Thursday, June 18, 2009
The ability to learn and to establish new memories is essential to
our daily existence and identity; enabling us to navigate through
the world. A new study by researchers at the Montreal Neurological
Institute and Hospital (The Neuro), McGill University and
University of California, Los Angeles has captured an image for the
first time of a mechanism, specifically protein translation, which
underlies long-term memory formation. The finding provides the
first visual evidence that when a new memory is formed new proteins
are made locally at the synapse - the connection between nerve
cells - increasing the strength of the synaptic connection and
reinforcing the memory. The study published in Science, is
important for understanding how memory traces are created and the
ability to monitor it in real time will allow a detailed
understanding of how memories are formed.
When considering what might be going on in the brain at a molecular
level two essential properties of memory need to be taken into
account. First, because a lot of information needs to be maintained
over a long time there has to be some degree of stability. Second,
to allow for learning and adaptation the system also needs to be
highly flexible.
For this reason, research has focused on synapses which are the
main site of exchange and storage in the brain. They form a vast
but also constantly fluctuating network of connections whose
ability to change and adapt, called synaptic plasticity, may be the
fundamental basis of learning and memory.
"But, if this network is constantly changing, the question is how
do memories stay put, how are they formed? It has been known for
some time that an important step in long-term memory formation is
"translation", or the production, of new proteins locally at the
synapse, strengthening the synaptic connection in the reinforcement
of a memory, which until now has never been imaged," says Dr. Wayne
Sossin, neuroscientist at The Neuro and co-investigator in the
study. "Using a translational reporter, a fluorescent protein that
can be easily detected and tracked, we directly visualized the
increased local translation, or protein synthesis, during memory
formation. Importantly, this translation was synapse-specific and
it required activation of the post-synaptic cell, showing that this
step required cooperation between the pre and post-synaptic
compartments, the parts of the two neurons that meet at the
synapse. Thus highly regulated local translation occurs at synapses
during long-term plasticity and requires trans-synaptic
signals."
Long-term memory and synaptic plasticity require changes in gene
expression and yet can occur in a synapse-specific manner. This
study provides evidence that a mechanism that mediates this gene
expression during neuronal plasticity involves regulated
translation of localized mRNA at stimulated synapses. These
findings are instrumental in establishing the molecular processes
involved in long-term memory formation and provide insight into
diseases involving memory impairment.
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McGill University
Thanks to McGill University for this article.