For patients considering TMS therapy in Delhi, understanding how the treatment actually works is often reassuring. Unlike medication, which works through complex neurochemistry inside the body, TMS is fundamentally an electromagnetic phenomenon — one whose principles have been understood since the 1830s. This guide walks through the TMS mechanism of action step by step.
At Mind Brain Institute, we prescribe medication when it’s clinically indicated and offer TMS as an additional or alternative treatment tool.
The physics — magnetism becomes electricity
The foundational principle behind TMS was discovered by Michael Faraday in 1831: when you pass a rapidly changing electrical current through a coil of wire, it generates a magnetic field. When that magnetic field passes through nearby conductive tissue, it induces a small electrical current in that tissue.
This is electromagnetic induction — the same principle that runs electric motors, MRI scanners, and wireless phone chargers.
In TMS, a small electromagnetic coil is held against the scalp. The machine sends rapid pulses of current through the coil, generating a focused magnetic field. That field passes painlessly through the skull (bone does not block magnetic fields) and induces a gentle electrical current in the brain tissue just below the coil.
Why the induced current matters
The tiny induced current is enough to make neurons in that small region fire — essentially, TMS temporarily forces neurons in the target area to become active.
For any single pulse, this effect is momentary. But repetitive TMS (rTMS) delivers many pulses per second over 20–40 minutes. And the full treatment involves 20–30 daily sessions over 4–6 weeks. Over this scale of stimulation, the brain begins to respond not just momentarily but structurally.
How TMS affects the brain — the neuroscience
Three key effects have been demonstrated:
- Direct neuronal firing: Neurons in the stimulated region fire in response to the magnetic pulses. This is the immediate effect.
- Long-term potentiation (LTP): Repeated stimulation of the same synapses strengthens the connections between them. This is the same neuroplastic process behind learning and memory.
- Neurochemical changes: TMS influences release of neurotransmitters (dopamine, serotonin, glutamate) and neurotrophic factors like BDNF — molecules that support neuronal health and new connection formation.
Together, these effects reshape brain circuits over the course of treatment.
Why we target specific brain regions
For depression, the target is usually the left dorsolateral prefrontal cortex (DLPFC) — roughly above and slightly forward of your left temple. In depression, this region is consistently underactive, and its dysfunction is linked to depressed mood, low motivation, and inability to break out of negative thought patterns.
By using magnetic pulses and brain stimulation focused on the left DLPFC, TMS gradually restores healthier activity in this region — which then supports better connectivity with the deeper limbic and reward-processing regions involved in mood.
Different conditions use different targets:
- OCD: supplementary motor area or medial prefrontal cortex
- Anxiety: right DLPFC (typically)
- Addiction: DLPFC (impulse control) or medial prefrontal cortex
- Chronic pain: motor cortex
The location and stimulation frequency change based on what condition is being treated.
The concept of neuroplasticity
Neuroplasticity — the brain’s ability to reorganise itself in response to experience — is the reason TMS produces lasting change rather than just temporary effect. Every neural circuit strengthens with use (“neurons that fire together, wire together”). Over a full TMS course, the treatment repeatedly activates target circuits, strengthening them structurally.
This is why TMS effects can persist for months after the treatment course ends — the underlying brain circuit has been physically strengthened.
How TMS compares to other brain-based treatments
Electroconvulsive Therapy (ECT): delivers a much larger electrical current that induces a controlled seizure. Highly effective for severe depression but requires anaesthesia and has memory side effects. TMS is milder — no seizure, no anaesthesia, no memory effects.
Deep Brain Stimulation (DBS): surgical implantation of electrodes in specific brain regions. Reserved for severe treatment-resistant cases. TMS is non-invasive; no surgery required.
Transcranial Direct Current Stimulation (tDCS): applies a very weak direct electrical current through the scalp. Less powerful than TMS. Different mechanism, different applications.
Does TMS change brain activity?
Yes — and this has been demonstrated with brain imaging. Functional MRI, PET, and EEG-based imaging studies have shown measurable changes in blood flow, glucose metabolism, and functional connectivity in the stimulated region and related brain networks after successful TMS courses.
FAQ
What is the mechanism of action of TMS?
TMS uses focused magnetic pulses to induce electrical currents in specific brain regions, causing neurons to fire. Repeated over multiple sessions, this strengthens the stimulated circuits through neuroplasticity.
How does TMS therapy affect the brain?
It temporarily activates neurons in the target region, and over multiple sessions, it strengthens neural connections, influences neurotransmitter release, and increases neuroplastic factors like BDNF.
How do magnetic pulses stimulate the brain during TMS?
The magnetic field from the coil passes painlessly through the skull and induces a small electrical current in the underlying brain tissue — enough to activate neurons in that region.
Does TMS change brain activity?
Yes. Brain imaging studies have documented measurable changes in activity, connectivity, and metabolism in stimulated brain networks after TMS courses.
What role does neuroplasticity play in TMS treatment?
Neuroplasticity is the mechanism that turns temporary stimulation into lasting change. Repeated firing of a circuit strengthens it structurally, which is why TMS effects can persist after the treatment course ends.
