The seemingly simple act of reaching for a cup of coffee requires a lot of effort from the brain.
It has to plan a trajectory to the cup, control dozens of muscles, make adjustments based on feedback from the eyes and fingers, and maintain its focus on the goal: a tasty jolt of caffeine.
And it turns out that medical textbooks may be wrong about how all this happens. The books show a model of the brain in which the motor cortex is solely controlling movement.
But scientists at Washington University School of Medicine in St. Louis have found that previously overlooked areas of the brain's motor cortex appear to link control of specific muscles with information about the entire body and brain.
As a result, the act of, say, reaching for a cup of coffee can directly influence blood pressure and heart rate. And the movement is seamlessly integrated into brain systems involved in planning, goals and emotion.
Textbooks, though, still portray a motor cortex in which "the region that controls your finger is not going to be connected to a region [that asks], 'what am I going to do today?' " says Dr. Nico Dosenbach, an author of the study and an associate professor of neurology and radiology.
But the MRI data leaves little doubt that "there is this interconnected system," says Evan Gordon, an assistant professor of radiology and the study's first author. "It always was there, but we had not perceived it because of our training, because of the things we learned in the first neuroscience class that we ever took."
The results, which were previewed online in 2022, have generated a lot of interest and support from brain scientists and neurosurgeons.
"I view this as a really fundamental change in how we're going to view the motor cortex," says Peter Strick, chair of neurobiology at the University of Pittsburgh.
Challenging the conventional wisdom
The finding involves a strip of brain tissue called the primary motor cortex. As its name suggests, this area is considered the main source of signals that control voluntary movements.
Textbooks show the primary motor cortex as a continuous ribbon with sections devoted to specific muscle groups, from tongue to toe.
That view dates back to the 1930s, when Canadian neurosurgeon Wilder Penfield began mapping the brains of his epilepsy patients by applying electrical currents to areas in the motor cortex. Ultimately, Penfield identified segments that would reliably cause a foot, finger, or the tongue to move.
Penfield's hand-drawn map of the primary motor cortex has dominated the field ever since, even though several teams have noted flaws with some of the details.
So Dosenbach's team was puzzled when they began seeing hints of a very different organization. The clues came in the form of data from high-resolution functional magnetic resonance imaging (fMRI) of individual brains.
What they were seeing "just didn't make sense if the textbooks were right," Dosenbach says.
Gordon noticed that the MRI data suggested there were important areas between Penfield's sections. These areas of cortex had lots of connections, but not to muscles. Instead, the connections led to areas all over the brain, including those that control internal organs like the heart and lungs.
At first, Gordon doubted what he was seeing. He wondered: "Is this just something weird about the data we have collected or is this present in other people?"
So the team began analyzing fMRI data collected by other groups. It confirmed their own findings.
"This heretical thought that maybe this is right and the book is wrong started to take hold," Dosenbach says.
But if these segments of brain tissue weren't for controlling muscles, what were they doing? To find out, the team turned to their lead scientist: Nico Dosenbach.
"We put Nico in the scanner for a long time and had him do a whole lot of different stuff until we figured it out," Gordon says with a chuckle.
They had Dosenbach perform complicated tasks like rotating his left hand in one direction while rotating his right foot in the opposite direction. These tasks required his brain to plan his movements before carrying them out.
The experiments revealed something surprising about the mysterious stretches of brain tissue.
"We found that these regions in the motor cortex were more active during this planning phase and that's what really pointed us in the right direction," Gordon says.
Another brain region, called the premotor cortex, is known to have a role in planning movements, but the areas found by Gordon and Dosenbach's team are woven into the primary motor cortex itself.
"There's two interleaved systems," Dosenbach says. So right below an area controlling the fingers, for example, the team would find an area involved in "whole body integrative action."
The team then looked at several huge databases that combine lots of MRI scans to show the connections in a typical brain.
And once again, Gordon says, they found evidence that the ribbon of motor cortex contained alternating areas: one for fine control of a specific muscle, then another keeping track of the entire body.
The team began to share their discovery with other scientists, including Strick, whose lab had observed a similar system in monkeys.
"Sometimes you have this aha experience," he says. "They showed me some of their data and it instantly clicked."
The new view of primary motor cortex may help explain how the brain solves a difficult problem, Strick says.
"Even simple movements require nuanced control of all organ systems," he says. "You have to control heart rate. You have to control blood pressure. You have to control so called fight and flight responses."
So it makes sense that the same ribbon of brain tissue involved in a movement like standing up would be connected to all those other brain areas.
A system that weaves together movement and mental states also could explain why our posture changes with our mood, or why exercise tends to make us feel better.
"How you move can have an impact on how you feel. And how you feel is going to have an impact on how you move," Strick says. "You know, my mother would tell me, 'stand up straight, you'll feel better.' And maybe that's true."
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