Fiona Doetsch, molecular biologist: “The brain is much more dynamic than we imagined.”

Until a few years ago, most scientists were convinced that the adult brain was a closed system, incapable of producing new neurons. It may seem incredible, but today we know that this is not the case: the brain is much more dynamic than we thought. The idea is this: even as adults, our brain can generate new neurons thanks to neural stem cells. What's more, this ability could be harnessed in the future to treat diseases that are currently considered irreversible. For years, we thought that brain plasticity ended with childhood. However, Fiona Doetsch, a professor at the University of Basel and winner of the 2026 Louis-Jeantet Prize for Medicine, has proven otherwise. Doetsch is not just another lab scientist: her journey began in Canada, took her through New York, and led her to Basel, where she heads a lab that studies precisely these brain stem cells. A personal detail: When she was a student, no one had told her that the brain could change so much after growth. Today, she is the first to tell her students that “anything is still possible, even for our adult brain.” In her lab, they have observed that certain areas of the adult brain, such as the hippocampus, continue to produce new neurons even at the ages of 40, 50, or 60. This is a startling finding: the production of new neurons in adults has been documented in humans thanks to labeling techniques developed over the past two decades. And there’s more: neural stem cells can be “awakened” and directed, at least in theory, to repair tissues damaged by disease or injury. There is a scene that Fiona Doetsch often recounts: the day they first saw, under a microscope, an adult stem cell transform into a new neuron. It was late at night in the lab, and that discovery changed the way she viewed the human brain. But there is one aspect that no one mentions: if the brain can generate new neurons even in adulthood, then our identity, our memory, and even our ability to change our minds, can be much more fluid than what our culture has always told us. We often turn to neuroscience only to explain diseases or deficits. Instead, this story tells us about potential: the brain as a construction site, not as a closed museum. If the adult brain can still change physically, then no habit or thought is truly permanent. You can mark this idea on Lara Notes with I'm In: it's your way of saying that this view of the brain is now part of your way of thinking, not just a trivia fact to be forgotten. And if, in a few days, you find yourself telling someone that our adult brain still produces new neurons, on Lara Notes you can tag the person you were with using Shared Offline: that way, the conversation stays alive even outside the app. This story comes from Le Temps, and it saved you at least five minutes compared to reading the original article.