Brian Handwerk
From National Geographic News

January 17, 2007
Amnesia may rob people of their imaginations as well as their memories, new research suggests.

"What we've shown is that people with amnesia really are stuck in the present," said lead study author Eleanor Maguire of the Wellcome Trust Centre for Neuroimaging at University College London.

"They can't recall the past, and now it seems that they can't even imagine the future or indeed richly imagine even fictitious experiences."

Amnesia, which is sometimes temporary, describes several conditions that involve partial or complete memory loss.

Brain damage, tumors, strokes, or even psychological issues that cause the brain to black out disturbing memories can cause the effect. (Related: "Beyond the Brain" in National Geographic magazine.)

Incomplete Picture

Reporting this week in the online edition of the journal Proceedings of the National Academy of Sciences, Maguire and colleagues examined patients who were "profoundly amnesic."

These patients were unable to acquire any new memories.

Several of the amnesiacs did have some past memories, but only of events that occurred 10 or even 20 years before the onset of their illness. Many had no detailed memories of anything that had ever happened in their lives.

The researchers asked the amnesiacs to imagine scenarios such as lying on a sandy beach and then to describe what the experience would be like—what they would see, hear, and smell.

But the patients could describe only fragmented scenes.

"They described many of the elements that would characterize the experience," Maguire said. "But they couldn't put them into a spatial context—they couldn't organize them into the location of that scenario."

"They would know there should be a sea, that there would be sand, but in the way they described it, they'd say, I just can't visualize the whole scene as you'd like," she added.

Without an environment or location to house a scene, amnesiacs may be unable to recreate or imagine normal experiences.

"If you think about memories, they are always somewhere, because things happen somewhere," Maguire explained. "So spatial context is very important for our experiences."

Placing a Memory

Scientists believe that the brain recalls past events by meticulously reconstructing the individual cues of an experience—the people, objects, and other aspects that composed the scene.

This process is thought to occur in a region of the brain known as the hippocampus, which was damaged in the amnesiac patients studied. (Related: "First Ever Brain 'Atlas' Completed" [September 26, 2006].)

The new study implies that similar processes in the hippocampus are also used to imagine future events, suggesting that memory and imagination are two sides of the same coin.

The hippocampus may provide the spatial context that binds and blends the people, objects, and other aspects of a memory—or an imagined event.

"Maybe the hippocampus," Maguire said, "is the basic scaffold around which memories are hung."