Introduction
Some people afflicted with a severe form of neurological disease are essentially “locked in” their own bodies. They are conscious but cannot move or communicate verbally due to paralysis of nearly all of their voluntary muscles except for their eyes (1); for those with total locked-in syndrome, even the eyes are paralyzed. While many locked-in patients retain awareness and cognitive capabilities, those with central nervous system damage enter into a minimally conscious state, showing fluctuating signs of awareness.
Neurodegeneration, the progressive loss of neuron structure or function, is a notable cause of locked-in syndrome (1). Of the many neurodegenerative disorders, amyotrophic lateral sclerosis and a minimally conscious state are often associated with the locked-in state. But with the recent advancements in technology, researchers can now develop brain-computer interfaces that assist these patients in interacting and communicating with the world.
Lou Gehrig’s Disease and Minimally Conscious State
Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that affects nerve cells in the brain and the spinal cord (2, 3). Often also called Lou Gehrig’s disease (after the hall-of-fame baseball player diagnosed with the disease in the 1930s), ALS affects over 30,000 Americans and has an incidence of 5,600 people per year in the U.S. (1, 2).
The distinct physical defects associated with ALS are easily deducible from its name. “Amyotrophic” means that the muscles have lost their nourishment; when this happens, they become smaller and weaker. “Lateral” indicates that the disease affects the sides of the spinal cord, where the nerves that nourish the muscles are located. Lastly, “sclerosis” means that the diseased part of the spinal cord develops hardened or scarred tissue in place of healthy nerves. The progressive degeneration of the motor neurons in ALS eventually leads to the inability of the brain to initiate and control muscle movement (2, 3).
It is also this loss of motor neurons that makes ALS patients likely to enter a state of being locked in. Motor neurons are nerve cells that control muscle movement, and the neuromuscular system that enables our body to move is made up of the brain, many nerves, and muscles. Unfortunately, ALS damages motor neurons in the brain and spinal cord (1, 2). Specifically, it results in the death of both upper and lower motor neurons in the motor cortex of the brain, the brain stem, and the spinal cord. Over time, ALS causes the motor neurons in the brain and spinal cord to shrink and disappear, causing the muscles to no longer receive the signals that induce movement (1, 2). In the absence of use, the muscles atrophy, becoming smaller and weaker. And when the muscles no longer work, the body becomes paralyzed. But despite paralysis, ALS patients, even at an advanced stage, can still see, hear, smell, and feel; the nerves that carry the sensation of hot, cold, pain, or pressure are not affected by ALS (2, 3). For some people with ALS, the parts of the brain that allow us to think, remember, and learn are also affected by the disease (3). Once ALS progresses, the person’s central nervous system motor neurons may be so damaged that the person becomes totally paralyzed, essentially locked in his or her own body.
Another severe neurological condition that leads to the loss of the ability to interact and communicate with the world is a minimally conscious state (MCS). People suffering from MCS are so impaired with immobility that they have trouble performing basic life activities. While they are usually able to breathe without a respirator, they lack the means to communicate meaningfully, have bladder and bowel incontinence, and require feeding tubes. MCS patients are also severely cognitively impaired, although they do seem to have some definite, but extremely limited, awareness of themselves and their environment, and limited means of communication (1). They are able to experience pain and suffering to some degree, although the degree of pain and suffering often cannot be determined.
Brain-Computer Interface
Brain cells communicate by producing tiny electrical impulses that facilitate processes such as thought, memory, consciousness, and emotion. Even people who are locked-in and unable to speak or gesture still produce these electrical impulses within the brain areas that plan movements. These signals can be detected by implanted micro-electrodes and computer chips that detect, pick up, and translate these impulses (4, 5). Using this technology, researchers are developing devices to help people with limited motor skills due to neurological damage. These devices will give the patients the opportunity to communicate by reading their brain signals.
Detecting a person’s brain activity may allow patients to activate prosthetics or command computers, providing them the ability to regain the functions they have lost to the disease (5, 6). If people afflicted with ALS could control a computer through thought alone, the computer could then serve as an interface for these patients to operate light switches, television, a robotic arm, and communicate to their loved ones – something that over 160,000 people in the United States who cannot move their arms and legs would surely welcome.
