According to the Duke University Medical Center neuroscientists the places a memory is processed in the brain may determine how someone can be absolutely certain of a past event that never occurred.
The discovery could help doctors better assess the changes in memory that accompany aging and possibly lead to breakthroughs in the diagnosis of Alzheimer's disease, said the study's lead author, neuroscientist Robert Cabeza.
Information retrieved from memory is simultaneously processed in two specific regions of the brain, each of which focuses on a different aspect of a past event. The medial temporal lobe (MTL), located at the base of the brain, focuses on specific facts about the event. The frontal parietal network (FPN), located at the top of the brain, is more likely to process the global gist of the event.
The specific brain area accessed when one tries to remember something can ultimately determine whether or not we think the memory is true or false, the researchers found.
"Human memory is not like computer memory -- it isn't completely right all the time. There are many occasions when people feel strongly about past events, even though they might not have occurred," said Cabeza.
In order to find out why some people can be so confident about false memories, Cabeza and his colleagues carried out MRI scans of the brains of healthy volunteers as they took memory tests, using the functional MRI imaging technique.
The brain scans showed that volunteers who had accurate memories of an event showed increased activity in the MTL at the base of the brain, which focuses on facts about a past event.
"This would make sense, because the MTL, with its wealth of specific details, would make the memory seem more vivid. For example, thinking about your breakfast this morning, you remember what you had, the taste of the food, the people you were with. The added richness of these details makes one more confident about the memory's truth," Cabeza said.
Conversely, volunteers who were confident in memories that turned out to be false showed increased activity in the impressionistic front parietal network (FPN) at the base of the brain, which tends to process the general meaning of an event without the details.
The study results along with other research shows that as humans age their brains lose the ability to recall facts faster than the capacity to recall more general impressions, Cabeza said.
"Specific memories don't last forever, but what ends up lasting are not specific details, but more general or global impressions. Past studies have shown that as normal brains age, they tend to lose the ability to recollect specifics faster than they lose the ability recall impressions. However, patients with Alzheimer's disease tend to lose both types of memories equally, which may prove to be a tool for early diagnosis," he said.
The findings are published in the Journal of Neuroscience.