Visual Noise Linearly Influences Tracking Performance.

This study investigates the influence of visual noise on motor performance in three degrees of freedom (DoFs) tracking task including translation against gravity and rotation. Participants were asked to follow a moving target, visually degraded according to four different levels of noise, plus one no-noise condition. Each noise level was represented with ten target replicas normally distributed around the main target's pose with a specific standard deviation. Performance, in term of error between cursor and target, significantly decreased (p < 0.001) with the increase of the standard deviation of the visual noise, in all movement directions. The relation between the level of visual noise and the performance appears to be linear (R2 > 0.8) for each DoF separately, as well as when we combine the translations using the Euclidean norm.

Tele-Impedance Control Approach Using Wearable Sensors.

Tele-operational tasks often suffer from instability issues and limited reliability during unpredictable interactions. We propose a real-time control law reproducing the impedance and kinematic behaviour of a subject's arm (shoulder and elbow) on a remote avatar in a 2-DoF task. The human arm impedance and kinematics are estimated respectively from EMG and M-IMU data and then mapped into the avatar arm through an impedance control. Contrary to literature methods, our portable tele-impedance controller relies only on wearable sensors and enables an easy use in unstructured environments. The good performance (R2> 0.7) of the muscle model used to map on the robot the human stiffness of five healthy subjects indicates the possibility of applying the proposed algorithm for a tele-impedance control.

Human performance in three-hands tasks.

The successful completion of complex tasks like hanging a picture or laparoscopic surgery requires coordinated motion of more than two limbs. User-controlled supernumerary robotic limbs (SL) have been proposed to bypass the need for coordination with a partner in such tasks. However, neither the capability to control multiple limbs alone relative to collaborative control with partners, nor how that capability varies across different tasks, is well understood. In this work, we present an investigation of tasks requiring three-hands where the foot was used as an additional source of motor commands. We considered: (1) how does simultaneous control of three hands compare to a cooperating dyad; (2) how this relative performance was altered by the existence of constraints emanating from real or virtual physical connections (mechanical constraints) or from cognitive limits (cognitive constraints). It was found that a cooperating dyad outperformed a single user in all scenarios in terms of task score, path efficiency and motion smoothness. However, while the participants were able to reach more targets with increasing mechanical constraints/decreasing number of simultaneous goals, the relative difference in performance between a dyad and a participant performing trimanual activities decreased, suggesting further potential for SLs in this class of scenario.

Osseointegration for lower and upper-limb amputation a systematic review of clinical outcomes and complications.

The conventional use of prosthetic custom-design socket is affected by discomfort related to wellknown problems: sweating, sores or skin irritation, excessive weight and harness, impaired body image, that lead to a high rate of abandonment. Osseointegrated prosthetic implants for limb amputation are progressively evolving to overcome limitations of socket. The aim of this article is to present a systematic review of the use, safety in terms of rate of infection and complications, and reported outcomes of upper and lower limb osseointegrated prosthetic implants. A systematic search was carried out for studies that evaluated outcomes of osseointegration technique in case of upper and lower limb amputees according to the PRISMA guidelines with a PRISMA checklist and algorithm. MINORS score was used for methodologic assessment. 17 articles about the treatment of patients with upper or lower limb amputation treated with an osseointegrated prostesis were included. The overall rate of infections was 32%. All the clinical outcomes reported were related to lower limb. No clinical data for upper limb was found. The postoperative mean value of MCS and PCS SF-36 and Q-TFA was 55.1, 45.4 and 73.8 respectively, while six minute walk test (6MWT) and the timed up and go (TUG) test scored an average value of 388 meters and 11.5 seconds respectively. MINORS score ranged from 5 to 13, with a median of 11 [interquartile range (IQR), 9-11]. The osseointegration is associated to a high rate of postoperative complications but, significant improvement in clinical outcomes compared to preoperative time are shown. The data available from the literature are limited but suggest good clinical outcomes and significant survivorship of the implants. Further clinical studies are needed to establish which kind of implant is associated to higher clinical performance and lower rate of postoperative complications and infections.

