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Courtesy of Christine Smith and Larry Squire, University of California, San Diego

Digital image of a hippocampus

The brain is built to make old memories stick

by Melissa Suran and Michelle Minkoff
Jan 27, 2009


Scientists of a new study used imaging to see why some people remember who killed John Lennon in 1980 better than they recall more recent events such as where U.S. officials found Saddam Hussein in 2003.

One reason is because of a little structure in the brain known as the hippocampus (try remembering that name). The study found that, as people get older, the structure becomes less needed to recall old memories, although it still is useful in creating new ones. And other parts of the aging brain help provide a support system to recall more distant times.

Although there is no consensus where memories are stored, scientists say that various parts of the memory rely on different parts of the brain. The hippocampus is one of the first parts of the brain impaired by illnesses such as Alzheimer's disease.

The study appears in The Journal of Neuroscience on Wednesday. Psychologist Christine Smith and neuroscientist Larry Squire from the University of California in San Diego and the San Diego Veterans Affairs Medical Center began the study in 2006 after working with memory-impaired patients with hippocampal damage.

 “We’re looking at how memory is represented in the brain and which parts of the brain help us learn and remember,” Smith said. “Memories made recently and up to several years ago depend on the hippocampus.”

“Alzheimer’s starts in the hippocampus and then progresses to the rest of the brain,” Smith said. “By the time people have a diagnosis of Alzheimer’s, the damage [usually] has extended past the hippocampus.”

After administering quizzes covering old and current news events to patients, Smith and Squire used imaging techniques to survey possible links between hippocampal damage and memory problems. Even with damage, patients could recall events that happened many years before.

Using 15 healthy test subjects between the ages of 50 and 64, Smith and Squire administered a similar quiz and received almost identical results when memories of old news events were involved.

Each test subject underwent brain imaging while answering 160 news event questions dating back to 1976. Smith said she found that hippocampal activity increased while recalling more recent news information. However, hippocampal activity decreased in recalling older events.

Konstantinos Arfanakis, associate professor of biomedical engineering at the Illinois Institute of Technology, said the method of the study makes sense. “Functional imaging can be used to acquire several images and study signals in the brain over time.”

It can be difficult to measure the difference in brain activities, said Arfanakis, a member of the core faculty at IIT’s Medical Imaging Research Center.

“You can’t just see the brain signals light up," said Arfanakis. “The signals increase in small measurements, and can be hard to see. You have to study the signal over time, and see which signal best matches the up and down pattern of when the patient is remembering certain things."

Although scientists can study which parts of the brain is functioning while recalling memories, it’s hard to say where these memories are stashed.

“It is our understanding that memories are stored across many different parts of the brain, usually the same brain regions that were involved in processing the experiences that comprise the memory itself,” Smith said.

However, Smith said, when lesions affect not only the hippocampus, but also remaining brain tissue in the temporal lobe, patients start to have difficulty remembering events that date back more than 30 years before the time of injury.

Although this study does not promise a cure for diseases that affect the hippocampus such as Alzheimer’s or amnesia, it gives an idea of how the hippocampus works in concert with other brain regions when we recall memories, and it will help doctors to better understand these diseases.

“What we’re trying to is create a fundamental understanding of how the brain works and then you can understand what happens when something goes wrong,” Smith said. “It will further the basic understanding of neuroanatomy that supports learning and memory.”

Squire, who co-authored the study, agreed.

“We like to say we want to fix the car, but first we have to understand how it works, and this study is a step in that direction,” Squire said.

By the way, in case your hippocampus is failing you, John Lennon was shot by Mark David Chapman and Saddam Hussein was captured in Iraq after being found in a hole.