TMS & Neuromodulation · Part 3

Overview

Transcranial magnetic stimulation (TMS) may feel futuristic, but it rests on nearly two centuries of physics and more than four decades of modern human neurophysiology. The key breakthrough was not the idea that nervous tissue could be stimulated; electrical stimulation had demonstrated that long before. The breakthrough was finding a practical way to induce current in the cortex through an intact scalp with far less pain than high-voltage transcranial electrical stimulation.¹²³⁴

TMS first became a research and diagnostic tool. Only later did repetitive stimulation become a treatment. Its clinical history is therefore a sequence of distinct advances: electromagnetic induction, noninvasive motor-cortex stimulation, safety standards for repetitive dosing, randomized depression trials, and device-specific FDA authorizations for additional indications and treatment schedules.

Key milestones include:

• 1831–1832: Michael Faraday demonstrates and publishes electromagnetic induction.¹
• Late 1800s: investigators show that time-varying magnetic fields can produce visual and vestibular sensations, although these experiments were not modern focal cortical TMS.⁵
• 1980: Merton and Morton stimulate human motor cortex electrically through the intact scalp, proving feasibility but with substantial discomfort.³
• 1985: Barker, Jalinous, and Freeston introduce modern transcranial magnetic stimulation and evoke a hand-muscle response noninvasively.⁴
• 1990s–2000s: repetitive TMS moves from a laboratory probe to a candidate treatment for depression.
• 2008: the first U.S. TMS system is cleared for major depressive disorder.⁶
• 2018–2022: theta-burst, OCD, and high-dose accelerated systems expand the field.⁹¹⁰¹²
• 2024–2026: adolescent depression, additional accelerated schedules, and a device-specific adult PTSD indication become part of the U.S. regulatory landscape.¹³¹⁴¹⁵

Evidence cutoff: This article reflects publicly available evidence and U.S. regulatory information through July 10, 2026. FDA authorizations are tied to particular devices, coils, age groups, targets, and treatment protocols.

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Before TMS: Electricity and the Nervous System

The concept of influencing the body with electricity is ancient. Physicians in the Greek and Roman world used shocks from electric fish for pain and other symptoms. Those practices were not scientific neuromodulation in the modern sense, but they reflected an early observation that electrical phenomena could change sensation and movement.⁵

By the nineteenth century, experiments in electrophysiology had established that nerves and muscles respond to electrical stimulation. Direct electrical stimulation later became important in neurosurgery for mapping motor, language, and sensory cortex. The unresolved challenge was how to stimulate the brain through the intact scalp in a tolerable and controllable way.

Faraday’s Foundation: Electromagnetic Induction

In 1831, Michael Faraday demonstrated electromagnetic induction; his first series of “Experimental Researches in Electricity” was published in 1832. The principle is simple to state but transformative: a changing magnetic field produces an electric field in nearby conductive material.¹

A modern TMS coil is a direct medical application of that principle. A brief current pulse through the coil generates a changing magnetic field, which induces an electric field in cortical tissue. Faraday did not build a brain stimulator, but no TMS device could exist without the relationship he described.

Early Magnetic Effects on the Nervous System

In the late nineteenth century, Jacques-Arsène d’Arsonval and other investigators exposed the head to alternating magnetic fields and reported phosphenes, vertigo, and sometimes faintness. These observations showed that time-varying magnetic fields could influence the human nervous system.⁵

They should not be described as the first modern TMS treatment. The coils were large, the fields were diffuse, and at least some effects were probably caused by stimulation of the retina, peripheral structures, or vestibular system rather than focal activation of a defined cortical target. The experiments were historically important demonstrations—not clinically targeted rTMS.

The Painful Proof of Principle: 1980

In 1980, Patrick Merton and Bert Morton reported transcranial electrical stimulation of the motor cortex in an intact human subject. A brief high-voltage discharge could activate corticospinal pathways and produce a muscle response.³

The experiment proved that the cortex could be reached noninvasively, but the current also activated pain-sensitive tissues in the scalp. The method was valuable for physiology but too uncomfortable for repeated routine treatment. A different route for delivering the electric field was needed.

