What’s the difference between transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS)*
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What TMS and tDCS devices look like:
TMS Devices: TMS machines are about the size of a large microwave or mini-fridge, depending on the model. They are always wall powered (220 V), heavy, and usually on a cart. The most commonly used TMS coil can look like a double-loop (figure-8). The coil is placed on the subjects head, connected to the machine by a heavy duty high voltage cable and is held in place by a mechanical arm. Additional equipment such as a neuronavigation system, which uses a sophisticated infrared camera or magnetic trackers, can be used to aid in accurate placement of the TMS coil over the targeted brain region. Additional equipment can also include an EMG machine which usses small sticky electrodes placed on the hand to monitor muscle twitches, which are a normal part of setting up the TMS device.
TDCS Devices: tDCS devices range in size from a cell-phone to a small microwave. They are almost always battery powered and light enough to be carried around or rested on a normal table top. The subject must wear head-gear which includes the electrodes. Electrodes are wet with saline (salty water) or gel filled. tDCS devise have small wires that run from the device to the head-gear on the subject head and connect to the electrodes.
The largest difference between tDCS and TMS devise is that tDCS is battery powered, small, and uses a headgear while TMS is wall powered, large and uses a coil held over the head. Furthermore, tDCS is investigational whereas TMS has been FDA approved for the treament of Major Depressive Disorder and is reimbursable by insurance.
How do TMS and tDCS devices work:
TMS: TMS devices send a short high-power electrical surge to the coil. This short pulse though the coil produces electrical current flow in the subject’s head though the principle of “induction”. Depending on where the coil is held, the part of the brain under the coil gets stimulated. The current produced in the head is pretty intense. When the coil is placed on the motor cortex, TMS makes the cells in the motor cortex active, leading to a finger twitch. TMS can be applied as a single pulse (single short surge) for example to produce a finger twitch. Or TMS can be applied as rapid series of pulses. This is what is called repetitive TMS or rTMS. These pulses come in a specified pattern. Treatment with TMS use rTMS of specific pulse patterns applied to specific brain regions. TMS is FDA Cleared for the treatmenet of depression. This protocol involves treating the DLPFC (F3) with a 10 Hz frequency at 120% of the motor-threshold.
tDCS: tDCS uses very low current applied for tens of minutes. The current is applied via electrodesand passes through the head to the brain. The current that reaches the brain is low power so it does not make cells active (the way TMS does) but it can change the tone of the brain. It can make the brain more active or responsive, which is called anodal tDCS, or make the brain less active or responsive, which is called cathodal tDCS.
The largest difference between how tDCS and TMS work is tDCS us a sustained low-power current that changes brain tone up or down while TMS and rTMS make the brain active with each pulse.
What are the side effects of TMS and tDCS
TMS: TMS can produce twitching in the scalp and some discomfort. Most people get used to it. The most serious side-effect of rTMS is the potential for seizures. The chances of seizure are very low.
tDCS: The main known side-effects of tDCS are itching and tingling that happen under the electrode. As a rule, people don't mind how tDCS feel. These stop as soon as the tDCS session stops.
So the biggest difference between tDCS and TMS as far as side-defects is TMS can be more uncomfortable and has a very low risk of seizure.
What works better, TMS or tDCS?
TMS: TMS has been investigated, meaning used in clinical trials and off-label for a range of different brain diseases. In the USA, TMS is cleared by the FDA only for the treatment of Major Depressive Disorder.
tDCS: TDCS is also being investigated and tested for a many different brain diseases. In the USA, tDCS has not been approved for the treatment of any disease while in Europe and other countries tDCS hase been approved for the treatment of Depression and Pain.
Bottom Line: So what works better as a treatment, tDCS or TMS? It is not fair to say one or the other because if depends on many things. First what the disease is as well as many personal factors. Just because the FDA has not approved a device for some disease is not an indication of whether the device works or does not work, it just means the FDA itself is not ready to endorse it. The best thing to do is to first do your own research and then talk to your doctor about the best options for you.
When do you get TMS or tDCS?
TMS: For TMS treatment you will need to find a physician who provides TMS service in their clinic. Access will vary with country and region. You can find provider on various websites such as Neuromodec Find a TMS Provider.
tDCS: tDCS that is intended for medical treatment is available only through a physician. Access will vary by country and region. You can additionally find a tDCS provider on the Neuromodec Find a tDCS Provider. tDCS devices that are not intended for medical purposes can be purchased online. Do your research first via our tDCS Device Comparison Table
Bottom line: TMS will always be an in-clinic treatment. tDCS can theoretically be done at home.