Wrist rehabilitation in chronic stroke patients by means of adaptive, progressive robot-aided therapy.

Despite distal arm impairment after brain injury is an extremely disabling consequence of neurological damage, most studies on robotic therapy are mainly focused on recovery of proximal upper limb motor functions, routing the major efforts in rehabilitation to shoulder and elbow joints. In the present study we developed a novel therapeutic protocol aimed at restoring wrist functionality in chronic stroke patients. A haptic three DoFs (degrees of freedom) robot has been used to quantify motor impairment and assist wrist and forearm articular movements: flexion/extension (FE), abduction/adduction (AA), pronation/supination (PS). This preliminary study involved nine stroke patients, from a mild to severe level of impairment. Therapy consisted in ten 1-hour sessions over a period of five weeks. The novelty of the approach was the adaptive control scheme which trained wrist movements with slow oscillatory patterns of small amplitude and progressively increasing bias, in order to maximize the recovery of the active range of motion. The primary outcome was a change in the active RoM (range of motion) for each DoF and a change of motor function, as measured by the Fugl-Meyer assessment of arm physical performance after stroke (FMA). The secondary outcome was the score on the Wolf Motor Function Test (WOLF). The FMA score reported a significant improvement (average of 9.33±1.89 points), revealing a reduction of the upper extremity motor impairment over the sessions; moreover, a detailed component analysis of the score hinted at some degree of motor recovery transfer from the distal, trained parts of the arm to the proximal untrained parts. WOLF showed an improvement of 8.31±2.77 points, highlighting an increase in functional capability for the whole arm. The active RoM displayed a remarkable improvement. Moreover, a three-months follow up assessment reported long lasting benefits in both distal and proximal arm functionalities. The experimental results of th- s preliminary clinical study provide enough empirical evidence for introducing the novel progressive, adaptive, gentle robotic assistance of wrist movements in the clinical practice, consolidating the evaluation of its efficacy by means of a controlled clinical trial.

Functional evaluation of robot end-point assisted gait re-education in chronic stroke survivors.

Gait re-education is a primary rehabilitation goal after stroke. In this study, we used instrumented gait analysis for evaluating the outcomes of gait training assisted by an endpoint robot in a population of six chronic stroke survivors. The preliminary results, based on spatial-temporal and kinematic analysis, suggest that (a) self-placed walking speed increases, with an improvement of both length and duration of the stride, (b) balance increases during standing and walking, (c) the non-affected side becomes less involved in attempting to correct for the deficiencies of the affected side, thus reducing the importance of compensatory strategies.

Wrist Coordination in a Kinematically Redundant Stabilization Task.

We investigated how the control of a compliant object is realized by the redundancy of wrist anatomy. Subjects had to balance a one degree-of-freedom inverted pendulum using elastic linkages controlled by wrist flexion/extension (FE) and forearm pronation/supination (PS). Haptic feedback of the interaction forces between the pendulum and the wrist was provided by a robotic interface. By tuning the mechanical properties of the virtual pendulum and the stiffness of the elastic linkages it was possible to study various dynamical regimes of the simulated object. Twenty subjects (divided in two groups) were tested in four days performing the same task but with different presentation order. The stabilization strategy adopted by the subjects was characterized by primarily using the PS DoF when the pendulum was linked to stiff springs and characterized by a relatively fast dynamic response; in contrast, the stabilization task was shared by both DoFs in case of lower spring stiffness and slower dynamics of the virtual object.

Multijoint arm stiffness during movements following stroke: implications for robot therapy.

