People come to me to determine if they have significant changes in memory. However, memory is a multifaceted series of skills — for example, knowing how to drive, knowing your birth date, knowing a body of facts, knowing how to get places, etc.

The most critical type of memory to the understanding of most dementias is short-term memory. Short-term memory is not a time but rather a process whereby new experiences or information are stored for later use.

For example, someone with a good short-term memory can read a book once and recite all of the facts. Someone with an average short-term memory may need to review the material a few times. Someone with a poor short term-memory may have to review the information 50 times. Short-term memory loss is the hallmark feature of Alzheimer’s disease.

We owe much of our knowledge of short-term memory to Henry Molaison, who died about a year ago at age 82. Molaison developed seizures as a boy. They worsened after an accident where he was knocked down by a bicycle and may have suffered a concussion. By the age of 26, he was so overwhelmed with seizures that he consented to surgery that had never before been done on a human being. He had the hippocampus from each side of his brain removed. The good news was that the surgery controlled the seizures. The bad news was that the surgery severely impaired his ability to learn new information.

Molaison loved to talk to people but within a few minutes after a conversation he would tell the same story again without remembering that he has just told it. Each time he met or re-met an acquaintance, it was as if it was the first time. When asked who the president of the United States was, he would always reply “Eisenhower.”

He appears to have had the feeling throughout his life that he was awakening from a dream. He was able to learn some new skills such as puzzles which he became better at with practice. But each time he was shown the puzzle he would state that he had never seen it before. In short, he had a severe deficit in learning new information.

If this all sounds familiar to those who live with someone with short-term memory loss caused by Alzheimer’s disease, stroke, head injury, etc., it is because this is the same process and brain structure that is affected in those conditions. The challenge in living with or working with someone with these kinds of dementias is that they, like Molaison, literally live in the moment. They cannot go back to the past 5 minutes and they cannot anticipate the future. It is like being stuck in a single frame of a movie. Treatment involves making those moments joyful with skills they already have.