Altered Proprioceptive Feedback Influences Movement Kinematics in a Lifting Task.

Movement control process can be considered to take place on at least two different levels: a high, more cognitive level and a low, sensorimotor level. On a high level processing a motor command is planned accordingly to the desired goal and the sensory afference, mainly proprioception, is used to determine the necessary adjustments in order to minimize any discrepancy between predicted and executed action. On a lower level processing, the proprioceptive feedback later employed in high level regulations, is generated by Ia sensory fibers positioned in muscle main proprioceptors: muscle spindles. By entraining the activity of these spindle fibers through 80Hz vibration of triceps distal tendon, we show the intriguing possibility of inducing kinematics adjustments due to negative feedback corrections, during a lifting task.

'Doublecheck: a sensory confirmation is required to own a robotic hand, sending a command to feel in charge of it'.

Over a lifetime of experience, the representation of the body is built upon congruent integration of multiple elements constituting the sensorimotor loop. To investigate its robustness against the rupture of congruency between senses and with motor command, we selectively manipulated in healthy subjects the binds between sight, proprioception, and efferent motor command. Two experiments based on the Moving Hand Illusion were designed employing Tendon Vibration Illusion to modulate proprioception and generate illusory altered feedback of movement. In Experiment A, visuomotor congruency was modulated by introducing adelay between complex multifingered movements performed by arobotic hand and real movement of each participant's hand. In the presence of the motor command, visuomotor congruency enhanced ownership, agency, and skin conductance, while proprioceptive-motor congruency was not effective, confirming the prevalence of vision upon proprioception. In Experiment B, the impact of visuo-proprioceptive congruency was tested in the absence of motor command because the robotic hand moved autonomously. Intersensory congruency compensated for the absence of motor command only for ownership. Skin conductance in Exp Band Proprioceptive Drift in both experiments did not change. Results suggest that ownership and agency are independently processed, and presence of the efferent component modulates sensory feedbacks salience. The brain seems to require the integration of at least two streams of congruent information. Bodily awareness can be generated from sensory information alone, but to feel in charge of the body, senses must be double-checked with the prediction generated from efference copy, which is treated as an additional sensory modality.

Different level of virtualization of sight and touch produces the uncanny valley of avatar's hand embodiment.

Humans increasingly often act through virtual and robotic avatars, which can feed back to their user only virtual sensory information. Since avatar is user's embodiment and body image is mostly based on senses, how virtualization of sensory inputs affects avatar self-attribution is a key question for understanding nowadays human behavior. By manipulating visual and tactile inputs in a series of experiments fashioned after the rubber hand illusion, we assessed the relative weight of the virtualization of sight (Real, Robotic, Virtual) and of touch (Real, Virtual) on artificial hand embodiment. Virtualization decreased embodiment, but unexpectedly lowest embodiment was found when only one sense was virtual. Discordant levels of virtualization of sight and touch elicited revulsion, extending the concept of the uncanny valley to avatar embodiment. Besides timing, spatial constraints and realism of feedback, a matched degree of virtualization of seen and felt stimuli is a further constraint in building the representation of the body.

Evaluation of hand-eye and robot-world calibration algorithms for TMS application.

In this paper we compare three approaches to solve the hand-eye and robot-world calibration problem, for their application to a Transcranial Magnetic Stimulation (TMS) system. The selected approaches are: i) non-orthogonal approach (QR24); ii) stochastic global optimization (SGO); iii) quaternion-based (QUAT) method. Performance were evaluated in term of translation and rotation errors, and computational time. The experimental setup is composed of a 7 dof Panda robot (by Franka Emika GmbH) and a Polaris Vicra camera (by Northern Digital Inc) combined with the SofTaxic Optic software (by E.M.S. srl). The SGO method resulted to have the best performance, since it provides lowest errors and high stability over different datasets and number of calibration points. The only drawback is its computational time, which is higher than the other two, but this parameter is not relevant for TMS application. Over the different dataset used in our tests, the small workspace (sphere with radius of 0.05m) and a number of calibration points around 150 allow to achieve the best performance with the SGO method, with an average error of 0.83 ± 0.35mm for position and 0.22 ± 0.12deg for orientation.

