The umbrella term you’re looking for is transcranial electrical stimulation, or tES. It is also called tACS (AC for alternating current), tDCS (for direct current), or tRNS (for random noise), depending on what type of electricity is being used. In most cases, conductive electrodes are placed on the head and a weak current is passed between them. This is thought to generate an electric field that polarizes the neurons between them and interacts with the cells’ on-going electrical activity.
The idea itself is very old: someone in 46 AD apparently cured headaches by applying electric fish to their foreheads. It’s been rediscovered a few times since then, and there’s been a huge boom since about 2000, with people trying it for everything under the sun in both healthy people and a wide variety of patients, with a lot of hype.
Despite that, it’s still unclear how it works, or indeed if it works at all. The electric field that reaches your brain is rather weak—-the skin and skull shunt away a lot of the current. A lot of the human experiments are not the greatest (small sample size, strange methodological problems) and there has been some concern that many of the effects either aren’t real or are due to confounds (e.g., placebo effects, or changes in attention/motivation due to the tingling sensation it causes on the scalp), and there’s been a lot of “counter-hype” about how the whole thing is bunk.
I am fairly certain it does something, though it needs to be applied (and evaluated) carefully. Over the last few years, I—-and some awesome collaborators—-have been recording neural activity from monkeys receving tES. We find neural effects at multiple levels ranging from single cells to long-range functional connectivity, along with effects on the animals’ behavior. We’ve got a few papers here: http://packlab.mcgill.ca/publications.html (look for my name; the lab does a lot of different things). There’s a lot more to be done though.....
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.
The umbrella term you’re looking for is transcranial electrical stimulation, or tES. It is also called tACS (AC for alternating current), tDCS (for direct current), or tRNS (for random noise), depending on what type of electricity is being used. In most cases, conductive electrodes are placed on the head and a weak current is passed between them. This is thought to generate an electric field that polarizes the neurons between them and interacts with the cells’ on-going electrical activity.
The idea itself is very old: someone in 46 AD apparently cured headaches by applying electric fish to their foreheads. It’s been rediscovered a few times since then, and there’s been a huge boom since about 2000, with people trying it for everything under the sun in both healthy people and a wide variety of patients, with a lot of hype.
Despite that, it’s still unclear how it works, or indeed if it works at all. The electric field that reaches your brain is rather weak—-the skin and skull shunt away a lot of the current. A lot of the human experiments are not the greatest (small sample size, strange methodological problems) and there has been some concern that many of the effects either aren’t real or are due to confounds (e.g., placebo effects, or changes in attention/motivation due to the tingling sensation it causes on the scalp), and there’s been a lot of “counter-hype” about how the whole thing is bunk.
I am fairly certain it does something, though it needs to be applied (and evaluated) carefully. Over the last few years, I—-and some awesome collaborators—-have been recording neural activity from monkeys receving tES. We find neural effects at multiple levels ranging from single cells to long-range functional connectivity, along with effects on the animals’ behavior. We’ve got a few papers here: http://packlab.mcgill.ca/publications.html (look for my name; the lab does a lot of different things). There’s a lot more to be done though.....