How your brain decides whether to run or walk
Two centres in the brain decide when you should walk or run.
Scientists have taken a step closer towards understanding what happens in the brain when we begin to run or walk.
A new research project shows that two centres in the midbrain sends signals to the spinal cord to communicate when your legs should start moving, and how fast.
When we begin to move, the brain first sends a signal to the spinal cord, then nerve cells in the spinal cord control the precise coordination of the muscles.
The results also indicate that each part of the brainstem controls a certain aspect of moving—either running or walking.
“It may seem surprising to many that the generation of locomotion is in the spinal cord itself, where the process is automated to a degree, so we don’t need to think about every step we take,” says Ole Kiehn, lead-author on the new study and professor at the Department of Neuroscience at the Faculty of Public Health at the University of Copenhagen, Denmark.
“Before the spinal cord can run on autopilot, it needs signals from the brain and we have now identified two areas in the midbrain that initiate locomotion and set the speed of locomotion,” he says.
The new results are published in the scientific journal Nature.
Lighting up mice brains to make them run faster
In the new study, Kiehn and colleagues studied mice, which they had genetically engineered to activate the two newly discovered regions in the brain when illuminated by a surgically implanted light.
The technique is called optogenetics, and uses light sensitive proteins from algae, which are inserted into certain nerve cells and stimulated by light.
When the scientists illuminated nerve cells in the cuneiform nucleus (CnF) region of the midbrain, the mice first began to walk, then trot, and then ran at speed depending on the stimulation frequency.
When they illuminated the nerve cells in another region called the pedunculopontine nucleus (PNN), the mice began to walk or trot, adopting the type of movement that animals use when looking for food.
When they shut down activity in these two regions of the brain the mice could neither run nor walk.
“We show that nerve cells in both PNN and CnF can initiate locomotion and that the activity in both these regions of the midbrain helps to maintain and regulate the speed of walking and trotting. Only CnF is able to initiate gallop or fast running, while PPN activity is associated with slow and exploitative walking,” says Kiehn.
Possible new treatments for Parkinson’s disease
The results have implications for a number of diseases where the body does not have full control over its movements, such as Parkinson’s disease, where locomotion is impaired.
Kiehn imagines that they may one day be able to stimulate these newly identified regions of the brain electronically, allowing Parkinson’s patients to better control their movements.
Electrical stimulation is already used to treat some symptoms in the late stages of the disease, but the new discovery could help to target this stimulation much more precisely to those regions of the midbrain where it could affect movement.
“We are already planning experiments to study whether these areas are affected in animal models, displaying symptoms of Parkinson’s disease. This will give important insights into treatment options,” says Kiehn.
Could one day develop new “skeletons”
Another exciting prospect is the development of so-called exoskeletons—a type of external skeleton that sits on the outside of the body, says Ernst Albin Hansen from Sport Sciences at the Department of Health Science and Technology at Aalborg University, Denmark.
These skeletons are of military interest but they may also be useful for people suffering from paralysis to move again, he says.
“Such an exoskeleton should be programmed to be able to interact with the body and here it’s important to know how, for example, walking and running are initiated. So the new study is really interesting because it is a step further in our understanding of how the brain functions while moving,” says Hansen. He was not involved in the study.
Kiehn and Hansen agree that the newly discovered centres could also be stimulated to help patients with mobility problems. Such trials would first have to take place in animals and then on people.
“This is what we’re working towards at some point,” says Hansen.
Translated by: Catherine Jex
- "Midbrain circuits that set locomotor speed and gait selection", Nature (2017), doi:10.1038/nature25448