04 Track 4

Unit 11

The Mystery of Memory

Chapter 1

The Mysteries of Memory Loss

Page 189

The Mysteries of Memory Loss

Many people claim to have a bad memory, and it’s true that we have trouble at times remembering where we put our house keys or recalling the names of people we’ve recently met.

But there are those who suffer more serious memory problems, including memory loss over time or memory loss due to injury, disease, or complications of surgery. These conditions are still not very well understood by doctors and scientists.

Many people experience memory loss as they age. In the past, neuroscientists, doctors who study the brain − had theories about how the brain contained only a certain number of cells and how, over time, these cells might get used up.

More recent research suggests that the brain may continue to manufacture new brain cells throughout a lifetime.

Also, there is now evidence that damage to the hippocampus an area of the brain thought to be important in the process of recalling information may play an important role in memory loss.

Studies conducted on patients who have suffered damage to this area of the brain show that while they can still recall memories stored before the brain was damaged, they are unable to remember new facts.

In addition, diseases associated with old age, (such as Alzheimer’s,) and other problems including short- and long-term memory loss, are now being traced to possible damage to the hippocampus.

Two very special patients have helped doctors study memory and the hippocampus in recent years. These two men are referred to only as EP and HM, and each of them suffered memory loss after the loss of this particular section of the brain.

HM suffered a head injury as a child and later underwent experimental brain surgery to remove most of his hippocampus. EP, in contrast, contracted a disease that ate away much of his hippocampus.

Both men are now unable to form new memories, but they can remember some things from before their traumas.

For example, both EP and HM are likely to recall things they learned in school or family memories from their youth, but both will also always think it’s the first time they’ve met you, no matter how many times you may have met previously.

Through HM, who has been studied much longer than EP, researchers have learned about different memory abilities. Even though HM couldn’t say what he’d had for breakfast or name the current U.S. President, there were some things that he could remember.

Scientists found that he was able to learn complicated tasks without even realizing it. In one study, he learned how to recreate a drawing by only seeing the drawing’s reflection in a mirror.

Each time HM did the task, he claimed never to have tried it before. And yet, each day his brain got better at guiding his hand to work in reverse.

Scientists generally classify memories into two categories: declarative and non-declarative. Declarative memories are things you know you remember, like the color of your car or what happened yesterday afternoon.

EP and HM have lost the ability to make new declarative memories. Non-declarative memories are the things you know, without consciously doing them, like how to ride a bike or how to walk from your bed to your bathroom.

Those unconscious memories don’t rely on the hippocampus. They happen in completely different parts of the brain. As EP and HM so strikingly demonstrate, you can damage one part of the brain and the rest will keep on working.

The exact process by which memories are coded and retrieved remains a mystery, but scientists and doctors are working to better understand the brain’s remarkable ability to store and recall information.