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PubMed1998

Coordination of multi-joint arm movements in cerebellar ataxia: analysis of hand and angular kinematics.

Kinematic abnormalities of fast multijoint movements in cerebellar ataxia include abnormally increased curvature of hand trajectories and an increased hand path and are thought to originate from an impairment in generating appropriate levels of muscle torques to support normal coordination between shoulder and elbow joints. Such a mechanism predicts that kinematic abnormalities are pronounced when fast movements are performed and large muscular torques are required. Experimental evidence that systematically explores the effects of increasing movement velocities on movement kinematics in cerebellar multijoint movements is limited and to some extent contradictory. We, therefore, investigated angular and hand kinematics of natural multijoint pointing movements in patients with cerebellar degenerative disorders and healthy controls. Subjects performed self-paced vertical pointing movements with their right arms at three different target velocities. Limb movements were recorded in three-dimensional space using a two-camera infrared tracking system. Differences between patients and healthy subjects were most prominent when the subjects performed fast movements. Peak hand acceleration and deceleration were similar to normals during slow and moderate velocity movements but were smaller for fast movements. While altering movement velocities had little or no effect on the length of the hand path and angular motion of elbow and shoulder joints in normal subjects, the patients exhibited overshooting motions (hypermetria) of the hand and at both joints as movement velocity increased. Hypermetria at one joint always accompanied hypermetria at the neighboring joint. Peak elbow angular deceleration was markedly delayed in patients compared with normals. Other temporal movement variables such as the relative timing of shoulder and elbow joint motion onsets were normal in patients. Kinematic abnormalities of multijoint arm movements in cerebellar ataxia include hypermetria at both the elbow and the shoulder joint and, as a consequence, irregular and enlarged paths of the hand, and they are marked with fast but not with slow movements. Our findings suggest that kinematic movement abnormalities that characterize cerebellar limb ataxia are related to an impairment in scaling movement variables such as joint acceleration and deceleration normally with movement speed. Most likely, increased hand paths and decomposition of movement during slow movements, as described earlier, result from compensatory mechanisms the patients may employ if maximum movement accuracy is required.

Adult↗
PubMedDate not supplied

[A rapid detection of motor block in patients with Parkinson disease during volitional movements of the hand].

INTRODUCTION: An algorithm to study hand movements in patients with Parkinson's disease (PD) who experience temporary, involuntary inability to move a hand have been developed. In literature, this rather engimatic phenomenon has been described in gait, speech, handwriting and tapping, and noted as motor blocks (MB) or freezing episodes. Freezing refers to transient periods in which the voluntary motor activity being attempted by an individual is paused. It is a sudden, unplanned state of immobility that appears to arise from deficits in initiating or simultaneously and sequentially executing movements, in correcting inappropriate movements or in planning movements. The clinical evaluation of motor blocks is difficult because of a variability both within and between individuals and relationship of blocks to time of drug ingestion. In literature the terms freezing, motor block or motor freezing are used in parallel. AIM: In clinical settings classical manifestations of Parkinson's Disease (akinesia, bradykinesia, rigidity, tremor, axial motor performance and postural instability) are typically evaluated. Recently, in literature, new computerized methods are suggested for their objective assessment. We propose monitoring of motor blocks during hand movements to be integrated. For this purpose we have developed a simple method that comprises PC computer, digitizing board and custom made software. Movement analysis is "off line", and the result is the data that describe the number, duration and onset of motor blocks. METHOD: Hand trajectories are assessed during simple volitional self paced point-to-point planar hand movement by cordless magnetic mouse on a digitizing board (Drawing board III, 305 x 457 mm, GTCO Cal Comp Inc), Fig. 1. Testing included 8 Parkinsonian patients and 8 normal healthy controls, age matched, with unknown neurologic motor or sensory disorders, Table 1. Three kinematic indicators of motor blocks: 1) duration (MBT%); 2) onset (t%); and 3) number (N) of MB episodes, allow identification and quantification of motor blocks. Duration of motor blocks (MBT) is defined as the time sequence when (x,y) coordinates do not change their values and is expressed in percentage from the whole movement duration MBT% = MBT/T (%). If during some movements more than one motor block occurs (N > 1) then this movement is decomposed. The whole movement motor block (mbt) is the sum of all motor blocks MBT; during the same movement and expressed in percentage from the whole movement duration mbt% = mbt/T (%). The onset of motor block (t) is determined with the beginning of motor block and expressed in percentage from the whole movement duration: t% = t/T (%). After the determination of kinematic indicators of motor blocks (MBT, N, t) for healthy controls, their mean values are calculated. Statistical package ANOVA is applied to determine statistical significance of the difference between PD patients and mean values from age matched control healthy group. PD patients are then classified into two groups: one group consisting of PD patients with motor blocks and the other without motor blocks, similar to healthy controls. RESULTS: Acquired movements are processed and analyzed. Fig. 2 is an example of hand trajectories. Time course of (x, y) coordinates indicates motor block appearance, Fig. 3. Detailed presentation of kinematic indicators of motor block (MBT, N, t) is in Fig. 4. Intra-subject variability of these parameters is presented in Figs 5, 6 and 7 for patient #3. The results for N show that 45% of all patients #3 movements had none motor blocks (N = 0); 20% had N = 1; 15% had N = 2; 11.5% had N = 3; 5.7% had N = 4; 0.3% had N = 5; 0.7% had N = 6; 0.3% had N = 7 and 1% had N = 8 motor blocks. The results for t% show that 3% of all patients' #3 blocks started at first quarter, 17% started in the second, 36% in the third, and 44% in the last quarter of movement. The results for MBT% show that 14.5% of all movements had MBT% in the range 0-5%; 56% had MBT% 5-10%; 22% had MBT% 10-15%; 5.5% had MBT% 15-20% and 2% had MBT% 20-25%. No block lasted more than 25% from the whole movement duration. Table 2 is the summary of mean variability for kinematic indicators of motor block (N, mbt%, t%) and for the movement duration T during a 7 day-testing of patients #3. The analysis of calculated data for eight tested PD patients revealed a significant difference (p < 0.01) between healthy controls and three PD patients; data on five PD patients were not significantly different (ns). This method clustered 3 PD patients in the group that experience motor blocks, while the rest were in the group without their significant occurrence. DISCUSSION: This algorithm is an additional instrument in classical evaluation of PD patients during their clinical evaluation and treatment. It provides to clinician a rapid feedback on the changes of voluntary hand movements in everyday progress of illness. Furthermore, this method could be of assistance for developing strategies to overcome motor blocks in arm movements at their beginning, as well as for the feedback of the success of drug therapy.

