[ARTICLE] Hybrid EEG/EOG-based brain/neural hand exoskeleton restores fully independent daily living activities after quadriplegia – Full Text

Abstract

Direct brain control of advanced robotic systems promises substantial improvements in health care, for example, to restore intuitive control of hand movements required for activities of daily living in quadriplegics, like holding a cup and drinking, eating with cutlery, or manipulating different objects. However, such integrated, brain- or neural-controlled robotic systems have yet to enter broader clinical use or daily life environments. We demonstrate full restoration of independent daily living activities, such as eating and drinking, in an everyday life scenario across six paraplegic individuals (five males, 30 ± 14 years) who used a noninvasive, hybrid brain/neural hand exoskeleton (B/NHE) to open and close their paralyzed hand. The results broadly suggest that brain/neural-assistive technology can restore autonomy and independence in quadriplegic individuals’ everyday life.

INTRODUCTION

Quadriplegia, the loss of motor function of both arms and legs, is often caused by traumatic cervical spinal cord injury (SCI) affecting 1 in 10,000 people worldwide (1, 2). Although SCI is associated with lower life expectancy and quality of life (3, 4), it typically affects younger individuals, leading to substantial loss of their independence and autonomy. Regaining hand and arm function was identified as the most critical need in this population (5). Although SCI remains an incurable condition with most treatment approaches aimed at minimizing secondary medical complications and maximizing residual function, the development of brain-machine interfaces (BMIs) has recently fueled hope that by bypassing the lesioned spinal system, independence and autonomy of individuals with severe paralysis could be restored (6–9). In particular, the possibility that repeated use of such BMI-based bypass could trigger neurological recovery despite clinically complete and chronic SCI (10) points to new avenues in the treatment of severe paralysis that build on fostering neuroplasticity through direct brain- or neural-robot interactions. BMIs translate electric, magnetic, or metabolic brain activity (e.g., associated with the intention to reach and grasp) into control signals of external machines, exoskeletons, or robots (11). Because mental imagery (e.g., the visualization of a closing hand) results in an actual hand-closing motion performed by a robotic device or exoskeleton in such a paradigm, BMI control is particularly intuitive.

Although implantable BMIs have recently been shown to allow versatile control of a robotic arm in patients with chronic quadriplegia (8, 12, 13), the required craniotomy entails the risk of surgical complications, for example, infections or bleedings. Also, implantable systems have to be explanted after some time, posing an ethical and clinical dilemma. Thus, implantation of a BMI for controlling such versatile robots is mainly attractive for individuals who are completely paralyzed, for example, after severe brainstem stroke or in the late stage of a neurodegenerative disease.

To date, we know of no patient who has used a BMI outside the laboratory to perform activities of daily living (ADLs), for example, having a full meal in an outside restaurant. The main obstacle for such application relates to the nonstationarity of brain activity and susceptibility to environmental artifacts, particularly in noninvasive brain activity recordings that provide lower signal-to-noise ratios compared with invasive recordings (14). Thus, hybrid systems that combine BMI technology with other biosignals (15–17) or eye gaze (18, 19) to improve system control have been proposed. Previous work demonstrated that the combination of electroencephalography (EEG) and electrooculography (EOG) can be used for hand exoskeleton control in healthy volunteers under laboratory conditions (16, 17). The translational value of this approach for restoration of hand function in real-life environments after quadriplegia, a condition for which there is currently no effective treatment, was not known. Here, we address this question and show the restoration of fully independent ADLs, such as eating and drinking, across six quadriplegic individuals with cervical SCI.

Study participants used a noninvasive brain/neural hand exoskeleton (B/NHE) that translates brain electric signals accompanying the intention to grasp into actual exoskeleton-driven hand-closing motions and EOG signals related to voluntary horizontal eye movements [horizontal oculoversions (HOVs)] into exoskeleton-driven hand-opening motions (Figs. 1 and 2). The participants were asked to perform self-initiated reaching and grasping actions, for example, eating and drinking in a nearby restaurant and outdoors. The ability to grasp and manipulate daily life objects was assessed using the Toronto Rehabilitation Institute–Hand Function Test (TRI-HFT) with and without the B/NHE system. Reliability, tolerability, and practicability to perform ADLs were rated by each participant after the end of the session.

Fig. 1 Scheme of process pipeline to control the hand exoskeleton. EEG and EOG signals were transmitted to a wireless tablet computer performing real-time signal processing and translation into control signals sent to a control box and actuators moving the hand exoskeleton via a flexible cable sheath system.

 

Fig. 2 Design of hybrid biosignal processing for reliable hand exoskeleton control. Signals related to the detection of HOVs and intention to grasp as measured by electrooculographic (A) and brain electric (B) activity were used for the hybrid BMI hand exoskeleton control (C). Hand exoskeleton closing movements were initiated by the detection of SMR-ERD, whereas hand exoskeleton opening movements were controlled by HOVs’ EOG activity exceeding the eye movement detection threshold [red dashed line in (A)]. In case EOG activity exceeded the eye movement detection threshold during SMR-ERD [indicated by the red dashed rectangle in (B)], the hand exoskeleton opened, and brain control was blocked for 1.5 s [indicated by the red rectangles in (C)] to ensure safety during performing daily life actions.

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