Sunday, October 22, 2006

Thanks for the memories

We're all pretty concerned about how well our memory works, right? There's now evidence that the quantity of the neurotransmitter acetylcholine present in the brains of test animals (rats, of course) is directly related to the level of detail of new memories:

Researchers discover mechanism that determines when detailed memories are retained
The levels of a chemical released by the brain determine how detailed a memory will later be, according to researchers at UC Irvine.

The neurotransmitter acetylcholine, a brain chemical already established as being crucial for learning and memory, appears to be the key to adding details to a memory. In a study with rats, Norman Weinberger, research professor of neurobiology and behavior, and colleagues determined that a higher level of acetylcholine during a learning task correlated with more details of the experience being remembered. The results are the first to tie levels of acetylcholine to memory specificity and could have implications in the study and treatment of memory-related disorders.

The findings appear in the November issue of the journal Neurobiology of Learning and Memory.

"This is the first time that direct stimulation of a brain region has controlled the amount of detail in a memory," said Weinberger, a fellow at UCI's Center for the Neurobiology of Learning and Memory. "While it is likely that the brain uses a number of mechanisms to store specific details, our work shows that the level of acetylcholine appears to be a key part of that process."

It isn't news that acetylcholine is related to memory. As a neurotransmitter, acetylcholine is released by presynaptic projections of a neuron's axon in order to cause activation (or inhibition) of a postsynaptic neuron. Normally, the neurotransmitter must be quickly degraded in the synapse so as not to continue to affect the postsynaptic neuron.

However, it was discovered that inhibiting the degradation of acetylcholine (which is normally done by the enzyme acetylcholinesterase) can improve memory performance of persons with early stage Alzheimer's disease. And so acetylcholinesterase inhibitors have turned out to be popular drugs for treating early Alzheimer's.

A little is known about how acetylcholine is involved in memory. It is generally assumed now that memory is a phenomenon of "synaptic plasticity" that occurs when the strengths of connections between neurons increase in proportion to how often signals pass between the neurons – so-called "long-term potentiation". (There has been experimental confirmation of this hypothesis only recently – see this report.) Acetylcholine has been shown to enhance the amplitude of synaptic potentials following long-term potentiation in many regions of the brain.

What the recent research reported here seems to show is that deliberately increasing the quantity of acetylcholine in the brain leads to the formation of more detailed memories.

Sounds like a useful thing to be able to do whenever one needs to cram for a crucial exam...

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