In the frontal lobe of the brain is the primary motor cortex, a ribbon of neurons that coordinates movement. Starting in the 1930s, scientists developed a map of this brain region called the homunculus map, describing how different sections of the primary motor cortex controlled specific parts of the body.
But now, in an article published Wednesday in the journal Nature, the researchers suggest that the homunculus map is missing some key parts. Based on fMRI data, they argue that the primary motor cortex also has distinct regions that play a role in whole-body action planning, rather than corresponding to a single body part.
“This study is very interesting and very important,” said Michael Graziano, a neuroscientist at Princeton University who did not contribute to the research. Nature News‘ Max Kozlov. The primary motor cortex doesn’t appear to be “just a list of muscles in the brain that control the toes of the tongue.”
This description is essentially what the homunculus map looks like – it depicts a deformed human body stretched over a slice of the brain, with each part of the body controlled by the neurons below. The researchers created the map by electrically stimulating the brains of surgical patients and noting where the patients felt corresponding sensations or movements. Body parts over which humans have precise control, such as our fingers and tongue, appear larger than life on the map because they occupy a disproportionate amount of primary motor cortex. Meanwhile, areas over which we have less complex control, such as the ankles, look smaller.
But for decades, research has suggested that the primary motor cortex may also be responsible for more coordinated movements.
“There’s a whole cohort of people who have known for 50 years that the homunculus isn’t quite true,” said Evan Gordon, co-author of the new study and neuroscientist at the University of Washington. Scientific News‘Nora Bradford.
In the new study, researchers scanned participants’ brains while they lay in an MRI machine. Seven people were measured while they were still, and two of those participants were also monitored performing simple movements, such as blinking or flexing a muscle.
The results suggest that the three general sections of the classic homunculus map—which control the face, arms, and lower body, respectively—should be interspersed with three areas more related to whole-body control. These newly proposed sections can be linked to movements involving several body parts or activate during movements linked to the midsection, writes new scientistby Jason Arunn Murugesu.
Whole-body control regions were connected to each other, as well as to the parts of the brain responsible for action planning, pain regulation, and blood pressure, by Nature News.
“We thought we knew everything about this region,” says Angela Sirigu, a neuroscientist at the Marc Jeannerod Institute of Cognitive Sciences in France, who was not involved in the study. Nature News. “But its organization is much more complex than traditionally thought.”
To support their findings, the team also looked at previous data from three large fMRI studies. By examining these brain scans of around 50,000 people, they found more evidence for the existence of new brain regions, for new scientist.
Finally, the researchers looked at the brains of children to study the development of the primary motor cortex. A newborn baby lacked all three whole-body control regions, but an 11-month-old showed signs of it. The scans of a 9-year-old child resembled those of the adults in the study, suggesting that these newly identified brain regions are developing early in life.
A better understanding of the homunculus could help improve treatments for damage related to stroke or injury to the primary motor cortex, Nature News reports. And the team wonders if whole-body control areas could one day play a role in treating Parkinson’s disease, which has movement-related symptoms, for example. new scientist.