New Clue to Understanding Fundamental Brain Mechanism
Researchers have found that they can enhance memory in fruit flies by boosting the level of a protein called PKM. The scientists could trigger memory enhancement in the flies by using either a fly or a mouse version of PKM. The study, published in the April issue of Nature Neuroscience, provides an important new clue about a fundamental mechanism of memory common to flies, humans, and most other animals.
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.”
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