The general idea is similar, but the details are quite different.
As you might remember from physics, moving a conductor relative to a magnetic field induces an electric current in the conductor. In a generator, the magnet is often fixed while the conductor is spun around by a water, wind, or steam-driven turbine. Neurons are conductive but tricky to move, so we move the magnetic field instead. TMS uses strong electromagnets to generate magnetic pulses. The changing field induces currents in the neurons.
Magnetic fields are not attenuated by the skull or scalp, so the resulting field is much, much stronger. In practice, TMS often produces an initial burst of activity, followed by a longer period of suppression. This can be used to temporarily and reversibly inactivate a tiny chunk of the brain, which is great for research. It may also be a way to “reset” neural circuits that have gotten stuck in some weird state (this is one hypothesis about depression, and TMS does seem to help with it).
I think of tES as “nudging” the neurons’ own activity towards some state that you want, while TMS is more like a sharp rap. It’s not obvious if one is always better than the other. TMS devices are pretty large (lots of capacitors) and fixed, while you could imagine tES being more suitable for use outside a clinic.
As you might remember from physics, moving a conductor relative to a magnetic field induces an electric current in the conductor. In a generator, the magnet is often fixed while the conductor is spun around by a water, wind, or steam-driven turbine. Neurons are conductive but tricky to move, so we move the magnetic field instead. TMS uses strong electromagnets to generate magnetic pulses. The changing field induces currents in the neurons.
Magnetic fields are not attenuated by the skull or scalp, so the resulting field is much, much stronger. In practice, TMS often produces an initial burst of activity, followed by a longer period of suppression. This can be used to temporarily and reversibly inactivate a tiny chunk of the brain, which is great for research. It may also be a way to “reset” neural circuits that have gotten stuck in some weird state (this is one hypothesis about depression, and TMS does seem to help with it).
I think of tES as “nudging” the neurons’ own activity towards some state that you want, while TMS is more like a sharp rap. It’s not obvious if one is always better than the other. TMS devices are pretty large (lots of capacitors) and fixed, while you could imagine tES being more suitable for use outside a clinic.