Deep TMS works by electromagnetic induction. A coil in a helmet produces brief magnetic pulses that pass through the skull and induce electrical currents in the left prefrontal cortex, a region that is underactive in depression. Daily 20-minute sessions over six weeks strengthen that circuit's activity and its connections to deeper mood-regulating structures, producing lasting symptom relief in most patients.
This page explains the mechanism in plain terms: what the magnetic pulse does to neurons, why the prefrontal cortex is the target in depression, how the Deep TMS H-coil differs from a standard coil, and what happens minute by minute in a treatment session at our Palm Beach Gardens office.
Who it is for
Understanding the mechanism matters most for two groups: patients deciding whether to commit to a six-week course, and family members who want to know whether this is a legitimate medical treatment or something fringe. It is legitimate. TMS has been studied since 1985, has been FDA-cleared for depression since 2008 (Deep TMS since 2013), and is endorsed in the American Psychiatric Association's treatment guidelines for depression that has not responded to medication. The patients who benefit are adults with major depressive disorder, OCD, anxious depression or nicotine dependence whose symptoms persist despite medication.
How it works
Faraday's law states that a changing magnetic field induces an electrical current in a nearby conductor. Brain tissue is a conductor. When the TMS coil discharges, a magnetic field of about 1.5 to 2 tesla, similar to an MRI scanner, rises and falls in under a millisecond. That rapid change induces a current in the cortex strong enough to make neurons fire. A single pulse over the motor cortex makes your thumb twitch, which is how we calibrate the dose. Repeated pulses delivered at 10 to 20 Hz over the left dorsolateral prefrontal cortex increase the excitability of that region, and that increase persists after the session ends. Over weeks, the effect consolidates through the same mechanisms that underlie learning: changes in synaptic strength, receptor density and gene expression in the stimulated circuit and in the regions it connects to, including the anterior cingulate cortex and the limbic structures that generate mood and motivation.
The Deep TMS H-coil stimulates to a depth of roughly 4 centimeters, compared with about 1.5 to 2 centimeters for a figure-8 coil, as measured in phantom and modeling studies.
Source: Roth et al., Journal of Clinical Neurophysiology, 2007; Deng, Lisanby and Peterchev, Brain Stimulation, 2013
In the pivotal Deep TMS depression trial, 212 patients were randomized to active or sham stimulation at 120 percent of motor threshold, 18 Hz, with remission rates of 32.6 percent versus 14.6 percent.
Source: Levkovitz et al., World Psychiatry, 2015
Functional imaging shows that TMS over the left dorsolateral prefrontal cortex changes activity in the anterior cingulate and subgenual cortex, regions that are not directly under the coil.
Source: Fox et al., Biological Psychiatry, 2012
The American Psychiatric Association practice guideline lists TMS as a recommended option for patients who have not responded to at least one antidepressant trial.
Source: APA Practice Guideline for the Treatment of Patients With Major Depressive Disorder
What to expect
At the start of your first session the technician fits the Deep TMS helmet, which contains the H-coil inside a padded shell, and positions it over the motor cortex to find your motor threshold. Once that number is set, the helmet moves forward to the prefrontal treatment position, about 6 centimeters anterior. You put in earplugs. The machine delivers a train of pulses lasting two seconds, rests for 20 seconds, then repeats. A depression session has 55 trains and takes about 20 minutes. You feel a tapping on the scalp and may feel your eyebrow or jaw twitch during each train. You stay awake, can talk during the rest intervals, and leave when it ends.
Benefits
- Targets the brain circuit directly rather than the whole body, so there are no systemic side effects
- Effect builds across sessions and persists after treatment ends
- Dosing is individualized to your own motor threshold on day one
- No sedation or recovery time; sessions fit before or after work
- Works through a different mechanism than antidepressants, so prior medication failure does not predict TMS failure
Risks and side effects
Because the pulse stimulates scalp muscles and nerves on its way to the cortex, the most common side effects are scalp discomfort and a mild headache, usually limited to the first week. Facial twitching during the pulse train is expected and harmless. The pulse that excites cortical neurons can, very rarely, trigger a seizure; the rate is under 0.1 percent per course and lower still when patients with seizure risk factors are screened out. Hearing protection is mandatory because the coil clicks at around 120 decibels.
Cost and insurance
The mechanism does not change what your insurer covers. Medicare and most commercial insurers cover TMS for major depressive disorder once you have documented failure of antidepressant trials. Prior authorization is required for commercial plans, and our TMS coordinator submits it. For self-pay patients, ask our TMS coordinator for current self-pay rates.
From a single pulse to a changed circuit
A single TMS pulse is a probe. Neuroscientists have used single pulses for decades to map the motor cortex, measure nerve conduction and study how the brain controls movement. On its own, a single pulse does nothing lasting. What makes TMS a treatment is repetition: trains of pulses delivered at a fixed frequency, session after session, that push a circuit toward a new steady state.
High-frequency stimulation, 10 Hz and above, increases cortical excitability. Low-frequency stimulation at 1 Hz decreases it. In depression the left dorsolateral prefrontal cortex is hypoactive, so the standard protocol applies high-frequency pulses on the left. Deep TMS uses 18 Hz. Each session delivers about 1,980 pulses in 55 trains, and across 36 sessions you receive more than 70,000 pulses. The cumulative effect depends on long-term potentiation, the same cellular process that strengthens synapses when you learn.
What the H-coil does differently
Standard rTMS uses a figure-8 coil: two circular windings side by side, with the strongest field at the point where they meet. It is precise and shallow. The H-coil used in Deep TMS wraps around the head inside a helmet, with windings arranged so that the field spreads over a broader area and attenuates more slowly with depth. Modeling and phantom studies put its effective depth at about 4 centimeters versus roughly 1.5 to 2 centimeters for a figure-8.
