Friday, January 15, 2010

A story about memory

Dear educated and interested readers,

Once upon a time, there was a man who suffered from anterograde amnesia, which is a serious condition where, following some sort of insult to the brain (via trauma or surgery), a person is unable to form long-term memories.
This man walked into a doctor's office and reached out to shake hands with the doctor - to his painful surprise, the doctor had a tack in his hand, which sharply pricked the patient's palm! The next day, this patient walked into the same office, and (having no memory, due to his amnesia) averred he had never met the doctor before. However, when the doctor reached out to shake his hand, the patient inexplicably answered, "I don't know why, but I am afraid to shake your hand!"

Now, let me tell you a story from my life that illustrates this same peculiar phenomena, and then I will explain to you why it takes place.

My friend Esther and I were riding our bikes on the interurban trail near where we live, and she told me (in more or less these words), "I'm always afraid I'll fall when we take the corners, because once when I was little I took a sharp corner up into a driveway. I fell and chipped my tooth, and my mouth was bleeding and I was all scratched up. Ever since then, I've been afraid I'll fall on the corners!"

Now for the explanation: As you probably know, there are several types of memory. There is declarative memory (for instance, facts), and procedural memory, which is made up of emotional and muscle memory. An example of muscle memory might be being able to tie your shoe, or type on the computer keyboard - you cannot exactly describe this to somebody, but your hands can do it seemingly "automatically" - that is to say, without the help of your declarative memory.
Emotional memory is also like this - we have emotional responses and reactions to things that we may not even be able to explain! These emotional memories seem to be stored in a structure in the brain called the amygdala (illustrated in the photo at right).

In Esther's case, she experienced intense fear and pain when her bike turned on the corner. Her brain associated the fear and pain with the action she was taking - turning on the corner - and now whenever she takes that action her amygdala sets off the alarms, warning her brain of what might happen again. This may seem very logical to us, but remember the man in the beginning of the story - he had no conscious, declarative memory of the event, but he was still, for some reason, afraid!

When I told this to Esther, she started laughing and told me another story. This story will nicely illustrate the phenomenon described in the beginning of this article.

"When I was little, I was at my friend Grace's house," she told me, "and I was pushing her on the tire swing. I pushed her too far, and she smacked her head into the tree! Of course, she went crying into the house, and I felt so bad. The other day Grace was at our house, and I asked her if she remembered the incident. She started laughing - and told me that she didn't remember me pushing her into the tree at all, but whenever she got onto the tire swing she was afraid, for some unexplainable reason, that she would hit the tree!"

You may actually know more than you know! With love and fond memories,

Mrs H
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