Your first TMS session is mostly about measurement. Before any treatment, the team finds the spot on your head that controls your right hand, turns the magnet up until your fingers or thumb twitch to find your motor threshold, and uses that number to set your treatment dose. Then they locate the treatment target over the front of the brain, record its position so every later session matches, and usually give your first treatment. That is why the first visit runs longer than the rest.
The billing code Medicare uses for the first session (CPT 90867) describes exactly this bundle: "cortical mapping, motor threshold determination, delivery and management." Here is what each part feels like from the chair, and why it matters.
Before the magnet switches on
You sit in a treatment chair, awake; TMS does not require anesthesia and is done in an office setting. Staff will confirm your safety screen and ask you to remove anything metal or electronic near your head, such as hearing aids, piercings, jewelry and glasses. You will put in earplugs: FDA guidance requires hearing protection rated for 30 dB of noise reduction during treatment, because each pulse makes a loud click.
Some systems use a head strap that the team fits and measures, so the coil can be placed in the same spot every day. Wear comfortable clothes, skip hair products that make the scalp slippery, and tie long hair back loosely.
Arrive a little early, and mention anything that has changed since your consultation: a new medicine, a missed night of sleep, a recent illness or a few drinks the night before. These can matter for seizure threshold, and the team would rather hear about them before they start than after. Bring a snack and water if the visit is likely to run long, and plan your day so you are not rushing out the door.
Step 1: Finding your motor "hotspot"
The coil starts over the motor cortex, the strip of brain that controls movement. Because the left side of the brain controls the right hand, the coil sits on the left side of your head while the team watches your right hand.
They give single pulses, a few seconds apart, and move the coil in small steps. Each pulse feels like a firm tap on the scalp. When the coil is over the hand area, a pulse makes your fingers or thumb jump on their own. It can be a surprising feeling, but it is not usually painful and stops the moment the pulse ends. The spot that gives the clearest twitch is your hotspot.
Clinics detect the movement in different ways. One cleared system describes motor threshold as found by "visual inspection of finger movement + EMG", meaning the team watches your hand and may also tape small sensors to it to record the muscle signal. Another system includes a dedicated accessory for locating the motor threshold position and level.
Step 2: Measuring your motor threshold
Once the hotspot is found, the team lowers and raises the strength of the pulses to find the lowest setting that still reliably makes your hand move. That setting is your motor threshold. It is a personal number. In one MRI study of 29 adults with depression, a longer distance from the coil to the motor cortex went with a higher threshold.
Your treatment dose is then set as a percentage of that threshold. Some examples from cleared protocols and pivotal trials:
| Protocol | Treatment strength | Pulses per session |
|---|---|---|
| Standard 10 Hz (pivotal trials) | 120% of motor threshold | 3,000 |
| Theta-burst (iTBS), first cleared version | 120% of motor threshold | 600 |
| Deep TMS (H1 coil, pivotal trial) | 120% of motor threshold | 1,980 |
| SAINT accelerated protocol | 90% of motor threshold, adjusted for depth | 1,800 per session, 10 sessions a day |
So "120%" does not mean 120% of the machine's power. It means a bit stronger than the level that just moved your hand. The motor area is used as a ruler because it gives a visible signal; the depression target in the frontal lobe does not.
FDA guidance flags one situation for extra care: patients whose motor threshold cannot be reliably determined should be monitored closely. If your hand does not twitch easily, the team may take longer, use the muscle sensors, or discuss other options. The physician's guide to motor threshold and TMS dosing explains the science in more depth.
Step 3: Locating the treatment target
Standard TMS for depression treats the left dorsolateral prefrontal cortex (DLPFC), an area toward the front and side of the head involved in mood regulation. There are three common ways to find it.
The 5 cm rule
The oldest method moves the coil a fixed 5 cm forward from your motor hotspot. It is simple, but in a 2001 imaging check of 22 people it landed on the intended DLPFC region in only 7. Heads differ in size and shape, so a fixed distance can drift.
Beam F3 measurements
The Beam F3 method uses three tape-measure readings of your head to find a standard EEG landmark over the left DLPFC. In a 2023 randomized trial of 105 patients, results with Beam F3 and a 5.5 cm rule were similar on every measure. If your team measures your head with a tape, this is likely why. One major system ships strap packs for both the 5 cm and Beam F3 methods.
MRI-guided neuronavigation
Some clinics load a brain MRI into a navigation system that tracks the coil in real time. An early randomized trial (2009, 51 people) found better depression scores at four weeks with MRI navigation than with the 5 cm rule, though the authors said larger studies were needed. Newer approaches pick the target from brain-connectivity scans, which is part of the SAINT protocol. The physician's guide to TMS targeting and neuronavigation compares the methods.
Step 4: Your first treatment
With the coil on target and the dose set, the first treatment usually follows. A standard 10 Hz session can take from about 19 minutes up to 37.5 minutes depending on the device settings; a theta-burst session takes about 3 minutes of stimulation. You will feel repeated tapping or knocking on the scalp and hear the clicks through your earplugs. Muscle twitching and facial discomfort are among the side effects one device maker lists.
Scalp discomfort at the treatment site is the most common side effect, and it usually eases after the first week. Some teams may start a little below the target strength and build up over the first sessions if the sensation is hard to tolerate; tell them how it feels rather than gritting your teeth. What TMS feels like covers the sensations in more detail.