Targeted muscle reinnervation for improved control of myoelectric upper limb prostheses.

Targeted muscle reinnervation (TMR) is a novel surgical technique developed to improve the control of myoelectric upper limb prostheses. Nerves transected by the amputation, which retain their original motor pathways even after being severed, are redirected to residual denervated muscles that serve as target for consequent reinnervation. Once the process is complete, reinnervated muscles will contract upon voluntary activation of transferred nerves while attempting to move missing regions of the amputated limb, generating EMG signals that can be recorded and used to control a prosthetic device. This allows creating new control sites that can overcome major drawbacks of conventional myoelectric prostheses by offering a more natural and intuitive control of prosthetic arms. TMR has been widely performed in individuals who underwent shoulder disarticulation amputation and transhumeral amputation since proximal amputations do not leave enough functional muscles exploitable to control independent degree of freedoms of multi-articulated prostheses. TMR application is currently under investigation in patients suffering further distal amputations, as well as for treating and preventing painful post-amputation neuromas. The purpose of this paper is to describe the physiologic basis and the surgical technique of TMR, reporting current knowledge on the clinical results.

Assessing bradykinesia in Parkinson's disease using gyroscope signals.

Parkinson's disease (PD) is a neurodegenerative brain disorder that slowly brings on the dopaminergic neurons death. The depletion of the dopaminergic signal causes the onset of motor symptoms such as tremor, bradykinesia and rigidity. Usually, neurologists regularly monitor motor symptoms and motor fluctuations using the MDS-UPDRS part III clinical scale. Nevertheless, to have a more objective and quantitative evaluation, it is possible to assess the cardinal motor symptoms of PD using wearable sensors and portable robotic devices. Unfortunately while there are several research papers on the use of these devices on PD patients, their use is not so common in clinical practice. In this work we recorded specific MDS-UPDRS motor tasks using magneto-inertial devices, worn by seven PD subjects and seven age-matched controls, in order to deeply analyze the kinematic and dynamic characteristics of goal-directed movements of upper limb, in addition to extract quantitative indices (peak velocity, smoothness, etc) useful for the assessment of motor symptoms. Using only gyroscope signals we looked at those parameters useful to assess bradykinesia. We observed parameters changes from OFF to ON phase congruent with the MDS-UPDRS changes, especially in the frequency domain. Our results suggest the prono-supination task is the more consistent to describe the bradykinesia symptom with the gyroscopes. Probably because of the amplitude of the movement performed. Moreover the peak power looks appropriate for bradykinesia symptom evaluation. We can conclude that, similar to the studies in which tremor symptom is evaluated, it is possible to monitor the bradykinesia using few wearable sensors and few simple parameters.

A teleoperated control approach for anthropomorphic manipulator using magneto-inertial sensors.

In this paper we propose and validate a teleoperated control approach for an anthropomorphic redundant robotic manipulator, using magneto-inertial sensors (IMUs). The proposed method allows mapping the motion of the human arm (used as the master) on the robot end-effector (the slave). We record arm movements using IMU sensors, and calculate human forward kinematics to be mapped on robot movements. In order to solve robot kinematic redundancy, we implemented different algorithms for inverse kinematics that allows imposing anthropomorphism criteria on robot movements. The main objective is to let the user to control the robotic platform in an easy and intuitive manner by providing the control input freely moving his/her own arm and exploiting redundancy and anthropomorphism criteria in order to achieve human-like behaviour on the robot arm. Therefore, three inverse kinematics algorithms are implemented: Damped Least Squares (DLS), Elastic Potential (EP) and Augmented Jacobian (AJ). In order to evaluate the performance of the algorithms, four healthy subjects have been asked to control the motion of an anthropomorphic robot arm (i.e. the Kuka Light Weight Robot 4+) through four magneto-inertial sensors (i.e. Xsens Wireless Motion Tracking sensors - MTw) positioned on their arm. Anthropomorphism indices and position and orientation errors between the human hand pose and the robot end-effector pose were evaluated to assess the performance of our approach.

