What Happens to the Brain when You Remove the Hippocampus After an Accident?

When Henry Molaison was a child his skull cracked during an accident. Due to the damage, he began to have seizures where he would lose all control of his bodily functions and blackout. (Kean) The accident had changed his life in a very negative way. Henry Molaison was searching for answers and to have a normal life once again so he went to Doctor William Scoville. Since Doctor Scoville was such a risk taker he suggested surgery, naturally, Molaison agreed. (Kean)

Henry Molaison’s surgery went very well.

Once his hippocampus was removed his seizures no longer occurred and his intelligence increased. However, issues began to arise when the doctors were testing his memory skills. The doctors discovered that he had forgotten everything that happened to him in his life. Though through other tests the doctors came across an amazing thing, Molaison “still retained information long enough from moment to moment to finish a sentence” (Kean). Even though his long-term memory was gone he was still able to form short-term memories.

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This caused many doctors to question how long-term and short-term work in the brain.

Many tests were given to Henry Molaison to test the effects of losing the hippocampus. The most important test given to him was the star task. He was given a piece of paper with two stars on it, one slightly larger than the other so the smaller star could fit inside the larger star. Molaison was then asked to draw a star in between the spaces of the other two stars.

The only catch in this seemingly simple task was that he must draw the star while looking at the paper through a mirror. (Kean) After multiple trials were conducted the stars improved, even though numerous times he had forgotten what he was doing. The test showed that ”His unconscious motor skills centers remembered what the conscious mind had forgotten” (Kean). This important experiment shed light on the differences between declarative and procedural memory; Procedural and declarative memory use different parts of the brain, declarative relies on the hippocampus to work but procedural does not. This explained why even though he no longer had a declarative memory he still had a procedural memory.

Although the surgery was somewhat of a failure, it still helped doctors immensely. The ted talks explain how the outcome of the surgery allowed doctors to discover that there are two types of memories, long-term, and short-term. In addition, the two types use different parts of the brain to function. Sam Kean also discusses how there are several steps in the memory process. After the initial stimulus happens, “It’s temporarily transcribed by neurons in the cortex, then travels to the hippocampus” (Kean); If the occurrence affected the person enough, the hippocampus then transfers the memory back to the cortex for permanent placement (Kean). Since Molaison’s hippocampus was removed, his brain was unable to complete the memory process, meaning that was the reason he no longer had long-term memory. Henry Molaison's surgery helped people grasp a better understanding of how memories are processed in the brain as well as the importance of the hippocampus.