MRI-tDCS Criticism Study

The Impact of tDCS on Substrates of Emotion Processing Using fMRI in Healthy Volunteers

This experimental study investigated how MRI-compatible transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (DLPFC) modulates neural and cognitive responses to social criticism in healthy volunteers.

Participants underwent two MRI sessions - one with active and one with sham stimulation - in a randomized, double-blind, cross-over design.

During stimulation, they completed resting-state and task-based fMRI scans including exposure to critical, neutral, and praising auditory comments, followed by behavioral and self-report measures of rumination, mood, and implicit self-esteem.

This study aimed to examine the effects of non-invasive brain stimulation on emotional and self-referential processing. Healthy right-handed female participants completed two identical MRI sessions separated by at least 48 hours and a maximum of 2 weeks. The localization of the left dorsolateral prefrontal cortex (DLPFC) was determined during the first session. Anatomical data were first acquired using a high-resolution T1-weighted structural scan. Participants were then briefly removed from the MRI scanner to define the stimulation target using two complementary methods: (1) the standard scalp position F3 according to the 10-20 international EEG system, and (2) an individualized neuronavigation procedure targeting the mid-center of the left middle frontal gyrus (Brodmann areas 9/46) based on each participant's structural MRI. For the actual tDCS sessions, only the neuronavigation-derived DLPFC target was used for electrode placement.

In each session, participants received either active or sham MRI-compatible tDCS (1.5 mA, 20 minutes) applied over the left DLPFC with the cathode placed over the contralateral supra-orbital region. The order of stimulation (active vs. sham) was randomized and counterbalanced. The location of the DLPFC electrode placement was based During fMRI, participants completed multiple scans: a T1 structural scan, resting-state sequences (pre-, during-, and post-stimulation), resting-state sequences (pre-, during-, and post-auditory criticism task with blocks of critical, neutral, and praising comments), and an arterial spin labeling (ASL) perfusion sequence.

Self-report measures of state rumination (Momentary Ruminative Self-focus Inventory, MRSI) and mood (visual analogue scales) were collected before and after stimulation and after the criticism paradigm. An implicit self-esteem task (Implicit Relational Assessment Procedure, IRAP) followed the MRI session. Trait questionnaires and a blood sample for DNA (e.g. 5-HTTLPR) analysis were collected at baseline only.

The primary goal was to assess whether active tDCS modulates neural and behavioral markers of self-referential processing and emotional regulation compared with sham stimulation.

No serious adverse events occurred during the study. Minor sensations (tingling, mild scalp discomfort) were transient and self-limited.

Inclusion Criteria:

• Female participants aged 18-35 years.
• Right-handed, healthy volunteers.
• No current or past psychiatric or neurological disorder as assessed by structured clinical interview (M.I.N.I.).
• MRI-compatible (no metal implants, pacemaker, or contraindications for MRI scanning).
• Not taking psychotropic medication.
• Fluent in Dutch.
• Provided written informed consent.

Exclusion Criteria:

• Current or past major depressive episode or any other psychiatric disorder.
• History of epilepsy or seizures in participant
• History of neurological illness or neurosurgical intervention.
• Pregnancy.
• Claustrophobia or inability to tolerate MRI environment.
• Metal implants or other MRI-incompatible devices.
• Skin lesions or dermatological conditions at electrode sites.
• Unstable medical condition.
• Use of medication that could influence brain activity or mood.