The role of kinaesthetic feedback in goal-directed movements

The purpose of this study was to investigate the role of kinaesthetic feedback in the control of goal-directed movements. The subjects were qualified basketball and handball players compared to weightlifters as controls. The body measures and the general motor tests verified fit physical condition of the subjects, and detected no sign that would disturb the execution of special motor tests. The special motor tests were free-throw shootings with basketball to the basket, free shootings with handball to a rectangular frame, zigzag dribbling with basketball to 14 m among traffic cones 2 m apart, and stopping at a mark after running to 10 m. These tests were performed both with open eyes and closed eyes. The results of all special motor tests decreased significantly in the lack of visual information. Furthermore, in contrast to the significantly different results obtained from the three different groups with open eyes, these groups produced equally minor results with closed eyes. It is concluded that the practice of goal-directed movement, learned under visual guidance, does not make the kinaesthetic feedback able to compensate the lack of visual input.     

Adaptational Modifications of the Vestibular Postural Response in Humans under Conditions of Horizontal Visual Reversal

In healthy volunteers, we recorded stabilograms and studied postural responses evoked by galvanic stimulation of the labyrinth (binaurally applied 1-mA current, 4 sec) with the subjects' eyes open and closed and under conditions of reversed visual perception. Horizontal reversal of the visual space was provided by using spectacles with the Dove's prisms. In series consisting of 10 sequential tests with eyes open, we observed a gradual drop in the response amplitude, while there were practically no changes in the maximum velocity of the displacement. Postural responses with eyes closed were considerably greater than those with eyes open, but their amplitude and velocity demonstrated no changes with sequential tests. Under conditions of reversal of the visual perception, both the amplitude and maximum velocity of the postural responses decreased with successive testing. Under the above conditions, at the beginning of a test series responses to vestibular stimulation were greater than those with eyes closed, but in repeated tests they decreased and attained the same magnitude as in the tests with eyes closed. Therefore, the effect of short-term adaptation to visual reversal on the system controlling vertical posture resulted in simple rejection of the information coming via the visual input. In another experimental mode, we studied the adaptation effects at longer (3 h long) visual reversal. Postural responses to galvanic stimulation of the labyrinth (monaurally applied, 2-mA current, 4 sec) were tested with 1-h-long intervals; tests with visual reversal and with eyes closed were made in a random order with each other. A 3-h-long interval with the prismatic spectacles on did not modify the amplitude and velocity of the vestibular postural responses when the tests were made with the eyes closed. When the tests were performed with the eyes open, but in the inverting spectacles, postural responses significantly decreased (by about 50-60%) to the 2nd and 3rd h of the experiment. Such selective suppression of the vestibular input under conditions of visual reversal can be interpreted as a result of adaptational transformation of the visual-vestibular relation directed toward minimization of the visual-vestibular conflict.     

The proprioceptive map of the arm is systematic and stable, but idiosyncratic

Visual and somatosensory signals participate together in providing an estimate of the hand's spatial location. While the ability of subjects to identify the spatial location of their hand based on visual and proprioceptive signals has previously been characterized, relatively few studies have examined in detail the spatial structure of the proprioceptive map of the arm. Here, we reconstructed and analyzed the spatial structure of the estimation errors that resulted when subjects reported the location of their unseen hand across a 2D horizontal workspace. Hand position estimation was mapped under four conditions: with and without tactile feedback, and with the right and left hands. In the task, we moved each subject's hand to one of 100 targets in the workspace while their eyes were closed. Then, we either a) applied tactile stimulation to the fingertip by allowing the index finger to touch the target or b) as a control, hovered the fingertip 2 cm above the target. After returning the hand to a neutral position, subjects opened their eyes to verbally report where their fingertip had been. We measured and analyzed both the direction and magnitude of the resulting estimation errors. Tactile feedback reduced the magnitude of these estimation errors, but did not change their overall structure. In addition, the spatial structure of these errors was idiosyncratic: each subject had a unique pattern of errors that was stable between hands and over time. Finally, we found that at the population level the magnitude of the estimation errors had a characteristic distribution over the workspace: errors were smallest closer to the body. The stability of estimation errors across conditions and time suggests the brain constructs a proprioceptive map that is reliable, even if it is not necessarily accurate. The idiosyncrasy across subjects emphasizes that each individual constructs a map that is unique to their own experiences.     

