including perceptual memory and motor memory, depend on different brain areas outside the medial temporal lobe.
But one additional contribution of that original Scoville and Milner paper cannot be overlooked. The report served as a grave warning to the neurosurgical community that the bilateral removal of the hippocampus should never be done again. H.M. lost his ability to form any new memories and spent the rest of his life depending on his family to care for him. The operation took away his ability to retain anything new about what happened to him and what was going on in the world. It was a terrible price to pay for the reduction of his epileptic seizures, and Scoville and Milner made sure that the entire neurosurgical community understood.
DIFFERENT KINDS OF MEMORY
The kind of memory that H.M. lost with his brain damage is called declarative memory, which refers to those forms of memory that can be consciously recalled. In addition, there are two major categories of declarative memory that depend on the structures of the medial temporal lobe:
• Episodic memory , or memory for the events of our lives, which are those memories of our favorite Christmas celebrations or summer vacations; such “episodes” make up our unique personal histories.
• Semantic memory , which includes all the factual information we learn throughout our lives, such as the name of the states, the multiplication table, and phone numbers.
We now know there are many forms of memory that do not depend on the medial temporal lobe, for example:
• Skills/habits: These are the motor-based memories that allow us to learn to play tennis, hit a baseball, drive, or put our keys in our front door automatically. They depend on a set of brain structures called the striatum.
• Priming: This describes the phenomenon that exposure to one stimulus can affect the response to another stimulus. For example, if you give someone an incomplete sketch of an object that she can’t identify but then show her a more complete sketch of the image, on the next round, she will be able to recognize the object even if less information is provided. Many different brain areas participate in priming.
• Working memory: This form of memory has been called the mental scratchpad and helps us keep relevant information in mind where it can be manipulated. For example, you are using your working memory during a talk with your financial adviser, who is describing the different mortgage rates for you as you try to decide which one is best for your situation. The ability to keep the figures in mind and manipulate them to come to a decision is an example of working memory. That H.M. could keep topics in mind enough to have normal conversations showed that his working memory was intact.
FINDING MY PLACE IN THE MEMORY MYSTERY
The groundbreaking report of Scoville and Milner in 1957 cracked the study of memory wide open and started an avalanche of new questions for neuroscientists to explore. Two questions at the top of the list were, first, figuring out which exact structures in the medial temporal lobe were critical for declarative memory: Was it just the hippocampus or the hippocampus and the amygdala? And, second, how do you visualize the specific change that occurs in the normal brain when a new declarative memory is formed? I didn’t know it when I first began graduate school, but I was going to tackle the first question as my graduate thesis and the second question when I was an assistant professor at NYU.
By the time I entered U.C. San Diego in 1987, we knew a lot more about the important contribution of the hippocampus to memory, but the raging debate at the time focused on whether it was damage to the hippocampus alone that was underlying H.M.’s deficit, as Scoville and Milner hypothesized, or if it was the combined damage to the hippocampus and the amygdala, another possibility that could not be ruled out. A benchmark finding in animals in
But one additional contribution of that original Scoville and Milner paper cannot be overlooked. The report served as a grave warning to the neurosurgical community that the bilateral removal of the hippocampus should never be done again. H.M. lost his ability to form any new memories and spent the rest of his life depending on his family to care for him. The operation took away his ability to retain anything new about what happened to him and what was going on in the world. It was a terrible price to pay for the reduction of his epileptic seizures, and Scoville and Milner made sure that the entire neurosurgical community understood.
DIFFERENT KINDS OF MEMORY
The kind of memory that H.M. lost with his brain damage is called declarative memory, which refers to those forms of memory that can be consciously recalled. In addition, there are two major categories of declarative memory that depend on the structures of the medial temporal lobe:
• Episodic memory , or memory for the events of our lives, which are those memories of our favorite Christmas celebrations or summer vacations; such “episodes” make up our unique personal histories.
• Semantic memory , which includes all the factual information we learn throughout our lives, such as the name of the states, the multiplication table, and phone numbers.
We now know there are many forms of memory that do not depend on the medial temporal lobe, for example:
• Skills/habits: These are the motor-based memories that allow us to learn to play tennis, hit a baseball, drive, or put our keys in our front door automatically. They depend on a set of brain structures called the striatum.
• Priming: This describes the phenomenon that exposure to one stimulus can affect the response to another stimulus. For example, if you give someone an incomplete sketch of an object that she can’t identify but then show her a more complete sketch of the image, on the next round, she will be able to recognize the object even if less information is provided. Many different brain areas participate in priming.
• Working memory: This form of memory has been called the mental scratchpad and helps us keep relevant information in mind where it can be manipulated. For example, you are using your working memory during a talk with your financial adviser, who is describing the different mortgage rates for you as you try to decide which one is best for your situation. The ability to keep the figures in mind and manipulate them to come to a decision is an example of working memory. That H.M. could keep topics in mind enough to have normal conversations showed that his working memory was intact.
FINDING MY PLACE IN THE MEMORY MYSTERY
The groundbreaking report of Scoville and Milner in 1957 cracked the study of memory wide open and started an avalanche of new questions for neuroscientists to explore. Two questions at the top of the list were, first, figuring out which exact structures in the medial temporal lobe were critical for declarative memory: Was it just the hippocampus or the hippocampus and the amygdala? And, second, how do you visualize the specific change that occurs in the normal brain when a new declarative memory is formed? I didn’t know it when I first began graduate school, but I was going to tackle the first question as my graduate thesis and the second question when I was an assistant professor at NYU.
By the time I entered U.C. San Diego in 1987, we knew a lot more about the important contribution of the hippocampus to memory, but the raging debate at the time focused on whether it was damage to the hippocampus alone that was underlying H.M.’s deficit, as Scoville and Milner hypothesized, or if it was the combined damage to the hippocampus and the amygdala, another possibility that could not be ruled out. A benchmark finding in animals in
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