At the age of 9, Mr.Molaison banged his head hard after being hit by a bicycle rider in his neighborhood near Hartford. This boy then developed severe seizures, but at the time, scientists had no way of looking inside his brain. They could not tell if the blow from the accident had anything to do with the seizures, or had they have any high understanding of how complex functions like memory or learning functioned biologically. After eighteen years, his condition got severe as he was blacking out frequently, had devastating convulsions and could no longer earn a living. He arrived at the office of Doctor Scoville, who after exhausting other treatments, decided to surgically remove two finger-shaped slivers of tissue from Mr. Molaison’s brain. These two slivers are now known to be a portion of temporal lobes- the hippocampus, an area deep in the brain, about level with the ears. The seizures disappeared, but the procedure left the patient radically changed. His short term memory worked without much of a notable change, however it became obvious that he could no longer transfer new information into long term memory. He could recall events from earlier in life, as he had long term memory from before the operation, but he could not make new memory. This incident, however, has become one of the great milestones in the history of modern neuroscience. In order to study his memory, doctors gave him tests and tasks.. Every time Molaison performed a task, it struck him as an entirely new experience. He had no memory of doing it before, however with practice he became proficient.
The implications of these studies were enormous. Although his condition was tragic, it helped us now know that that the temporal lobe is important for forming and storing memory, as well as that the hippocampus, which they removed, plays a key role in forming new memories Scientists could now determine that there were at least two systems in the brain for creating new memories, which was a big step from the old theory, that both short-term and long-term memory were wired together in the brain. One of these systems is known as declarative memory, and we now know that it records names, faces and new experiences and stores them until they are consciously retrieved. This system depends on the function of medial temporal areas, particularly in the hippocampus, which is what Molaison lacked. The other system, commonly known as motor learning, is subconscious and depends on different brain systems. “This explains why people can jump on a bike after years away from one and take the thing for a ride, or why they can pick up a guitar that they have not played in years and still remember how to strum it.”
Soon after information from this study was revealed, scientists wanted an amnesic study and researches began to map out other dimensions of memory. Since they saw that Molaison’s short-term memory was fine, and he could hold on to it for about 20 seconds, they inferred that it was holding on to them without a hippocampus was impossible. This came opened a way to study the explicit and implicit systems of the brain, and provided a basis for all research that came after.
No comments:
Post a Comment