Another example of technology that assists people with severe neurological damage is the brain-computer interface, designed to assist patients suffering from MCS (6, 7). Dr. Ali Rezai and colleagues at Ohio State University, and Maysam Ghovanloo at the Georgia Tech Bionics Lab are developing techniques in neuromodulation, or deep brain stimulation (DBS). DBS is a surgical procedure that can create dramatic improvements for a patient suffering from neurological disorders. In a DBS procedure, the surgeon implants millimeter-thin electrodes in the brain and a small device that powers the electrodes in the patient’s chest (7). The electrodes deliver tiny electrical signals that block abnormal brain signals. The results produced by Rezai’s team have shown that people who have spent years in a near-vegetative state have made dramatic recoveries following treatment to stimulate his or her brain with electrical pulses.
To address deficiencies with current brain-computer interfaces, such as a limitation of implantable recording sites and the degradation of the electrodes’ recording performance over time, researchers at Berkeley are developing a system that will allow thousands of ultra-tiny neural-dust chips to be inserted into the brain to monitor neural signals at high resolution (7, 8). The particles of neural dust are no more than 100 micrometers across and each particle is a sensor capable of measuring electrical activity in neurons. The system is covered in polymer to render it biologically neutral and backed by a piezoelectric material that can convert electrical signals into ultrasound (8, 9). The researchers envision a system in which thousands of neural dust sensors are constructed at the tips of fine wire arrays, which would then be inserted directly into brain tissue. Signals from the brain would be detected by a sub-dural transceiver that sits just above and ultrasonically powers the dust chips. The transceiver would then relay the data to an external transceiver resting just outside the skull, which in turn would communicate wirelessly with a computing device (9). Once the sensors are pulled free of the wire, the arrays would withdraw. One of the serious design challenges to overcome in this system is to make sure the system is efficient enough to avoid producing heat between the skull and brain.
Conclusions and Future Directions
For people suffering from neurodegenerative diseases such that they are locked in their body and unable to interact and communicate directly with the world, a brain-computer interface may provide them with a means to communicate and control prosthesis. For people with MCS, an implantable electrode stimulating the brain may allow them to regain consciousness and awareness of their environment. The development of these brain-computer interfaces could not have been possible without the manufacturing of inexpensive computer hardware and software, the scientific research on the nature and functional correlates of brain signals, and the improved methods for recording these signals. Nevertheless, more research will be needed to develop better brain-computer interfaces that further improve the quality of life for people locked in their own bodies or suffering from MCS.
In summary, brain-computer interfaces may assist those locked in their body with the ability to communicate and interact with the world. As shown by the Berkeley team, the new technology currently under development may greatly assist those with other severe neurological disorders. Given the recent developments in brain-computer interfaces, the future holds great promise for people locked-in their own bodies, aware and awake but unable to move or communicate verbally due to complete paralysis of nearly all voluntary muscles in the body (1). Finally, the use of implantable electrodes within the person’s brain may also provide a way to treat those in a MCS.
Contact Jessica Barfield at
jessica.k.barfield.16@dartmouth.edu
References
1. Hardiman, O., and Doherty, C. P., 2011, Neurodegenerative Disorders: A Clinical Guide, Springer Publisher.
2. Lou Gehrig’s Disease, Available at http://kidshealth.org/kid/grownup/conditions/als.html, accessed (September 12 2013).
3. Engdahl, S., 2012, Lou Gehrig’s Disease: Perspectives on Diseases and Disorders, Greenhaven Press.
4. Graimann, B., Allison, B. Z., and Pfurtscheller, G., 2013, Brain-Computer Interfaces: Revolutionizing Human-Computer Interaction (The Frontiers Collection), Springer; 2011 edition.
5. Wolpaw, J., and Wolpaw, E.W., 2012, Brain-Computer Interfaces: Principles and Practice (Jan 24, 2012), Oxford University Press, USA; 1 edition.
6. Cyberkinetics, Company Web Site, Available at http://www.cyberkineticsinc.com/, accessed (September 14 2013).
7. Ali Rezai, Ohio State University, Deep Brain Stimulation, Available at http://www.osu.edu/features/2013/rezai.html, accessed (September 14 2013).
8. Peckham, M., Your Future Brain-Machine Implant: Ultrasonic Neural Dust, http://techland.time.com/2013/07/17/your-future-brain-machine-implant-ultrasonic-neural-dust/, accessed (August 12 2013).
9. Dongjin Seo, Jose M. Carmena, Jan M. Rabaey, Elad Alon, Michel M. Maharbiz, Neural Dust: An Ultrasonic, Low Power Solution for Chronic Brain-Machine Interfaces, http://arxiv.org/abs/1307.2196, accessed (August 12 2013).