It is widely believed that memories are stored as changes in the number and strength of the connections between brain neurons, called synapses. A typical brain neuron makes thousands of synapses with other neurons. However, only a subset of those synapses is involved in a particular memory or learned skill.
Neuroscientists are interested in determining how molecules that strengthen synapses are targeted to some synapses but not to others.
"We believe that PKM may be involved in a process that 'tags' synapses during memory formation," says Jerry Yin, a scientist at Cold Spring Harbor Laboratory and the principle investigator in the new study. "In this way, those synapses and only those synapses corresponding to a particular memory are strengthened in response to experience."
To explore the role of PKM in memory, Yin and his colleagues used a method (pioneered by another CSHL researcher, Tim Tully) for training fruit flies to avoid a particular odor. The method involves pairing an odor with a mild electric shock, training the flies to avoid the odor, and subsequently measuring the flies's ability to remember to avoid the odor.
Depending on the training regimen, fly memories based on this type of "associative" learning (made famous by Pavlov's Dogs) are initially robust, but fade away completely over one to seven days (the lifespan of a fruit fly is 30-40 days). However, when Yin and his colleagues used a genetic trick to boost the level of PKM in the flies, a substantial proportion of flies retained the "avoid that odor" memory at times after training when the memory would normally be long gone.
According to Thomas Carew, Professor and Chair of the Department of Neurobiology and Behavior at the University of California, Irvine, "Much of what we know about memory processing comes from studies in which memory is disrupted. This study takes on added significance because it is a rare example that demonstrates actual enhancement of memory formation."
Cold Spring Harbor Laboratory is a private, non-profit basic research and educational institution with programs focusing on cancer, neurobiology, plant biology, and bioinformatics. The Laboratory is headed by Bruce Stillman (Director) and James D. Watson (President). For more information, visit the Laboratory's web site at www.cshl.org or call the Department of Public Affairs at (516) 367-8455.
Nature Neuroscience