Adult↗
PubMed1982

Compensatory head and eye movements in the frog and their contribution to stabilization of gaze.

Compensatory head movements, recorded in unrestrained frogs, were compared to compensatory eye movements recorded from animals that had their head fixed. Movements were evoked by oscillating the animal in the dark (vestibular stimulation) or in the light in front of an earth-fixed, patterned visual background (combined stimulation) or by rotating vertical black and white bars (optokinetic stimulation) around the stationary animal. Oscillations occurred in the horizontal plane at frequencies between 0.025 and 0.5 Hz. Gain and phase values of head and eye movements, relative to stimulus movements were calculated. Evoked eye movements were limited in amplitude to +/- 3-6 degrees, increasing with the size of the animal. Head movements were limited to +/- 30-40 degrees. Resetting fast-phases of both head and eyes were very rarely observed during sinusoidal stimulation and no eye movements were recorded in the absence of intended head movements. Vestibularly evoked head movements exhibited a frequency-dependent threshold that was not observed for vestibulo-ocular responses. Above threshold, the gain of evoked head responses increased and reached a frequency-dependent plateau at which the system behaved approximately linearly. Within the linear range, gain of vestibularly evoked responses increased with frequency (from 0.04 at 0.025 Hz to 0.75 at 0.5 Hz) and phase lead decreased (from about 80 degrees to 0 degrees). Vestibularly evoked eye movements similarly increased in gain from 0.05 to 0.56 and decreased in phase lead from about 56 degrees to 10 degrees over the same frequency range. Optokinetically evoked head and eye movements had their highest gains (about 0.8 and 0.5) at low constant velocities (less than or equal to 1-4 degrees/S) or frequencies (less than or equal to 0.025 Hz). At higher constant velocities or frequencies the gain dropped. The phase lag increased from close to zero (at 0.025 Hz) to about 60 degrees for the head and to about 20 degrees for the eye movements (at 0.25 Hz). These phase lags are explained by reaction times of the evoked movements of about 600 ms (head) and 200 ms (eyes). Combined stimulation evoked compensatory head movements with gain and phase values that were frequency-independent in the linear range. Head movements compensated for about 80-90% of the imposed gaze shift with a small phase lag (0-10 degrees). Evoked eye movements were found to be large enough in amplitude and fast enough in time to enable a frog to stabilize its gaze exclusively with slow phase compensatory movements for a large variety of frequency and amplitude combinations. The two motor systems controlling movements of the head and the eye are matched in such a way that the non-linearities of the evoked eye movements can compensate for the non-linearities of the evoked head movements.

