Amnestic Disorder: Definition, Causes and Treatment for Amnesia

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  • 0:04 Amnesia
  • 0:52 Types of Amnesia
  • 2:58 Causes and Treatment
  • 4:08 Lesson Summary
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Instructor: Natalie Boyd

Natalie is a teacher and holds an MA in English Education and is in progress on her PhD in psychology.

Our memories shape, and in many ways define who we are. But what happens when you lose your memories? In this lesson, we'll look at amnestic disorders, their causes and treatments.


In 1953, Henry Molaison had brain surgery to remove part of the left side of his brain. He suffered from severe epileptic seizures, and the doctors hoped that by removing a part of his brain they'd be able to stop the seizures.

They were right; after the surgery, Molaison no longer had seizures. But he had another problem: he also no longer had the ability to make new memories.

Amnestic disorder, also called amnesia, is a psychological disorder that involves a disruption of memory. This can mean that the person loses memories from the past, that they lose the ability to make new memories, or a combination of both.

Let's look a little closer at the types, causes, and treatment of amnesia.

Types of Amnesia

There are many types of amnestic disorders. The most commonly studied ones are retrograde and anterograde amnesia.

Remember Henry Molaison? After he had surgery to remove part of his brain, many of his childhood memories were still intact. He could remember where he went to school, the time that he fell off his bike, and other important moments from his past.

But every day for the rest of his life, he woke up believing that he had just had the surgery. Even over 50 years after his surgery, he didn't remember his life past the day of the surgery!

Molaison, who is sometimes referred to in psychology circles by the initials H.M., suffered from severe anterograde amnesia. This type of amnestic disorder involves an inability to form new memories. Patients like H.M. can learn how to do new things, but they don't remember learning them.

For example, if H.M. was taught a new computer game one day, the next day he would say that he had never played the game before. But when he played it, he would do much better than he had the first time he played it, and much better than other first-time players. He had learned how to play the game but didn't remember learning it.

Imagine for a moment that H.M.'s surgery had a different outcome. He woke up from the surgery and had no problem making new memories. The day after the surgery, he woke up and remembered the day before, when he'd had the surgery.

But imagine that H.M. could not remember anything at all from before the surgery. All of his childhood memories, his parents, his favorite restaurant, his least favorite vegetable: all of these memories gone. That is retrograde amnesia, an amnestic disorder that involves losing memories that have already been formed.

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