The role of the TemporoParietal Junction in interpersonal trust

Previous research has shown that the TemporoParietal Junction (TPJ) is involved
in interpersonal trust. However, previous studies were all correlational
studies. In the current study, we aim to prove a causal role between TPJ
activity and interpersonal trust.

Het objective of this study is to investigate a causal role between brain
activity in the TemporoParietal Junction (TPJ) and interpersonal trust.

The study design consists of a double-blind, randomized experimental study,
where "continuous theta-burst stimulation (cTBS)" will be administered to the
temporoparietal junction (TPJ). cTBS is a variant of transcranial magnetic
stimulation (TMS) and results in lowered brain activation of the stimulated
brain region for about hour. 33% of the participants will receive cTBS to the
left TPJ, 33% to the right TPJ, and 33% received placebo-cTBS to the left TPJ
(by tilting away the magnetic coil by 90 degrees, so magnetic pulses will not
enter the brain).

After having received cTBS, the participant will perform behavioural
experiments, while functional MRI is recorded simultaneously.

Participants will receive "continuous theta-burst stimulatie (cTBS)". cTBS is a
variant of transcranial magnetic stimulation (TMS) and results in lowered brain
activation of the stimulated brain region for about hour. 33% of the
participants will receive cTBS to the left TPJ, 33% to the right TPJ, and 33%
received placebo-cTBS to the left TPJ (by tilting away the magnetic coil by 90
degrees, so magnetic pulses will not enter the brain). Each participant will be
randomly assigned to one of the experimental conditions.

Participants need to visit the lab 2 times and need to fill in questionnaires
and practice the behavioural tasks once during an online experimental sessions.
During the first lab visit, the participant will be screened to prevent adverse
effects during the rest of the study. During this initial screening sessions,
the resting motor threshold of the participant will be assessed twice with the
use of TMS, followed by the acquisition of an anatomical MRI-scan of their
brain. After successful medical screening, the participant will fill in a few
personality-questionnaires and practice the behavioural task (at home, online).
The second lab visit is the main test day. During the test day, the active
motor threshold of the participant will be assessed twice and participants will
perform a couple of simple computer tasks, while their brain activation is
measured with functional MRI. Prior to the functional MRI measurements, the
participants will receive cTBS to the left TPJ, the right TPJ or placebo-cTBS
to the linker TPJ. In addition, participants need to follow specific
instructions about drugs and alcohol intake prior to the test day and during
the test day.

TMS can produce side effects, among which dizziness, nausea and headaches. In
very rare occasions, an epileptic seizure may occur. Previous studies have
reported that healthy participants tolerate cTBS well. As a screening proceeds
the actual brain stimulation protocols, we expect no serious side effects.