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Summary: Biological Perspectives on Memory

A famous brain surgery patient known as H.M. helped convince psychologists that primary and secondary memory were distinct. H.M. had normal primary memory; he could hold a conversation and form complex thoughts.

H.M.'s specific problem was an inability to form new long-term memories. He could not remember anything once his attention was distracted from it.

Evidence from brain-injury patients implicates the hippocampus and neighboring regions in event memory. The hippocampus was one of the areas removed in H.M.'s brain operation.

The hippocampus seems to integrate information from different areas of the brain, creating memory for facts and events. Memory for sequences and routines, on the other hand, involves other areas of the brain. That is called procedural memory.

Procedural memory can be spared even when there is hippocampal damage. H.M. learned new procedures such as mirror-tracing normally, even though he never remembered the practice sessions.

Adrenaline, in small doses, facilitates the formation of new memories. Rats who are deeply anesthetized can remember classical conditioning that takes place under anesthesia, if they receive an injection of adrenaline.

Alcohol, on the other hand, does not help memory and may lead to state-dependent forgetting. That is memory loss continuing until the same chemical environment is present in the brain. State-dependent memory occurs with depressants but not with stimulants.

Karl Lashley tried to discover the location of memory traces or engrams. No matter where he cut the brain of a rat, the animals still remembered the route through a maze.

Lashley concluded that engrams were stored diffusely throughout the brain, not in specific locations. Modern neuroscientists have drawn the opposite conclusion.

Memories for complex tasks such as maze running involve many multiple specialized neural systems for sight, odor, touch, and spatial orientation. Each system probably has its own memory processes, and Lashley never disrupted them all, no matter where he cut.

The one type of memory that appears localized and unitary is event memory. It is localized near the hippocampus, and it integrates many different forms of information (cognitive, emotional, and sensory). Other types of memory seem to be stored in the neural structures that represent an experience when it first occurs.

Write to Dr. Dewey at

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