---
title: "How memories last: what neuroscience knows about long-term memory"
description: "Why some memories fade and others last decades: how long-term memory forms through consolidation, sleep and spaced repetition, and what new studies add."
url: "https://eclair.world/news/how-memories-last"
lang: "en"
author: "Thierry Gustin"
published: "2026-11-12"
updated: "2026-11-12"
---

# How memories last: what neuroscience knows about long-term memory

> **Key takeaways** — Long-term memories last because the brain strengthens connections between neurons, then reorganises and reinforces them over days to years, much of it during sleep. Recent mouse studies have identified molecules and gene programmes that keep memories stable.

Memories last because the brain physically changes when it learns, then stabilises those changes over time in a process called consolidation. A new memory starts out fragile and depends heavily on the hippocampus; with repetition and sleep it is reinforced and integrated into wider networks in the cortex. Recent studies in mice have begun to identify the molecules and gene programmes that keep these changes in place for months or longer.

> **Key points** — Most forgetting happens soon after learning, a pattern first measured by Hermann Ebbinghaus in the 1880s and replicated in 2015.  
> Sleep, especially slow-wave sleep, helps consolidate new memories by replaying them.  
> Spacing out study sessions improves long-term retention, according to a review of 317 experiments.  
> A 2024 study found a molecular pair, KIBRA and PKMzeta, that keeps synapses strong despite constant protein turnover.

## Why do we forget most things so quickly?

We forget most new information within hours or days because it was never consolidated into long-term memory. In the 1880s the German psychologist Hermann Ebbinghaus measured his own forgetting of nonsense syllables and found that loss is steepest soon after learning and then slows. In 2015 researchers at the University of Amsterdam [replicated his forgetting curve](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0120644), testing relearning after intervals from 20 minutes to 31 days, and obtained results similar to the original data.

Their analysis also suggested the curve is not perfectly smooth. In Ebbinghaus's data and one replication, retention showed a small upward jump starting around the 24-hour point, which the authors noted is consistent with research on sleep and memory, though their study did not test sleep directly.

## What happens in the brain when a memory forms?

A memory forms when experience strengthens the connections, or synapses, between particular groups of neurons. Strengthening that lasts requires new proteins, which is why early memories are vulnerable: if that process is disrupted, the memory may not stabilise.

Consolidation happens at two levels. At the synapse, changes are locked in over hours. Across the brain, memories initially depend on the hippocampus and are gradually integrated into long-term networks in the cortex, a slower process known as systems consolidation. A 2025 study in *Nature* from Rockefeller University found that in mice this second stage relies on a sequence of gene-regulating programmes acting on different timescales, which the team likened to [molecular timers](https://www.sciencedaily.com/releases/2025/11/251130050712.htm). Three regulators, Camta1 and Tcf4 in the thalamus and Ash1l in the anterior cingulate cortex, were not needed to form a memory but were needed to keep it.

## How does sleep help memories last?

Sleep helps memories last by reactivating what was learned during the day and transferring it into long-term storage. A major review by Björn Rasch and Jan Born in *Physiological Reviews* describes [sleep as a brain state optimising memory consolidation](https://pmc.ncbi.nlm.nih.gov/articles/PMC3768102/), while the waking brain is optimised for taking in new information.

According to that review, consolidation begins with the reactivation of newly encoded memories during slow-wave sleep, the deepest stage of non-REM sleep, which transforms them for integration into long-term memory; REM sleep may then help stabilise them. How much sleep adults actually need is covered in our explainer on [sleep duration for adults](https://eclair.world/news/how-much-sleep-adults-need).

## What keeps a memory stable for years?

A memory stays stable when the strengthened synapses that store it are actively maintained, even though the proteins inside them are replaced within days. That paradox puzzled neuroscientists for decades. In 2024 a team from SUNY Downstate, New York University and other institutions reported in *Science Advances* that [a protein called KIBRA acts as a persistent tag](https://www.eurekalert.org/news-releases/1049128) at strong synapses and anchors PKMzeta, an enzyme that keeps them strong. When the researchers blocked the two molecules from binding in mice, established memories were erased.

> PKMzeta then attaches to the KIBRA-synaptic-tag and keeps those synapses strong.
>
> — Todd Sacktor, SUNY Downstate Health Sciences University, in a June 2024 news release

A 2026 study in *Science* points to structure as well as chemistry. Using artificial hibernation in mice, which removed more than half of synapses, researchers found the animals still [retained their memories](https://www.news-medical.net/news/20260813/Mouse-study-reveals-memories-survive-massive-loss-of-brain-synapses.aspx). The authors suggest memories depend on resilient patterns of connected synapse clusters rather than on individual connections. All three findings come from mouse studies and have not been shown directly in humans.

