Abstract
Individuals with tetraplegia identify restoration of hand function as a critical, unmet need to regain their independence and improve quality of life. Brain-Computer Interface (BCI)-controlled Functional Electrical Stimulation (FES) technology addresses this need by reconnecting the brain with paralyzed limbs to restore function. In this study, we quantified performance of an intuitive, cortically-controlled, transcutaneous FES system on standardized object manipulation tasks from the Grasp and Release Test (GRT). We found that a tetraplegic individual could use the system to control up to seven functional hand movements, each with >95% individual accuracy. He was able to select one movement from the possible seven movements available to him and use it to appropriately manipulate all GRT objects in real-time using naturalistic grasps. With the use of the system, the participant not only improved his GRT performance over his baseline, demonstrating an increase in number of transfers for all objects except the Block, but also significantly improved transfer times for the heaviest objects (videocassette (VHS), Can). Analysis of underlying motor cortex neural representations associated with the hand grasp states revealed an overlap or non-separability in neural activation patterns for similarly shaped objects that affected BCI-FES performance. These results suggest that motor cortex neural representations for functional grips are likely more related to hand shape and force required to hold objects, rather than to the objects themselves. These results, demonstrating multiple, naturalistic functional hand movements with the BCI-FES, constitute a further step toward translating BCI-FES technologies from research devices to clinical neuroprosthetics.
Highlights
130,000 people suffer a Spinal Cord Injury (SCI) worldwide every year
We showed proof-of-concept that a person with C5-level paralysis could use a microelectrode arrays (MEAs)-Brain-Computer Interface (BCI) to control a transcutaneous Functional Electrical Stimulation (FES) system to enable six independent finger, wrist, and hand movements (Bouton et al, 2016) We demonstrated that the system could be used to perform a functional grasp-pourand-stir task, providing the user with simultaneous, differential control of Hand Open, palmar grasp, and lateral key grip
The cortically controlled FES system consisted of three main components: (1) an implanted 96-channel Utah MEA for recording neural signals, (2) a computer running data processing and a machine learning algorithm to decode the user’s intended movement from the neural activity, and (3) a non-invasive FES cuff wrapped on the participant’s forearm to stimulate the appropriate muscles to evoke the desired hand movement (Figure 1)
Summary
130,000 people suffer a Spinal Cord Injury (SCI) worldwide every year. Half of these SCI cases are at the C6 level or above, resulting in significant paralysis, impaired quality of life, and need for self-care assistance (ICCP, 2017). Patients with C6 or higher cervical level of SCI lack the critical ability to grasp objects that prevents them from living independently (Nas et al, 2015). In a survey of individuals with tetraplegia following SCI, more than 75% indicated that Functional Electrical Stimulation (FES) neuroprosthetics for hand grasp would be “very helpful” to restore function that would positively impact quality of life (Collinger et al, 2013). The FES systems that have been demonstrated to date are either limited to providing only a few hand functions or lack the ability to enable dynamic motor control for performing complex functional tasks that require synergistic integration of paralyzed and non-paralyzed muscles
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