Helen is a 72-year-old widow who immigrated to America from Poland at the age of 11. About ten years ago, even though she was otherwise healthy, her family began to notice small slips in her memory, which included forgetting people's names and dates as well as repeating herself numerous times during the course of a conversation. Gradually, these slips worsened to the point that Helen would go out for a walk and find herself across town without having any idea how she got there or how to get back home. Worried for her safety, her family placed her in a nursing home three years ago. Since then, Helen's cognitive decline has only worsened. She does not recognize her family and she has lost the ability to speak in English. Helen now relies completely on others for self-care. Given this information, Helen would most likely be diagnosed with __________.