Surface EEG-Transcranial Direct Current Stimulation (tDCS) Closed-Loop System

Conventional transcranial direct current stimulation (tDCS) protocols rely on applying electrical current at a fixed intensity and duration without using surrogate markers to direct the interventions. This has led to some mixed results; especially because tDCS induced effects may vary depending on the ongoing level of brain activity. Therefore, the objective of this preliminary study was to assess the feasibility of an EEG-triggered tDCS system based on EEG online analysis of its frequency bands. Six healthy volunteers were randomized to participate in a double-blind sham-controlled crossover design to receive a single session of 10 min 2 mA cathodal and sham tDCS. tDCS trigger controller was based upon an algorithm designed to detect an increase in the relative beta power of more than 200%, accompanied by a decrease of 50% or more in the relative alpha power, based on baseline EEG recordings. EEG-tDCS closed-loop-system was able to detect the predefined EEG magnitude deviation and successfully triggered the stimulation in all participants. This preliminary study represents a proof-of-concept for the development of an EEG-tDCS closed-loop system in humans. We discuss and review here different methods of closed loop system that can be considered and potential clinical applications of such system.
Authors are grateful to Paula Faria, Camila Cosmo and Letizzia Dall' agnol for their help in the previous versions of this manuscript. This study was supported by Center for Integration of Medicine and Innovative Technology (CIMIT). Felipe Fregni is supported by a research grant funded by NIH (5R01HD082302-02). Jorge Leite (SFRH/BPD/86027/2012) and Sandra Carvalho (IF/00091/2015) are supported by the Portuguese Foundation for Science and Technology (FCT) and European Union (FSE-POPH). Jorge Leite and Sandra Carvalho are members of CIPSi, supported by the Portuguese Foundation for Science and Technology and the Portuguese Ministry of Science, Technology and Higher Education through national funds and cofinanced by FEDER through COMPETE2020 under the PT2020 Partnership Agreement (POCI-01-0145-FEDER-007653 and P2020-PTDC/MHC-PCN/3950/2014). Leon Morales-Quezada received funding support from an Institutional National Research Service Award from the National Center for Complementary and Integrative Health grant T32AT000051, the Ryoichi Sasakawa Fellowship Fund, and by the Program in Placebo Studies at Beth Israel Deaconess Medical Center. Aurore Thibaut is supported by the Wallonie-Bruxelles International (WBI), the Leon Fredericq Foundation and the Belgian American Educational Foundation.