Researchers have uncovered the neurological basis for humans’ alternation between memory production and retrieval.

Although they can sometimes appear as distinct mechanisms, the two processes of creating new memories and remembering are actually one and the same. These systems, which appear to be removed from one another, are really interconnected and are essential for similar brain congregations, as per a concentrate presently distributed in the journal Current Science, which uncovers the main logical proof of people’s memory elements.

Experts Llus Fuentemilla and Ludovico Saint Amour di Chanaz from the Faculty of Psychology and the Institute of Neurosciences of the University of Barcelona (UBneuro) led the study, which provides the first description of a specific neural mechanism by which the hippocampus coordinates the possibility of switching the formation and retrieval states of human memories.

How do you code and retrieve memories in your brain?
The memory arrangement and recovery process includes a few mind regions; however, in this organ, the hippocampus is especially significant in the early development of recollections and in its itemized recovery. Nonetheless, what instrument does the hippocampus use to substitute the development of new recollections and the recovery of existing recollections without the two cycles impeding one another?

The existence of rhythmic waves of activity known as oscillations has been demonstrated through recordings of neuronal activity made with electrodes that are inserted into the brain. These appear when enormous quantities of neurons fire in a synchronized way. The accounts uncover that the recurrence of these motions — the quantity of patterns of a wave each second, estimated in Hertz — can shift inside a solitary locale after some time. Additionally, oscillations of varying frequencies can interact with one another and coexist.

“People are able to instantly link fresh memories to ones that already exist by dynamically encoding them. Thus, it appears that memory encoding and retrieval are independent processes that can operate in parallel.”

Lluís Fuentemilla, member of the Department of Cognition, Development and Educational Psychology of the UB.

Two types of oscillations dominate in the hippocampus, one of the brain’s most important structures for forming and recalling memories: gamma and theta waves. Theta waves have a frequency between 4 and 8 Hz and are relatively slow. Between 30 and 140 Hertz, these slow waves synchronize and regulate the gamma oscillatory activity, allowing it to be coupled in various theta rhythm phase states.

According to one study, theta oscillations function as a “switch” that enables the alternation of optimal neural states for memory retrieval and new memory formation.

“Past examinations with creatures showed that the manner in which gamma action is coupled to the theta cadence affects memory (encoding and recollections). However, Professor Llus Fuentemilla, who is also a researcher at the Bellvitge Biomedical Research Institute (IDIBELL), says, “We did not know if the same neural mechanism was important in humans.”

By examining the interactions between the neuronal brain waves underlying the formation and retrieval of memories, the Dynamics of Memory Formation group, which is led by Ludovico Saint Amour di Chanaz and coordinated by Llus Fuentemilla, has deciphered the dynamics of memory in humans for the very first time.

As a feature of the review, the group had the option to record the hippocampal action of ten epileptic patients in a joint effort with the Clinic Clnic in Barcelona and the Pitié-Salpetrière Emergency Clinic in Paris. The patients watched a series of images depicting a real-life incident as part of the experimental protocol. They were asked to recall the subsequent sequence of images after being shown the first image from each series once more after a period of 24 hours.

As per the outcomes, when patients framed new recollections, there was a particular example of oscillatory action in the gamma band connected with the theta cadence. Gamma neuronal activity was coupled to one phase of the theta waves during the process of encoding novel memories, while gamma activity was coupled to the opposite phase during memory retrieval.

Not-really-separate neurophysiological capabilities
One more important aftereffect of the review is that the design was predictive of memory status (encoding or review) and, furthermore, of the precision of the patients’ reactions during the memory recovery. As a result, the patients’ memories improved as the pattern got stronger.

“People are able to dynamically encode new memories and immediately link them to the ones they already have.” According to Llus Fuentemilla, a member of the UB Department of Cognition, Development, and Educational Psychology, “we have the impression that memory encoding and retrieval are separate functions that can work simultaneously.”

“In addition, the modulation of our brain’s state by the theta rhythm ensures that it changes state anywhere from four to eight times per second. This gives us the impression that the processes of encoding information, integrating it, and retrieving it are all in constant motion. With a superior comprehension of how recollections are framed and recovered in people, we will actually want to foster new medicines for individuals with memory challenges, as well as better grasp our past, future, and, to put it plainly, what makes us what our identity is: human,” he says.

More information: Ludovico Saint Amour di Chanaz et al, Gamma amplitude is coupled to opposed hippocampal theta-phase states during the encoding and retrieval of episodic memories in humans, Current Biology (2023). DOI: 10.1016/j.cub.2023.03.073

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