The practical consequences are three. First, Deep TMS is less sensitive to small errors in coil placement, because the field covers a wider area. Second, it reaches prefrontal tissue that sits in sulci below the surface. Third, it allows specialized coils for other targets: the H7 coil for OCD aims at the medial prefrontal cortex and anterior cingulate, structures that a figure-8 coil cannot reach from the scalp. The tradeoff is focality: Deep TMS cannot stimulate one small spot while sparing its neighbors.
A session, minute by minute
| Time | What happens |
|---|---|
| 0 to 3 min | Check in, remove earrings and hair clips, sit in the treatment chair, insert earplugs |
| 3 to 6 min | Technician fits the helmet and aligns it to the marks recorded on day one |
| 6 to 26 min | 55 trains of 18 Hz pulses, 2 seconds on and 20 seconds off; you feel tapping and hear clicking |
| 26 to 30 min | Helmet off, brief check of how you feel, schedule confirmed, you leave |
Day one is longer, about 60 minutes, because of motor threshold mapping. The technician delivers single pulses over the motor cortex while watching your right hand, lowering the intensity until a visible twitch appears in about half the pulses. That value is your motor threshold, and your treatment intensity is set at 120 percent of it. We remeasure if you change medications that affect cortical excitability or if the sensation changes noticeably.
Why prior medication failure does not predict TMS failure
Antidepressants work by changing neurotransmitter availability throughout the brain and body, and they rely on the brain adapting to that change over weeks. TMS bypasses neurotransmitter chemistry and acts on the circuit's electrical activity directly. That is why response to TMS is largely independent of how many antidepressants you have tried. In the Levkovitz trial, every participant had already failed one to four medications in the current episode, and the active group still remitted at more than twice the sham rate.
The strongest predictors of TMS response in registry data are completing the full course, having a shorter current episode, and continuing an antidepressant during treatment. Age, sex and number of prior medications matter much less.
What TMS does not do
TMS does not heat the brain, does not cause tissue damage, and does not affect memory. Cognitive testing before and after TMS courses shows either no change or small improvements in attention and processing speed, likely because depression itself impairs those functions. There is no sedation and no drug exposure, so there are no interactions with your medications, no weight gain and no sexual side effects.
Deep TMS in Palm Beach Gardens
Stedfast Psychiatry delivers Deep TMS at our Palm Beach Gardens office, 11641 Kew Gardens Ave, Suite 209, just off PGA Boulevard and I-95. Patients travel to us from Jupiter, West Palm Beach, Boynton Beach, Stuart and Royal Palm Beach, and most find the drive manageable because a Deep TMS session takes about 20 minutes and you drive yourself home. Call (561) 437-2199 to schedule a TMS consultation, or ask your current Stedfast provider for an internal referral. Our TMS coordinator handles insurance verification, prior authorization and scheduling so you can start as soon as approval comes through.
Frequently asked questions
What does TMS stand for?
TMS stands for transcranial magnetic stimulation. Transcranial means across the skull, magnetic refers to the pulsed magnetic field that carries the stimulation, and stimulation describes what the field does to the neurons underneath. You will also see rTMS, for repetitive TMS, which is the form used for treatment, and dTMS or Deep TMS, which refers to the H-coil design that reaches deeper brain tissue.
Is TMS the same as electroconvulsive therapy?
No. ECT passes electrical current directly through the brain under general anesthesia to induce a controlled seizure. TMS induces a small, focused current in a specific region without anesthesia and without a seizure. You are awake, you can talk, and you leave on your own afterward. ECT remains more effective for severe or psychotic depression, but TMS has none of its memory side effects or anesthesia risk.
Why is the left prefrontal cortex the target?
Imaging studies consistently show reduced activity in the left dorsolateral prefrontal cortex in depression, along with weakened connections to the anterior cingulate and limbic regions that regulate mood. High-frequency stimulation increases activity in that region and, through its connections, in the deeper structures. Some protocols instead apply low-frequency stimulation to the right side, which is overactive in depression; both approaches have evidence behind them.
What is motor threshold mapping?
Motor threshold is the lowest pulse intensity that makes a muscle in your hand twitch when the coil is over the motor cortex. It is measured on your first treatment day and sets your personal dose, since treatment pulses are delivered at 120 percent of that value. People vary widely in skull thickness and cortical excitability, so this calibration is what makes the dose both safe and effective for you specifically.
How does Deep TMS reach deeper than regular TMS?
The H-coil is wound so that its magnetic field falls off more slowly with distance than a figure-8 coil's. A figure-8 coil produces a tight, focused field that is strong at the surface and weak 2 centimeters down. The H-coil produces a broader field that stays above the neuron-firing threshold to about 4 centimeters. The tradeoff is less focality, which is why Deep TMS cannot target a single small region the way a figure-8 can.
How long does it take for TMS to work?
Most patients notice early changes in sleep, energy or concentration during week two or three. Mood improvement usually becomes clear between weeks four and six. In the large post-marketing registry of Deep TMS, the average patient reached sustained response at about 16 sessions. A minority respond in the first week and a minority not until the taper phase, which is why we encourage completing the full 36-session course.
Does TMS change my brain permanently?
TMS produces durable but not necessarily permanent changes. The improvements in circuit activity persist for months after the course ends, and most responders stay well for a year or more. Some people need a retreatment course if symptoms return. The changes are the same kind the brain makes when it learns a skill or recovers from an injury: strengthened connections, not structural alteration or damage.
Where this treatment is offered
Conditions this treats
If you are in crisis, call or text 988 or go to the nearest emergency room. Educational content; individual results vary. Reviewed by Dr. David Husted, board-certified psychiatrist.