Applying Force Perturbations Using a Wearable Robotic Neck Brace

Force perturbation is used in this paper to study cervical neuromuscular responses which can be used in the future to assess impairments in patients with neurological diseases. Current literature on this topic is limited to applying forces on the head in the anterior-posterior direction, perhaps due to technological limitations. In this paper, we propose to use a robotic neck brace to address these shortcomings due to its lightweight portable design and the ability to control forces. A controller is implemented to apply direction-specific perturbations on the head. To demonstrate the effectiveness of this capability, a human study was carried out with able-bodied subjects. We used this robotic brace to apply forces on the head of the subjects and observed their movement and muscle responses both when their eyes were open and closed. Our results suggest that the robotic brace is capable of perturbing the head and tracking the kinematic response. It revealed that ablebodied subjects reacted to the perturbations differently when their eyes were closed. They showed longer head trajectories and more muscle activation when the eyes were closed. We also show that the direction-specific perturbation feature enables us to analyze kinematic and muscle variables with respect to the direction of perturbation. This helps better understand the neuromuscular response in the head-neck.

I. Introduction

Stabilizing the head-neck under perturbations is a task that we routinely perform in our daily life. Imagine sitting in a moving vehicle on an uneven terrain, we are able to keep balance of the head and maintain a proper posture. This is because our central nervous system quickly reacts to the perturbations and commands the neck muscles to stabilize the head. The same, however, cannot be said for individuals with neural impairments. Amyotrophic lateral sclerosis (ALS) patients with head drop, for example, use rigid cervical collars to keep their head upright while being transported in a vehicle. In clinics, physicians use their hands to gently push the head of patients with cerebral palsy (CP) and visually assess the impairment based on the patient’s response. However, such an evaluation may be subjective and heavily depends on the experience of the treating physician.