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Explaining how memories stick together

Over the past few decades, neuroscientists have revealed much about how long-term memories are stored. For significant events– for example, being bit by a dog–a number of proteins are quickly made in activated brain cells to create the new memories. Some of these proteins linger for a few hours at specific places on specific neurons before breaking down. This series of biochemical events allows us to remember important details about that event–such as, in the case of the dog bite, which dog, where it was located and so on.

One problem scientists have had with modeling memory storage is explaining why only selective details and not everything is strongly remembered. Now Terrence Sejnowski and his group have created a new model of memory that explains how neurons retain select memories a few hours after an event. This new framework provides a more complete picture of how memory works, which can inform research into conditions such as Parkinson’s, Alzheimer’s, post-traumatic stress disorder and learning disabilities.

Cian O’Donnell and Terrence Sejnowski

“Previous models of memory were based on fast activity patterns,” says Sejnowski, a Howard Hughes Medical Institute investigator and holder of Salk’s Francis Crick Chair. “Our new model of memory makes it possible to integrate experiences over hours rather than moments.”

By incorporating data from previous literature, Sejnowski and postdoctoral researcher Cian O’Donnell developed a model that bridges findings from both molecular and systems observations of memory to explain how this memory window works. Using computational modeling, they showed that despite the proteins being available to a number of neurons in a given circuit, memories are retained when subsequent events activate the same neurons as the original event. They found that the spatial positioning of proteins at both specific neurons and at specific areas around these neurons predicts which memories are recorded.

The new model, reported in Neuron, also provides a potential framework for understanding how generalizations from memories are processed during dreams. While much is still unknown about sleep, research suggests that important memories from the day are often cycled through the brain, shuttled from temporary storage in the hippocampus to more long-term storage in the cortex. Researchers observed most of this memory formation in non-dreaming sleep. Little is known about if and how memory packaging or consolidation is done during dreams. O’Donnell and Sejnowski’s model, however, suggests that some memory retention does happen during dreams, and by applying their findings, they came up with a theoretical model for how the memory abstraction process might work during sleep.