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Neuroscience
Decoding the Secrets of Brain Connectivity
Multiple brain areas are connected via “bow tie” shaped neural networks.
Posted November 7, 2013
Two new studies help explain the architecture of how neural networks connect different brain areas. In a study from Duke, researchers were able to teach monkeys how to control the movement of both arms and hands of a computer generated avatar using only their thoughts. In another study from Notre Dame, physicists have created a model that explains how the brain connects multiple areas using “bow tie” shaped neural networks.
In the study led by Duke researchers, monkeys have learned to control the movement of both arms of an avatar using just their brain activity. The findings were published November 6, 2013 in the journal Science Translational Medicine. Advancements in this area offer hope for technologies that will eventually allow bilateral movement in brain-controlled prosthetic devices for paralyzed patients.
The Duke researchers believe that the monkeys' brains literally incorporate the avatar arms and hands into an internal image of their own bodies. The avatar appears to become a virtual extension of a monkey's sense of proprioception and self.
Another paper published in a special November 2013 issue of the journal Science offers a new understanding of brain connectivity using a network representation of connections within the brain. Physicists at Notre Dame used data from stem cell research in France to create a hypothesis that the cortex creates a network of connections based on a simple "bow tie" structure that efficiently connects multiple brain areas.
The original data for the Notre Dame paper was generated by collaborator Henry Kennedy, director of the Stem-cell and Brain Research Institute in Lyon, France, and his research group.
“Bow Tie” Architecture Connects Multiple Brain Areas
The authors note that a streamlined bow tie network creates the most efficient connectivity between functional areas in the brain. The wings of the bow tie create what authors refer to as a ‘counterstream organization’ meaning that the hub simultaneously incorporates information from feedforward and feedback pathways in multiple directions.
Zoltán Toroczkai, professor of physics at the University of Notre Dame and co-director of the Interdisciplinary Center for Network Science and Applications, is a co-author of a paper titled, "Cortical High-Density Counterstream Architectures."
Bow Tie Shaped Neuronal Network
The bow tie shape is highly efficient because it has a dense core that serves as a hub for feedforward and feedback pathways from the “wings” that fan out throughout the entire brain. Neural networks are also called ‘engrams.’ In the past it was believed that the tapestry of neurons was more randomized. This new model proposes the importance of having a higher density core that is able to filter incoming and outgoing information to connect multiple brain areas.
The bow tie assemblies create a feedforward and feedback loop that connects somatosensory, motor, and cognitive functions between different brain regions which include the occipital, parietal, temporal, and frontal lobes, as well as, the prefrontal cortex.
This bow tie architecture is a typical feature of self-organizing information processing systems, according to the researchers. The paper notes that the human cortex has some analogies with information technology processing networks such as the World Wide Web.
The researchers found that, contrary to previous beliefs, having high-density core with ‘wings’ can create strong and efficient connectivity between any two brain areas. The bow tie structure, they say, is "an evolutionarily favored structure for a wide variety of complex networks" because "these systems are not in thermodynamic equilibrium and are required to maintain energy and matter flow through the system."
A Well-Connected Brain Can Control Both Arms of an Avatar
Monkeys in a Duke study were trained in a virtual environment in which they viewed realistic avatar arms on a screen and were then trained to place their virtual hands on specific targets in a bimanual motor task. The monkeys first learned to control the avatar arms using a pair of joysticks, but were eventually able to learn how to use just their brain activity to move both avatar arms without moving their own arms.
As the monkeys' ability to control both arms improved, the Duke researchers observed widespread neuroplasticity which connected multiple areas of their brains. The researchers also found that brain regions showed specific patterns of neuronal electrical activity during bimanual movements that differed from the neuronal activity produced for moving each arm separately.
"Bimanual movements in our daily activities—from typing on a keyboard to opening a can—are critically important," said senior author Miguel Nicolelis, M.D., Ph.D., professor of neurobiology at Duke University School of Medicine. "Future brain-machine interfaces aimed at restoring mobility in humans will have to incorporate multiple limbs to greatly benefit severely paralyzed patients."
The study suggests that very broad neuronal ensembles—not single neurons—define normal bimanual and bipedal motor functions. Small neuronal samples of the cortex from just one hemisphere of the cerebrum are not sufficient for controlling complex motor behaviors using a brain-machine interface.
"When we looked at the properties of individual neurons, or of whole populations of cortical cells, we noticed that simply summing up the neuronal activity correlated to movements of the right and left arms did not allow us to predict what the same individual neurons or neuronal populations would do when both arms were engaged together in a bimanual task," Nicolelis said. "This finding points to an emergent brain property—a non-linear summation—for when both hands are engaged at once."
Nicolelis is part of an international team working to build a brain-controlled neuroprosthetic device through The Walk Again Project. The team plans to demonstrate its first brain-controlled exoskeleton, which is currently being developed, during the opening ceremony of the 2014 FIFA World Cup.
Conclusion: A Better Understanding of Brain Connectivity Has Broad Implications
These two studies offer valuable insights on how brain areas are connected from a group of physicists and neuroscientists. Bringing together multidisciplinary insights on brain connectivity could lead to practical applications that can be used to improve people’s lives and levels of performance.
The more we understand about how neural networks are connected, the more options we have for practical applications that will fortify stronger brain connectivity. These breakthroughs could lead to creating interfaces that will someday translate brainpower into bionic limbs for paralyzed patients.
Unfortunately, these breakthroughs in understanding brain connectivity could lead to the development of robots manned by the thoughts of well-trained humans in remote locations and used for destructive military purposes, like the drones of today. If mishandled, these breakthroughs in the understanding of brain connectivity could create a dystopia straight out of science fiction.
On a positive note, understanding brain connectivity can also help people make daily lifestyle choices here and now that improve brain symmetry and synchronicity to achieve personal best.
"Biological data is extremely complex and diverse," Zoltán Toroczkai concludes. "However, as a physicist, I am interested in what is common or invariant in the data, because it may reveal a fundamental organizational principle behind a complex system. I believe that with additional consistent data, as those obtained by the Kennedy team, the fundamental principles of massive information processing in brain neuronal networks are within reach."
If you'd like to read more on this topic please check out my Psychology Today blogs, "Video Gaming Can Increase Brain Size and Connectivity", "Brain Asymmetry Changes a Dog's Wag and a Human's Mind", "Better Motor Skills Linked to Higher Academic Scores", "Einstein's Genius Linked to Well-Connected Brain Hemispheres" and "The Neuroscience of Superfluidity."