Human Postural Responses to Vibratory Stimulation of Calf Muscles under Conditions of Visual Inversion

The authors studied postural responses to bilateral vibratory stimulation (70 Hz, 1 mm, 2 s) of the calf triceps proprioceptors or anterior tibial muscles. Anteroposterior body tilts evoked by vibration were recorded by stabilography. The authors compared the values of postural responses under various conditions of visual control, namely, with normal vision, eyes closed, right–left inversion of the visual space by prismatic spectacles, central vision, and diffuse light. Visual inversion influenced the subjects' proprioceptive postural responses. The amplitude of vibration-evoked shifts of the feet pressure center was minimal with eyes open and significantly increased with eyes closed and inverted vision. Postural responses with visual inversion were significantly stronger than with eyes closed. Since inversion spectacles enabled a subject to see only the central part of the visual field (20°), the reference point was the condition of central vision, i.e., spectacles with same visual angle and without prisms. Postural responses were significantly weaker under these conditions than with visual inversion and eyes closed. Visual field inversion by prismatic spectacles made it impossible to use visual information for stabilizing the human upright posture and, moreover, destabized it. True, this holds only for a randomized experimental protocol, which prevents adaptation to prisms.     

Effects of Manipulations with Visual Feedback on Postural Responses in Humans Maintaining an Upright Stance

We studied postural reactions evoked by vibrational stimulation of the anterior tibial and posterior neck muscles under three different conditions of visual control (in a darkened room): (i) upon standing with the eyes open, EO, with perception of a stationary 2D image of the visual environment on the screen, (ii) under conditions of perception of a 3D virtual visual environment, VVE, and (iii) upon standing with the eyes closed, EC. Vibrational stimulation of both muscle groups evoked forward inclinations of the body; average values of the latter under control conditions (EC) were close to each other. The VVE mimicking a real visual environment possessed two planes, a mobile foreground one, whose shifts were programmed in such a manner that they correlated with oscillations of the body, and a stable background one. The tested subjects were asked to use the latter as a visual reference. Under VVE conditions, the amplitude of postural reactions depended on the feedback coefficient between the body movements and shifts of the VVE foreground and the direction of this feedback (its synphase or antiphase, sph or aph, mode). Postural responses at the feedback sph direction became greater with increase in the feedback coefficient (i.e., with increases in the magnitude of shifts of the VVE foreground) and reached values typical of standing under EC conditions. In the case of the aph type of feedback, the responses changed insignificantly. If the lowest feedback coefficient, 1.0, was used, the postural responses tended to decrease, as compared with those under EO conditions. The difference between the values observed at the sph and aph types of feedback with similar coefficients was manifested more intensely in the case of stimulation of the neck muscles. This fact shows that postural reactions triggered by afferent signals from the neck muscles depend more considerably on the ongoing visual afferentation.     

Positioning Errors in Simple Targeted Movements of the Forearm Realized in the Absence of Visual Control: Effects of Vibrational Stimulation of Antagonist Muscles

