In a novel study, researchers focus on brain coding and claim new ways to improve memory for people with traumatic brain diseases like Alzheimer’s.
The findings published in PNAS and Science show how the brain works while encoding time and place in memories. The findings not only add to the body of fundamental research on memory, but could eventually provide the basis for new treatments to combat memory loss from major diseases.
A group of neurons known as ‘time cells’ was discovered in rats, in a study conducted about a decade ago. The researchers found that the cells appeared vital and played a unique role in recording events, which then correctly marked the order of what happens in episodic memory.
Bradley Lega, MD, associate professor of neurological surgery at UTSW and lead author of the PNAS study, explained that the cells, located in the brain’s hippocampus, displayed a characteristic pattern of activity that animals encode while recalling events. By firing in a reproducible sequence, they allow the brain to organize itself when events occur. The timing of their firing is controlled by 5 Hz brain waves, called theta oscillations, in a process known as precession, ”Lega said.
Lega and his colleagues recruited volunteers from the Epilepsy Monitoring Unit at UT Southwestern’s Peter O’Donnell Jr. Brain Institute to investigate whether humans also have time cells by using a memory task that places high demands on weather related information.
For the research, epilepsy patients were made to stay for several days before surgery to remove the damaged parts of their brains that cause seizures. Lega said electrodes implanted in the brains of those patients helped his surgeons find valuable information about the inner workings of the brain.
The ‘free memory’ tasks that involved reading a list of 12 words for 30 seconds, were practiced with those 27 patients that were done after a short math problem to distract them from rehearsing the lists and then remembering as many words from the list as possible for the next 30 seconds. The task required associating each word with a time segment, allowing Lega and his team to search for time cells.
What the team found was exciting and exceptional: Not only did they identify a robust population of time cells, but the activation of these cells predicted how well individuals could link words together in time (a phenomenon called temporal clustering). Ultimately, those cells appeared to exhibit phase precession in humans, as predicted.
According to Lega, “For years, scientists have proposed that the cells of time are like the glue that holds together the memories of the events in our lives. This finding specifically supports that idea in an elegant way. “
In the second study, Brad Pfeiffer, PhD, an assistant professor of neuroscience, led a team investigating locus cells – a population of hippocampal cells in animals and humans that records where events occur.
According to the researchers, as rats actively explore an environment, place cells further organize themselves into ‘mini-sequences’ that represent a virtual sweep of locations ahead of the rat. These radar-like sweeps occur approximately 8 to 10 times per second and are believed to be a brain mechanism for predicting immediate events or outcomes.
While these ‘reverse reproduction’ events were known to be important for memory formation, it was not clear how the hippocampus was able to produce such sequences. Considerable work indicated that experience should strengthen forward sequences, “look ahead,” but weaken reverse replay events.
To determine how these backward and forward memories work together, Pfeiffer and his colleagues placed electrodes on the rats’ hippocampus, allowing them to explore two different locations: a square arena and a long, straight track, and then analyzed cell activity. from the place of the animal to see how it corresponded to the locations.
The particular neurons fired as the rats roamed the spaces, encoding information about the location. The same neurons fired in the same sequence that the rats retraced their tracks, periodically firing in reverse as they completed different stages of their travels. However, upon taking a closer look at the data, the researchers found that as the rats moved through the gaps, their neurons exhibited not only forward predictive mini-sequences, but backward retrospective mini-sequences. The forward and backward sequences alternated with each other, each taking only a few dozen milliseconds to complete.
“As these animals progressed, their brains constantly switched between waiting for what would happen next and remembering what had just happened, all within split-second time frames,” said Pfeiffer.
In theory, Pfeiffer said it might be possible to hijack the system to help the brain more faithfully remember where an event occurred. Similarly, Lega added that stimulation techniques could eventually mimic the precise pattern of time cells to help people more accurately remember temporal sequences of events.
(This story was posted from a cable agency feed with no changes to the text.)
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