The science
of repetitive
brain stimulation
A comprehensive guide to how rTMS works — the physics, the neuroscience, the clinical protocols, and the evidence base — for patients who want to understand the technology before they commit to treatment.
How magnetic pulses change the brain
Electromagnetic induction
A brief, powerful electrical current passes through a copper coil held against your scalp. By Faraday's law, this generates a rapidly changing magnetic field — around 1.5–2 Tesla, similar in strength to an MRI scanner.
Cortical penetration
The magnetic field passes painlessly through the skull and scalp, inducing a secondary electrical current in the cortical neurons directly beneath the coil — to a depth of approximately 2–3cm for standard figure-of-eight coils.
Neuronal depolarisation
The induced current is sufficient to depolarise neurons in the targeted region, triggering action potentials. This directly modulates the excitability and firing patterns of the targeted cortical circuit.
Lasting synaptic change
Repeated stimulation over days and weeks induces lasting changes in synaptic strength — a process analogous to long-term potentiation (LTP) and long-term depression (LTD). This is how rTMS produces durable therapeutic effects.
Three principles that make rTMS possible
rTMS sits at the intersection of electromagnetic physics and clinical neuroscience. Understanding the underlying principles helps explain why it works — and why it is safe.
Faraday's Law of Induction
A changing magnetic field induces an electromotive force in any conductor within its field. In rTMS, neurons in the brain act as the conductor. The coil's rapidly switching current creates the changing magnetic field needed to stimulate them without direct electrical contact.
Focality of Stimulation
The figure-of-eight coil design concentrates the induced electrical field at the intersection of its two loops. This creates a focal stimulation zone of approximately 1–2 cm² at the cortical surface, allowing clinicians to target specific brain regions with precision.
Frequency-Dependent Modulation
The direction of effect depends on the stimulation frequency. High-frequency rTMS (≥5Hz) increases cortical excitability — used to stimulate underactive regions. Low-frequency rTMS (≤1Hz) decreases excitability — used to suppress overactive regions. This allows bidirectional modulation of specific circuits.
"The key distinction between rTMS and ECT is not merely the absence of seizure or anaesthesia — it is the spatial precision. rTMS targets a circuit; ECT treats the whole brain. This precision is both the source of its advantages and the reason it requires careful clinical mapping."
Where we stimulate — and why
The clinical effect of rTMS depends critically on which brain region is targeted. Different psychiatric conditions involve dysfunction in different circuits, and the stimulation target is chosen accordingly.
Left Dorsolateral Prefrontal Cortex
The most established target in rTMS. The left DLPFC is hypoactive in major depression and plays a central role in mood regulation, executive function, and emotional processing. High-frequency (10Hz or iTBS) stimulation increases its activity, normalising the hypofrontality seen in depressive states.
Right Dorsolateral Prefrontal Cortex
The right DLPFC is relatively hyperactive in anxiety disorders, contributing to excessive threat monitoring and rumination. Low-frequency (1Hz) inhibitory rTMS reduces this overactivity, producing anxiolytic effects. Some protocols combine bilateral stimulation — inhibiting the right and exciting the left simultaneously.
Orbitofrontal Cortex & Anterior Cingulate
The OFC-striatal circuit is hyperactive in OCD, driving compulsive behaviours and intrusive thoughts. Deep TMS using the H7 coil targets this circuit at greater depth than standard coils, producing clinically meaningful reductions in OCD symptom severity — the basis for its FDA clearance in 2018.
Temporoparietal Junction (TPJ)
The left TPJ and adjacent temporal cortex are implicated in auditory verbal hallucinations in schizophrenia. Low-frequency inhibitory rTMS to this region has shown benefit in patients with persistent hallucinations that are refractory to antipsychotic medication.
"Target selection is not a protocol decision — it is a clinical decision. The right target for a given patient depends on their primary diagnosis, their comorbidities, and their individual neuroanatomy. This is why a full psychiatric assessment before rTMS is not a formality, but a clinical necessity."
Standard, iTBS and Deep TMS
Not all rTMS is the same. Three principal protocols are used in clinical practice, each with different pulse patterns, session durations, and evidence bases.
Standard High-Frequency rTMS
The original and most extensively studied protocol. Trains of 10Hz pulses are delivered in 4-second bursts with 26-second inter-train intervals. This is the protocol used in the pivotal O'Reardon (2007) and George (2010) FDA registration trials.
Intermittent Theta Burst Stimulation (iTBS)
A newer, faster protocol that mimics the brain's natural theta rhythm. Bursts of 3 pulses at 50Hz are applied in an intermittent pattern. The landmark Stanford study (Cole et al., 2022) using accelerated iTBS achieved remission in 78.6% of patients in just 5 days.
Deep TMS (dTMS) — H-Coil
Uses a specially designed H-coil worn in a helmet, stimulating to a depth of 4–6cm — double that of standard figure-of-eight coils. The H7 coil targets the OFC-striatal circuit for OCD; the H1 coil targets deeper limbic structures for depression.