Impaired arm movements in stroke appear as a set of stereotypical kinematic patterns, characterized by abnormal joint coupling, which have a direct consequence on arm mechanics and can be quantified by the net arm stiffness at the hand. The current available measures of arm stiffness during functional tasks have limited clinical use, since they require several repetitions of the same test movement in many directions. Such procedure is difficult to obtain in stroke survivors who have lower fatigue threshold and increased variability compared to unimpaired individuals. The present study proposes a novel, fast quantitative measure of arm stiffness during movements by means of a Time-Frequency technique and the use of a reassigned spectrogram, applied on a trial-by-trial basis with a single perturbation. We tested the technique feasibility during robot mediated therapy, where a robot helped stroke survivors to regain arm mobility by providing assistive forces during a hitting task to 13 targets covering the entire reachable workspace. The endpoint stiffness of the paretic arm was estimated at the end of each hitting movements by suddenly switching of the assistive forces and observing the ensuing recoil movements. In addition, we considered how assistive forces influence stiffness. This method will provide therapists with improved tools to target the treatment to the individual's specific impairment and to verify the effects of the proposed exercises.

A novel mechatronic system for measuring end-point stiffness: mechanical design and preliminary tests.

Measuring arm stiffness is of great interest for many disciplines from biomechanics to medicine especially because modulation of impedance represents one of the main mechanism underlying control of movement and interaction with external environment. Previous works have proposed different methods to identify multijoint hand stiffness by using planar or even tridimensional haptic devices, but the associated computational burden makes them not easy to implement. We present a novel mechanism conceived for measuring multijoint planar stiffness by a single measurement and in a reduced execution time. A novel mechanical rotary device applies cyclic radial perturbation to human arm of a known displacement and the force is acquired by means of a 6-axes commercial load cell. The outcomes suggest that the system is not only reliable but allows obtaining a bi-dimensional estimation of arm stiffness in reduced amount of time and the results are comparable with those reported in previous researches.

Stabilizing unstable object by means of kinematic redundancy.

The paper aims to investigate how humans deal with unstable objects under the possibility of choosing different strategy of interaction. The presented task consisted in balancing a 1 degree of freedom (DoF) elastic inverted pendulum by means of 2 DoF of the wrist (fexion/extension and pronation/supination). The pendulum was simulated using a virtual environment and the haptic feedback was generated by a robotic wrist device. The task is a redundant because the subject can choose how to use the 2 DoF in order to move and stabilize a 1 DoF simulated mechanical system: the inverted pendulum. Six subjects volunteered to participate and were tested in four different days performing the same task but experiencing different mechanical systems (pendulum) characterized by lower or higher dynamics due to the possibility to tune the stiffness of the pendulum. Subjects were asked to balance the inverted pendulum maintaining it in a vertical position for a required amount of time. It was found the adopted stabilization strategy was mainly characterized by using only one of the 2 available DoFs of their wrist when the pendulum was stiffer, while in case of lower stiffness of the pendulum (slower dynamic) wrist input redundancy was a more suitable strategy to perform the balancing task.

Abnormal adaptation in children affected by cerebral palsy to robot generated dynamic environment.

This paper aims to investigate how robotic devices can be used to understand the mechanism of sensorimotor adaptation in pediatric subjects affected by hemiparetic cerebral palsy. Previous studies showed how healthy adults, after training in presence of a systematic structured disturbing force field, show an "after effect" and therefore they highly adapt and compensate the external disturbance. An open issue is whether this adaptive capability is preserved or disrupted in pediatric impaired subjects when they experience a robot generated dynamic environment. Fourteen pediatric Cerebral Palsy subjects (CP group), and age-matched control group were exposed to a robot generated speed-dependant force field; during familiarization (no forces generated by the robot) the movement of the CP subjects were more curved, displaying greater and variable directional error; in the force field phase both the groups showed an after-effect, but the CP group had a non significant adaptation rate. This outcome suggests the CP subjects have reduced ability to learn external force and they make greater aiming error because of an inefficient anticipatory strategy during visuomotor task.

Training stroke patients with continuous tracking movements: evaluating the improvement of voluntary control.

We report on a pilot study of robot therapy with stroke patients. Patients were requested to track a continuously moving target according to a figure-of-eight. Assistance was provided by an attractive force field, whose magnitude was regulated according to a principle of minimal assistance and a principle of consolidation of the learned memory trace. From the analysis of the assistive forces, we show that subjects improve their degree of voluntary control.