The Modern Breakthrough: Barker’s TMS Device in 1985

In 1985, Anthony Barker, Reza Jalinous, and Ian Freeston at the University of Sheffield reported noninvasive magnetic stimulation of the human motor cortex. A pulse delivered over motor cortex produced a measurable hand-muscle response with much less discomfort than transcranial electrical stimulation.⁴

This was the birth of modern TMS. The apparatus used a coil near the scalp to generate a rapidly changing magnetic field. The field crossed the scalp and skull with relatively little attenuation and induced an electric field in the cortex. The method made repeatable, awake, non-surgical brain stimulation practical.

TMS began as a measurement tool. Its early uses included testing central motor conduction, mapping motor cortex, studying corticospinal excitability, and probing causal relationships between brain regions and behavior. Therapeutic use emerged later, after researchers learned that repeated pulse trains could produce effects that outlasted the stimulation.

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From Single Pulses to Repetitive TMS

A single TMS pulse is useful for mapping and physiology. Repetitive TMS (rTMS) delivers trains of pulses and can alter cortical and network activity for minutes or longer after a session. During the 1990s, investigators developed safer repetitive protocols and began studying prefrontal rTMS for major depression.⁵

The therapeutic rationale grew from converging observations:

• depression involves distributed mood-regulation circuits, including prefrontal and cingulate regions;
• TMS can influence not only the cortex under the coil but also connected regions;
• repeated sessions can produce longer-lasting physiological and clinical effects than a single pulse;
• prefrontal stimulation can be delivered repeatedly without anesthesia or an implanted device.

Large multisite randomized trials in the 2000s established that active left-prefrontal rTMS could outperform sham treatment in selected adults with major depression who had not improved adequately with medication.⁷⁸

The U.S. Clinical Era

Why “FDA-Approved TMS” Is Imprecise

Most TMS systems are medical devices that reached the U.S. market through 510(k) clearance, in which the FDA determines substantial equivalence to an appropriate legally marketed device for the stated use. The first adult OCD device category entered through the De Novo pathway. “FDA-authorized” is a useful umbrella term, while “approved” is usually reserved for drug approvals or premarket-approval devices.¹⁰¹⁶

The distinction is not merely semantic. A clearance applies to a defined device and label. It may specify:

• the diagnosis and age range;
• whether treatment is standalone or adjunctive;
• the coil and target;
• pulse pattern and intensity;
• number and spacing of sessions;
• screening, warnings, and contraindications.

A clinic cannot assume that because one TMS system is cleared for depression, it is automatically cleared for OCD, smoking cessation, PTSD, migraine, adolescents, or every accelerated schedule.

How TMS Changed Without Becoming One Single Treatment

The phrase “TMS” now covers multiple technologies:

• conventional high-frequency and low-frequency rTMS;
• intermittent theta-burst stimulation;
• H-coil systems often marketed as deep TMS;
• portable single-pulse migraine devices;
• structural-MRI neuronavigation;
• functional-connectivity-guided targeting;
• accelerated schedules with several sessions per day;
• EEG-informed frequency selection.

These are related by core electromagnetic physics, but they should not be treated as interchangeable. Evidence from one coil, target, diagnosis, or schedule cannot automatically be transferred to another.

The Role of ECT in This History

TMS is sometimes described mainly by contrasting it with electroconvulsive therapy (ECT). The treatments are different, but ECT should not be portrayed as obsolete or crude. Modern ECT is performed under general anesthesia and intentionally induces a therapeutic seizure. It remains one of the most effective treatments for severe depression, psychotic depression, catatonia, and other urgent conditions.¹⁶

Routine therapeutic TMS does not intentionally induce a seizure, generally requires no anesthesia, and usually has fewer cognitive adverse effects. Its advantages in tolerability and outpatient delivery do not mean it is the right substitute when ECT’s speed or strength of evidence is clinically necessary.

