Between oblivion and persistence: how the brain decides what is worth remembering
The brain does not retain all that we have lived, but rather that which it has considered useful to guide our future
At every moment, our brain receives a flood of stimuli. Images, sounds, bodily sensations, emotions, and fleeting thoughts constantly invade our minds. Most disappear without a trace, while others are etched with surprising persistence, to the point of accompanying us throughout our lives. Why do we remember an apparently trivial conversation with such clarity, and yet forget facts that may seem important? of accompanying us throughout our lives. Why do we remember an apparently trivial conversation with such clarity, and yet forget facts that may seem important?This question, which has been part of psychology for decades, has entered a new phase thanks to recent work showing that memory is not a passive storage process, but an active and dynamic decision regulated in time, which is inscribed in the molecular biology of specific brain circuits. A study published in Natureby researchers from The Rockefeller University and Memorial Sloan Kettering Cancer Center in New York, led by neuroscientist Priya Rajasethupathy, shows that the brain uses internal “timers” to decide what is worth remembering, a mechanism that favors memory and contributes to building our mental identity.Traditionally, research on memory has focused on the hippocampus, a structure of the limbic system known to be key for the formation of episodic memories. These are memories of specific personal experiences, situated in a particular time and place, and include the emotional context in which they were generated. It has also long been known that new experiences activate specific sets of neurons and that, if the neuronal connections formed are sufficiently reinforced, the memory is consolidated and transferred to the cerebral cortex, where it is stored long-term. This model, however, does not explain why apparently very similar experiences can have such different fates in memory.
A gradual process
The key, as Rajasethupathy and his collaborators have shown, is that memory consolidation is not a one-time event, but a gradual process that goes through several successive stages, each of which is under specific temporal control. After an experience, the brain opens a first window of a few minutes, during which the memory is extremely fragile. If the experience remains relevant, meaning if it stimulates an emotion, if it is repeated, or if it implies an important consequence, a second timer is activated that can last for hours. Finally, if the memory "demonstrates" its usefulness, a third period is initiated that can extend for days or weeks. Each stage involves different molecular changes, as if the brain were subjecting each memory to scrutiny before granting it long-term stability.One of the most innovative aspects of this work is the central role of the thalamus. This brain structure, associated with attention and the regulation of the threshold of consciousness, receives most of the sensory and motor information and distributes it to the cerebral cortex. This research has shown that these circuits, instead of merely transmitting information, also participate in the selection of memories that will receive the appropriate molecular support for consolidation.At the cellular level, this selection is concretized in successive waves of gene activation. Global patterns of sequential gene expression have been identified in the neurons involved in the establishment and consolidation of a memory, which have been called “cellular macrostates”. Memories that are consolidated go through various of these stages, while those that are forgotten get stuck in the initial phases.
The proteins CAMTA1, TCF4, and ASH1L stand out, forming a cascade of temporally ordered activations that are essential for memory stabilization. When any of these steps fail, the memory is not consolidated, establishing a direct link between molecular biology and the subjective experience of remembering or forgetting. It also highlights the importance of each individual's genetic makeup in the ability to consolidate memories. If any of these proteins function with lower efficiency, memories take longer to consolidate.
Sleep to remember
The study also highlights the decisive role of sleep. During deep sleep, thalamocortical circuits show patterns of activity that facilitate the transition from one molecular macrostate to the next. Sleeping is not just about resting the brain, but about providing it with the necessary physiological context for these molecular timers to advance, underscoring the importance of sufficient and quality sleep.Beyond the implications for learning at any educational level, these results also invite us to rethink the relationship between memory and identity. If what we remember is the result of an active selection process, influenced by emotion, context, repetition, and a sense of usefulness, our mental autobiography ceases to be a faithful reflection of the past. The brain does not preserve everything we have lived, but rather what it has considered useful to guide our future.