Subtle upper limb impairment in asymptomatic multiple sclerosis subjects.

We evaluated upper limb function in multiple sclerosis (MS) subjects (11 clinically definite MS patients and seven clinically isolated syndrome (CIS) subjects), with a normal upper limb standard neurological examination. Subjects performed center-out reaching movements under visual control, with and without vision of the hand. Their movements were recorded through a digitizing tablet. Motor performance was also related to lesion load, estimated from magnetic resonance imaging (MRI). We found that in MS and CIS subjects, under the hand vision condition, movements were significantly less smooth, and had a less symmetric speed profile. However, the observed impairment did not correlate with MRI findings. This result may be interpreted as evidence of a compensatory strategy, elicited by subtle alterations in sensorimotor control.

Real-time MR artifacts filtering during continuous EEG/fMRI acquisition.

The purpose of this study was the development of a real-time filtering procedure of MRI artifacts in order to monitor the EEG activity during continuous EEG/fMRI acquisition. The development of a combined EEG and fMRI technique has increased in the past few years. Preliminary "spike-triggered" applications have been possible because in this method, EEG knowledge was only necessary to identify a trigger signal to start a delayed fMRI acquisition. In this way, the two methods were used together but in an interleaved manner. In real simultaneous applications, like event-related fMRI study, artifacts induced by MRI events on EEG traces represent a substantial obstacle for a right analysis. Up until now, the methods proposed to solve this problem are mainly based on procedures to remove post-processing artifacts without the possibility to control electrophysiological behavior of the patient during fMRI scan. Moreover, these methods are not characterized by a strong "prior knowledge" of the artifact, which is an imperative condition to avoid any loss of information on the physiological signals recovered after filtering. In this work, we present a new method to perform simultaneous EEG/fMRI study with real-time artifacts filtering characterized by a procedure based on a preliminary analytical study of EPI sequence parameters-related EEG-artifact shapes. Standard EEG equipment was modified in order to work properly during ultra-fast MRI acquisitions. Changes included: high-performance acquisition device; electrodes/cap/wires/cables materials and geometric design; shielding box for EEG signal receiver; optical fiber link; and software. The effects of the RF pulse and time-varying magnetic fields were minimized by using a correct head cap wires-locked environment montage and then removed during EEG/fMRI acquisition with a subtraction algorithm that takes in account the most significant EPI sequence parameters. The on-line method also allows a further post-processing utilization.

A new type of very low-power modulated laser: soft-tissue changes induced in osteoarthritic patients revealed by sonography.

Patients with symptomatic osteoarthritis of the cervical spine were studied by ultrasound examination. The region of interest was the soft connective tissue layer above the right and the left superior trapezium that revealed a significant difference in thickness between the left and right side. The aching side was treated with a new type of very low-power, modulated laser for 3 min. Immediately after application, the sonographic examination revealed a significant symmetrization of the subcutaneous tissue.

Can muscle stiffness alone stabilize upright standing?

A stiffness control model for the stabilization of sway has been proposed recently. This paper discusses two inadequacies of the model: modeling and empiric consistency. First, we show that the in-phase relation between the trajectories of the center of pressure and the center of mass is determined by physics, not by control patterns. Second, we show that physiological values of stiffness of the ankle muscles are insufficient to stabilize the body "inverted pendulum." The evidence of active mechanisms of sway stabilization is reviewed, pointing out the potentially crucial role of foot skin and muscle receptors.

Computational implications of modeling grasping as a form of (multiple-parallel) reaching.

Although it is true that the specific research on grasping has been dominated in recent years by the canonical transport + grip model originally formulated by Jeannerod (1984), still one can find in the research on reaching a number of links and anticipations to the new view on grasping made explicit by the authors of the target article. This paper reviews some of the relevant concepts and outlines a modeling framework that aims at biological plausibility.

Internal models in the control of posture.

