Devices, systems, and methods for treating dementia or Alzheimer's disease in a subject in need thereof. In one example, chronic visual stimuli having a frequency of about 30Hz to about 50 Hz, and more specifically about 40 Hz, are non-invasively delivered to the subject to entrain gamma oscillations in multiple brain regions of the subject, including the prefrontal cortex (PFC) and the hippocampus. The entrained gamma oscillations modulate neuronal activity across multiple brain regions (e.g., facilitate functional binding of neural networks at low gamma frequencies) to induce various neuroprotective effects (e.g., amelioration of amyloid plaques and tau hyper-phosphorylation) and reduce neurodegeneration. Neuronal activity mediated by the chronic visual stimuli reduces an immune response in microglia and ameliorates aberrantly modified genes and proteins involved in membrane trafficking, intracellular transport, synaptic function, neuroinflammation and DNA damage response. Behavior modification including enhanced learning and memory is observed.