In 17 healthy subjects, we examined the characteristics of targeted movements of the forearm, flexion from the initial position of full extension taken as 0 deg to a 50 deg target angle in the elbow joint (flexor tests, FTs) and extension from the initial angle of 100 deg to the same target angle (extensor tests, ETs) with return to the initial positions. A standard movement (its trajectory corresponded to a simple trapezium) was performed under conditions of visual feedback (the value of the target angle and trajectory of the movement were visualized on the screen of a monitor); then, this movement should be reproduced by the subject (according to an acoustic signal) in the absence of visual control. Target-reaching test movements in the absence of visual feedback differed from the standard ones in a higher velocity. Blindfold reproduction of standard movements realized under kinesthetic control was accompanied in all subjects by noticeable positive systematic errors of targeted positioning (in the group, on average, 5.16 ± 0.55 and 4.83 ± 0.58 deg under FT and ET conditions, respectively). Vibrational stimulation of the muscles whose activity mainly provided the movement and positioning (m. biceps brachii in the FT cases and m. triceps brachii in the case of ETs) resulted in decreases of the errors of kinesthetic positioning; intragroup means of these errors were 2.55 ± 0.36 deg (FTs) and 2.26 ± 0.40 deg (ETs). The positioning errors demonstrated even greater decreases upon vibrational stimulation of the muscles, which were relatively inactive under conditions of the tests and underwent passive stretching in the course of the movements (m. triceps in FTs and m. biceps in ETs). Mean intragroup values of the errors in these cases were 0.46 ± 0.25 and 0.52 ± 0.31 deg, respectively. The nature of systematic positioning errors in the reproduction of targeted movements in the absence of visual control and the mechanisms underlying the influence of vibrational stimulation of the muscles involved in realization of these movements on the positioning errors under kinesthetic control are discussed.     

The role of the cognitive context in the conservatism of unconscious visual sets

Rigidity of a verbal set was compared in three series of experiments: (1) pseudowords were presented at the set-forming stage and were changed for common words at the testing stage; (2) in the same conditions as in 1, an additional task of target localization in the matrix by two distinctive features was introduced; (3) in the additional target localization task, the spatial component was strengthened whereas image recognition component was reduced. The results confirmed our hypothesis about the context-dependence of the rigidity of the visual set. This characteristic substantially depends on a working memory loading and cognitive tasks performed by a subject, in particular, the relationship between the degrees of involvement of the ventral and dorsal visual systems into the cortical processing of sequential verbal and nonverbal visual stimuli. The experimental paradigm can serve as a model for the investigation of the roles of the ventral and dorsal visual systems in the recognition function.     

An unexpected role for visual feedback in vehicle steering control

Some motor tasks can be completed, quite literally, with our eyes shut. Most people can touch their nose without looking or reach for an object after only a brief glance at its location. This distinction leads to one of the defining questions of movement control: is information gleaned prior to starting the movement sufficient to complete the task (open loop), or is feedback about the progress of the movement required (closed loop)? One task that has commanded considerable interest in the literature over the years is that of steering a vehicle, in particular lane-correction and lane-changing tasks. Recent work has suggested that this type of task can proceed in a fundamentally open loop manner, with feedback mainly serving to correct minor, accumulating errors. This paper reevaluates the conclusions of these studies by conducting a new set of experiments in a driving simulator. We demonstrate that, in fact, drivers rely on regular visual feedback, even during the well-practiced steering task of lane changing. Without feedback, drivers fail to initiate the return phase of the maneuver, resulting in systematic errors in final heading. The results provide new insight into the control of vehicle heading, suggesting that drivers employ a simple policy of "turn and see," with only limited understanding of the relationship between steering angle and vehicle heading.     

Positioning of the Human Forearm in Tracking Movements and Their Reproduction under Conditions of Limited Visual Control

In 14 healthy persons, we studied movements of the forearm with its positioning on a target level. A double trapezium was used as the command trajectory (flexion in the elbow joint from the state of full extension, 0°, with positioning on the level of 50 or 60° and further flexion to the 100° angle, and a similar reverse movement). We compared (i) tracking movements, when the subject tried to adequately reproduce the movement of the target along the command trajectory visualized on the monitor screen and obtained visual information about the performed movement (shifts of the second light point in time/joint angle coordinates), and (ii) reproduction of these movements under conditions of limitation of the visual feedback (when there was no information about the performed movement). Parameters of the tracking movements and of their reproductions (delays of initiation of the movement phases as compared with the command signal, durations of these phases, and angle velocities of the forearm movement), as well as the quality of positioning after oppositely directed movements, were compared. Positioning on the target level performed under proprioceptive control (when visual control was limited) was accompanied by systematic errors, whose sign in most test series performed by most subjects coincided with the direction of the preceding movement phase. The pattern of signs of systematic positioning errors after movements of opposite directions was quite individual (typical of a given subject) and demonstrated no dependence on the value of the extensor loading. Averaged intragroup systematic errors of positioning after movement phase 1 (flexion to the target level) and phase 3 (extension to the same level) under conditions of a minimum extensor loading (0.5-1.0 N · m) were 2.57° and 2.52°, respectively. When the loading was substantial (3.6-6.0 N · m), the respective errors were 3.85° and 3.48°. The nonlinear properties of muscle stretch receptors in the elbow flexors and extensors (responsible for the significant dependence of the parameters of afferent signals produced in these receptors on the movement prehistory) are considered the primary reason for systematic errors when positioning is performed exclusively under proprioceptive control. The influence of alpha-gamma co-activation in active muscles on the characteristics of the above signals is discussed.     

