Marco Capozza

Clinical multisegmental posturography: Age-related changes in stance control

Unlike conventional platform posturography, which analyses the sway in the projection of the body baricentre on a supporting plane, multisegmental posturography provides information about body segmental movements during stance, including those that keep the baricentre still. This paper presents a new technical approach to multisegmental posturography using Virtual Reality electromagnetic tracking devices. This device was used to study age-related differences in normal subjects in the control of upright posture. Body sway was studied by recording the oscillations of two trackers placed on the head and the hip during the Romberg test. The tracking device allowed us to detect age-related differences in postural stance strategies. Although the amplitude and velocity of the oscillations measured at the head did not differ in the two groups, the flexibility of the ankle-hip head axis differed significantly: elderly subjects exhibited a more rigid stance. Closing the eyes increased rigidity in both age groups and this change appear more pronounced in the young.

EEG mean frequency changes in healthy subjects during prefrontal transcranial direct current stimulation

In this pilot study we evaluated electroencephalographic (EEG) mean frequency changes induced by prefrontal transcranial direct current stimulation (tDCS) and investigated whether they depended on tDCS electrode montage. Eight healthy volunteers underwent tDCS for 15 min during EEG recording. They completed six tDCS sessions, 1 wk apart, testing left and right direct current (DC) dipole directions with six different montages: four unipolar montages (one electrode on a prefrontal area, the other on the opposite wrist) and two bipolar montages (both electrodes on prefrontal areas), and a single sham session. EEG power spectra were assessed from four 1-min EEG epochs, before, during, and after tDCS. During tDCS the outcome variable, brain rate (fb), changed significantly, and the changes persisted for minutes after tDCS ended. With the DC dipole directed to the left (anode on the left prefrontal area or wrist), fb increased, and with the DC dipole directed to the right (anode on the right prefrontal area or wrist), fb decreased, suggesting asymmetric prefrontal cortex functional organization in the normal human brain. Anodal and cathodal effects were opposite but equally large. Gender left these effects unchanged.

A biologically inspired neural network controller for ballistic arm movements

BackgroundIn humans, the implementation of multijoint tasks of the arm implies a highly complex integration of sensory information, sensorimotor transformations and motor planning. Computational models can be profitably used to better understand the mechanisms sub-serving motor control, thus providing useful perspectives and investigating different control hypotheses. To this purpose, the use of Artificial Neural Networks has been proposed to represent and interpret the movement of upper limb. In this paper, a neural network approach to the modelling of the motor control of a human arm during planar ballistic movements is presented.MethodsThe developed system is composed of three main computational blocks: 1) a parallel distributed learning scheme that aims at simulating the internal inverse model in the trajectory formation process; 2) a pulse generator, which is responsible for the creation of muscular synergies; and 3) a limb model based on two joints (two degrees of freedom) and six muscle-like actuators, that can accommodate for the biomechanical parameters of the arm. The learning paradigm of the neural controller is based on a pure exploration of the working space with no feedback signal. Kinematics provided by the system have been compared with those obtained in literature from experimental data of humans.ResultsThe model reproduces kinematics of arm movements, with bell-shaped wrist velocity profiles and approximately straight trajectories, and gives rise to the generation of synergies for the execution of movements. The model allows achieving amplitude and direction errors of respectively 0.52 cm and 0.2 radians.Curvature values are similar to those encountered in experimental measures with humans.The neural controller also manages environmental modifications such as the insertion of different force fields acting on the end-effector.ConclusionThe proposed system has been shown to properly simulate the development of internal models and to control the generation and execution of ballistic planar arm movements. Since the neural controller learns to manage movements on the basis of kinematic information and arm characteristics, it could in perspective command a neuroprosthesis instead of a biomechanical model of a human upper limb, and it could thus give rise to novel rehabilitation techniques.

Postural responses to low-intensity, short- duration, galvanic vestibular stimulation as a possible differential diagnostic procedure

Rinalduzzi S, Cipriani AM, Capozza M, Accornero N. Postural responses to low‐intensity, short‐duration, galvanic vestibular stimulation as a possible differential diagnostic procedure.
Acta Neurol Scand: 2011: 123: 111–116.
© 2010 The Authors Journal compilation

Three-dimensional mapping of brainstem functional lesions

The human brainstem is a highly complex structure where even small lesions can give rise to a variety of symptoms and outward sings. Localising the area of dysfunction within the brainstem is often a difficult task. To make localisation easier, a neural net system has been developed which uses 72 clinical and neurophysiological data inputs to provide a display (using 5268 voxels) on a three-dimensional model of the human brainstem. The net was trained by means of a back-propagation algorithm, over a pool of 580 example cases. Assessed on 200 test cases, the net correctly localised 83.6% of the target voxels; furthermore the net correctly localised the lesions in 31 out of 37 patients. Because this computer-assisted method provides reliable and quantitative localisation of brainstem areas of dysfunction and can be used as a 3D interactive functional atlas, it is expected to prove useful as a diagnostic tool for assessing focal brainstem lesions.