## Do memories change each time we recall them?

Yes, at least some memories become changeable again when they are recalled. In a landmark 2000 study in *Nature*, Karim Nader, Glenn Schafe and Joseph LeDoux showed that a consolidated fear memory in rats [returned to a fragile state after retrieval](https://pubmed.ncbi.nlm.nih.gov/10963596/): blocking protein synthesis in the amygdala shortly after reactivation caused later amnesia, while the same treatment without reactivation left the memory intact. This process, called reconsolidation, helps explain why recalled memories can be updated or distorted.

## How can you make memories last longer?

The best-supported technique is spacing: reviewing material over several sessions separated in time rather than cramming. A 2006 meta-analysis led by Nicholas Cepeda examined [839 assessments of distributed practice in 317 experiments](https://www.evullab.org/pdf/CepedaPashlerVulWixtedRohrer-PB-2006.pdf) and found that the gap between study sessions and the time until the test work together: the longer you need to remember something, the longer the best gap between sessions.

**What the evidence says helps memories last. Sources: Cepeda et al. 2006; Rasch and Born 2013; Murre and Dros 2015.**

| Factor | What research shows |
| --- | --- |
| Spaced review | Spreading study over sessions improves long-term retention; the ideal gap grows with how long you need to remember |
| Sleep | Slow-wave sleep reactivates and consolidates newly learned material |
| Repetition | In mice, repeated experiences engage the gene programmes that stabilise memories |
| Timing | Most forgetting happens soon after learning, so early review matters most |

Memory changes with age as well, a growing public-health question as societies grow older; our report on the [ageing world population](https://eclair.world/news/ageing-world-population) sets out the demographic trend.

## Frequently asked questions

### How long does it take for a memory to become long-term?

There is no single moment. Synaptic changes are stabilised over hours after learning, while systems consolidation, the gradual integration of memories from the hippocampus into the cortex, unfolds over days to much longer. Studies in mice show that different gene programmes act at different stages, with later ones gradually strengthening memories that are repeated.

### Does sleep really improve memory?

Yes. More than a century of research shows sleep benefits memory retention, according to a 2013 review by Rasch and Born. Current evidence suggests newly learned memories are reactivated during slow-wave sleep and integrated into long-term memory, with REM sleep possibly helping stabilise them afterwards.

### Why do I remember some things for decades but forget others in days?

Memories that are repeated, recalled and consolidated during sleep are more likely to be stabilised in long-term networks. A 2025 Rockefeller University study in mice found that repeated experiences engaged molecular programmes that maintained memories, while less important ones were not promoted onto these timers and faded.

### Is cramming before an exam effective?

Cramming can help for a test the next day but is a poor way to remember material long term. A meta-analysis of 317 experiments found that spacing study sessions improves retention, and that the best gap between sessions grows as the time you need to remember the material increases.

### Can memories be erased?

In laboratory animals, yes. Disrupting the bond between the proteins KIBRA and PKMzeta erased established memories in mice, and blocking protein synthesis after recall disrupted fear memories in rats. These techniques are experimental and have not been used to erase specific memories in people.

## Sources

- [PLOS ONE — Murre and Dros, Replication and analysis of Ebbinghaus' forgetting curve](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0120644) (6 July 2015)
- [Physiological Reviews — Rasch and Born, About sleep's role in memory](https://pmc.ncbi.nlm.nih.gov/articles/PMC3768102/) (April 2013)
- [Psychological Bulletin — Cepeda et al., Distributed practice in verbal recall tasks: a review and quantitative synthesis](https://www.evullab.org/pdf/CepedaPashlerVulWixtedRohrer-PB-2006.pdf) (2006)
- [Nature — Nader, Schafe and LeDoux, Fear memories require protein synthesis in the amygdala for reconsolidation after retrieval (PubMed record)](https://pubmed.ncbi.nlm.nih.gov/10963596/) (2000)
- [EurekAlert! — KIBRA and PKMzeta study in Science Advances](https://www.eurekalert.org/news-releases/1049128) (26 June 2024)
- [ScienceDaily — Rockefeller University study on memory timers in Nature](https://www.sciencedaily.com/releases/2025/11/251130050712.htm) (30 November 2025)
- [News-Medical — Mouse study reveals memories survive massive loss of brain synapses (Science)](https://www.news-medical.net/news/20260813/Mouse-study-reveals-memories-survive-massive-loss-of-brain-synapses.aspx) (13 August 2026)

— Thierry Gustin, Editor-in-chief · November 12, 2026