Neurobiological after-effects of non-invasive brain stimulation.

BACKGROUND: In recent years, many studies have evaluated the effects of noninvasive brain stimulation (NIBS) techniques for the treatment of several neurological and psychiatric disorders. Positive results led to approval of NIBS for some of these conditions by the Food and Drug Administration in the USA. The therapeutic effects of NIBS have been related to bi-directional changes in cortical excitability with the direction of change depending on the choice of stimulation protocol. Although after-effects are mostly short lived, complex neurobiological mechanisms related to changes in synaptic excitability bear the potential to further induce therapy-relevant lasting changes. OBJECTIVE: To review recent neurobiological findings obtained from in vitro and in vivo studies that highlight molecular and cellular mechanisms of short- and long-term changes of synaptic plasticity after NIBS. FINDINGS: Long-term potentiation (LTP) and depression (LTD) phenomena by itself are insufficient in explaining the early and long term changes taking place after short episodes of NIBS. Preliminary experimental studies indicate a complex scenario potentially relevant to the therapeutic effects of NIBS, including gene activation/regulation, de novo protein expression, morphological changes, changes in intrinsic firing properties and modified network properties resulting from changed inhibition, homeostatic processes and glial function. CONCLUSIONS: This review brings into focus the neurobiological mechanisms underlying long-term after-effects of repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) recently obtained from in vitro and in vivo studies, both in animals and humans.

Biomechanical and neural changes evaluation induced by prolonged use of non-stable footwear: a systematic review.

The aim of this review is to collect and discuss the current best evidence published in literature about the effect of the Masai Barefoot Technology(MBT) shoes on gait and muscle activation and try to draw conclusions on the possible benefits. We searched Medline, CINAHL, Embase and the Cochrane Central Registry of Controlled Trials. The reference lists of the previously selected articles were then examined by hand. Only studies comparing biomechanical and clinical outcomes were selected. Review, anatomical studies, letter to editor and instructional course were excluded. Finally, all the resulting articles were reviewed and discussed by all the authors to further confirm their suitability for this review: in the end, 22 articles were included. A total of 532 patients presenting a mean age of 34.3 years were studied. All patients evaluated were healthy or amateur sports except in two studies where only obese subjects and knee osteoarthritis patients were involved. Seven studies evaluated only male subjects, whereas four studies evaluated only female. Twelve of twenty-two studies performed electromyographic analyses. Weight was reported in 19 studies, whereas body mass index were reported only in a five studies. All studies reported kinematic analysis of shoe effects and compared the relationship between muscle recruitment and electromyographic activity. Unstable footwears were shown to immediately alter the stability in gait during daily-life activities. The center of body pressure is moved posteriorly with a consequent posterior displacement of the upper part of body in order to regain an appropriate body balance, and these postural changes are associated with an overall increase in the activity of lumbar erector spine muscles, as well as certain lower limb muscles. Current literature provides enough cues to conclude for a beneficial role of MBT shoes in the postural and proprioceptive recovery, but from the same literature cannot be drown clear and appropriate guidance to determine more in detail their indication for specific pathological conditions or for particular phases of the musculoskeletal recovery process.

Wakefulness delta waves increase after cortical plasticity induction.

