• Transcranial direct current stimulation (tDCS) is a promising non-invasive brain stimulation technique for neurological and psychiatric disorders.
• Current placebo (sham) protocols for tDCS have significant limitations in blinding, particularly for participants who have undergone previous tDCS sessions.

Purpose of the Study:

• To develop and evaluate a novel "active" sham tDCS protocol (ActiSham) designed to improve participant blinding in tDCS studies.
• To create a sham condition that replicates the scalp sensations of real tDCS without inducing cortical excitability changes.

Main Methods:

• A model-based multielectrode technique was employed to optimize current delivery for both real and sham tDCS conditions.
• Participants rated scalp sensations (presence, intensity, localization) using a questionnaire.
• Blinding was assessed by comparing participant discrimination between traditional (Bifocal-tDCS) and novel (Multifocal-tDCS) stimulation methods and their respective sham conditions.
• Corticospinal excitability was measured using Motor Evoked Potentials (MEPs) via Transcranial Magnetic Stimulation (TMS) and electromyography (EMG).

Main Results:

• ActiSham induced scalp sensations (intensity, localization) highly similar to real Multifocal-tDCS.
• Traditional Bifocal-tDCS sham was perceived as more painful and annoying than its active counterpart, with differing sensation localization.
• MEP amplitudes were significantly affected by Bifocal-Sham stimulation, indicating a difference in corticospinal excitability.

Conclusions:

• ActiSham provides superior blinding compared to traditional sham tDCS protocols.
• The ActiSham protocol effectively mimics real tDCS scalp sensations without altering corticospinal excitability, thus enhancing the reliability of tDCS clinical trials.