Why the first visit is longer, and watched more closely
Mapping and threshold-finding add time, and so does the paperwork of recording your coil position and settings. There is also a safety reason for close attention early on. A large survey found that seizures, though rare, "were most likely to occur within the first few exposures to TMS." With TMS given within guidelines to people without risk factors, the rate was fewer than 1 seizure per 60,000 sessions.
Staff also know how to tell a seizure from a simple faint. International guidance notes that brief jerks during a faint can look like a seizure, and recommends lowering the head, fluids and reassurance. Eat normally and sleep well the night before; that alone helps. More on overall safety is in TMS side effects.
| Part of the visit | What you notice | Why it is done |
|---|---|---|
| Safety check and earplugs | Questions, removing metal items | Protects hearing and avoids interaction with the field |
| Hotspot search | Single taps; your hand twitches | Finds the hand area of the motor cortex |
| Motor threshold | Taps getting weaker and stronger | Sets your personal dose |
| Target location | Head measurements, a strap or a navigation screen | Puts the coil over the treatment area |
| First treatment | Rhythmic tapping and clicking | Starts the course |
Re-mapping during a course
Your threshold is not fixed forever. Medicare has a separate billing code for "subsequent motor threshold re-determination", which shows that rechecking is a recognized part of care. Teams may recheck if you start or stop a medicine that acts on the brain, if sessions suddenly feel very different, if the coil position seems off, or at set points in the course. A recheck is short and feels like the original mapping.
Between sessions, you help by keeping things steady: similar sleep, consistent caffeine, no heavy drinking, and telling the team about any medication change. Caffeine, alcohol and sleep during TMS explains why. For the rest of the course, see a typical TMS course, week by week.
Questions to ask at your first session
- How are you finding my motor threshold: by watching, with sensors, or both?
- Which method are you using to find my treatment target?
- What percentage of my threshold will I be treated at, and will that change?
- When would you recheck my threshold?
- Who should I tell if the sensation is too strong?
The TMS preparation checklist covers what to wear and bring, the TMS guide has every related topic, and TMS therapy is where to start a conversation about your own care.
Sources
- Billing and Coding: Transcranial Magnetic Stimulation (A57528). Centers for Medicare & Medicaid Services, 2026. cms.gov
- Safety and recommendations for TMS use in healthy subjects and patient populations, with updates on training, ethical and regulatory issues: Expert Guidelines. Clinical Neurophysiology, 2021. europepmc.org
- Class II Special Controls Guidance Document: Repetitive Transcranial Magnetic Stimulation (rTMS) Systems. U.S. Food and Drug Administration, 2011. fda.gov
- K231926 510(k) Summary - NeuroStar Advanced Therapy System. U.S. Food and Drug Administration, 2024. accessdata.fda.gov
- K220177 510(k) Summary - Magnus Neuromodulation System with SAINT Technology. U.S. Food and Drug Administration, 2022. accessdata.fda.gov
- Efficacy and safety of transcranial magnetic stimulation in the acute treatment of major depression: a multisite randomized controlled trial. Biological Psychiatry, 2007. pubmed.ncbi.nlm.nih.gov
- K173620 510(k) Summary - MagVita TMS Therapy System w/Theta Burst Stimulation. U.S. Food and Drug Administration, 2018. accessdata.fda.gov
- Efficacy and safety of deep transcranial magnetic stimulation for major depression: a prospective multicenter randomized controlled trial. World Psychiatry, 2015. pmc.ncbi.nlm.nih.gov
- Transcranial magnetic stimulation in therapy studies: examination of the reliability of 'standard' coil positioning by neuronavigation. Biological Psychiatry, 2001. pubmed.ncbi.nlm.nih.gov
- An efficient and accurate new method for locating the F3 position for prefrontal TMS applications. Brain Stimulation, 2009. pubmed.ncbi.nlm.nih.gov
- A randomized trial comparing beam F3 and 5.5 cm targeting in rTMS treatment of depression demonstrates similar effectiveness. Brain Stimulation, 2023. pubmed.ncbi.nlm.nih.gov
- A randomized trial of rTMS targeted with MRI based neuro-navigation in treatment-resistant depression. Neuropsychopharmacology, 2009. pubmed.ncbi.nlm.nih.gov
- Safety Information. NeuroStar (Neuronetics), 2026. neurostar.com
- Seizures from transcranial magnetic stimulation 2012-2016: Results of a survey of active laboratories and clinics. Clinical Neurophysiology, 2019. europepmc.org
- How coil-cortex distance relates to age, motor threshold, and antidepressant response to repetitive transcranial magnetic stimulation. Journal of Neuropsychiatry and Clinical Neurosciences, 2000. pubmed.ncbi.nlm.nih.gov
- Brain Stimulation Therapies. National Institute of Mental Health (NIMH), 2024. nimh.nih.gov
- Side Effects. NeuroStar (Neuronetics), 2026. neurostar.com
FAQs
Does the motor threshold test hurt?
Most people describe it as a firm tap on the head and an odd, involuntary twitch of the hand. It is not usually painful, and each twitch stops as soon as the pulse ends.
Why does my hand move if the treatment is for depression?
The hand area gives a visible signal, so it works as a ruler for setting your dose. The depression target in the front of the brain does not produce a visible movement.
Do I need an MRI before TMS?
Not for standard TMS, which can be targeted with head measurements. Some protocols, such as SAINT, use MRI scans to choose a personal target.
Can I drive home after the first session?
TMS does not require anesthesia. Ask the team about driving after your first visit, and if you feel unwell or lightheaded, wait and tell the staff.
What if my dose seems too strong?
Say so. Teams can adjust how they build up to the target dose, and discomfort usually eases over the first week.