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.     

Shift in arm-pointing movements during gravity changes produced by aircraft parabolic flight.

It has been shown that target-pointing arm movements without visual feedback shift downward in space microgravity and upward in centrifuge hypergravity. Under gravity changes in aircraft parabolic flight, however, arm movements have been reported shifting upward in hypergravity as well, but a downward shift under microgravity is contradicted. In order to explain this discrepancy, we reexamined the pointing movements using an experimental design which was different from prior ones. Arm-pointing movements were measured by goniometry around the shoulder joint of subjects with and without eyes closed or with a weight in the hand, during hyper- and microgravity in parabolic flight. Subjects were fastened securely to the seat with the neck fixed and the elbow maintained in an extended position, and the eyes were kept closed for a period of time before each episode of parabolic flight. Under these new conditions, the arm consistently shifted downward during microgravity and mostly upward during hypergravity, as expected. We concluded that arm-pointing deviation induced by parabolic flight could be also be valid for studying the mechanism underlying disorientation under varying gravity conditions.     

Modulation of pre-programmed muscle activation and stretch reflex to changes of contact surface and visual input during movement to absorb impact.

The purpose of this study was to examine the extent of modification of the preactivation and stretch reflex response in ankle joint muscles to different contact surfaces and visual input during movement to absorb impact. Experimental movements like landing were performed using a special sliding apparatus. Seven subjects made landings on the hard surface (Hard-S) of a metal force platform or soft surface (Soft-S) of a foam cushion with eyes open or closed. The electromyographic activities from the medial gastrocnemius (MG), soleus (Sol), and tibialis anterior (TA) muscles, contact force, and ankle joint angle were recorded. The preactivation levels of MG and TA to Hard-S increased compared to Soft-S. After foot contact, dorsiflexion velocity, impulse, and responses of the stretch reflex in MG and Sol were significantly larger on Hard-S than Soft-S. With eyes closed, there were trends of decrease in the preactivation. Although the dorsiflexion velocity and impulse showed no significant differences between both visual conditions, the stretch reflex responses with eyes closed were larger than those with eyes open for both surfaces. These results suggest that the preactivation is modulated to different surface and the reflex gain is enlarged by visual suppression.     

Saccadic adaptation to moving targets

Saccades are so called ballistic movements which are executed without online visual feedback. After each saccade the saccadic motor plan is modified in response to post-saccadic feedback with the mechanism of saccadic adaptation. The post-saccadic feedback is provided by the retinal position of the target after the saccade. If the target moves after the saccade, gaze may follow the moving target. In that case, the eyes are controlled by the pursuit system, a system that controls smooth eye movements. Although these two systems have in the past been considered as mostly independent, recent lines of research point towards many interactions between them. We were interested in the question if saccade amplitude adaptation is induced when the target moves smoothly after the saccade. Prior studies of saccadic adaptation have considered intra-saccadic target steps as learning signals. In the present study, the intra-saccadic target step of the McLaughlin paradigm of saccadic adaptation was replaced by target movement, and a post-saccadic pursuit of the target. We found that saccadic adaptation occurred in this situation, a further indication of an interaction of the saccadic system and the pursuit system with the aim of optimized eye movements.     

