Table 1.

Target regions and modes of action

Modality	Pre-treatment	Target region	Mode of action	References
ECT	Anesthesia or muscle relaxant	Cerebral cortex	Small electrical current to induce seizure	[19]
tDCS	–	Cerebral cortex	Low-intensity direct current (1–2 mA) modulates neuronal excitability	[27–29]
rTMS	–	Cerebral cortex	Magnetic pulse induces electrical current which depolarizes target neurons	[40, 41]
VNS	Implantation of pulse generator in left chest wall and electrodes by minor surgery	Electrode wrapped around left vagus nerve	Modulates levels of neurotransmitters or their metabolites along with functional activity of CNS regions	[56–58]
DBS	Frame-based stereotaxis; approaching deep brain targets through a small skull opening	Nucleus accumbens, ventral striatum, inferior thalamic nucleus, peduncle, lateral habenula, subgenual cingulate	High-frequency stimulation (130–185 Hz); reduces neuronal transmission in targeted brain region by inactivating voltage-dependent ion channels, which modulates and restores neuronal circuits involved in depression	[15, 77, 78]