Decoding the neural dynamics of movement
Mapping the Motor System Is Well Within Reach
When we walk, run, reach, gesture, jump, or throw, our muscles are receiving instructions from our brain–this much is well understood.
How the brain does this is less well understood, but research undertaken by Mark Churchland, PhD, Assistant Professor of Neuroscience at Columbia University, is bringing that knowledge within reach.
“Our brain does a lot of important things,” he says, “but the most important, I would argue, is enabling our body to move. Movement is our only way of obtaining what we need in life. From an evolutionary standpoint, faculties such as memory, emotion, and decision making exist only so that the brain can direct the right movement at the right time. Movement may seem a trivial task compared to, say, making a difficult decision. What could be easier than picking up a glass of water and drinking it? But that act requires exceedingly complex neural processes that no one working in the field of robotics has been able to replicate. When something goes wrong with these processes–as in the case of paralysis, Parkinson’s disease, or ALS–you realize how hard it is to make those simple movements.”
According to Dr. Churchland, the goal of his lab is to understand how the brain produces movement–in other words, what are the dynamics that allow the motor cortex in the brain to generate movement. To answer that, an even deeper mystery must first be explored: How does the brain produce its own activity?
The brain is not a reflex machine
“The brain has long been studied as a reflex machine,” says Dr. Churchland, “a device that simply and automatically translates sensory input into action output. But we’re not simply reflex machines. We all appreciate this at an intuitive level: our brains do lots of things that are not reflexive. For example, how is that we are able to come up with ideas, thoughts, decisions, and plans?
“If everything we did were purely reflexive,” he continues, “a baseball pitcher would just throw a pitch as soon as the umpire yelled ‘Play ball!’ But instead, he sets up, processes signals from the catcher, changes the way he holds the ball, considers his options, and delivers a pitch when he’s ready to do so. What I’m interested in is how does the brain internally generate such a movement? How does it decide when it is ready? How does it initiate the movement and then terminate it?”
If the neural networks within the brain are not purely reflexive, responding directly and immediately to external stimuli, then they must be able to generate their own activity. Dr. Churchland, a 2012 Searle Scholar and recipient of a 2012 NIH Director’s New Innovator Award who came to Columbia last year from the University of Stanford, studies brain activity in monkeys who perform simple reaching tasks when prompted by a makeshift video game. Small electrodes are placed on their brains–this same technology has been approved for use in human patients for such things as epilepsy monitoring–and as they reach out to different targets on a screen, Dr. Churchland is able to measure both the neural and muscular activity and correlate his data with his observations.
“It’s critical to record the activity of the brain while it’s in motion,” he says. “When the body is in motion the brain is in motion, constantly changing its activity as it creates movement. By measuring the movements of the animal, and the changes in its muscles and motor cortex, we can begin to track how neural activity is generated and how it produces muscle movement.”
The rhythm of the reach
As mentioned before, a reach may seem like a simple motion but a single motion is the result of many processes and factors – some of which are known and some of which are still being explored. The range of inquiries into this specific area is very broad. How is a movement initiated? How is it ceased? How are direction, distance, and speed accounted for?
In prior research conducted at Stanford, Dr. Churchill proposed a new theory of the brain activity behind arm movements: instead of encoding external spatial information the way that the visual cortex records color, intensity, and form, the motor cortex sends quasi-rhythmic signals down the spinal cord. The electrical signal that governs a movement, then, is not a single impulse, but rather a combination of several rhythmic patterns produced by motor neurons at a given moment.
“At least conceptually, this relates to a discovery by the 19th-century French mathematician Joseph Fourier, who found that two discrete rhythms could be summed to produce a third, more complex pattern,” he says. “Thus, if your brain wishes to build a particular pattern to send to the muscles, a good strategy may be to build that pattern from a few simple rhythmic patterns.”
A translational focus on the future
Of course, once one knows how a thing works, one can then deduce what happens when it doesn’t work. Dr. Churchland explores how movements are initiated; for people with Parkinson’s disease, initiating a movement is very difficult. Understanding how to spark that initial impulse could lead to a treatment that would restore or prolong mobility for people with Parkinson’s–and perhaps even for people who have suffered full or partial paralysis.
“In terms of future work, my laboratory is very interested in translating basic science knowledge regarding dynamics into better neural prostheses: brain-machine interfaces that directly translate neural activity into movement, thus bypassing an injured limb or spinal cord,” he says. “If we can better understand how motor cortex functions, then we can leverage that knowledge to help engineer better neural prosthetics.”