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.

The analysis will involve assessing self-report measures, fMRI signatures, and autonomic reactivity to cues and task stimuli, similar to Experiment 1. The analysis will also explore the mediating role of interpersonal response (IPIX scores) and participants' initial responses to placebo.

The researchers plan to control for sex, age, and experimenter effects in all analyses and will test for potential biological sex differences, disaggregating the data if necessary. MRI data will not be acquired during tDCS to avoid artifacts, and the study is not designed to directly compare placebo tDCS with verum tDCS. However, it aims to investigate interpersonal and suggestion-related contributions to open-label treatment responses, providing a foundation for future studies on tDCS and its interactions with placebo effects.

• No self-reported current or history of depression, bipolar disorder, or other psychiatric diagnosis
• No self-reported current seizure disorder (i.e., seizure within past 10 years), or history of stroke or other major neurological diagnosis that can cause cognitive impairment
• No self-reported current chronic pain, or acute pain within three months of the study period
• No current migraine disorder (i.e., 15 headache days or more in 1 month)
• No use of central nervous system-effective medication or other medication for neurological/psychiatric treatment
• No self-reported substance abuse within the last six months
• No contraindication to MRI or tDCS (e.g., pregnancy, claustrophobia, pacemakers, ear/cochlear implants, shrapnel injuries, clips, or other ferromagnetic/electrical objects/devices, diagnosed brain abnormality such as tumor, or skin lesions on the scalp.)
• No contraindications for induced pain (e.g., no heart disease, high blood pressure, heart surgery, heart problems of any kind, severe asthma, respiratory problems of any kind, fibromyalgia, Raynaud's Syndrome or Disease, chronic pain, diabetes)
• Participants must be capable of performing experimental tasks (e.g., are able to read), are fluent or native speakers of English
• Participants must be able to tolerate the maximum level of thermal pain stimuli (for thermal stimuli)