Measurement of involuntary arm movement in athetotic patients

A Riemannian Geometry Theory of Synergy Selection for Visually-Guided Movement

Bringing together a Riemannian geometry account of visual space with a complementary account of human movement synergies we present a neurally-feasible computational formulation of visuomotor task performance. This cohesive geometric theory addresses inherent nonlinear complications underlying the match between a visual goal and an optimal action to achieve that goal: (i) the warped geometry of visual space causes the position, size, outline, curvature, velocity and acceleration of images to change with changes in the place and orientation of the head, (ii) the relationship between head place and body posture is ill-defined, and (iii) mass-inertia loads on muscles vary with body configuration and affect the planning of minimum-effort movement. We describe a partitioned visuospatial memory consisting of the warped posture-and-place-encoded images of the environment, including images of visible body parts. We depict synergies as low-dimensional submanifolds embedded in the warped posture-and-place manifold of the body. A task-appropriate synergy corresponds to a submanifold containing those postures and places that match the posture-and-place-encoded visual images that encompass the required visual goal. We set out a reinforcement learning process that tunes an error-reducing association memory network to minimize any mismatch, thereby coupling visual goals with compatible movement synergies. A simulation of a two-degrees-of-freedom arm illustrates that, despite warping of both visual space and posture space, there exists a smooth one-to-one and onto invertible mapping between vision and proprioception.

Improving Target Acquisition for Computer Users With Athetosis

Prior work has highlighted the challenges faced by people with athetosis when trying to acquire on-screen targets using a mouse or trackball. The difficulty of positioning the mouse cursor within a confined area has been identified as a challenging task. We have developed a target acquisition assistance algorithm that features transition assistance via directional gain variation based on target prediction, settling assistance via gain reduction in the vicinity of a predicted target, and expansion of the predicted target as the cursor approaches it. We evaluated the algorithm on improving target acquisition efficiency among seven participants with athetoid cerebral palsy. Our results showed that the algorithm significantly reduced the overall movement time by about 20%. Considering the target acquisition occurs countless times in the course of regular computer use, the accumulative effect of such improvements can be significant for improving the efficiency of computer interaction among people with athetosis.

Characterizing head motor disorders to create novel interfaces for people with cerebral palsy: creating an alternative communication channel by head motion

This paper aims to validate a head mounted inertial interface to characterize disorder movements in people with cerebral palsy (CP). The kinematic patterns extracted from this study will be used to design an alternative communication channel (using head motion) adapted to user's capabilities and limitations. Four people with CP participated (GMFCS level V) and three healthy subjects as reference group. The main outcome measures were divided into 1) Time-domain, 2) Frequency-domain and 3) Spatial domain. Results showed that the inertial interface succeeds assessing the pathological motion. Firstly, the system differentiates between voluntary and involuntary motion in terms of motor control, frequency and range of motion. Secondly some motion disorders such as hypertonia, hypotonia can be identified. These results suggest that people with motor disorders could benefit from the developed inertial system in three fields: 1) diagnosis of motor disorder by means of an objective quantification, 2) physical and cognitive rehabilitation by means of proprioceptive enhancement through visual-motor feedback and 3) functional compensation by means of an inertial person-machine interface for controlling computer and assistive devices (e.g. wheelchairs or walkers).

Motoscopic analysis of gross motor patterns in athetotic cerebral palsied children

Rolling, sitting, and crawling patterns were motoscopically analyzed in 51 athetotic cerebral palsied children. In rolling, rotation of the trunk and support on the elbows were difficult in some subjects. When sitting, most of the subjects had a "W" sitting pattern in which the hips were adducted and the knees were flexed. As for crawling, reciprocal movements of the four extremities were disturbed. The reciprocal hip movements were insufficient and accompanied the lateral bending of the trunk in many of the children. The hips supported the weight in flexion, and the synchronized extension of the hips, with or without lateral bending of the trunk, propelled the body in some. Creeping on the elbows was shown only in the younger children.

Toward quantification of athetotic movements by frequency spectrum analysis

The frequency spectrum of the elbow movements of one normal subject and six handicapped subjects were obtained in order to investigate the possibility of using this technique in quantifying athetosis. The frequency spectrum technique appears to be useful but data from more subjects must be obtained and specific details regarding scaling need to be investigated.

