Why do some experiences stick for years while others vanish by morning? A new study suggests the answer may come down to energy.
Researchers have found that slightly extending how long mitochondria – the energy-producing structures inside brain cells – stay activated after learning can transform a fleeting memory into a lasting one.
By prolonging a natural calcium signal inside neurons, the team boosted cellular energy production at a critical moment, allowing animals to form long-term memories after just a single training event.
The findings recast energy as more than background fuel. Instead, the brain’s timing of energy production may help decide which memories endure.
Prolonging the energy burst
Within memory-forming neurons, mitochondria normally take in calcium during activity and release it soon after, bringing energy production back down.
Jaime de Juan-Sanz and colleagues at the Paris Brain Institute (ICM) demonstrated that slowing that exit allowed calcium to linger inside these mitochondria, sustaining their heightened output beyond the initial burst of activity.
Instead of flooding cells with more calcium, the intervention simply prolonged a natural signal that usually fades within seconds.
That prolonged signal was enough to alter how long memories endure, setting the stage for evidence across species that the brain’s energy timing can shape what lasts.
Holding fuel production longer
After neurons fired, the team targeted a calcium exit route that normally shuts down mitochondrial fuel production.
That route depends on LETM1, a protein that helps move calcium out of mitochondria and brings their energy output back to baseline.
Rather than increasing calcium entry, the researchers suppressed LETM1. That slowed calcium exit, allowing mitochondria to remain stimulated longer after neurons stopped firing.
Because LETM1 sits at the end point of this process, altering it offered a clean way to test whether extending energy production could strengthen memory.
With calcium lingering inside mitochondria, key enzymes stayed active and kept converting fuel into ATP – the molecule cells use to do work.
The extra ATP did not make every thought faster, but it provided enough sustained power for certain memory-building steps to finish. In effect, the researchers extended the brain’s energy window just long enough to influence what stuck.
Memory boost appears across species
The effect first showed up in fruit flies. Normally, a single odor-punishment lesson lasts a few hours before fading within a day. But when the team targeted mushroom body neurons – the cells that store odor memories – a single lesson lasted more than 24 hours.
Spaced training sessions usually force flies to invest in long-term storage. Here, however, boosted energy production allowed long-lasting memory after just one session.
The researchers then tested the same mechanism in mice. Thirsty animals were trained to avoid a smell paired with a nausea-inducing injection.
Ten days later, mice with suppressed LETM1 still avoided the punished odor, while control animals drank from both bottles.
Importantly, locomotion and water intake remained normal, ruling out simple changes in motivation. Seeing the same memory extension in insects and mammals points to a shared, evolutionarily conserved energy-control system.
Energy cost of long-term memory
Not every memory was affected. Short-lived memories that normally fade within hours still followed their usual timeline, even when mitochondria held onto calcium longer during learning.
Long-term storage requires hours of additional cellular work, including new protein production and rewiring of synaptic connections. That extended effort demands sustained energy.
“It appears that our manipulation does not enhance all forms of memory indiscriminately, but specifically those that require sustained energy investment,” said de Juan-Sanz.
At rest, the human brain makes up about two percent of body weight, yet it consumes roughly 20 percent of the body’s total energy. Neurons constantly pump ions, recycle signaling molecules, and reset connections for future activity.
Instead of treating energy as background fuel, this study suggests it may act as a gatekeeper. Once energy availability becomes adjustable, memory looks less like a fixed outcome and more like a performance limit that can shift – within biological boundaries.
Energy has consequences
Too much calcium inside mitochondria can damage neurons, so any attempt to prolong the signal has to stay within safe limits.
LETM1 is also involved in Wolf-Hirschhorn syndrome, a rare genetic condition, which ties this protein to human health risks.
Because the new work used genetic suppression, not a drug, it does not show a clear path to safe memory enhancers.
Careful tests at ICM will have to map when extra energy helps, when it harms, and which brain circuits tolerate the change.
Turning energy on demand
Fine control would mean turning this energy boost on only during key moments, then allowing mitochondria to return to normal.
One possible route uses optogenetics – controlling cells with light-sensitive proteins – to push or pause mitochondrial calcium signals in selected neurons.
By holding calcium in mitochondria slightly longer, the study linked extra ATP production to stronger long-term memories in animals.
The findings suggest that even brain circuits that already function efficiently may have unexpected room for optimization.
Future work at ICM will require safer, more precise molecular switches. Even if human applications remain distant, the results already challenge old assumptions about what limits learning – and offer a new way to test how cellular energy sets the boundaries for memory.
The study is published in the journal Nature Metabolism.
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