June 10, 2013
Understanding How Brain Cells Make Long-Term Memories
Michael Harper for redOrbit.com — Your Universe Online
Our brain is capable of remembering all sorts of things for very long periods of time, yet the reason and mechanism behind how and why these memories are stored for so long has never been fully understood.Scientists from the Gladstone Institute in San Francisco now believe they´ve mapped the process by which the human brain stores long-term memories in its cells. Senior investigator with Gladstone Institute Steve Finkbeiner says a protein in the brain called Arc helps regulate the activity of neurons and thereby creates memories in the brain´s stores.
Dr Finkbeiner´s findings were recently published in the journal Nature Neuroscience.
The research focuses on synapses and their role in the brain. Synapses are tiny connections between neurons in the brain where information is shared and processed. It´s been previously shown in lab rats that as new tasks are learned and new memories are formed, new synapses are created between neurons. During an individual´s life, these synapses can be broken or bolstered as new memories and skills are learned or lost. While this is a natural process, overworking these neurons can be dangerous and even lead to epileptic shock.
Scientists then set out to discover why the brain doesn´t collapse every time it learns something new and found a mechanism they call “homeostatic scaling.” This process gives neurons the ability to protect themselves from becoming overworked as new synapses are formed. Though this mechanism was known to be crucial in how the brain learns and expands its abilities, the exact mechanism behind how it worked continued to elude scientists. They were left with one clue, however: a protein known as Arc.
“Scientists knew that Arc was involved in long-term memory, because mice lacking the Arc protein could learn new tasks, but failed to remember them the next day,” said Finkbeiner in a statement.
“Because initial observations showed Arc accumulating at the synapses during learning, researchers thought that Arc´s presence at these synapses was driving the formation of long-lasting memories.”
Finkbeiner and his team, including lead author Erica Korb, began to observe the movements of the Arc protein in lab animals and petri dishes and found something astonishing.
“When individual neurons are stimulated during learning, Arc begins to accumulate at the synapses — but what we discovered was that soon after, the majority of Arc gets shuttled into the nucleus,” said Korb.
“A closer look revealed three regions within the Arc protein itself that direct its movements: one exports Arc from the nucleus, a second transports it into the nucleus, and a third keeps it there.”
Korb said she believes this tightly regulated system means that it is important and necessary for the brain´s protection and survival.
In the end the team discovered that as synapses are created and memories are formed, a very specific set of genetic switches must be flipped on and off in a precise manner. This genetic switching generates the homeostatic scaling proteins. Finkbeiner and Korb say they found the protein Arc is responsible for directing the scaling process and protecting the neurons. With these synapses protected, memories are stored for a longer period of time. Without the Arc protein kicking off the entire process, memories may never last for any length of time in our brain´s gray matter.
Finkbeiner says this discovery could have huge implications for the study of other neurological diseases, such as Alzheimer´s disease.