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.

 “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.

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.

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.

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

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.

“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.