Do you ever wonder what happens in the brain when we go right or left? Most people do not; they just do it without thinking. Yet, this simple movement is actually controlled by a complex process.
In a new study, researchers have discovered the missing piece of the complex nerve network required for left-right turns. The discovery was made by a research team consisting of Assistant Professor Jared Cregg, Professor Ole Kiehn, and their colleagues from the University of Copenhagen’s Department of Neuroscience.
In 2020, Ole Kiehn, Jared Cregg, and their colleagues identified the „steering wheel of the brain“ – a network of neurons in the lower part of the brainstem that controls right and left movements when walking. However, back then, they were unclear about how this right-left circuit was controlled by other parts of the brain, such as the basal ganglia.
„We have now discovered a new group of neurons in the brainstem that directly receive information from the basal ganglia and control the right-left circuit.“
– Professor Ole Kiehn, Department of Neuroscience, University of Copenhagen
Ultimately, this discovery could help people suffering from Parkinson’s disease. The study was published in the prestigious journal Nature Neuroscience.
The basal ganglia are deep in the brain. For many years, it has been known that they play a key role in controlling voluntary movements.
Years ago, scientists found that by stimulating the basal ganglia, they could influence the movements of the right and left hand in mice. They just didn’t know how.
„When walking, you shorten the stride length of the right leg before a right turn and the left leg before a left turn. The newly discovered network of neurons is located in a part of the brainstem known as the PnO. They are the ones receiving signals from the basal ganglia and adjusting the stride length when we make a turn, determining whether we move right or left,“ explained Jared Cregg.
Therefore, the study provides a key to understanding how these absolutely essential movements are generated by the brain.
In the new study, the researchers examined the brains of mice since their brainstem is very similar to the human brainstem. Therefore, the researchers expect to find a similar right-left circuit in the human brain.
People with Parkinson’s Have Difficulty Turning Right and Left
Parkinson’s disease is caused by a lack of dopamine in the brain. This affects the basal ganglia, and the researchers responsible for the new study believe that this results in the right-left circuit of the brainstem not being activated.
It makes sense when looking at the symptoms people with Parkinson’s feel at a late stage – they often have difficulty turning when walking.
In the new study, the researchers examined this in mice with symptoms similar to those of people with Parkinson’s disease. They created a so-called Parkinson’s model by removing dopamine from the brains of mice and giving them motor symptoms similar to those of people with Parkinson’s disease.
„These mice had difficulty turning, but by stimulating the PnO neurons, we were able to alleviate the difficulty turning,“ Jared Cregg said.
With the help of deep brain stimulation, scientists could eventually be able to develop a similar stimulation for humans. However, they are currently unable to stimulate human brain cells as precisely as in mouse models, where they used advanced optogenetic techniques.
„The neurons in the brainstem are chaotic, and the electrical stimulation, the type of stimulation used in human deep brain stimulation, cannot distinguish between the cells. However, our knowledge of the brain is constantly growing, and eventually, we may be able to think about targeted deep brain stimulation for humans,“ Ole Kiehn concluded.
Facts: What the Researchers Did
The researchers used optogenetics to stimulate the network of neurons in the PnO (Pontine reticular nucleus, oral part). In short, optogenetics is a technique for genetically modifying specific brain cells to make them light-sensitive and thus susceptible to light stimulation.
When the researchers activated the light, mice that could previously only perform left turns could now also walk straight and make right turns.
University of Copenhagen – Faculty of Health and Medical Sciences
Cregg, JM, et al. (2024). Basal ganglia-spinal cord pathway controlling movement asymmetries in mice. Nature Neuroscience. doi.org/10.1038/s41593-024-01569-8.