New imaging technologies are helping scientists to unlock secrets about the human brain and how it functions. One of those technologies is the functional magnetic resonance imaging machine, fMRI. An fMRI allows researchers to 'see' and monitor changing blood flows in the brain as subjects perform different activities.
Researcher Christine Smith from the University of California at San Diego used an fMRI to look at how the brain stores memories. She says the fMRI has been a powerful tool for learning about memory.
"It's hard to say where any particular memory is stored in the brain. Memories are stored in a distributed way, kind of across the brain," Smith says
She says scientists believe areas in the brain involved in creating memories are usually the areas where they're also stored. One of those areas long known to be associated with memory creation is called the hippocampus. The reason scientists know about the hippocampus is from people who have had hippocampal damage, from strokes or trauma, for example.
"If you damage the hippocampus, you get classic amnesia where you have trouble remembering new things," Smith says.
To study memory, Smith put subjects into an fMRI and then asked them to answer questions about news events over the past 30 years. She found that as people answered questions about more recent events, different parts of the brain - including the hippocampus - responded differently. The difference depended on how old the memory was.
She says they found that the hippocampus is involved for some time after memories are learned.
"Activity in that region was highest for the most recent memories, and then activity tapered down for memories about one to 12 years into the past," Smith says.
Smith was also able to observe where older memories were stored. The outermost part of the brain, the cortex, became more active when those older memories were recalled, and the hippocampus became less active.
"You need the hippocampus to recall memories that are between one and 10 years old," she concludes. "And after that, you don't need a hippocampus. So what happens is, the role of the hippocampus seems to diminish with time, and so you don't need it anymore after 10 or so years to recall the memories older than that. It seems that the cortex then can support the recall of memories... those more remote memories."
Smith says these findings shed new light on the dynamics of the memory loss associated with aging, Alzheimer's disease and other cognitive problems.
Smith's research is published in the Journal of Neuroscience.