Think Abour Yesterday's lunch and a variety of details may leap to mind, each of them em-ploying a different section of your brain. The olfactory system calls up what the meal smelled like, while the visual cortex retrieves images of the restaurant you ate in and the temporal lobe recalls the sound of your waitress's voice. Scientists have long suspected that every recollection-from the mundane to the momentous-ignites a distinct pattern of neurons. But for decades, they have struggled to understand how the brain assembles such disparate elements into a single coherent memory, one that can be retrieved intact, spontaneously or on demand, hours, days or even years after the fact. "It's not like a tape recorder where you store it all on one cassette," says Lynn Nadel, a neuroscientist at die University of Arizona in Tucson. "There's more than one PLAY button to hit." It's no trivial matter. One of die most devastating effects of dementia and Alzheimer's disease (expected to afflict 14 million Americans by 2040) is the loss of what's known as episodic memory-the capacity to remember experiences in detail. Despite years of research and some initial progress, the ability to restore this function to aging or diseased brains continues to elude doctors. But research published earlier this month in the journal Science has provided some important clues into how the brain builds memories.
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