BDNF and major depressive disorder: Non-invasive brain stimulation (NIBS) techniques, including transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS), have shown therapeutic efficacy in MDD, potentially exerting neuroprotective effects through the upregulation of BDNF and NGF, improved cerebral perfusion, and modulation of neuroinflammatory and oxidative stress pathways [41].