Split-belt adaptation and gait symmetry in transtibial amputees walking with a hybrid EMG controlled ankle-foot prosthesis

Our ability to automatically adapt our walking pattern to the demands of our environment is central to maintaining a steady gait. Accordingly, a large effort is being made to extend and integrate this adaptability to lower-limb prostheses. To date, the main focus of this research has been on short term adaptation, such as in response to a terrain transition or a sudden change in the environment. However, long term adaptation and underlying sensorimotor learning processes are critical to optimizing walking patterns and predictively changing our gait when faced with continued perturbations. Furthermore, investigating these processes in lower-limb amputees may provide a unique window into the interplay between sensory driven adaptation and top-down cerebellar modulation of locomotor reflexes and may potentially help alleviate gait asymmetries. In the current exploratory study, we therefore investigated adaptation, sensorimotor learning, and gait symmetry in a group of transtibial amputees walking with a hybrid-EMG controlled powered prosthesis and matched controls (both groups N=3). Participants were asked to perform a split-belt walking trial during which the belt on the affected side ran at twice the speed of the contralateral belt (1.0m/s and 0.5m/s respectively). Adaptation, sensorimotor learning, and symmetry are compared to two baseline conditions. Initial results illustrate that the amputees were readily able to use the hybrid controller, modulated their EMG depending on treadmill speed, and successfully adapted their gait during split-belt walking. However, the temporal gait parameters suggest that amputees used a different adaptation technique and showed reduced sensorimotor learning, while gait symmetry was improved, in the short term, post-adaptation

Volitional control of ankle plantar flexion in a powered transtibial prosthesis during stair-ambulation.

Although great advances have been made in the design and control of lower extremity prostheses, walking on different terrains, such as ramps or stairs, and transitioning between these terrains remains a major challenge for the field. In order to generalize biomimetic behaviour of active lower-limb prostheses top-down volitional control is required but has until recently been deemed unfeasible due to the difficulties involved in acquiring an adequate electromyographic (EMG) signal. In this study, we hypothesize that a transtibial amputee can extend the functionality of a hybrid controller, designed for level ground walking, to stair ascent and descent by volitionally modulating powered plantar-flexion of the prosthesis. We here present data illustrating that the participant is able to reproduce ankle push-off behaviour of the intrinsic controller during stair ascent as well as prevent inadvertent push-off during stair descent. Our findings suggest that EMG signal from the residual limb muscles can be used to transition between level-ground walking and stair ascent/descent within a single step and significantly improve prosthesis performance during stair-ambulation

Proportional EMG Control of Ankle Plantar Flexion in a Powered Transtibial Prosthesis

The human calf muscle generates 80% of the mechanical work to walk throughout stance-phase, powered plantar flexion. Powered plantar flexion is not only important for walking energetics, but also to minimize the impact on the leading leg at heel-strike. For unilateral transtibial amputees, it has recently been shown that knee load on the leading, intact limb decreases as powered plantar flexion in the trailing prosthetic ankle increases. Not surprisingly, excessive loads on the leading, intact knee are believed to be causative of knee osteoarthritis, a leading secondary impairment in lowerextremity amputees. In this study, we hypothesize that a transtibial amputee can learn how to control a powered anklefoot prosthesis using a volitional electromyographic (EMG) control to directly modulate ankle powered plantar flexion. We here present preliminary data, and find that an amputee participant is able to modulate toe-off angle, net ankle work and peak power across a broad range of walking speeds by volitionally modulating calf EMG activity. The modulation of these key gait parameters is shown to be comparable to the dynamical response of the same powered prosthesis controlled intrinsically (No EMG), suggesting that transtibial amputees can achieve an adequate level of powered plantar flexion controllability using direct volitional EMG control.United States. Dept. of Defense (award number 6920559)United States. Dept. of Defense (award number 6920877)Swiss National Science Foundation (grant PBELP3_140656

