April 17, 2014

New Memory Model Explains How Neurons Select Memories

redOrbit Staff & Wire Reports - Your Universe Online

In research that should provide a more detailed picture of how memory works, scientists from the Salk Institute have developed a new model explaining how neurons retain select memories a few hours after an event.

“Previous models of memory were based on fast activity patterns,” study author and Howard Hughes Medical Institute Investigator Terry Sejnowski explained in a statement on Wednesday. “Our new model of memory makes it possible to integrate experiences over hours rather than moments.”

Neuroscientists have discovered much about how long-term memories are stored in recent decades. For example, a number of proteins are quickly made in activated brain cells in order to create new memories for significant events, and some of those proteins remain at specific places on certain neurons for a few hours before breaking down.

It is this chain of biochemical occurrences that make it possible for people to remember key details about a particular event. However, one difficulty when it comes to modeling memory storage is trying to explain why only certain details and not everything that happened in that one or two hour window is retained.

Using data from previous research in the field as a starting point, Sejnowski and his colleagues developed a model that bridges the gap between molecular findings and memory systems observations in order to better explain how this 60 to 120 minute memory window works. Their findings, which could provide new insight in dealing with conditions such as Alzheimer’s and PTSD, appear in the latest edition of the journal Neuron.

The researchers were able to use computational modeling to demonstrate that even though proteins are available to a number of neurons in a particular circuit, memories are actually retained when a subsequent event activates the same neurons as those activated during the original happening.

They also found that the spatial positioning of proteins at both particular neurons and certain surrounding locations can foretell which memories are recorded. Memory retention as a mathematical function of time and location overlap can be successfully predicted by using this spatial patterning framework, the authors noted.

“One thing this study does is link what's happing in memory formation at the cellular level to the systems level,” said first author and postdoctoral researcher Cian O'Donnell. “That the time window is important was already established; we worked out how the content could also determine whether memories were remembered or not. We prove that a set of ideas are consistent and sufficient to explain something in the real world.”

Furthermore, O’Donnell and Sejnowski believe that their new model could establish a way to understand how generalizations from memories are processed when a person dreams. Research suggests that a day’s important recollections are often cycled through the brain during sleep, and while that process takes place, memories are transferred from the hippocampus (temporary storage) to the cortex (long-term storage).

The majority of this memory formation process takes place during non-dreaming sleep, according to researchers. It is not known how or if the brain packages or consolidates memories during dreams, but the Salk Institute study suggests that at least some memory retention does occur while a person is dreaming.

“During sleep there's a reorganizing of memory—you strengthen some memories and lose ones you don't need anymore. In addition, people learn abstractions as they sleep, but there was no idea how generalization processes happen at a neural level,” said O'Donnell. By combining their findings, the study authors were able to develop a theoretical model for how the memory abstraction process could take place during slumber.