Evolution Favors Forgetting as Much as Remembering

 We tend to celebrate memory, not forgetting; however, forgetting may be what keeps our minds flexible enough to adapt and learn.

At Flinders University, a team of researchers has shown that the same brain chemical that helps us learn – dopamine – also helps us forget.

“We often think of forgetting as a failure, but it’s actually essential,” said lead author Dr. Yee Lian Chew, a senior lecturer at Flinders University. 

Why forgetting is productive

Forgetting sounds like a defect; however, researchers are now treating it as an active, adaptive process that keeps brains adaptable. Active forgetting removes outdated or irrelevant information, allowing neural circuits to encode new, useful signals. Experimental and theoretical work argue that this is an advantage: a system that never prunes memories would be slower, less flexible and more error-prone.

“If the environment changes, the brain must adapt to a new reality. Therefore, forgetting aspects of the old environment no longer relevant to the new is critical for survival,” Chew told Technology Networks.

“If we remembered everything, our brains would be overwhelmed,” she added.

Previous work in fruit flies found that the neurotransmitter dopamine, known for playing a role in learning, may also be just as important in the process of forgetting.

The Flinders team turned to a tiny, transparent worm to probe how the brain forgets. The nematode Caenorhabditis elegans is a millimeter long, with around 300 neurons, but it shares many of the same memory genes as humans. Its simplicity makes it an ideal model for pinpointing how specific brain chemicals shape behavior.

The new study aimed to determine how dopamine controls the act of forgetting and whether the same molecular logic might underlie memory flexibility in larger brains.

Dopamine-driven forgetting

The researchers trained worms to link the smell of butanone with food – a simple form of associative learning. After training, the worms were tested immediately and again over the next two hours to see how long they would remember that the odor signaled food.

The team compared normal worms with several genetically modified strains. Some could not make dopamine (cat-2 mutants), others could make it but had trouble recycling it (dat-1 mutants) and others lacked dopamine receptors (dop-1, dop-2 and dop-3). These differences allowed the team to isolate which parts of the dopamine system are needed for forgetting.

Memory retention was measured every half hour for two hours after training, and dopamine-deficient worms consistently outperformed normal ones across all time points.

“The worms without dopamine that we tested kept their memories for at least two hours – much longer than the ‘normal’ worms,” said Chew. “We tried to wait out to see how long the dopamine-lacking worms would take to forget, up to twice that duration, and they never did.”

The result reinforces the idea that forgetting isn’t a breakdown; it’s an active, energy-dependent process that keeps memory systems from jamming with outdated information.

When both DOP-2 and DOP-3 receptors were disabled, forgetting almost stopped altogether. The DOP-1 receptor, in contrast, made little difference.

Worms without dopamine also showed a modest boost in learning compared to normal worms, suggesting the change is not just about slow forgetting but an altered learning-memory balance.

Restoring dopamine production in specific neurons did not fix the effect, meaning the entire dopamine network needed to be active for normal forgetting.

These experiments point to a clear message: dopamine doesn’t just help the brain learn new things – it also helps it let go. Forgetting, like remembering, is a carefully managed chemical process.

Forgetting keeps the brain adaptable

By showing that dopamine actively regulates how memories fade, the Flinders team reframes forgetting as a process that helps the brain stay efficient and adaptable. Rather than random decay, it appears to be a fine-tuned, dopamine-driven mechanism shaped by evolution.

“It’s important to forget things that are no longer relevant or important to the current environment,” said Chew. “It keeps the brain flexible and adaptable to new environments or conditions.” This flexibility gives animals – and humans – the ability to respond to change, rather than remain trapped by old experiences.

The parallels between the worm results and earlier studies in fruit flies point to a shared biological mechanism. “It’s exciting to see that something so fundamental is shared across species,” Chew said. The same chemical that teaches the brain new information also helps it clear out the clutter, suggesting a universal neural principle that may extend to mammals, including humans.

“Our findings could give us some new understanding of how conditions in which dopamine is lacking (such as Parkinson’s disease) may relate to how brain cells become less adaptable to changing conditions,” Chew explained.

Dopamine imbalances also feature in schizophrenia and age-related memory loss. Understanding how dopamine supports forgetting could guide new ways to adjust this process – boosting forgetting where traumatic memories persist or slowing it where memory fades too quickly.

Chew cautions that worms are only a starting point: “Despite the wonderful usefulness of worms as an experimental lab model, they are very much not humans.” The study tested short-term memory only and focused on three dopamine receptors; others may also play a role.

“We only tested young adult worms in this particular study, but we would love to see what would happen in older worms. The ability to remember things starts to drop with age, so it would be a very interesting experiment to look at dopamine levels during ageing in different parts of the brain,” she said.

“We are now trying to identify exactly how dopamine acts on neurons in the brain to ‘forget’ old memories,” Chew added.

The message, however, is already clear: forgetting is not failure. It’s a feature that keeps the brain nimble – proof that remembering wisely sometimes means letting go.

 

Reference: McMillen A, Minervini C, Green R, Johnson ME, Ansaar R, Chew YL. Dopaminergic modulation of short-term associative memory in Caenorhabditis elegans. J Neurochem. doi: 10.1111/jnc.70200

 

About the interviewee:

Dr. Yee Lian Chew is a senior lecturer at Flinders University who studies nematode worms to identify brain pathways that can be targeted for the treatment of neurological conditions such as chronic pain. An early career academic, Chew earned her BSc (2010) and PhD (2015) from the University of Sydney. In 2015, she moved to Cambridge, UK, to study worms in colder weather at the MRC Laboratory of Molecular Biology. She returned to Australia in 2019 as a teaching-research academic at the University of Wollongong and is currently a Mary Overton Senior Research Fellow at Flinders University.

Outside the joy of experiments, Chew is a budding science communicator. She has given public lectures at National Science Week, contributed to a children’s outreach program at the Cambridge Science Festival, recorded a podcast and filmed an Elevator Pitch for ABC Science. She was part of the 2021-2022 cohort of Superstars of STEM, a program run by Science & Technology Australia to promote the profile of women STEM professionals.