Pins & Needles: Towards Limb Disownership in Augmented Reality

The seemingly stable construct of our bodily self depends on the continued, successful integration of multisensory feedback about our body, rather than its purely physical composition. Accordingly, pathological disruption of such neural processing is linked to striking alterations of the bodily self, ranging from limb misidentification to disownership, and even the desire to amputate a healthy limb. While previous embodiment research has relied on experimental setups using supernumerary limbs in variants of the Rubber Hand Illusion, we here used Augmented Reality to directly manipulate the feeling of ownership for one's own, biological limb. Using a Head-Mounted Display, participants received visual feedback about their own arm, from an embodied first-person perspective. In a series of three studies, in independent cohorts, we altered embodiment by providing visuotactile feedback that could be synchronous (control condition) or asynchronous (400ms delay, Real Hand Illusion). During the illusion, participants reported a significant decrease in ownership of their own limb, along with a lowered sense of agency. Supporting the right-parietal body network, we found an increased illusion strength for the left upper limb as well as a modulation of the feeling of ownership during anodal transcranial direct current stimulation. Extending previous research, these findings demonstrate that a controlled, visuotactile conflict about one's own limb can be used to directly and systematically modulate ownership - without a proxy. This not only corroborates the malleability of body representation but questions its permanence. These findings warrant further exploration of combined VR and neuromodulation therapies for disorders of the bodily self

Distinct locomotor control and awareness in awake sleepwalkers

Sleepwalking is a common parasomnia permitting complex actions to occur outside of consciousness. Kannape et al. show that, also in awake behaviour, sleepwalkers have a different level of conscious awareness when walking under cognitive load, mimicking nocturnal sleepwalking episodes

Suppression of the N1 auditory evoked potential for sounds generated by the upper and lower limbs.

Sensory attenuation is typically observed for self-generated compared to externally generated action effects. In the present study we investigated whether auditory sensory suppression is modulated as a function of sounds being generated by the upper or lower limbs. We report sensory attenuation, as reflected in a reduced auditory N1 component, which was comparable for sounds generated by the lower and the upper limbs. Increasing temporal delays between actions and sounds did not modulate suppression of the N1 component, but did have an effect on the latency of the N1 component. In contrast, for the P2 component sensory suppression was only observed for sounds generated by the hands and presented at short latencies. These findings provide new insight into the functional and neural dynamics of sensory suppression and suggest the existence of comparable agency mechanisms for both the upper and the lower limbs

Cognitive loading affects motor awareness and movement kinematics but not locomotor trajectories during goal-directed walking in a virtual reality environment.

The primary purpose of this study was to investigate the effects of cognitive loading on movement kinematics and trajectory formation during goal-directed walking in a virtual reality (VR) environment. The secondary objective was to measure how participants corrected their trajectories for perturbed feedback and how participants' awareness of such perturbations changed under cognitive loading. We asked 14 healthy young adults to walk towards four different target locations in a VR environment while their movements were tracked and played back in real-time on a large projection screen. In 75% of all trials we introduced angular deviations of ±5° to ±30° between the veridical walking trajectory and the visual feedback. Participants performed a second experimental block under cognitive load (serial-7 subtraction, counter-balanced across participants). We measured walking kinematics (joint-angles, velocity profiles) and motor performance (end-point-compensation, trajectory-deviations). Motor awareness was determined by asking participants to rate the veracity of the feedback after every trial. In-line with previous findings in natural settings, participants displayed stereotypical walking trajectories in a VR environment. Our results extend these findings as they demonstrate that taxing cognitive resources did not affect trajectory formation and deviations although it interfered with the participants' movement kinematics, in particular walking velocity. Additionally, we report that motor awareness was selectively impaired by the secondary task in trials with high perceptual uncertainty. Compared with data on eye and arm movements our findings lend support to the hypothesis that the central nervous system (CNS) uses common mechanisms to govern goal-directed movements, including locomotion. We discuss our results with respect to the use of VR methods in gait control and rehabilitation