OBJECTIVE: Delta waves (DW) are present both during sleep and in wakefulness. In the first case, DW are considered effectors of synaptic plasticity, while in wakefulness, when they appear in the case of brain lesions, their functional meaning is not unanimously recognized. To throw light on the latter, we aimed to investigate the impact on DW exerted by the cortical plasticity-inducing protocol of intermittent theta burst stimulation (iTBS). METHODS: Twenty healthy subjects underwent iTBS (11 real iTBS and nine sham iTBS) on the left primary motor cortex with the aim of inducing long-term potentiation (LTP)-like phenomena. Five-minute resting open-eye 32-channel EEG, right opponens pollicis motor-evoked potentials (MEPs), and alertness behavioral scales were collected before and up to 30 min after the iTBS. Power spectral density (PSD), interhemispheric coherence between homologous sensorimotor regions, and intrahemispheric coherence were calculated for the frequency bands ranging from delta to beta. RESULTS: Real iTBS induced a significant increase of both MEP amplitude and DW PSD lasting up to 30 min after stimulation, while sham iTBS did not. The DW increase was evident over frontal areas ipsilateral and close to the stimulated cortex (electrode F3). Neither real nor sham iTBS induced significant modifications in the PSD of theta, alpha, and beta bands and in the interhemispheric coherence. Behavioral visuo-analogic scales score did not demonstrate changes in alertness after stimulations. No correlations were found between MEP amplitude and PSD changes in the delta band. CONCLUSIONS: Our data showed that LTP induction in the motor cortex during wakefulness, by means of iTBS, is accompanied by a large and enduring increase of DW over the ipsilateral frontal cortex. SIGNIFICANCE: The present results are strongly in favor of a prominent role of DW in the neural plasticity processes taking place during the awake state.

An MR-compatible force sensor based on FBG technology for biomedical application.

Fiber Bragg Grating (FBG) technology is very attractive to develop sensors for the measurement of thermal and mechanical parameters in biological applications, particularly in presence of electromagnetic interferences. This work presents the design, working principle and experimental characterization of a force sensor based on two FBGs, with the feature of being compatible with Magnetic Resonance. Two prototypes based on different designs are considered and characterized: 1) the fiber with the FBGs is encapsulated in a polydimethylsiloxane (PDMS) sheet; 2) the fiber with the FBGs is free without the employment of any polymeric layer. Results show that the prototype which adopts the polymeric sheet has a wider range of measurement (4200 mN vs 250 mN) and good linearity; although it has lower sensitivity (≈0.1 nm-N(1) vs 7 nm-N(1)). The sensor without polymeric layer is also characterized by employing a differential configuration which allows neglecting the influence of temperature. This solution improves the linearity of the sensor, on the other hand the sensitivity decreases. The resulting good metrological properties of the prototypes here tested make them attractive for the intended application and in general for force measurement during biomedical applications in presence of electromagnetic interferences.

Does an intraneural interface short-term implant for robotic hand control modulate sensorimotor cortical integration? An EEG-TMS co-registration study on a human amputee.

PURPOSE: Following limb amputation, central and peripheral nervous system relays partially maintain their functions and can be exploited for interfacing prostheses. The aim of this study is to investigate, for the first time by means of an EEG-TMS co-registration study, whether and how direct bidirectional connection between brain and hand prosthesis impacts on sensorimotor cortical topography. METHODS: Within an experimental protocol for robotic hand control, a 26 years-old, left-hand amputated male was selected to have implanted four intrafascicular electrodes (tf-LIFEs-4) in the median and ulnar nerves of the stump for 4 weeks. Before tf-LIFE-4s implant (T0) and after the training period, once electrodes have been removed (T1), experimental subject's cortico-cortical excitability, connectivity and plasticity were tested via a neuronavigated EEG-TMS experiment. RESULTS: The statistical analysis clearly demonstrated a significant modulation (with t-test p < 0.0001) of EEG activity between 30 and 100 ms post-stimulus for the stimulation of the right hemisphere. When studying individual latencies in that time range, a global amplitude modulation was found in most of the TMS-evoked potentials; particularly, the GEE analysis showed significant differences between T0 and T1 condition at 30 ms (p < 0.0404), 46 ms (p < 0.0001) and 60 ms (p < 0.007) latencies. Finally, also a clear local decrement in N46 amplitude over C4 was evident. No differences between conditions were observed for the stimulation of the left hemisphere. CONCLUSIONS: The results of this study confirm the hypothesis that bidirectional neural interface could redirect cortical areas -deprived of their original input/output functions- toward restorative neuroplasticity. This reorganization strongly involves bi-hemispheric networks and intracortical and transcortical modulation of GABAergic inhibition.

