Interactions Between Placebo Effects and Mindful Awareness State

This study aims to investigate the effects of interpersonally induced placebo effects and a mindful awareness induction on negative affect. The study will involve 120 participants recruited from the Dartmouth College community, aged between 18 and 55, with an equal distribution of 60 males and 60 females. Participants will be assigned to the role of "patient" and will undergo fMRI scanning and physiological recording while performing the Multimodal Negative Affect Task (MNAT).

The study design follows a 2 x 2 factorial design, examining the effects of interpersonally induced placebo effects (sham tDCS vs. control) and a mindful awareness induction (mindful state vs. control), as well as their interaction. A follow-up transfer assessment (1 week follow-up, session 2) will be conducted to examine the effects of the mindful state on verum motor tDCS stimulation. The participants will be randomly assigned to either the Mindfulness group or the No-mindfulness group, with 60 participants in each group and two sessions for each participant.

In session 1, participants in the Mindfulness group will undergo a Mindful State Induction procedure aimed at promoting safety, relaxation, and receptivity. This induction procedure consists of two stages. In the first stage, participants will receive education about the brain's connection to and regulation of the body, emphasizing the endogenous brain regulatory capacities. The second stage involves a hypnotic induction of a relaxed state of receptivity using the Stanford Hypnotic Induction Profile (HIP) test of hypnotizability. This stage includes reclining the participant, suggesting that they are always in control, and making somatic suggestions to deepen the receptive state. A guided body scan, derived from mindfulness meditation, will further deepen the induced receptive state.

In contrast, participants in the No-mindfulness group will go through comparable stages but with different instructions. In the first stage, they will receive education about pain and affect as protective processes of the body. In the second stage, they will be seated in an upright, alert posture and receive suggestions to focus on the task and suppress attention to the body.

During the transfer test, conducted in a second fMRI session one week later, we will assess transfer to verum, open-label motor-cortex tDCS in an off-on-off design (both groups), with no explicit mindful state induction. No MRI data will be acquired during tDCS to avoid MR artifacts. We will also assess spontaneous use of strategies, including self-regulation and spontaneous adoption of states of mindful acceptance, and test whether these differ across groups.