Public release date: 21-Nov-2006
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Lee Siegel
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801-581-8993
The University of Utah
The Brain Institute at the University of Utah
Proteins anchor memories in our brain
Math study: Holding nerve-signal receptors in place is crucial
University of Utah mathematician Paul Bressloff has completed a study suggesting that our memories are held in our brains with the help of proteins that serve as anchors for other...
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A University of Utah study suggests that memories are held in our brains because certain proteins serve as anchors, holding other proteins in place to strengthen synapses, which are connections between nerve cells.
"The essential idea is that synapses are in a constant state of flux, so how can they be the seat of memories that can last a lifetime?" says mathematics Professor Paul Bressloff, a member of the Brain Institute at the University of Utah. "Part of the answer is that there are anchors inside the synapse that keep proteins in place, and these proteins help determine how strong a synapse is, which in turn contributes to forming and retaining memories."
The research is relevant not only to how memory and learning work, but to Alzheimer's disease, which is believed to involve, at least in part, a breakdown in the normal movement of proteins within synapses.
The study will be published Wednesday, Nov. 22, 2006, in The Journal of Neuroscience. Bressloff conducted the research with Berton Earnshaw, a doctoral student in mathematics. It was funded by the National Science Foundation.
Bressloff says the big debate about consciousness is, "Can it be explained simply in terms of a bunch of nerve impulses in the brain? In my opinion, the answer has to be yes" - an answer reinforced by his findings.
"Memories, behavior, feelings all are determined by patterns of nerve impulses in the brain," he adds. "If you change the pattern of nerve impulses, then that changes the memories, behavior and feelings.
What determines that pattern of nerve impulses is a mixture of stimuli we are receiving from the outside world and the strength of connections between nerve cells."
"Our knowledge and memories are determined by these connections in the brain. Who we are is determined by the strength of connections between neurons in the brain."
The Anatomy of Memory and Learning
A synapse is the junction between nerve cells or neurons. The synapse includes three parts: the end or "axon" of the upstream nerve cell, the microscopic gap between nerve cells, and a mushroom-shaped "dendritic spine," which is part of the downstream nerve cell.
What we learn and hold in our memory is believed to be distributed across many synapses, Bressloff says. Some memories, such as a person's face, may be held by just a few synapses, while other memories may be distributed across a large number, he adds.
While a nerve cell has only one axon to transmit outgoing signals, it has numerous structures called dendrites, which are like branches of a tree. Each dendrite, in turn, branches into twig-like dendritic spines. A single nerve cell may have 10,000 dendritic spines, and each spine is part of a synapse. So a single nerve cell can receive signals from 10,000 other nerve cells.
Nerve cells fire electric impulses. When an electrical nerve signal from one nerve cell arrives at the synapse, it triggers the release of chemicals called neurotransmitters. Those chemicals travel across the synapse and attach or "bind" to proteins on the dendritic spine that are called receptors.
One of the most important neurotransmitters is named glutamate, and it binds to proteins known as "AMPA receptors," which are embedded in the dendritic spines on the receiving end of nerve cells. The AMPA receptor proteins are held in the membrane by other proteins called "scaffolding proteins." Bressloff says AMPA is one of two key nerve-signal receptors known to "play a crucial role in learning and memory."
Earlier research indicates learning and memory depend on the strength of synapses between nerve cells. Bressloff says a synapse's strength depends not only on how much neurotransmitter is released by the upstream nerve cell, but on other factors, including the number of receptors like AMPA.