A study by researchers at the University of Washington School of Medicine indicates that the hypothesis that the body and mind are inextricably intertwined is more than just an abstraction. The study shows that parts of the area of the brain that control movement are connected to networks involved in thinking and planning, as well as controlling involuntary bodily functions such as blood pressure and heartbeat. The findings represent a literal mind-body link in the very fabric of the brain.
The research, published this Wednesday, April 19, in the journal Nature, could help explain some puzzling phenomena, such as why anxiety makes some people want to walk from one place to another; why stimulating the vagus nerve, which regulates internal organ functions such as digestion and heart rate, can alleviate depression; and why people who exercise regularly show a more positive outlook on life.
"People who meditate say that by calming their body they also calm their mind. These types of practices can be really helpful for people with anxiety, although until now we had no scientific evidence to explain it. Now we have found a connection. We have found the where the highly active, goal-oriented part of your mind connects to the parts of the brain that control breathing and heart rate," explains Evan M. Gordon, one of the study authors, in the publication.
Gordon and fellow author Nico Dosenbach point out that they did not set out to answer longstanding philosophical questions about the relationship between the body and the mind. They set out simply to verify the long-established map of the areas of the brain that control movement, using modern brain-imaging techniques.
In the 1930s, neurosurgeon Wilder Penfield mapped these motor areas of the brain by delivering small electrical shocks to those undergoing brain surgery, noting their responses. He found that stimulating a narrow strip of tissue in each half of the brain causes specific parts of the body to contract. Furthermore, the control areas of the brain are arranged in the same order as the body parts they target, with the toes at one end of each strip and the face at the other. Penfield's map of the motor regions of the brain, depicted as a homunculus, has become a staple of neuroscience studies.
Gordon, Dosenbach, and their colleagues began to replicate Penfield's work with functional magnetic resonance imaging (fMRI). They recruited seven healthy adults to undergo hours of fMRI brain scanning while they rested or performed tasks. From this high-density data set, they built individualized brain maps for each participant. They then validated their results using three large publicly available fMRI datasets: the Human Connectome Project, the Adolescent Brain Cognitive Development Study, and the UK Biobank, which together contain brain scans of approximately 50,000 people.
To their surprise, they found that the Penfield map was not quite right. The foot control was in the place Penfield had identified. The same for the hands and face. But interspersed with those three key areas were three other areas that didn't seem to be directly involved in movement at all, even though they were in the motor area of the brain.
Also, the non-movement areas looked different than the movement areas. They appeared thinner and were strongly connected to each other and to other parts of the brain involved in thinking, planning, mental activation, pain, and control of internal organs and functions, such as blood pressure and heart rate. Other imaging experiments showed that while the motionless areas are not activated during movement, they are activated when the person thinks about moving.
"All of these connections make sense if you think about what the brain is really for," Dosenbach says. "The brain is there to behave successfully in the environment so that you can achieve your goals without hurting or killing yourself. You move your body for a reason. Of course, motor areas must be connected to executive function and control of basic bodily processes, such as blood pressure and pain. Pain is the most powerful feedback, right? You do something and it hurts, and you think, 'I'm not going to to do that again.'"
Dosenbach and Gordon named their newly identified network Somato-Cognitive Action Network, or SCAN. To understand how this network develops and evolves, they scanned the brains of a newborn, a one-year-old and a nine-year-old. They also analyzed data that had previously been collected on nine monkeys. The web was not detectable in the newborn, but was clearly evident in the one-year-old and almost adult-like in the nine-year-old. Monkeys had a little more rudimentary system, without the extensive connections seen in humans.
"This may have started out as a simpler system to integrate movement with physiology so that we don't pass out, for example, when we stand up," Gordon says. "But as we become organisms that do thinking and doing much more complex planning, the system was upgraded to connect a lot of very complex cognitive elements."
"Penfield was brilliant, and his ideas have been dominant for 90 years, and they created an avenue of research," Dosenbach says. "Once we started down it, we found a lot of published data that didn't agree with his ideas and alternative interpretations that had been ignored. We gathered a lot of different data on top of our own observations, zoomed it out, and synthesized it, and we came up with a new way of thinking about how the body and mind are tied together."
