Transcranial Magnetic Stimulation (TMS) and Transcranial Direct Current Stimulation (TDCS) are both non-invasive methods for stimulating parts of the brain. TMS and TDCS are active neuro devices, in the sense that they change the firing rates and activity levels of neurons, and groups of neurons in the brain. Major differences between TMS and TDCS are described below.
Transcranial Magnetic Stimulation-TMS
TMS devices use a large magnetic coil to pulse a rapidly changing electromagnetic field into the brain, generally through the forehead, or top of the head. The changing electromagnetic field produces a weak electrical current in targeted parts of the brain.
Repetitive TMS (rTMS) is the clinically available method to treat a range of brain disorders such as major depression, and to help with recovery from brain injuries such as ischemic stroke. Available research indicates that rTMS can be moderately beneficial in the treatment of major depression for some patients.
Side effects from TMS can include headache and feeling light headed (common), seizures (uncommon), and mania (uncommon).
rTMS treatment protocols typically include 20 sessions (30-45 minutes each) over the course of a month.
Cost of a typical rTMS treatment course is $6,000 to $10,000.
Transcranial Direct Current Stimulation-TDCS
TDCS devices deliver a small, constant electrical current to the brain via electrodes that are placed on the forehead. Compared to large, heavy, relatively expensive TMS systems, TDCS devices can be lightweight and fairly inexpensive ($500 or less.)
TDCS devices are being tested for a wide range of applications, including therapy for Parkinson’s disease, brain injury and stroke recovery, and major depression treatment. In addition, TDCS devices are being tested for a variety of “brain fitness” uses, such as to improve attention and working memory capacity.
Side effects of TDCS can include initial phosphene effect (flash of light in the eyes) when the device is turned on, and skin irritation where the electrodes are placed.
Given the consumer friendly size and cost of TDCS devices, we expect to see more use of these devices outside the traditional clinical environment.
Transcranial Random Noise Stimulation-TRNS
TRNS devices are the same as TDCS devices, except for the added ability to change the frequency of the delivered current (typically 100hz – 700hz). This means that a TRNS device delivers an alternating current (AC) to the brain, vs. a direct current (DC).
A recent study published in Current Biology related the use of TRNS devices to stimulate the dorsolateral prefrontal cortex (DLPFC), a key brain area for arithmetic skills, while subjects underwent five days of cognitive training with math calculation exercises.
The results showed that the group receiving TRNS performed significantly better on both math calculations and recall of arithmetic principles, compared to the control group. In addition, the TRNS group still showed the positive training effects six months later.
As with TDCS, we should see some interesting applications in education and workplace settings for TRNS devices.
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