Continuous Theta Burst Stimulation to Reduce Responses to Ideological Threats

Begin with a human participant wearing electromyography electrodes on the tibialis anterior muscle to record motor signals and a reference electrode on the wrist.

Position a magnetic coil over the primary motor cortex. Deliver pulses to stimulate cortical neurons that trigger leg muscle contractions.

While the muscle is voluntarily contracted, determine the active motor threshold, which is the minimum stimulation intensity that elicits a response.

Reposition the coil above the posterior medial frontal cortex (pMFC) to investigate its role in ideological threat responses, which are defensive reactions to challenges against deeply held beliefs.

Apply continuous theta burst stimulation to deliver high-frequency pulses for an extended period.

Prolonged stimulation reduces excitatory neurotransmitter release, causing a low-level calcium influx that promotes excitatory receptor internalization and weakens excitatory signaling.

The temporary pMFC activity suppression decreases responsiveness to ideological threats.

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 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.