A neurally-interfaced hand prosthesis tuned inter-hemispheric communication.

PURPOSE: This work investigates how a direct bidirectional connection between brain and hand prosthesis modifies the bi-hemispheric sensorimotor system devoted to the movement control of the lost limb. Hand prostheses are often unable to satisfy users' expectations, mostly due to the poor performance of their interfacing system. Neural Interfaces implanted inside nerves of the stump offer the advantage of using the bidirectional neural pathways 'naturally' dispatching signals to control proper hand actions and feed-back sensations. Learning to control a neurally-interfaced hand prosthesis and decode sensory information was previously observed to reduce the inter-hemispheric asymmetry of cortical motor maps and the clinical symptoms of phantom limb syndrome. METHODS: Electroencephalographic (EEG) data was analysed using Functional Source Separation (FSS), a semi-blind method that incorporates prior knowledge about the signal of interest into data decomposition to give access to cortical patch activities. RESULTS: Bi-hemispheric cortices showed normalization of their activity (topographical and spectral patterns) and of functional connectivity between homologous hand controlling areas, during the delivery of the motor command to the cybernetic prosthesis. CONCLUSIONS: The re-establishment of central-peripheral communication with the lost limb induced by a neurally-interfaced hand prosthesis produces beneficial plastic reorganization, not only restructuring contralateral directly-connected control areas, but also their functional balance within the bi-hemispheric system necessary for motor control.

Preliminary investigations on laminin coatings for flexible polyimide/platinum thin films for PNS applications.

The aim of this work was to investigate the possibility to obtain stable bioactive coatings for polyimide/platinum neural interfaces based on thin film technology for applications into the peripheral nervous system (PNS). Laminin (LI), a glycoprotein of the extracellular matrix, which guides and promotes differentiation and growth of neurons, was selected to deposit bioactive coatings. Dip-coating was performed on dummy structures at different LI concentrations. Indirect methods allowed to identify and characterize laminin on coated samples. Mechanical stability was also confirmed by indirect evaluations. Pilot experiments with differentiated PC12 cells, by the addition of nerve growth factor (NGF), showed improved neurite outgrowth on the coated probes compared to bare polyimide samples.

ODEs model of foreign body reaction around peripheral nerve implanted electrode.

The foreign body reaction that the neural tissue develops around an implanted electrode contributes to insulate the probe and enhances the electrical and mechanical mismatch. It is a complex interaction among cells and soluble mediators and the knowledge of this phenomenon can benefits of formal and analytical methods that characterize the mathematical models. This work offers a lumped component model, described by ordinary differential equations, that taking into account the main geometrical (size, shape, insertion angle) and chemical (coating surface) properties of the implant predict the thickness of the fibrotic capsule in a time frame when the reaction stabilizes. This tool allows to evaluate different hypothetical solutions for accounting the tissue-electrode mismatch.

Intrafascicular thin-film multichannel electrodes for sensory feedback: Evidences on a human amputee.

The performance of motor neuroprostheses or robotic arm prostheses can be significantly improved by delivering sensory feed-back related to the ongoing motor task (e.g. the slippage of an object during grasping). Microfabricated neural electrodes implantable in peripheral nervous system seem a promising approach to this aim. New generation of thin-film intrafascicular electrodes longitudinally implantable in peripheral nerves (tf-LIFE4) has been developed and tested for afferent stimulation in human amputee case study.