Non-invasive brain stimulation (NIBS) techniques are powerful, safe tools in cognitive neuroscience and clinical neurology, letting researchers and clinicians modulate cortical excitability without surgery. Established modalities include Transcranial Magnetic Stimulation (TMS), using alternating magnetic fields to induce focal electrical currents that trigger neuronal firing, and Transcranial Electrical Stimulation (tES), encompassing methods like Transcranial Direct Current Stimulation (tDCS). Rather than forcing action potentials, tDCS applies weak currents to sub-threshold modulate membrane potentials, shifting neurons toward hyperpolarization or depolarization depending on electrode polarity. These techniques offer insights into functional brain mapping and low-side-effect therapeutic avenues for treating neuropsychiatric disorders such as major depressive disorder and stroke rehabilitation.