Why is memory so important to identity—and losing it, so destructive?
In every situation I’m in, I am calling on my memory to tell me how to act appropriately, to say, “Who is this person I’m talking to? What is our history together? What sort of history do I have personally?” Not consciously, necessarily, but unconsciously. Everything I am today is based on what happened to me throughout my life. If somebody mentions my parents, I instantly have pictures in my mind of them. Both have died, but I remember their voices and the things they told me, the things I loved about them and the things that drove me crazy. All this context we operate in, all day, every day, is tied up with memory. In a sense, you are your memories.
Memory is directed by a region of the brain called the hippocampus. Today, neuroscientists are making revolutionary discoveries about its function. Give us some highlights.
Even before the modern ago of neuroscience, people wondered what memory is. Some people have good memories, some bad. And the sense that your memory is an essence of who you are has been with us for a long time. Early on, neuroscientists tried to figure out where memory is located in the brain. Some people thought it was in a specific region, so they would do experiments with animals and snip out different regions. But they had a hard time finding a region that was specifically devoted to memory.
Nobody had any idea what function the hippocampus, which is buried deep within the brain, had. The best guess was that it was somehow involved in the sense of smell. Now neuroscientists are beginning to appreciate that the hippocampus is vitally important for our ability to navigate through our mental and physical world, and keep track of all of our experiences and visual inputs. The neurons in the hippocampus seem to have this specialized function of tying together all the sights, sounds, sensations, and information we’ve gathered in coherent patterns, like a central switchboard. It’s what coordinates everything else.
Photograph by Ilona Szwarc
One of the most important historical cases of memory loss was a man named Henry Molaison, or “H.M.” as he was known in the scientific literature. Tell us his story—and what scientists learned from him.
He grew up with severe epilepsy that got worse and worse as he got into his twenties. No medication would help; he couldn’t hold down a responsible job and had to live with his parents. So, in 1952, a neurosurgeon decided to try an experimental surgery, in which he cut out H.M.’s hippocampus, which seemed to be the focus of the seizures.
When Henry came out of the surgery, it was immediately clear that something very bad had happened. He had the same symptoms as Lonni Sue Johnson has today: no memory of specific incidents and an inability to form new memories. The doctor would come in, introduce himself, and say, “How are you doing?” They would have a conversation and then the doctor would leave. When he came back five minutes later, Henry would have no idea that he had ever seen this person before.