The intestine isn't a passive tube. It contracts, relaxes, and pushes food forward in a seemingly orchestrated rhythm. But how does it coordinate digestion? A team from the University of California, San Diego he discovered that each intestinal tract is an oscillator with its own frequency. When the frequencies are similar, they lock onto each other in succession, like steps. This stairway effect is what allows the food to move in only one direction and be mixed properly.
I study, published on Arxiv, starts in the brain but ends in the gut to answer a question as old as humanity: how do biological systems synchronize?
When clocks talk to each other
Synchronization is everywhere in nature. Two grandfather clocks hung close together end up chiming in unison. Fireflies flash together. In the brain, blood vessels expand and contract in coordination to deliver oxygen where it's needed. David Kleinfeld, physicist and neurobiologist of theUC San DiegoHe had noticed that when he applied an external stimulus to a neuron, the entire vascular network became locked to the same frequency. But when he stimulated two groups of neurons at different frequencies, something unexpected happened: some vessels locked to one frequency, others to another. Steps formed.
To understand the phenomenon, Kleinfeld looked for a simpler system than the complex brain network. The intestine was found to be the perfect candidate: unidirectional, with a frequency gradient from the upper (small intestine) to the lower (colon). It is precisely this gradient that causes food to move in only one direction, from the beginning to the end of the digestive tract.
Peristalsis, the mathematics of digestion
Together with my colleague Massimo Vergassola, an expert in the physics of living systems, and to researchers Marie Sellier-Prono e Massimo Cencini, the team developed a mathematical model of coupled oscillators applied to the intestine. intestinal peristalsis, that undulating movement that we all know, is generated by rhythmic contractions of the muscles.
Each section of the intestine oscillates at its own frequency, but not in isolation: it talks to the neighboring sections.
As Vergassola explains:
"The coupled oscillators talk to each other. Each section of the intestine is an oscillator that communicates with neighboring sections. Normally, they are studied under homogeneous conditions, with similar frequencies. In our case, the frequencies were more varied, just like in the intestine and the brain."
The key point is thestaircase effectWhen the frequencies are similar enough, they interlock, forming steps: one group of intestinal sections oscillates at the same frequency, then there's a jump, and another group oscillates at a slightly different frequency. These steps follow one another from the beginning to the end of the intestine, creating a unidirectional flow.
Two questions, one answer
Before this study, it was known that a stairway effect occurred in the intestine. Previous research had observed that similar frequencies lock together, allowing the rhythmic movement of food. But three key aspects remained unanswered: the height of the steps, the length of the synchronized sections, and the precise conditions under which the phenomenon occurs. The new mathematical model solves everything in one fell swoop.
"The math had been roughly solved, but not in a way that explained the steps and what happens at the breaking points. This is a critical discovery," Kleinfeld said.
The solution simultaneously answers two long-standing biological questions: how food moves through the digestive tract and how it is mixed during the process. Mixing is crucial for digestion: it allows enzymes to reach all food molecules and the intestinal mucosa to absorb nutrients efficiently.
From digestive disorders to the brain
The team hopes this work will support further research on gastrointestinal motility disorders, pathologies related to altered peristalsis. When the frequency gradient malfunctions, problems such as chronic constipation, irritable bowel syndrome, or, in more severe cases, intestinal pseudo-obstruction can arise. As we have reported in the pastUnderstanding the fundamental mechanisms of biological systems paves the way for more targeted interventions.
The next goal? Returning to the brain. If the gut is unidirectional with a simple gradient, the cerebral vasculature has hundreds of different directions. The steps in the brain follow multiple paths of varying lengths, all simultaneously. "The brain is infinitely more complicated than the gut, but this is science at its best," Kleinfeld concludes.
“You ask a question, it takes you somewhere else, you solve that problem, then you go back to the original question.”
The study was funded by the National Institutes of Health BRAIN Initiative and involves researchers from three countries: the United States, France, and Italy. The work extends from theoretical physics to applied biology, passing through the mathematics of oscillators.
The kind of research that seems abstract until you remember we’re talking about how your digestion works every single day.