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What the History Teaches Patients

Three lessons are especially useful:

1. TMS is not an overnight invention. It developed from established physics, human neurophysiology, and decades of controlled clinical research.
2. Innovation occurs in complete protocols. A new coil, target, dose, schedule, or algorithm requires its own evidence and safety evaluation.
3. Regulatory milestones do not end scientific uncertainty. They establish a defined authorized use; they do not prove that every personalization claim, off-label indication, or commercial variation is superior.

Bottom line: modern TMS began in 1985 as a way to stimulate motor cortex noninvasively, became a regulated depression treatment in 2008, and has since expanded into shorter, accelerated, circuit-guided, and condition-specific forms. Its history supports both confidence and caution: confidence in a mature technology, and caution against treating every new use as equivalent to the protocols that have actually been tested.

Previous: How TMS Works: The Science of Magnetic Brain Stimulation
Next: TMS for Depression: What the Evidence Shows

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References

1. Faraday M. Experimental researches in electricity. Philos Trans R Soc Lond. 1832;122:125-162. doi:10.1098/rstl.1832.0006.
2. Wagner T, Rushmore J, Eden U, Valero-Cabré A. Biophysical foundations underlying TMS. Cortex. 2009;45(9):1025-1034. doi:10.1016/j.cortex.2008.10.002.
3. Merton PA, Morton HB. Stimulation of the cerebral cortex in the intact human subject. Nature. 1980;285:227. doi:10.1038/285227a0.
4. Barker AT, Jalinous R, Freeston IL. Non-invasive magnetic stimulation of human motor cortex. Lancet. 1985;1(8437):1106-1107. doi:10.1016/S0140-6736(85)92413-4.
5. Horvath JC, Perez JM, Forrow L, Fregni F, Pascual-Leone A. Transcranial magnetic stimulation: a historical evaluation and future prognosis of therapeutically relevant ethical concerns. J Med Ethics. 2011;37(3):137-143.
6. U.S. Food and Drug Administration. NeuroStar TMS Therapy System: 510(k) Summary (K083538). Decision December 16, 2008.
7. O’Reardon JP, Solvason HB, Janicak PG, et al. Efficacy and safety of transcranial magnetic stimulation in the acute treatment of major depression: a multisite randomized controlled trial. Biol Psychiatry. 2007;62(11):1208-1216. doi:10.1016/j.biopsych.2007.01.018.
8. U.S. Food and Drug Administration. BrainsWay Deep TMS System for Major Depressive Disorder: 510(k) Summary (K122288). 2013.
9. Blumberger DM, Vila-Rodriguez F, Thorpe KE, et al. Effectiveness of theta burst versus high-frequency repetitive transcranial magnetic stimulation in patients with depression (THREE-D). Lancet. 2018;391:1683-1692. doi:10.1016/S0140-6736(18)30295-2.
10. U.S. Food and Drug Administration. De Novo Classification Request: BrainsWay Deep TMS System for adult obsessive-compulsive disorder (DEN170078). Decision August 17, 2018.
11. U.S. Food and Drug Administration. BrainsWay Deep TMS System for short-term smoking cessation: 510(k) Summary (K200957). August 24, 2020.
12. U.S. Food and Drug Administration. Magnus Neuromodulation System with SAINT Technology: 510(k) Summary (K220177). September 1, 2022.
13. U.S. Food and Drug Administration. NeuroStar Advanced Therapy System adolescent major-depression labeling: 510(k) Summary (K231926). March 22, 2024.
14. U.S. Food and Drug Administration. MagVenture Accelerated TMS Therapy System: 510(k) Summary (K260189). May 22, 2026.
15. U.S. Food and Drug Administration. MeRT System for adjunctive treatment of adult PTSD: 510(k) Summary (K260402). June 3, 2026.
16. National Institute of Mental Health. Brain Stimulation Therapies. Accessed July 10, 2026.

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