Continuous Theta Burst Stimulation of the Posterior Medial Frontal Cortex to Experimentally Reduce Ideological Threat Responses
September 28th, 2018
Threats reliably evoke shifts in high-level ideological investment, but little work to date has explored the neural mechanisms underlying these dynamics. This paper describes how continuous theta burst transcranial magnetic stimulation may be employed to test the contribution of the posterior medial frontal cortex (and/or other regions) to threat-related ideological shifts.
This method can help answer key questions in social neuroscience, such as how the brain supports shifts in nationalistic or religious beliefs. The main advantage of this technique is that it allows us to actually go in and change the level of activity in a given brain region. This allows us to infer causal contributions of that given brain region in a particular behavior.
Begin by seating the participant in the testing room, and go over in depth with them how TMS works and all potential side effects. Have the participant fill out the TMS safety screen to ensure that they have no pre-existing factors that cause adverse effects. Make sure to remove all metal jewelry or accessories.
Next, fit a grid-marked swim cap to the participant's head. Clean the skin over the tibialis anterior muscle thoroughly. Then attach two differential EMG recording electrodes to this area.
Attach a third ground electrode to the skin over a bone somewhere else on the hand or arm. Next, on the swim cap, measure and mark the center location, CZ, on the participant's head. Have the participant sit comfortably and begin recording the EMG electrode output to software that will filter and display the signal.
Next, to perform thresholding on the primary motor cortex, place the center of a double-cone coil over the motor cortex, held over to the scalp surface. Apply single-pulse TMS at 50%of the maximum stimulus output, or MSO, and observe whether a motor-evoked potential, or MEP, was present in the EMG signal following the stimulation. If no MEP is seen following the stimulation, reposition the coil one centimeter away in any direction, and try the stimulation again.
Continue moving the coil once one centimeter at a time, marking on the cap the stimulation sites that result in an MEP of 50 millivolts or greater. Next, have the participant contract the target muscle. Stimulate the located region for 10 repetitions separated by about seven seconds, at decreasing intensities, until a corresponding observable twitch in the leg muscle no longer occurs for 50%of the stimulations.
Navigate the coil to 3.5 centimeters anterior to the motor cortex, where the posterior medial frontal cortex is located. Finally, apply cTBS as follows:Three pulses at 50 hertz, repeated at 200 millisecond intervals for 40 seconds, totalling at 600 pulses, and ensure that the coil is perfectly still throughout the stimulation. Begin by seating a participant at a desktop computer to perform the computer-mediated survey tasks.
Remind the participant that their responses will be anonymous, confidential and inaccessible to the research assistant, particularly to the extent that the target judgments are likely to raise self-presentation concerns, which might obscure the effect of the cTBS manipulation. Then, present the participant with instructions for the first filler task for 10 minutes before starting the main task, in order to obtain the maximal effective cTBS and minimize demand effects. First, administer the multiple-source interference task, or MSIT, followed by an unrelated survey task.
Challenge the participant to estimate the number of colors present in images of jelly beans and sea shells that have been converted to grayscale. Following the unrelated survey task, instantiate the threat context. If the ideological shifts of theoretical interest pertain to responses to death, ask the participant to write two brief passages on the subject of their mortality.
Following the threat induction task, administer the positive and negative effects schedule-expanded form, to allow self-reporting of potential effects of the cTBS intervention on emotional responses to the threat induction, as well as to distract the participants from the death prime encountered earlier in the protocol. Next, administer the ideological judgment tasks by presenting the participant with two essays, one pro-US and the other anti-US, written by immigrants to the United States from Latin America, and ask participants to evaluate the authors and their arguments. After presenting each essay, ask participants to rate their agreement with six statements using an eight-point Likert scale, with one meaning strongly disagree and eight meaning strongly agree.
Finally, measure religious conviction by presenting the participant with the supernatural beliefs scale on the screen, in which two distinct sub-scales tap into positive and negative aspects of Western religious belief, narrowing the positive and negative valence of the two essays in the group bias measure. As predicted, cTBS of the PMFC increased positive evaluations of the critical immigrant author, who was rated 28.5%more positively in the TMS condition than in the sham condition. Further, participants who received cTBS reported an average of 32.8%less positive religious conviction in God, angels and heaven, relative to the sham participants.
While attempting this procedure, it's very important that your participant feel comfortable at all times, and that you hold the coil very steady during stimulation. In addition to TMS, neuroimaging methods should be used to clarify the precise mechanisms involved in threat-related ideological responses. This technique allows researchers to explore the neural basis of high-level shifts in social cognition.
Don't forget that working with transcranial-magnetic stimulation comes with serious potential risks. So all participants must be thoroughly screened and provide informed consent before stimulation.
