NeuroStar is the most widely studied TMS system in the United States. Understanding the science behind how it works — from the physics of magnetic stimulation to the neuroscience of neuroplasticity — helps patients make informed treatment decisions and set accurate expectations.
The Physics: How Magnetic Pulses Affect Neurons
TMS is based on the principle of electromagnetic induction, described by Michael Faraday in 1831: a changing magnetic field induces an electrical current in a nearby conductor. In TMS, the "conductor" is the human brain. The NeuroStar device generates brief, powerful magnetic pulses through a figure-eight coil placed against the scalp. These pulses penetrate the skull — which, unlike radio waves, magnetic fields pass through without significant attenuation — and induce small electrical currents in the neurons directly beneath the coil.
When these currents are sufficiently strong and the pulse frequency is in the therapeutic range (typically 10 Hz for standard rTMS), neurons in the targeted region are depolarized — they fire. Repeated depolarization of this kind is the trigger for neuroplastic change.
Changing magnetic field → induced electrical current in neurons → neuronal depolarization → repeated stimulation → neuroplasticity. This is the chain of events from coil to clinical improvement.
Why the DLPFC? The Neuroanatomy of Depression
The left dorsolateral prefrontal cortex (DLPFC) is the primary TMS treatment target for depression. This is not arbitrary — it reflects consistent neuroimaging findings across multiple research groups showing that the left DLPFC is measurably hypoactive in patients with Major Depressive Disorder compared to healthy controls.
The DLPFC plays a critical role in executive function, working memory, emotional regulation, and top-down modulation of the limbic system — the brain's emotional processing network. When the DLPFC is underactive, its regulatory influence over the amygdala and related structures is diminished, contributing to the emotional dysregulation, anhedonia, and rumination that characterize depression.
TMS stimulation of the left DLPFC is designed to reverse this hypoactivity — increasing baseline activity in this region through repetition-induced neuroplasticity.
Neuroplasticity: The Mechanism of Lasting Change
The reason TMS produces lasting results — not just acute effects during stimulation — is neuroplasticity. Repeated stimulation of a neural circuit strengthens synaptic connections within that circuit through a process called long-term potentiation (LTP). "Neurons that fire together, wire together" — the principle first articulated by Donald Hebb in 1949 — describes the mechanism by which TMS promotes durable functional change in the targeted circuitry.
This is why TMS requires a full course of 36 sessions rather than producing immediate results: the neuroplastic changes that underlie sustained clinical improvement accumulate gradually over weeks of repetitive stimulation. Most patients begin noticing clinical improvement between weeks two and three — as the neuroplasticity changes reach a functional threshold — with continued improvement through the end of the course.
NeuroStar's Figure-Eight Coil Design
The figure-eight (or butterfly) coil design used in NeuroStar is specifically engineered to concentrate the magnetic field at the intersection of the two coil loops — the point where the two magnetic fields add constructively. This creates a focused stimulation volume at the intended depth in the cortex, with the field strength dropping off rapidly outside this focal point. The result is more precise targeting of the left DLPFC with less incidental stimulation of adjacent cortical regions — a critical factor in both efficacy and tolerability.
Precise DLPFC targeting is associated with better clinical outcomes in TMS. NeuroStar's coil design and built-in positioning system ensure consistent, reproducible coil placement at every session — a key factor in maintaining treatment efficacy across 36 sessions.