Food-Related Inhibitory Control and Transcranial Direct Current Stimulation: Bilateral Prefrontal or Excitatory Right-Hemispheric Stimulation?

OBJECTIVES: Brain stimulation treatments for eating disorders are rapidly emerging as neurobiologically driven interventions, including low-threshold electric stimulation with transcranial direct current stimulation (tDCS). Previous research has targeted inhibitory control and food craving with tDCS with different electrode placements-targeting the right prefrontal cortex (PFC) either unilaterally, or bilaterally with opposite polarity at the left and right PFC. There is, however, no systematic evidence showing whether unilateral and bilateral tDCS are equally effective, or whether (concurrent) cathodal tDCS might show detrimental effects.

MATERIALS AND METHODS: We systematically manipulated electrode placement and randomized healthy participants after at least three hours of fasting in four tDCS groups (bilateral, unilateral left/right, and sham). We analyzed food- and non-food-related false alarms in a stop-signal task before, during, and after tDCS. We further quantified participants' global stop-signal reaction time (SSRT) and state food craving. All placements were modeled computationally.

RESULTS: Our main analyses did not show an effect of tDCS. A post hoc contrast indicated opposite trajectories of SSRT during unilateral cathodal tDCS (impaired) and anodal tDCS (improved), but with immediate recovery after stimulation. Computational modeling indicated that electric fields in inferior frontal regions were denser for unilateral tDCS than for bilateral tDCS.

DISCUSSION: Possible effects of tDCS are subtle and transient. For more robust results, individual targeting might be considered. Reaching inferior frontal regions might be crucial for modulating inhibitory control. The neural and behavioral consequences of bilateral vs unilateral tDCS should be critically considered in future research.