The Influence of Visual Feedback on the Mental Representation of Gait in Patients with THR: A New Approach for an Experimental Rehabilitation Strategy

Due to total hip replacement (THR), patients reveal abnormal gait patterns which post-operative do often not return to “normal”. The restoration towards normal gait reduces stress on the adjacent joints which consequently reduces risk of osteoarthrosis development. Motor-performance is related to the structure of the movement in long-term memory, thus it seems to be essential to imprint correct gait patterns in there. Mental representation structures can develop over the course of training and visual feedback presumably helps regaining a better representation of gait in long-term memory. The purpose of this study is to evaluate the effect of visual feedback on mental representation in patients with THR. In a randomized controlled trial, 20 women (57 ± 6 years) with THR have been enrolled. Subjects were randomly assigned to a control group (CG) or intervention group (IG). Additionally to inpatient treatment, all subjects participated in a standardized gait training including either an intervention based on verbal information from a physiotherapist (CG) or an intervention based on real-time visual feedback (IG). Mental representation was measured in pre-test and post-test using the structure-dimensional analysis. Results indicate significant improvements in mental representation of gait in the post-test only in IG, suggesting that beneficial effects were provoked by visual feedback.     

Eye-Hand Synergy and Intermittent Behaviors during Target-Directed Tracking with Visual and Non-visual Information

Visual feedback and non-visual information play different roles in tracking of an external target. This study explored the respective roles of the visual and non-visual information in eleven healthy volunteers who coupled the manual cursor to a rhythmically moving target of 0.5 Hz under three sensorimotor conditions: eye-alone tracking (EA), eye-hand tracking with visual feedback of manual outputs (EH tracking), and the same tracking without such feedback (EHM tracking). Tracking error, kinematic variables, and movement intermittency (saccade and speed pulse) were contrasted among tracking conditions. The results showed that EHM tracking exhibited larger pursuit gain, less tracking error, and less movement intermittency for the ocular plant than EA tracking. With the vision of manual cursor, EH tracking achieved superior tracking congruency of the ocular and manual effectors with smaller movement intermittency than EHM tracking, except that the rate precision of manual action was similar for both types of tracking. The present study demonstrated that visibility of manual consequences altered mutual relationships between movement intermittency and tracking error. The speed pulse metrics of manual output were linked to ocular tracking error, and saccade events were time-locked to the positional error of manual tracking during EH tracking. In conclusion, peripheral non-visual information is critical to smooth pursuit characteristics and rate control of rhythmic manual tracking. Visual information adds to eye-hand synchrony, underlying improved amplitude control and elaborate error interpretation during oculo-manual tracking.     

The effect of eye movement on the control of arm movement to a target

Abstract

The purpose of this study was to investigate the effect of eye movement on the control of arm movement to a target. Healthy humans flexed the elbow to a stationary target in response to a start tone. Simultaneously, the subject moved the eyes to the target (saccade eye movement), visually tracked a laser point moving with the arm (smooth pursuit eye movement), or gazed at a stationary start point at the midline of the horizontal visual angle (non-eye movement—NEM). Arm movement onset was delayed when saccade eye movement accompanied it. The onset of an electromyographic burst in the biceps muscle and the onset of saccade eye movement were almost simultaneous when both the arm and the eyes moved to the target. Arm movement duration during smooth pursuit eye movement was significantly longer than that during saccade eye movement or NEM. In spite of these findings, amplitudes of motor-evoked potential in the biceps and triceps brachii muscles were not significantly different among the eye movement conditions. These findings indicate that eye movement certainly affects the temporal control of arm movement, but may not affect corticospinal excitability in the arm muscles during arm movement.     

Influence of adaptation to horizontal body position on pointing errors and visual estimation of a target position in humans