Overview
This study investigates the neural mechanisms behind ideological shifts in response to threats using continuous theta burst transcranial magnetic stimulation (cTBS). It focuses on the role of the posterior medial frontal cortex in shaping nationalistic and religious beliefs.
Key Study Components
Area of Science
- Social neuroscience
- Neuroimaging
- Transcranial magnetic stimulation
Background
- Threats can influence high-level ideological beliefs.
- Understanding the brain's role in these shifts is crucial.
- cTBS allows for manipulation of brain activity.
- Previous studies have not extensively explored these dynamics.
Purpose of Study
- To examine how cTBS affects ideological shifts related to threats.
- To identify the contribution of the posterior medial frontal cortex.
- To explore the causal relationship between brain activity and belief changes.
Methods Used
- Participants undergo safety screening and informed consent.
- cTBS is applied to the posterior medial frontal cortex.
- Participants complete tasks assessing ideological judgments.
- Emotional responses are measured post-threat induction.
Main Results
- cTBS increased positive evaluations of immigrant authors.
- Participants reported lower religious conviction after stimulation.
- Findings suggest a causal link between brain activity and ideological shifts.
- Further research is needed to clarify underlying mechanisms.
Conclusions
- cTBS is a valuable tool for studying social cognition.
- Results highlight the brain's role in ideological belief changes.
- Future studies should integrate neuroimaging for deeper insights.
Frequently Asked Questions
Executive Industry Relevance
This method enables causal interrogation of neural substrates underlying high-level social cognitive shifts, offering a mechanistic bridge between brain function and ideological belief systems. By experimentally modulating posterior medial frontal cortex activity, researchers can de-risk hypotheses about neural drivers of threat-related attitudinal changes relevant to behavioral biomarker discovery. The approach supports target validation in neuropsychiatric and cognitive therapeutic areas where social cognition domains are implicated.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Interrogates causal contributions of cortical regions to threat-induced ideological adherence shifts.
- Operational Value: Enables reversible, focal neuromodulation to isolate brain-behavior relationships without permanent lesion.
- Scientific Value: Supports hypothesis testing for neural targets involved in social conformity, prejudice, and belief updating.
Screening & Assay Development
- Scientific Value: Produces quantifiable shifts in ideological judgment tasks and religious conviction scales as downstream phenotypic readouts.
- Operational Value: Standardized cTBS protocol (600 pulses over 40 seconds) enables reproducible dosing across sessions.
- Scientific Value: Generates measurable effect sizes (e.g., 28.5% increased immigrant author evaluation, 32.8% decreased religious conviction) for assay sensitivity benchmarking.
Translational & Preclinical Research
- Scientific Value: Models threat-induced ideological shifts as a disease-relevant system for studying cognitive inflexibility or extremism susceptibility.
- Operational Value: Facilitates preclinical continuity by linking cortical modulation to measurable changes in coalitional bias and supernatural belief scales.
- Scientific Value: Enables mechanistic de-risking of targets modulating salience networks implicated in social threat processing.
Pipeline & Workflow Integration
The method fits within early discovery workflows where neural target engagement must be linked to complex behavioral outputs before lead identification efforts.
- Discovery Biology: Tests whether posterior medial frontal cortex downregulation causally influences ideological flexibility under threat priming.
- Screening: Delivers standardized neuromodulation with quantifiable electrophysiological (MEP) and behavioral (Likert-scale) outputs for hit confirmation.
- Analytics: Provides continuous, interval-based stimulation parameters (3 pulses at 50 Hz, 200 ms intervals) enabling precise dose-response modeling.
- Translational Research: Connects cortical manipulation to shifts in coalitional prejudice and afterlife belief scales, aligning with preclinical biomarker continuity.
- Enterprise Reuse: Establishes a reusable platform for probing any cortical region’s role in socially mediated cognitive phenotypes.
Operational & Enterprise Impact
- Scientific Value: Reduces mechanistic ambiguity in social cognition targets by establishing causal direction from neural activity to belief change.
- Operational Value: Enables within-subject sham-controlled designs that increase statistical power and reduce inter-individual variability.
- Strategic Value: Improves go/no-go decisions in neuropsychiatric target validation by de-risking biological plausibility of cortical targets.
- Portfolio Impact: Supports risk-adjusted prioritization of targets modulating threat response networks linked to affective dysregulation.
Implementation Considerations
- Requires expertise in transcranial magnetic stimulation safety, neuronavigation, and electrophysiological monitoring.
- Depends on precise coil positioning infrastructure (e.g., swim cap fiducials, motor cortex mapping) to target posterior medial frontal cortex accurately.
- Necessitates standardization across sites for threat induction protocols (mortality salience tasks) and ideological judgment assays.
- Involves adaptation considerations when translating protocols to different model systems or clinical populations with varying baseline excitability.
- Limited by the need for rigorous screening to exclude contraindications (e.g., epilepsy risk, metallic implants) before stimulation.
