Researchers identify cerebral signals hidden behind working memory

According to a new study, prolonging the lifespan of a specific type of brain pattern improves short-term memory in the rat.

Posted online by the journal Science On June 14, for example, the study focused on "working memory", the temporary activation of brain cells during a visit to a new neighborhood, and the memory of our journey through the day.

Led by researchers at the NYU School of Medicine, this new study shows that signals created by brain cells (neurons) – called wave ripples – are longer by several milliseconds and capture more information when they are heard. an animal discovers a new place a familiar setting.

When the research team artificially doubled the length of the signals involved in recalling the best route to follow in a maze, it was found that rats with extended ripples had a better ability to find a sweet reward than rats without manipulation.

"Our study is the first in our field to have artificially altered the intrinsic neuronal trigger patterns of the region of the brain called the hippocampus, which has increased learning ability, instead of interfering as previous attempts "says György Buzsáki, MD. D., Biggs Professor, Department of Neuroscience and Physiology, NYU School of Medicine. "After decades of study, we have finally understood the mammalian brain well enough to modify certain mechanisms to guide the design of future treatments for diseases that affect memory."

The results of the study revolve around nerve cells, which "quickly trigger or change the balance of their positive and negative charges – to transmit electrical signals that coordinate memories." Buzsaki's team has discovered in recent years that sets of neurons are triggered within milliseconds, other in rhythmic cycles – creating tightly connected signal sequences that can encode complex information.

This observed pattern – where the hippocampus cells in different parts of the circuit glow briefly – creates "sharp wave ripples". The patterns are named after their shape when they are captured graphically by electroencephalography or EEG, a technology that records the activity of the brain with electrodes.

According to Buzsaki, the ripples represent the "repetition" and combination of scholarly information fragments, part of the process that integrates them into an animal's memory.

In the ripple

In the current study, the team designed experiments such that the right way to get sweet water alternated between the left arm and the right arm of a labyrinth each time a rat was placed there. To get their reward, the rats had to use their working memory, remember how they had gone to the previous test and choose the opposite way next time.

Studies conducted in recent years in many laboratories have established that hippocampal "place cells" code each labyrinth room or arm as they are introduced and then reignite as rats or humans remember. to have visited this place or are planning to do so. The authors of the study recorded the firing of space cells as a rat performed the memory task in the labyrinth and predicted the route taken as reflected in the captured cell firing sequence in each ripple sharp wave.

In order to artificially double the duration of the only ripples caused by rat brain cells during task-oriented navigation, the researchers designed hippocampus cells to include light-sensitive channels. Bright light through tiny neurons activated by glass fibers, adding more neurons to the natural sequence, thus coding the labyrinth representation in more detail.

Importantly, the study also found that extended ripples allowed slower-triggering neurons to be recruited into their sequences. Previous studies by the authors have shown that these paralyzed neurons are better able to modify their properties (more plastic) as they acquire new knowledge.

On the other hand, faster firing partners in a ripple tended to start the sequence regardless of the route taken by the rat. Buzsáki's team has demonstrated that such "rigid" neurons are spreading from one experiment to another, coding the familiar aspects (instead of the found elements) of each recently encountered site.

"Our next step will be to try to understand how nonviolent waves can be prolonged by non-invasive means, which, if we succeed, would have consequences for the treatment of memory disorders," says the first author Antonio Fernandez- Ruiz, Ph.D., postdoctoral fellow at the Buzsaki laboratory.