Stance Postural Strategies in Patients with Chronic Inflammatory Demyelinating Polyradiculoneuropathy.

Introduction Polyneuropathy leads to postural instability and an increased risk of falling. We investigated how impaired motor impairment and proprioceptive input due to neuropathy influences postural strategies. Methods Platformless bisegmental posturography data were recorded in healthy subjects and patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Each subject stood on the floor, wore a head and a hip electromagnetic tracker. Sway amplitude and velocity were recorded and the mean direction difference (MDD) in the velocity vector between trackers was calculated as a flexibility index. Results Head and hip postural sway increased more in patients with CIDP than in healthy controls. MDD values reflecting hip strategies also increased more in patients than in controls. In the eyes closed condition MDD values in healthy subjects decreased but in patients remained unchanged. Discussion Sensori-motor impairment changes the balance between postural strategies that patients adopt to maintain upright quiet stance. Motor impairment leads to hip postural strategy overweight (eyes open), and prevents strategy re-balancing when the sensory context predominantly relies on proprioceptive input (eyes closed).

Video color perimetry: impairment in glaucoma suspects.

Purpose: To detect mild visual field impairment in asymptomatic glaucoma suspect patients. Methods: Color perception within the visual field was tested with customized color video perimetry. The key features of the system were stimuli color desaturation, low-level luminance and equiluminant gray background. Twenty patients with asymptomatic glaucoma were tested and compared with a group of age-matched control subjects. Results: Automated perimetry test findings differed significantly in the two groups, particularly for short-wavelength sensitivity (blue). The severity of color impairment correlated directly with intraocular pressure. Conclusion: Desaturated low-luminance video perimetry will reliably detect and quantify asymptomatic visual field defects. A previous work on multiple sclerosis has detected a mild long-wavelength (red) impairment in asymptomatic patients after an episode of optic neuritis, even in clinically unaffected fellow eyes. Our findings in glaucoma suspect patients indicate that a mild blue impairment could be the initial sign of this disease.

The Ideomotor Principle Simulated - An Artificial Neural Network Model for Intentional Movement and Motor Learning

Although the ideomotor principle (IMP), the notion positing that the nervous system initiates voluntary actions by anticipating their sensory effects, has long been around it still struggles to gain widespread acknowledgement. Supporting this theory, we present an artificial neural network model driving a simulated arm, designed as simply as possible to focus on the essential IMP features, that demonstrates by simulation how the IMP could work in biological intentional movement and motor learning. The simulation model shows that IMP motor learning is fast and effective and shares features with human motor learning. An IMP extension offers new insights into the so-called mirror neuron and canonical neuron systems.

A Neural-based Model for the Control of the Arm During Planar Ballistic Movements

A software model simulating the learning process of planar ballistic movements of the arm was developed, using the following scheme: an artificial neural network (modelling the neural system), a pulse generator (a computational block driving the biomechanical model of the arm), a two degrees of freedom manipulator guided by a six-muscles model. The learning scheme was implemented in an unsupervised way, thus not back-propagating the error information on the arm final position with respect to the expected target, but associating movements between two space positions (network inputs) to muscular activations (network outputs). After a training consisting of about 45.000 simulated movements, the model reached a mean distance error consistent with the experimental data found in typical ballistic movements.

An Artificial Neural Network for 3D Localization of Brainstem Functional Lesions

The human brainstem is a highly complex structure where even small lesions can give rise to a variety of symptoms and signs. Localizing the area of dysfunction within the brainstem is often a difficult task.To make localization easier, we have developed a neural net system, which uses 72 clinical and neurophysiological data inputs and displays it (using 5268 voxels) on a three-dimensional model of the human brainstem. The net was trained by means of a back-propagation algorithm, over a pool of 580 example-cases. Assessed on 200 test-cases, the net correctly localized 83.6% of the target voxels; furthermore the net correctly localized the lesion in 31/37 patients. Because our computer-assisted method provides a reliable and quantitative localization of brainstem areas of dysfunction and can be used as a 3D interactive functional atlas, we expect that it will prove useful as a diagnostic tool for assessing focal brainstem lesions.