When traditional antidepressants fail older adults with treatment-resistant depression, where can they turn? Standard therapies, built on the monoamine hypothesis, often fall short in aging brains or those affected by neurodegenerative diseases like Alzheimer's, as the pathways they rely on may be dysfunctional. This episode dives deep into a systematic review exploring a paradigm-shifting alternative: ketamine and its derivatives, esketamine and arketamine. These compounds sidestep conventional mechanisms, instead targeting the NMDA receptor to promote widespread neuroplasticity. We uncover the powerful clinical findings, revealing that ketamine provides rapid, robust relief and is equally effective in geriatric and non-geriatric populations. Discover how ketamine not only improves mood but also restores vital executive functions, helping patients think more clearly. We'll explore the neurological data showing how the treatment restores the brain's crucial "excitation-inhibition" balance, leading to more organized cognitive processing. While the immediate benefits are profound, we also confront the critical unresolved question of long-term sustainability. Join us to understand how this research challenges us to move beyond targeting single chemicals and toward therapies that aim to rebuild the entire circuitry of the mind.