TABLE 3.

Overview, advantages, and risks of various neurostimulation techniques.

Technique	Overview	Advantages	Risks and disadvantages
Repetitive Transcranial Magnetic Stimulation (rTMS)	Uses a figure-8 coil to generate a magnetic field that induces electricity within brain region right underneath the center of the coil. RTMS uses trains of magnetic pulses at specific intervals called inter-train interval (ITI). Frequencies of stimulation lower than 5 Hz are considered inhibitory, while over 5 Hz are considered excitatory.	RTMS is the most traditional application of brain stimulation that has been FDA-approved for several interventions. There are several devices available that administer rTMS safely (Rossi et al., 2021) and a wide body of literature that characterizes parameter differences exists and can inform novel interventions.	RTMS can be painful or uncomfortable for up to 40% of those who undergo this treatment modality. There is a very low likelihood for seizures, especially with excitatory stimulation. Other risks are scalp, jaw, or face muscle contractions, mild headaches, and transient mood changes. Treatments that involve rTMS alone may require daily visits to a site where equipment to administer it exists.
Deep Transcranial Magnetic Stimulation (dTMS)	Uses an H-shaped coil, which is inserted in a spherical helmet placed on the head. The resulting magnetic field can induce electrical current in deeper brain regions than rTMS. The gain in depth comes with reduced stimulation precision.	Deeper structures, such as the medial prefrontal cortex or the anterior cingulate cortex, can be targeted using this technology. The use of a helmet to host the coil may make it easier to administer than rTMS.	Potential risk of dTMS are similar to rTMS with the addition of possible facial, tooth, or neck pain usually just during the stimulation.
Theta Burst Stimulation (TBS)	Uses a figure-8 coil, like rTMS but instead of trains of single pulses, delivers trains of triple pulses at a higher frequency.	The main advantage is that the same amount of stimulation achieved with a 35–40 min rTMS session can be achieved with only 3 min of iTBS. This allows for accelerated sessions (i.e., having multiple stimulation sessions in the same day)	The trade-off of increases efficiency of TBS comes with an increased risk for seizure. However, seizures are still considered a rare event.
Transcranial Direct Current Stimulation (tDCS)	Uses direct electrical currents to stimulate a brain network. Two electrodes placed over the head modulate neuronal activity via a steady current. Has two different types depending on need: anodal, which excites the network it targets, and cathodal, which reduces neuronal activity, thus allowing for greater control.	TDCS devices are much cheaper and easier to maintain than rTMS/dTMS/TBS devices. Naïve adults can be taught to use these devices in their own homes, increasing feasibility of dissemination. Furthermore, integration with MRI and EEG is easier to accomplish with tDCS than with other stimulation modalities.	The risks of tDCS are similar to those of rTMS. There is also a low probability for scalp burns. A disadvantage of this technology is that the results for its efficacy are mixed (e.g., Santos et al., 2018), and, therefore, it may be less effective than other types of neurostimulation. Currently, there is no FDA approved treatment that relies on tDCS, and experts highlight the need for more mechanistic understanding for this technology (Fregni et al., 2015).