The aim of the paper is to investigate the application of control schemes based on "internal models" to the stabilization of the standing posture. The computational complexities of the control problems are analyzed, showing that muscle stiffness alone is insufficient to carry out the task. The paper also re-visits the concept of the cerebellum as a Smith's predictor.

Neuromotor control in handwriting and drawing: introduction and overview.

In this introduction to the Special Issue on Neuromotor Control in Handwriting and Drawing, an overview is given of the themes and sub-themes covered by these proceedings of the eighth Biennial Conference of the International Graphonomics Society (IGS) on handwriting and other graphic tasks, held in Genoa, Italy, 24-28 August, 1997. Section overviews are given for Neuromuscular and Biophysical Models; Learning and Cognitive Models; and Neuropsychological Issues. Moreover, to guide researchers in the field, this introduction also provides a summary list of major publications following the preceding IGS conferences.

Can non-linear muscle dynamics explain the smoothness of handwriting movements?

The paper addresses the issue of the role of non-linear muscle dynamics in determining the smoothness and invariance of handwriting trajectories. In particular, a specific neuromuscular control model is described that has recently been shown to explain the detailed time course of hand stiffness during arm reaching movements. In the paper the model is applied to more complex handwriting trajectories, with the purpose of verifying to which extent the load compensation capabilities of the periphery can subserve motor equivalence. Simulations show the power of the mechanism for movements of "normal" speed. For quicker movements periphery alone is not enough and a central load compensation action is clearly required.

Neural network learning of robot arm impedance in operational space.

Impedance control is one of the most effective control methods for the manipulators in contact with their environments. The characteristics of force and motion control, however, is determined by a desired impedance parameter of a manipulator's end-effector that should be carefully designed according to a given task and an environment. The present paper proposes a new method to regulate the impedance parameter of the end-effector through learning of neural networks. Three kinds of the feed-forward networks are prepared corresponding to position, velocity and force control loops of the end-effector before learning. First, the neural networks for position and velocity control are trained using iterative learning of the manipulator during free movements. Then, the neural network for force control is trained for contact movements. During learning of contact movements, a virtual trajectory is also modified to reduce control error. The method can regulate not only stiffness and viscosity but also inertia and virtual trajectory of the end-effector. Computer simulations show that a smooth transition from free to contact movements can be realized by regulating impedance parameters before a contact.

Human hand impedance characteristics during maintained posture.

The present paper examines human hand impedance characteristics, including inertia and viscosity as well as stiffness, in multi-joint arm movements. While a subject maintains a given hand location, small external disturbances are applied to his hand by a manipulandum. The corresponding force-displacement vectors are measured and sampled over time in order to estimate the hand impedance by means of a second-order linear model. The experimental results in different subjects and hand locations are summarized as follows: (1) the estimated inertia matrices of the human hand well agrees with computed values using a two-joint arm model, (2) spatial variations of the stiffness ellipses are consistent with the experimental results of Mussa-Ivaldi et al. (1985), (3) hand stiffness and viscosity increase with the grip force of the subject, and (4) viscosity and stiffness ellipses tend to have similar orientation. The accuracy of the impedance estimation method is validated with a mechanical spring-mass system with known parameters.

Neurocomputing aspects in modelling cursive handwriting.

This paper describes a distributed modelling framework of the motor control processes that underly the planning of cursive handwriting. The model, that focuses on the hypothetical functions of the posterior parietal cortex combines a paradigm of self-organization (for building robust and coherent maps of the different motor spaces) with relaxation dynamics (for run-time incorporation of task constraints) and non-linear integration (for a smooth integration between via-points).

Human face representation by means of polynomial expansion of the harmonic descriptors of tomograms.

A method is presented to obtain realistic modifications of faces represented as sequences of tomograms, to be used for geometrical modelling or for planning of plastic surgery. This method uses a mathematical model consisting of the harmonic expansion of tomograms whose harmonic parameters are represented by cubic spline functions of the z variable. Based on this model a three dimensional shape editor is proposed that allows for local modifications. The results obtained using tomograms of a plaster mould are presented.