Summary: Researchers have shown that age-related memory loss and some symptoms of Alzheimer’s disease may not be irreversible. Using a targeted form of “partial reprogramming” on specific neurons known as engrams—the sparse cell ensembles that store individual memories—a team at EPFL restored learning and memory abilities in aged mice.
The scientists used a gene-therapy combination called “OSK” (Oct4, Sox2 and Klf4) to reset molecular markers of aging in those memory-holding neurons. By briefly returning these cells to a younger, more plastic state, the team recovered recent memories linked to the hippocampus and remote, long-term memories associated with the prefrontal cortex. This targeted strategy suggests a new avenue for treating age-related cognitive decline and forms of dementia.
Key Facts
- The “OSK” cocktail: The approach relies on three transcription factors—Oct4, Sox2 and Klf4—delivered in a controlled, short pulse to partially reprogram neurons without erasing their identity.
- Targeting engrams: Instead of reprogramming large brain regions, the method specifically targets engram neurons, the small populations of cells activated during learning and reactivated during recall.
- Alzheimer’s models: In mouse models of Alzheimer’s disease, OSK-based reprogramming improved spatial learning strategies during training and restored long-term memory that had been impaired.
- Molecular rejuvenation: Treated engram neurons displayed hallmarks of a younger state, including improved nuclear structure and normalized firing patterns that typically degrade with age.
Source: EPFL
Age-related memory decline and neurodegenerative diseases like Alzheimer’s are often considered irreversible, but the brain remains dynamic. Neurons constantly adjust the strength of their connections—synaptic plasticity—which underlies learning and memory. Aging and disease disrupt many cellular processes that support this plasticity, raising the question: can affected neurons be helped to regain youthful function?
Memories depend on sparse groups of neurons called engrams that are activated during learning and reactivated during recall, forming the brain’s physical memory trace. In aged brains and in animal models of Alzheimer’s disease, engram function deteriorates and recall becomes unreliable or fails entirely.
Led by Johannes Gräff at EPFL’s Brain Mind Institute, the research team asked whether rejuvenating engram neurons could recover memory after decline had already begun. In a paper published in Neuron, they report that partial reprogramming of these memory cells restores memory performance across several behavioral settings in mice. The method uses a brief, controlled pulse of Oct4, Sox2 and Klf4—collectively referred to as OSK.
Previous work has shown that carefully timed expression of these factors can reverse multiple aging-related cellular features. In this study, the investigators directed OSK specifically to the engram neurons that were active during learning, rather than applying reprogramming broadly across the entire brain.
Tagging and controlling OSK
In mice, the team used adeno-associated viral vectors delivered by precise injections to combine two capabilities: a fluorescent tag to label neurons activated during learning and a molecular switch to turn OSK on briefly within a defined time window. They targeted two brain regions with distinct memory roles: the dentate gyrus of the hippocampus, important for acquiring and recalling recent memories, and the medial prefrontal cortex, which supports remote recall weeks later.
Back to a younger state
In aged mice, a short activation of OSK in hippocampal engram neurons restored performance on learning and memory tasks to levels comparable with young controls. Applying the same approach to prefrontal cortex engrams recovered remote memories that had been formed weeks earlier. Importantly, reprogrammed neurons retained their neuronal identity while acquiring molecular and structural features associated with a younger state.
When tested in mouse models of Alzheimer’s disease, reprogramming dentate gyrus engrams improved navigation strategies during spatial learning, and targeting prefrontal engrams restored long-term spatial memory. Molecular analyses showed that some Alzheimer’s-linked changes in gene expression and neuronal excitability within engram cells were partly reversed by OSK activation.
A proof of concept
This study provides a proof of concept that selectively rejuvenating the specific neurons that store memories can restore cognitive function even after decline has started. By restricting OSK expression both spatially and temporally—to small engram populations and to brief pulses—the approach harnesses beneficial rejuvenation effects while minimizing risks that would accompany broad, long-term reprogramming.
Key Questions Answered:
A: In these mouse experiments, yes in effect. The memory traces remained encoded but the neurons that held them had become less able to support recall. Rejuvenating those neurons restored their function so the memories could be accessed more reliably.
A: No. The key advance is precise targeting: only the neurons active during learning were reprogrammed. That reduces the risk of unwanted effects that could occur with widespread reprogramming.
A: This work is a meaningful proof of concept in mice and shifts how we think about cognitive decline—toward restoring function rather than only preventing cell loss. Translating the approach to humans will require substantial further research to ensure safety and efficacy.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full.
- Additional context was provided by staff.
About this memory and neuroscience research news
Author: Nik Papageorgiou
Source: EPFL
Contact: Nik Papageorgiou – EPFL
Image: Image credited to Neuroscience News
Original Research: Open access. “Cognitive rejuvenation through partial reprogramming of engram cells” by Gabriel Berdugo-Vega, Cesar Sierra, Simone Astori, Veronika Calati, Jules Orsat, Marianne Julie Scoglio, Carmen Sandi, Johannes Gräff. Neuron. DOI:10.1016/j.neuron.2025.11.028
Abstract
Cognitive rejuvenation through partial reprogramming of engram cells
Regenerative medicine aims to counteract cognitive decline. Partial cellular reprogramming has shown promise in restoring cellular function in tissues, but its effects when applied to the neurons that underlie memory have been unclear. This study reports that OSK-mediated partial reprogramming of engram neurons reverses cellular hallmarks of senescence and disease in aged mice and in models of Alzheimer’s disease. The treatment re-established epigenetic and transcriptional patterns linked to synaptic plasticity and reduced disease-associated neuronal hyperexcitability.
Across different brain areas and behavioral paradigms, engram reprogramming recovered learning and memory to levels seen in healthy young animals, supporting the idea of cognitive rejuvenation. These findings indicate that selectively reprogramming specific neuronal populations could be a strategy for restoring cognitive function in aging and disease.