Walking around on two legs seems like a simple activity, most of us have literally been doing it since we were babies, but it is the product of a brain that has evolved over millions of years to process incoming sensory information and balance dozens of connected systems. Understanding it contributes to better neuroscience, rehabilitation, and public health.
Professor Peyman Mirtaheri at OsloMet’s ADEPT lab studies just how the brain turns these sensory inputs into motion. “What’s really exciting for me is how we have this amazing organ that processes this information at incredibly optimized levels and is always trying to optimize further”.
The standing problem
Mirtaheri is trying to understand a very complex system. By some estimates, around 70% of the brain is dedicated to processing somatosensory information. That’s our sense of touch and all the internal systems that let us know how our muscles are working and where our limbs are. He is figuring out how this neural network is connected, how it manages all the incoming information, and how it can optimize for different conditions so well.
Mirtaheri says standing and balancing on two legs is one of the things that makes us unique among the creatures on this planet. All of our body components – from feet and legs, hips and torso, to neck and head – have to work together. That requires communication between sensory nerves, muscles, and the brain. Most of this process is done unconsciously by our nervous system.
This ability to balance segments is known as tensegrity. It relies on the brain quickly responding to sensory inputs to modify and update its instructions and codes. When it doesn’t work right, our brains have to work much harder.
And things get even more complex when we start moving.
Information in symmetry
Figuring out how the brain performs this amazing feat requires biomechanics, neuroscience, biology, programming, and much more. Fortunately, all of this cross-disciplinary expertise is available at OsloMet’s ADEPT lab. There, Mirtaheri and the rest of the team use a technology called fNIRS (functional Near-infrared spectroscopy and EEG (electroencephalogram)) to observe which parts of the brain are active during stimulation of the extremities and more complex activities like walking. Participants wear a tight cap with an array of infrared lights probes and electrodes to monitor the brain’s symphony. The light harmlessly penetrate the cerebral cortex to show the researchers where oxygen is being delivered and used. More oxygenation means more activity in that region of the brain.
He and the other researchers use fNIRS to watch people’s brains activate during walking or other physical activities.
Each side does the brain processing, and the communication between them is similar to a multi-core parallel processing, just like how CPUs in computers do it.– Peyman Mirtaheri
Walking switches between left and right control because we are symmetrical, so the brain patterns are also symmetrical and switch with each step. “The certain symmetrical interactions here are quite fascinating” says Mirtaheri. As we walk, he says, parts of the brain activate and other ‘helping circuits’ come in to contribute and make the process much smoother. Everything is about optimization and conserving energy and metabolism.
Each side of the brain runs this program independently and in cooperation. “Evolution has concluded that we need to have two processes, one on each half, because then you can do motions without any interruption. Each side does the brain processing, and the communication between them is similar to a multi-core parallel processing, just like how CPUs in computers do it.”
Watching these interactions gives Mirtaheri a clue about how these processes are related.
Breaking the symmetry
What is really interesting is what happens to the brain in unfamiliar situations.
“You see immediately that when subjects that are not trained to walk on a certain surface, they have a sort of asymmetrical approach.”
Changing the walking surface, wearing different shoes, or an injury forces the brain to adjust and adapt a new model. The resulting brain signals have asymmetry that reveals how the brain processes inputs from different regions of the cortex.
Mirtaheri’s research shows that the brain can adapt to these new situations, quickly figuring out how to turn different sensory input into regular motion. Experiencing these new conditions and developing new programs is an important part of keeping our brains healthy. Just like how muscles get weaker when we don’t exercise them, if those sensory information feedback cells are not activated, they don't need to be there, so those connections fade.
How the brain of a competative skier works
On the other hand, training and rewiring the brain in this way could lead to better health and rehabilitation practices. The ADEPT lab recently had a competitive skier come in for testing after a leg injury. Despite healing the leg, the skier still wasn’t back to form. In a sport where milliseconds mean the difference between a medal and going home emptyhanded, this was a problem.
Mirtaheri and the ADEPT team used their fNIRS system and found asymmetry in the brain. The skier’s injured side was still taking much more energy to control than the healthy side. Based on this information, the ADEPT team recommended specific rehabilitation exercises to address the imbalance and trigger the brain to develop new pathways.
Mirtaheri thinks this technique could become part of standard rehabilitation programs. He is providing the fundamental methods to anyone interested so they can help athletes and people \who have lost their neural connections and need to build new ones, like stroke patients. In his next project, Mirtaheri will be looking at how new approaches could provide the stimulus needed to help people get back to walking much faster than traditional methods.
Next steps
ADEPT’s next projects will incorporate other sensory information like visual and audio into the models to examine how the brain responds. The big question here is how the heart and the gut play a major role in brain metabolism and its interactions with environment.
Mirtaheri says this is a huge undertaking and a complex problem; he’s not sure whether he will be able to answer all these questions in his career. Conducting research on human subjects has great potential, but it is also extremely difficult. However, given how much external sensory information from just the feet affects the brain, he’s pretty excited to find out how other inputs affect it.
