Alzheimer disease

An 85-year-old man comes to the clinic for his 6-month follow-up appointment. He has a history of mild cognitive impairment and is accompanied by his 50-year-old son with whom he lives. His vital signs are unchanged since his last visit, and he and his son both report no medical issues since his last appointment other than his continued memory difficulties. He performs poorly on a short-term memory task with an intervening distractor, and his short-term memory has experienced a significant decline compared to his last appointment. On mini-mental status exam, the patient has a score of 8. He is diagnosed with Alzheimer disease and begins a therapeutic course of memantine. Which of the following best describes the mechanism of action of memantine?