Why Can’t I Remember What I Had for Lunch?

Dr. Rich O’Brien, MD, PhD, the Disque D. Deane University Professor of Neurology and chair of the Department of Neurology, is an expert in memory disorders. He discusses why a person might be able to recall a retirement party they attended thirty years ago, but not what they had for lunch that day.





Lindsay Key
Welcome to head scratchers, a mini cast from the Duke University School of Medicine. We asked Duke experts to help us understand the questions in science that have us scratching our heads. Today we're speaking with Dr. Rich O'Brien, an expert in memory disorders. We asked Dr. O’Brien, my mother has dementia. She can remember her retirement party 30 years ago, but now what she had for lunch today. Why is that? 

Dr. Richard O'Brien
What you're essentially asking me is the difference between short term and long term memories. Short and long term memories are stored in different parts of the brain. Short term memories are dependent on the hippocampus. For a short term memory to become consolidated takes about a week. Once that week has passed, you can remove the hippocampus and the memory will stay there forever.

What memory is, is a reenactment of the actual event by the parts of the brain that processed it initially. So when you recall a memory you essentially re-process and go through the event again, just like you initially experienced it. Your mother's retirement party 30 years ago is a series of sounds that she remembers, visions that she remembers, and emotions. Because it was a highly emotional event she is far more likely to retain that memory, just like most of us have very strong memories of September 11th. What she had for lunch today might have been incredibly dull,  something she has quite frequently, and she might have been distracted while she was eating it. And for all those reasons, she might not remember what she had for lunch and have absolutely nothing wrong with her.

However, if her husband is concerned that she can't remember what she had for lunch or dinner, can't remember her keys, seems to get lost when she's out of the house, and keeps asking the same question over and over, like, “When is it time for lunch?” even though she's just eaten lunch, then it could be because she has a memory disorder. The rule we use in clinic is that if you're worried about your memory, there's nothing wrong. If someone else is worried about your memory, that's a big problem.

Lindsay Key
Thanks for listening. This podcast was produced by the Duke University School of Medicine. Visit us online at headscratcherspodcast.duke.edu