Determination of the parameters for an athetotic arm model

A model is developed to represent elbow motions of a cerebral palsied arm with athetotic movements. The parameters of the model are defined and determined. The resulting computer model can then be used to either generate athetotic motions or to regenerate prerecorded experimental data.

Attempted rapid elbow flexion movements in patients with athetosis

Voluntary rapid elbow flexion movements were studied in 14 patients with athetosis on the basis of cerebral palsy. When the movement was attempted with one arm, other muscles inappropriate for the task, such as muscles in the opposite limb, were also activated. EMG activity of the biceps and triceps was analysed in detail, and the patterns seen in the different patients were divided into six groups: (1) The normal "ballistic" triphasic pattern, with bursts of normal duration, alternating in biceps and triceps, but the triceps might be activated first, causing the limb to extend rather than flex, (2) The triphasic pattern, with bursts of long duration, (3) Repetitive cycles of the triphasic pattern with particularly long antagonist bursts, apparently limiting the movement in each cycle, (4) Long bursts synchronous in agonist and antagonist muscles, (5) Continuous activity of the agonist, with reduction in activity of the antagonist, (6) Failure to be able to do the task. The pathophysiology of athetosis is that voluntary movement is characterised by excessive muscular activity, most prominently in inappropriate muscles, both extraneous to the task and directly antagonistic.

Pathophysiology of dysarthria in cerebral palsy

Electromyograms were recorded with hooked-wire electrodes from sixteen lip, tongue and jaw muscles in six normal and seven cerebral palsied adult subjects during a variety of speech and non-speech tasks. The recorded patterns of muscle activity fail to support a number of theories concerning the pathophysiology of dysarthria in cerebral palsy. There was no indication of weakness in individual articulator muscles. There was no evidence of uncontrolled sustained background activity or of abnormal tonic stretch reflex responses in lip or tongue muscles. Primitive or pathological reflexes could not be elicited by orofacial stimulation. No imbalance between positive and negative oral responses was observed. The view that random involuntary movement disrupts essentially normal voluntary control in athetosis was not supported. Each cerebral palsied subject displayed an idiosyncratic pattern of abnormal muscle activity which was reproduced across repetitions of the same phrase, indicating a consistent defect in motor programming.

A microprocessor-based ultrasonic limb movement monitoring system

A system has been devised, using a spark-gap ultrasonic transmitter and an array of four ultrasonic receivers, to monitor the unrestrained movement of a physically handicapped child's fingertip as he attempts to perform some specific task. A microprocessor is used to measure the time taken for a pulsed ultrasonic shock-wave to travel from the fingertip-mounted spark-transmitter to each of the four ultrasonic receivers, and hence compute the Cartesian co-ordinates of the transmitter. It is hoped that this equipment will enable the voluntary components in the poorly-controlled limb movements of some of the physically handicapped children to be isolated and used to control external equipment.

The role of action reflexes in the damping of mechanical oscillations

Reflex responses measured during voluntary contraction of the muscle being stretched are known to differ markedly from reflex responses elicited from passive muscle. The term 'action tonic stretch reflex' or 'action TSR' has been used previously to describe a reflex response to continuous stretch, separated from voluntary activity by means of a cross-correlational and spectrographic analysis. In this paper it is proposed that the action TSR play a functional role during voluntary movement by damping the transient oscillations associated with the natural resonant frequencies of the limbs. It is suggested that oscillations excite an action TSR force response with phase lead ahead of muscle stretch. This force response can be resolved into two force components, one of which has a 90 degree phase lead ahead of muscle stretch and behaves like a viscous friction reaction force causing damping of oscillations. Three experiments which support this proposition are described. (1) Analog computer model stimulation studies of a muscle supporting a mass-spring load reveal that damping only occurs when the force response has a phase lead ahead of muscle stretch. When the force response has a phage lag behind muscle stretch, the system is unstable and the amplitude of oscillation increases with time. (2) It is demonstrated that when a mass-spring load is supported as rigidly as possible by the human arm, reaction forces from the arm damp and mass-spring oscillations more rapidly than when the mass-spring is rigidly supported. Electromyogram (EMG) recordings reveal that mass-spring oscillations excite action TSR responses with phase lead ahead of muscle stretch. (3) Recordings of elbow angle and biceps EMG during rapid forearm flexion or extension movements followed by sudden stops reveal critically damped oscillations in the elbow angle signal (i.e. no more than one or two small overshoots), which are accompanied by EMG action TSR responses with phase lead ahead of muscle stretch.