Devices, systems and methods are disclosed for treating or preventing dementia, such as Alzheimer's disease. The methods comprise transmitting impulses of energy non-invasively to selected nerve fibers, particularly those in a vagus nerve, that modulate the activity of a patient's locus ceruleus. The transmitted energy impulses, comprising magnetic and/or electrical energy, stimulate the selected nerve fibers to cause the locus ceruleus to release norepinephrine into regions of the brain that contain beta-amyloids. The norepinephrine counteracts neuroinflammation that would damage neurons in those regions and the locus ceruleus, thereby arresting or slowing the progression of the disease in the patient.