Effects of Transcranial Magnetic Stimulation (TMS) and Stimulus Controllability on Pain Perception

Transcranial magnetic stimulation (TMS) is a minimally invasive brain stimulation technology
that can focally stimulate the brain of an awake individual.1,2 A localized pulsed magnetic
field transmitted through a figure-8 coil (lasting only microseconds) is able to focally
stimulate the cortex by depolarizing superficial neurons3,4 which induces electrical currents
in the brain.5 If TMS pulses are delivered repetitively and rhythmically, the process is
called repetitive TMS (rTMS).

rTMS over the prefrontal cortex has been shown to produce temporary analgesic effects in
healthy adults using laboratory pain methods and in patients with chronic pain of various
etiologies. However, little is known about mechanisms of action.

Evidence from functional MRI studies suggests that participants' perceived controllability
over pain stimuli is associated with decreased pain experience and decreased activation of
cortical and subcortical areas involved with pain perception.6 Perceived controllability may
involved prefrontal cortical circuits and may be involved in inhibition of limbic system
responses to painful stimuli.

To date, no studies have investigated the interaction between prefrontal TMS and perceived
controllability on pain perception in healthy adults. Building on extensive pilot work and
experience in the area of laboratory pain assessment and TMS in the Brain Stimulation
Laboratory at MUSC, the investigators propose to investigate the effects of perceived
controllability and prefrontal TMS on pain perception in healthy adults. This study may help
determine whether TMS can be used to stimulate a cortical area thought to be involved in
perceived controllability, thus enhancing one's sense of controllability and thereby
substantially reduce pain intensity and unpleasantness.

Although transcranial magnetic stimulation (TMS) is now considered a minimal risk
intervention, is approved for the treatment of depression, and is widely used around the
world, little is known about mechanisms of action of prefrontal rTMS for depression or pain.
There is some evidence that the prefrontal cortex is involved in perception of control and
may moderate the effects of perceived controllability on emotional reactivity to painful
stimuli. The present study aims to investigate the effects of prefrontal rTMS and perceived
controllability on pain perception in healthy adults.

Inclusion Criteria:

- 18-75 years of age

Exclusion Criteria:

- history of seizures or epilepsy

- family history of seizures

- history of chronic pain conditions

- current depression

- anxiety disorders

- taking any medications shown to lower seizure threshold

- metal implants above the waist

- pregnant

- brain tumors or lesions

- pacemaker