Transcranial direct current electrical stimulation, or tDCS, is a non-invasive and painless brain neuromodulation technique that involves the application of a low-intensity galvanic current to the patient's scalp in order to electrically stimulate specific areas of the brain
Transcranial magnetic stimulation (TMS) is a procedure that uses magnetic fields to stimulate nerve cells in the brain to improve brain function in the face of certain pathologies. It's called a non-invasive procedure because it's done without using surgery or cutting the skin.
An electroencephalogram (EEG) is a test that measures the electrical activity of the brain using small metal discs (electrodes) attached to the scalp. Brain cells communicate using electrical impulses and are active all the time, even during sleep. This activity shows up as wavy lines in an EEG recording.
Near-infrared spectroscopy (fNIRS) is a noninvasive optical imaging technique that measures changes in oxygenated and deoxygenated hemoglobin concentrations within the brain using their characteristic wavelength absorption spectra.