The central program of a targeted movement includes a component intended for to compensate for the weight of the arm; this is why the accuracy of pointing to a memorized position of the visual target in darkness depends on orientation of the moving limb in relation to the vertical axis. Transition from the vertical to the horizontal body position is accompanied by a shift of the final hand position along the body axis towards the head. We studied how pointing errors and visual localization of the target are modified due to adaptation to the horizontal body position; targeted movements to a real target were repeatedly performed during the adaptation period. Three types of experiments were performed: a basic experiment, and two different experiments with adaptation realized under somewhat dissimilar conditions. In the course of the first adaptation experiment, subjects received no visual information on the hand’s position in space, and targeted movements of the arm to a luminous target could be corrected using proprioceptive information only. With such a paradigm, the accuracy of pointing to memorized visual targets showed no adaptation-related changes. In the second adaptation experiment, subjects were allowed to continuously view a marker (a light-emitting diode taped to the fingertip). After such adaptation practice, the accuracy of pointing movements to memorized targets increased: both constant and variational errors, as well as both components of constant error (i.e.,X andY errors) significantly dropped. Testing the accuracy of visual localization of the targets by visual/verbal adjustment, performed after this adaptation experiment, showed that the pattern of errors did not change compared with that in the basic experiment. Therefore, we can conclude that sensorimotor adaptation to the horizontal position develops much more successfully when the subject obtains visual information about the working point position; such adaptation is not related to modifications in the system of visual localization of the target.     

Analysis of the segmental structure of EEG alpha-activity in humans

Phasic organisation of human EEG alpha activity was studied in a pilot investigation using a previously suggested EEG segmental analysis methodology. The EEG was recorded in three normal subjects under resting conditions. The segmentation procedure enabled effective identifying of the periods with different amplitude in alpha band and the short-term transitions between them. Mean intersegmental variability of amplitude envelope were computed for the eyes closed and eyes open EEG in each of 16 standard derivations. Analysis of segment amplitude distributions showed that the difference between the average alpha activity amplitude in these conditions were determined mainly by variations in the number of segments of different amplitude classes and not by a shift of the distribution or by change of its width. Distribution and quartile analysis of mean segment amplitudes provide evidence for possible functional heterogeneity of upper and middle subranges of the amplitude range.     

Saccadic target selection as a function of time

Recent evidence indicates that stimulus-driven and goal-directed control of visual selection operate independently and in different time windows (van Zoest et al., 2004). The present study further investigates how eye movements are affected by stimulus-driven and goal-directed control. Observers were presented with search displays consisting of one target, multiple non-targets and one distractor element. The task of observers was to make a fast eye movement to a target immediately following the offset of a central fixation point, an event that either co-occurred with or soon followed the presentation of the search display. Distractor saliency and target-distractor similarity were independently manipulated. The results demonstrated that the effect of distractor saliency was transient and only present for the fastest eye movements, whereas the effect of target-distractor similarity was sustained and present in all but the fastest eye movements. The results support an independent timing account of visual selection.     

Movement-related cortical potentials preceding sequential and goal-directed finger and arm movements in patients with cerebellar atrophy

To determine the influence of cerebellar involvement on the preparatory state of the cerebral cortex for voluntary movements, we studied the movement-related cortical potentials (Bereitschaftspotential, BP) preceding sequential and goal-directed finger and arm movements in patients with cerebellar atrophy (CA). The first task (paradigm 1) consisted of a sequential finger movement at a self-placed rate of every 3 sec or longer, in which patients and control subjects pushed rapidly 7 keys on a keyboard in a sequence visually predetermined on a screen. The second task (paradigm 2) consisted of a goal-directed self-paced movement with visual feedback on a screen. In both paradigms, control subjects and patients had distinct movement-related cortical potentials, but peak amplitudes (close to movement onset) were reduced in the patient group (paradigm 2), whereas in the overall analysis the mean amplitude 600–800 msec before movement onset (NS1) was larger in the patient group (paradigms 1 and 2). Accordingly, the difference (NS2) between peak amplitude and NS1 was smaller in the patient group (paradigms 1 and 2). Whereas control subjects' peak amplitude (paradigm 2) and NS2 (paradigm 1) were focused at Cz, this topographical differentiation was abolished in the patient group. The onset of the BP was earlier in the patients than in the control subjects (paradigms 1 and 2). Our results suggest that pathways from the cerebellum to the cortex do play a role in generating movement-related cortical potentials. A strong input from the cerebellum seems to be crucial for the generation of a normal motor potential close to the movement onset, reflecting a specific deficit in patients with CA. Patients with CA may try to compensate for their motor deficits by a longer cortical activation preceding voluntary movements (earlier onset of the BP). The increased NS1 could be the result of larger effort, by which patients try to compensate for their motor deficits as well.