The Clinical Potential of Wireless, Implantable Brain-Computer Interfaces

Post by Ewina Pun

What is a BCI?

Brain-computer interfaces (BCI) aim to provide improved access to assistive technologies for people with paralysis. People with paralysis due to brainstem stroke, amyotrophic lateral sclerosis, spinal cord injury, or other disorders can become unable to move or speak despite being awake and alert. Yet, researchers have shown that neural pathways modulating movement intention are still active even years after the injury. But what if we could bypass the damaged motor pathways and engineer a system that decodes and sends movement intentions straight from the brain to an external device? This kind of neural interface could allow the user to directly interact with and control devices (say, a computer cursor) in real time just by imagining or attempting natural hand movements.

Implantable devices such as microelectrode arrays or electrocorticography are placed directly on top of the motor cortex to record neural activities. Unlike devices placed further from actual brain cells – for example, devices placed on the scalp – implanted devices can record high-resolution, information-rich signals, and enable effective and intuitive neural control compared to traditional assistive devices that rely on residual motor functions. Recently, the development of wireless BCI signal transmission has moved us toward functional, everyday BCI use. Wireless BCI can provide a greater range of unconstrained mobility and many other potential clinical benefits.

BCI’s for restoring communication and mobility

Restoration of communication is a top priority for people with locked-in syndrome, a condition of total paralysis and inability to communicate despite complete awareness, as well as other forms of paralysis. One method of communication for people with locked-in syndrome is through typing. An online decoder can guide cursor movements by interpreting brain activity differences in motor areas when attempting various movements. Intracortical BCIs can offer reliable point-and-click cursor control for patients with tetraplegia to type ~39 correct characters per minute (ccpm) on a virtual keyboard. A more recent paper demonstrated an intracortical BCI that decodes attempted handwriting with a recurrent neural network. This resulted in double the performance, with a typing rate of ~85 ccpm, significantly outperforming non-implanted technology and approaching the typing speed of an able-bodied person on a typical smartphone. Beyond the ability to type, participants can also use the same cursor control on a personal desktop computer, tablet, and smart phone for other activities such as web browsing, listening to music, and sending emails and texts.

Another main goal of BCI is mobility restoration and rehabilitation. Decoded movement intentions can be fed as commands to control a prosthesis system that restores mobility of individuals with paralysis. One impressive example is the ability to use brain signals to perform complex reach-and-grasp movements using a robotic arm. Combining BCI with functional electrical stimulation, a person with cervical spinal cord injury (paralysis from the neck down) was able to perform multi-joint arm movements using his own paralyzed arm to drink from a mug and feed himself. These tools provide disabled individuals ways to interact with their environment independently without the help of a caregiver. 

The benefits of wireless systems

Many standard intracortical BCI systems limit the range of movement because neural recordings from the implanted device are sent to the decoding computer via a connected cable. Alternatively, a wireless recording system can overcome this limitation. In 2021, Simeral and colleagues demonstrated the first human use of a wireless broadband intracortical BCI for two participants with tetraplegia. Not only does the wireless system offer reliable closed-loop control performance equivalent to the wired configuration, the transmitter is also lightweight, low-power, and more importantly, allows continuous, long-term use for over 24 hours at the user’s home. To restore mobile and complex motor activities for people with paralysis (like walking), an implantable wireless communication system will be a critical design consideration to provide the unconstrained movement needed to perform daily activities.

What's the takeaway?

For people with severe motor impairment, untethered wireless recording of intracortical signals is a major step toward clinically viable neuroprostheses that can provide independent communication and restore mobility. High-resolution BCI technology also provides neuroscientists a unique opportunity to understand how ensembles of individual neurons encode information. While researchers devote their efforts to advancing BCIs for various applications, careful attention must continue to be placed on mitigating risk, maximizing potential benefit, and assessing the safety of emerging neurotechnology.

References +

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Willett et al. High-performance brain-to-text communication via handwriting. Nature (2021).

Nuyujukian et al., Cortical control of a tablet computer by people with paralysis. PLoS One. (2018)

Collinger et al. High-performance neuroprosthetic control by an individual with tetraplegia Lancet. (2013)

Wang et al. An Electrocorticographic Brain Interface in an Individual with Tetraplegia. Plos One (2013)

Wodlinger et al. Ten-dimensional anthropomorphic arm control in a human brain-machine interface: difficulties, solutions, and limitations. J. Neural Eng. (2015)

Ajiboye et al. Restoration of reaching and grasping movements through brain-controlled muscle stimulation in a person with tetraplegia: a proof-of-concept demonstration. Lancet. (2017)

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Johns Hopkins Applied Physics Laboratory. Quadriplegic patient uses brain signals to feed himself with two advanced prosthetic arms. (2020)

Simeral et al. Home Use of a Percutaneous Wireless Intracortical Brain-Computer Interface by Individuals with Tetraplegia. IEEE Trans. Biomedical Engineering (2021).

Borton et al. An implantable wireless neural interface for recording cortical circuit dynamics in moving primates. Journal of Neural Engineering (2013).