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Sea slugs and yeast prod understanding of memory

By tinkering with yeast and sea slugs, scientists have found a surprising possible explanation for the way the human brain stores long-term memories.

These lowly creatures possess an unusual protein that exists in two shapes. In one shape, the protein is sluggish or inactive. In its second shape, the protein perpetuates itself indefinitely but can also harmlessly switch back to the inactive form.

Researchers believe that in higher organisms the same protein may exploit this second shape to confer lasting stability to sites on brain cells, called synapses, that store the memories of a lifetime.

Surprisingly, the shape-shifting protein in yeast and slugs has all the hallmarks of another protein, the infamous prion, found in humans and other animals.

Such prions also assume two shapes. One serves a normal function in the brain. The second sets into motion a runaway process that converts normal prions into a toxic form. As a result, deadly clumps of protein leave holes in the brain and cause disorders like mad cow disease.

The disease-causing prion and the memory-storage protein are not identical, said Eric Kandel, a neuroscientist at Columbia Uni-versity who shared the 2000 Nobel Prize in Physiology or Medicine for his research on memory formation. But they share attributes that make prion-like behavior a perfect mechanism for storing memories.

With experience and learning, new synapses are formed and others are strengthened, Kandel said. Indeed, mechanisms determining short- and long-term memories are formed have largely been worked out. But questions of how long-term memories are actually stored and what keeps synapses from losing their connectivity under the onslaught of cellular remodeling are outstanding mysteries in biology.
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