Non-invasive neuromodulation techniques for cognitive impairment intervention

Cognitive impairment involves sustained deficits across several key domains: memory, executive function, attention, and behavioral regulation. The condition encompasses cognitive dysfunction linked to Alzheimer's disease, mild cognitive impairment, vascular cognitive impairment, and other forms of neurodegeneration. Existing pharmacotherapies frequently yield inconsistent clinical benefits, are often accompanied by side effects, and generally lack disease-modifying properties. These limitations have spurred increasing attention toward safe, repeatable non-pharmacological strategies. Non-invasive brain stimulation, a central non-pharmacological tool, can regulate excitability in targeted brain regions, shape network-level connectivity, and facilitate activity-dependent neuroplasticity. Evidence from multiple clinical settings supports its potential to improve cognitive outcomes. This review centers on major NIBS techniques: repetitive transcranial magnetic stimulation, transcranial electrical stimulation, gamma-frequency sensory stimulation, photobiomodulation, and transcranial ultrasound stimulation. We synthesize their underlying mechanisms, clinical applications, and supporting evidence, aiming to provide an evidence-based framework to guide standardized clinical implementation and future research design in this area.