A 76-year-old man is brought to clinic by his daughter because of progressively worsening short-term memory loss over the past 3 years. He has difficulty managing finances, frequently misplaces items, and repeats the same questions. Neurologic examination shows no focal deficits. He was started on donepezil 8 months ago with modest improvement, but his cognitive function has continued to decline. His physician adds another medication. Two weeks later, the patient develops intermittent dizziness and appears more confused than baseline; he also reports seeing “small animals running across the floor” that his daughter cannot see. Which of the following best describes the mechanism of the newly added medication?

(Assume no illicit substance use and no acute infection.)