Participants
skin abnormalities, psychiatric, substance abuse, pain
CHRONIC PAIN, DISEASES
The study was conducted in accordance with the Declaration of Helsinki and approved by the ethics committee at LMU Munich (18–328). All subjects gave written informed consent. Healthy participants were recruited through university campus and social media advertisements between August 2018 and February 2019. Inclusion criteria were as follows: (1) adult with sufficient knowledge of German; (2) no psychiatric, neurological, or internal diseases, substance abuse, or chronic pain; (3) no contraindications for cranial t-DCS (active implants (e.g., pacemakers), cranial bone gaps, bone plates or screws, or local skin abnormalities); (4) not pregnant or breast-feeding; (5) no acute/chronic pain or pain medication within 2 days prior to participation.Expected effect sizes were unknown, especially for the effect of t-DCS on endogenous pain modulation. We therefore based the sample size on our earlier work showing the influence of different interventions on spinal nociception as quantified by the RIII reflex (