In order to stimulate the brain cells along the neural pathways, the technician has to find two areas of the brain - the homunculus or "motor strip" and the left dorsolateral prefrontal cortex. This process is called mapping. There is no pain during this process, only the tapping sensation that accompanies the magnetic pulses.
The "motor strip" or homunculus is a portion of the brain that runs across the head from ear to ear and it controls your movement on the opposite side of your body. Scientists have found that a magnetic pulse administered to this region on the left side of the head causes a response in the right thumb and fingers in the form of a twitch—like a reflex when the doctor taps your knee.
To find the "motor strip", a single magnetic pulses of increased strength is administered until there is a twitch in the thumb or fingers. We refer to this as your motor threshold.
Once your motor threshold is determined, the technician must hunt for the left dorsolateral prefrontal cortex. The magnetic coil is moved forward of the "motor strip" in five centimeter increments. This is referred to as “the hunt”. At each stop, a pulse is emitted to stimulate the fingers on the right hand. The strength of the finger twitch, or lack thereof, determines whether or not the location is correct. Once the strongest response is observed, the location is recorded so treatment can be administered in that exact spot during every treatment session.
The left dorsolateral prefrontal cortex is a nexus of nerve cells involved in depression. Think of this area as a trailhead for your limbic system. By stimulating this portion of the brain, the magnetic pulses continue to stimulate neurons along neural pathways, ultimately stimulating deeper brain structures involved with depression.