A typical rTMS session, step by step
Understanding exactly what happens during a session removes uncertainty and helps patients arrive relaxed. Here is what every session involves.
Arrival & preparation
You arrive and sit comfortably in a reclining chair. Any metal hair accessories are removed. No gown or preparation is required. The session begins without delay.
Coil positioning
The coil is positioned precisely over the target region using a standardised anatomical landmark method (the "5cm rule" or neuronavigation). The position is recorded for consistency across sessions.
Motor threshold determination
At your first session only, single pulses are delivered over the motor cortex to find your individual motor threshold — the minimum intensity needed to produce a visible finger twitch. Treatment is calibrated to 120% of this threshold.
Treatment delivery
You sit quietly while the coil delivers pulses. You will hear a rhythmic clicking sound and feel a tapping sensation on your scalp. You remain fully awake and can speak, read, or listen to music. No movement is required.
Post-treatment
There is no recovery time. You can drive immediately, return to work, eat and drink normally, and take your usual medication. Some patients notice a mild scalp tenderness or headache in the first few sessions, which settles quickly.
Progress monitoring
Validated rating scales (PHQ-9, MADRS, GAD-7) are completed at baseline and at sessions 10, 20, and at the end of the course. Your consultant reviews these at each clinical check-in to assess response and adjust the protocol if needed.
Key trials and what they showed
rTMS has been studied in over 300 randomised controlled trials. The following represent the landmark studies that established its clinical credibility and drove regulatory approval.
O'Reardon et al. — Multisite RCT (2007)
The pivotal FDA registration trial. 301 medication-free patients with MDD randomised to active vs sham rTMS over 4–6 weeks. The study that led directly to FDA clearance for depression in 2008.
George et al. — OPT-TMS Trial (2010)
US multisite sham-controlled trial in 190 patients with treatment-resistant MDD. Confirmed efficacy with a rigorous double-blind sham coil design. Established rTMS as a credible option after medication failure.
Berlim et al. — Meta-Analysis (2014)
Systematic review and meta-analysis of 29 double-blind RCTs (n=1,371). Provided the most rigorous pooled estimate of rTMS efficacy in MDD, confirming significant superiority over sham stimulation.
Carmi et al. — OCD Deep TMS (2019)
Double-blind RCT of deep TMS (H7 coil) in 94 patients with OCD, using a provocation protocol immediately prior to stimulation. The trial that supported FDA clearance for OCD.
Cole et al. — Stanford SAINT (2022)
The most dramatic recent trial. Accelerated iTBS (10 sessions/day for 5 days) in 29 patients with severe treatment-resistant depression. Used MRI-guided personalised targeting of the subgenual ACC-connected DLPFC node.
Dunner et al. — Durability Study (2014)
Prospective naturalistic follow-up of 257 rTMS responders over 52 weeks. Examined the durability of acute treatment response and the effectiveness of retreatment when symptoms returned.
A well-established and manageable safety record
Over three decades of clinical use and hundreds of controlled trials have established a clear safety profile. rTMS is not without side effects, but serious adverse events are rare.
The most comprehensive safety review (Rossi et al., 2021, covering over 300,000 sessions) found no evidence of cumulative neurological harm, no long-term cognitive impairment, and no structural brain changes attributable to rTMS.
What rTMS does not cause
One of the most clinically important aspects of rTMS is the absence of systemic side effects that affect tolerability with medications.
The seizure risk of ~0.01% per session is comparable to the seizure risk associated with commonly prescribed antidepressants — and substantially lower than the risk of untreated severe depression.
rTMS versus other treatments for depression
Placing rTMS in context alongside antidepressant medication, psychotherapy, ketamine, and ECT helps patients make genuinely informed decisions.
| Feature | rTMS | Antidepressants | Psychotherapy | Ketamine / Esketamine | ECT |
|---|---|---|---|---|---|
| Anaesthesia required | ✗ None | ✗ None | ✗ None | Sedation | ✓ General |
| Inpatient admission | ✗ No | ✗ No | ✗ No | ✗ No | Often yes |
| Cognitive side effects | Minimal | Moderate | None | Transient dissociation | Significant memory effects |
| Systemic side effects | Very low | Weight, sexual, GI | None | Dissociation, BP | Cardiovascular |
| Speed of response | 2–4 weeks | 4–8 weeks | Weeks to months | Hours to days | 1–2 weeks |
| Response rate (TRD) | ~58% | ~30–40% | ~40–50% | ~55–70% | ~70–80% |
| Durability | 6–12 months avg. | Ongoing required | Good if completed | Short; retreatment needed | Maintenance needed |
| Drive / work same day | Yes | Usually | Yes | No (24h restriction) | No |
| Suitable in pregnancy | Possibly | Selected agents | Yes | Not recommended | Case-by-case |
This table is a summary for educational purposes. Individual suitability for any treatment requires clinical assessment. TRD = treatment-resistant depression.
Questions patients often ask about the technology
These questions go deeper than the standard FAQs — for patients who want to understand the science before committing to treatment.