When a rat at the University of Freiburg in Germany feels a small vibration under its paw, it releases a lever and receives a drop of sugar water. That simple exchange—feel, react, reward—is helping scientists answer one of the oldest questions about the brain: how do we plan movements before we actually make them?
A team of 15 researchers at the university's BrainLinks–BrainTools research center spent years studying this question. Their findings, published in the journal Cell Reports, reveal how the brain switches from thinking about a movement to actually doing it. The research could one day help people with mobility challenges regain movement through smart prostheses that read their brain signals.
"We now have a better understanding of the neural processes in the brain that control movements," said Dr. Ilka Diester, the center's spokesperson and a professor of optophysiology. "In the long term, these findings could be used to develop treatments or aids for people with mobility impairments."
The researchers trained rats to push a lever with their paw and hold it until they felt a vibration. The rats knew sugar water awaited them if they did this correctly. While the animals performed the task, the scientists recorded the electrical activity in their brains.
The team focused on two brain regions that exist in both rats and humans: the premotor cortex and the primary motor cortex. Both areas become active when movements are planned and executed, but scientists had never fully understood why they showed activity even before any movement occurred.
The researchers discovered that during movement planning, neurons in the premotor cortex communicate with special helper cells in the primary motor cortex called inhibitory and excitatory neurons. The brain can only tell the muscles to move once this communication shifts away from the inhibitory neurons—which slow things down—toward the excitatory neurons, which speed things up. An external signal, like the lever's vibration in the experiment, then triggers the actual movement.
The team calls this idea the "switching population hypothesis." It replaces two older theories about how movement planning works.
Making this discovery required a rare combination of expertise. Diester's group uses light to control individual brain cells. Dr. Joschka Bödecker and his computer science team built an artificial intelligence model that predicted how different groups of neurons would affect behavior. And Dr. Andreas Vlachos used powerful microscopes to photograph the physical connections between neurons, confirming the theory at a cellular level.
The study's first authors—Dr. Julian Ammer, Dr. Mansour Alyahyay, Dr. Gabriel Kalweit, and Hao Zhu—each brought different skills to solve the puzzle together.
For people with paralysis or limb loss, this research offers real hope. If sensors can detect the brain's movement-planning signals and pass them to a smart device, that device could help restore mobility. What started with rats learning to feel and release has opened a door to helping humans move again.