2023-05-01 14:45:09
Helping your mother make pancakes when you were three… riding a bike without training wheels… your first kiss… How do we keep memories vivid events of long ago? Researchers at the Albert Einstein School of Medicine (United States) have found the explanation.
“The ability to learn new information and store it for long periods is one of the most remarkable features of the brain. We have done a amazing discovery in mice on the molecular basis of the creation of these long-term memories”, explained Dr. Robert H. Singer, co-author of the research, which has been published in the scientific journal ‘Neuron’.
Some aspects of the cellular basis of memory. They are manufactured by neurons (nerve cells) and stored in a region of the brain called hippocampus. They are formed when repeated neural stimulation strengthens synapses, that is, the connections between nerve cells. Proteins are needed to stabilize the long-lasting synaptic connections necessary for long-term memories. The blueprints for these proteins are messenger RNA (mRNA) molecules, which, in turn, are transcribed (copied) from memory-associated genes.
“The paradox is that it takes a long time – several hours – to form a lasting memory and yet mRNAs and proteins associated with protein manufacturing disappear in less than an hour. How is that possible?” explained Sulagna Das, PhD, first author and co-author of the paper. To answer that question, the research team developed a mouse model in which they fluorescently labeled all mRNA molecules flowing from Arc, a critically important gene for turning our activities and other experiences into long-term memories.
the researchers stimulated synapses in mouse hippocampal neurons and then – using high-resolution imaging techniques developed by them – they observed the results in individual nerve cells in real time. To their astonishment, they observed that a single stimulus in the neuron triggered numerous cycles in which the Arc gene, which codes for memory, produced mRNA molecules that were then translated into Arc proteins that strengthened the synapses.
“We saw that some of the protein molecules produced by that initial synaptic stimulus they returned to Arc and reactivated it, initiating another cycle of mRNA formation and protein production, followed by several more,” Singer detailed. “With each cycle, we saw more and more protein accumulate to form ‘hot spots’ in the synapse, which is where cement the memories we had discovered a hitherto unknown feedback loop that explained how short-lived mRNAs and proteins can create long-lived memories,” added Das.
Das points out that faulty expression of the Arc gene has been implicated in memory difficulties in humans and is linked to neurological disorders such as Autistic spectrum and the disease of Alzheimer’s. “What we learn about Arc’s response to nerve cell stimulation may help us better understand the causes of these health problems,” she said.
How are temporary memories maintained?
As for the temporary memoriesnew research from the Del Monte Institute for Neuroscience at the University of Rochester (United States) has shown that rhythmic brain activity it is key to temporarily keeping important information in memory. According to his findings, published in the scientific journal ‘Current Biology’, brain rhythms -or patterns of neural activity- organize the bursts of activity in the brain that maintain short-term connections.
“Until now it was thought that the temporary storage of important information was linked to brain neurons that simply fired up and retained that information until it was no longer needed. Recent research has shown that it may not be that persistent brain activity that matters most for the temporary storage of information, but rather short-term strengthening of the connections between the neurons that are representing the information. Our research shows that brain rhythms organize these transient bursts over time. The rhythmic coordination of brain activity over time is important because it allows overlapping populations of neurons to store different pieces of information at the same time,” said Ian Fiebelkorn, lead author of the study.
Fiebelkorn’s earlier research on how the brain processes external information made a similar discovery. Fiebelkorn and other researchers found that brain rhythms help coordinate different functions related to sampling important information or switching to another source of information. In this context, brain rhythms help balance focus on the task with preparation for the unexpected.
In this new investigation, the researchers focused on the sampling of internally represented (or remembered) information. Using EEG, participants viewed images with vertical or horizontal lines and were asked to recall both the direction of the line and the location of the image.
The researchers found that the strength of the internal representations of these different images alternated over time, on a sub-second time scale, with rhythmic fluctuations in brain activity. This coordination of brain activity over time allows the functions of some neurons they overlap without conflicting.
“These rhythmic brain processes could also explain how we can stay focused while multitasking, like when we try to remember an address while driving a car. Instead of simultaneously concentrating on these tasks, we could be switching between them on a sub-second time scale,” says Fiebelkorn.
The next step for Fiebelkorn’s lab is to determine how the brain multitasks: “What happens when the brain has to do external and internal sampling at the same time, do we see the same kind of rhythmic temporal coordination? That’s what we try to understand below.The more we know about the typical operation of these processes, the more we will understand how they go bad in neurological disorders“.
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