Scientists have used advanced imaging techniques to find how the brain forms memories.
The insights into the molecular basis of memory were made possible by a mouse model in which molecules crucial to making memories were given fluorescent "tags" so they could be observed travelling in real time in living brain cells.
Efforts to discover how neurons make memories have long confronted a major roadblock: Neurons are extremely sensitive to any kind of disruption, yet only by probing their innermost workings scientists can view the molecular processes that culminate in memories, researchers said.
To peer deep into neurons without harming them, researchers at Albert Einstein College of Medicine of Yeshiva University, US, fluorescently tagged all molecules of messenger RNA (mRNA) that code for beta-actin protein - an essential structural protein found in large amounts in brain neurons and considered a key player in making memories.
The mRNA is a family of RNA molecules that copy DNA's genetic information and translate it into the proteins that make life possible.
"It's noteworthy that we were able to develop this mouse without having to use an artificial gene or other interventions that might have disrupted neurons and called our findings into question," said Robert Singer, the senior author of the research.
Researchers stimulated neurons from the mouse's hippocampus, where memories are made and stored, and then watched fluorescently glowing beta-actin mRNA molecules form in the nuclei of neurons and travel within dendrites, the neuron's branched projections.
They discovered that mRNA in neurons is regulated through a novel process described as "masking" and "unmasking," which allows beta-actin protein to be synthesised at specific times and places and in specific amounts.
"We know the beta-actin mRNA we observed was 'normal' RNA, transcribed from the mouse's naturally occurring beta-actin gene," said Singer.
Neurons come together at synapses, where slender dendritic "spines" of neurons grasp each other, much as the fingers of one hand bind those of the other.
Evidence indicates that repeated neural stimulation increases the strength of synaptic connections by changing the shape of these interlocking dendrite "fingers."
Beta-actin protein appears to strengthen these synaptic connections by altering the shape of dendritic spines.
Memories are thought to be encoded when stable, long-lasting synaptic connections form between neurons in contact with each other.
The research was published in journal Science.
