Transcranial Direct Current Stimulation and Modulation of Affect and Pain

This double-blind randomized crossover study aims to examine the effects of left primary motor cortex (M1) tDCS on evoked thermal pain perception, pain-related decision making, and placebo effects by manipulated pain and monetary offers accepted by others. The investigators plan to collect data for up to 50 participants who undergo four separate sessions: an initial pain calibration session and three experimental sessions with either anodal, cathodal, or sham tDCS. Each session includes pain testing before and after a single tDCS protocol (either anodal, cathodal, or sham), a pain-monetary decision-making task, and social placebo pain tests. All tasks following tDCS will take place inside the MR scanner. The investigators hypothesize that anodal M1 tDCS will decrease pain ratings, and that cathodal tDCS will increase them, both relative to the sham condition. The investigators will also examine the effects of M1 tDCS on social decision-making to examine whether it affects participants' valuation of pain and their altruistic behavior, as well as how these same factors impact pain sensation in the placebo task. The investigators hypothesize that participants will behave hyperaltruistically during the decision-making task, and that the same factors that influence choice will also impact pain perception in the same context.