Animals↗
PubMed2004

Muscle activation patterns in point-to-point and reversal movements in healthy, older subjects and in subjects with Parkinson's disease.

When young, healthy subjects perform rapid point-to-point and reversal movements over a range of distances, the patterns of muscle activation associated with accelerating the limb toward the target are modulated in the same way for both movement tasks. Differences in patterns of muscle activation for these two movement types are not observed until the deceleration phase of the movements. In this study, we first test the hypothesis that healthy, older subjects and subjects with Parkinson's disease will modulate the pattern of muscle activation in the same way during the acceleration phase of point-to-point and reversal elbow movements. Second, we test the hypothesis that healthy, older subjects and subjects with Parkinson's disease exhibit the same relationship in muscle activation patterns between the two movement types that have been observed for the young in the deceleration phase of the movements. Subjects performed point-to-point and reversal movements initiated in the direction of flexion over three distances (36, 54 and 72 degrees) "as fast as possible". Angle, velocity, acceleration and surface EMGs from biceps and triceps were recorded. With respect to the first hypothesis, the EMG, kinetic, and kinematic measures related to the acceleration phase of the movements were modulated in the same way for both movement types in the healthy older subjects. In the Parkinson's disease group, the kinematic and kinetic measures during the acceleration phase of the movements were the same in both movement types; however, the flexor and extensor EMG activation was smaller during reversal movements than during point-to-point movements. With respect to the second hypothesis, in contrast to that found in young subjects, in healthy older subjects, there was no significant difference between the movement types in the flexor EMG activity immediately after the time of peak velocity. This difference between younger and older subjects may be attributed to the fact that older subjects perform both movement types more slowly than do younger subjects. Although subjects with Parkinson's disease also move slowly, the flexor EMG shuts off more abruptly and more completely just after the time of peak velocity during reversal movements than during point-to-point movements. These results show that (1) for healthy subjects, when the task requirements are the same for the two movement types (acceleration phase), muscle activation patterns are modulated in the same way, and (2) both age and disease alter the relationship of muscle activation, kinetics and kinematics between point-to-point and reversal movements.

Aged↗
PubMed1976

Use of an extraretinal signal by monkey superior colliculus neurons to distinguish real from self-induced stimulus movement.

1. In order to see whether cells in the superficial layers of the monkey superior colliculus can differentiate between real stimulus movement and self-induced stimulus movement we compared the discharge of these cells to stimulus movement in front of the stationary eye with stimulus movement generated by eye movements across a stationary stimulus. 2. Most of the cells recorded (65% of 231 cells) responded to stimulus velocities in front of the stationary eye as fast as those occurring during the peak velocity of a saccadic eye movement. Those cells that do respond usually have weak inhibitory regions and tend to have receptive fields further from fovea. 3. Move (61% of 105 cells) of the cells that did respond to rapid stimulus movement did not respond when an eye movement swept the receptive field over a stationary stimulus. 4. About half of these cells differentiated between these stimulus conditions when we used stimuli at least 1 log unit above background illumination; the remaining cells differentiated for stimuli 2 and 3 log units above background. Many cells differentiated between the two stimulus conditions over a wide range of directions of movement and the effect appears with about equal frequency in receptive fields at all distances from the fovea. 5. The differentiation is present for most cells even when the background illumination is reduced, indicating that visual factors are not the cause of the effect on these cells but may modify the response of other cells. 6. The suppression of background activity accompanying eye movements in the light is present following eye movements made in total darkness; the suppression, therefore, must result from an extraretinal signal. 4. The failure of these cells to respond to visual stimulation during eye movements is due to the same extraretinal signal that produces the suppression since a) the cells that show this suppression tend to be those that fail to respond to stimuli during eye movements, b) the time course of the suppression matches the time at which the effects of visual stimulation during an eye movement would reach the colliculus, and c) the cells which differentiate also show a decreased responsiveness to visual stimulation during the time of background suppression. While this extraretinal signal has the characteristics one would expect of a corollary discharge, proprioception as a source of the signal cannot be excluded. 8. Cells which differentiate between the two stimulus conditions usually also show an enhanced response to a visual stimulus in their receptive field when it is to be the target for a saccadic eye movement. These cells in the superior colliculus receive an extraretinal input which permits them to differentiate betweent real stimulus movements and stimulus movements resulting from the monkey's own eye movements. This differentiation would provide an uncontaminated visual movement signal and facilitate the detection of real movement in the environment...

Action Potentials↗
PubMed1991

Three-dimensional trajectory analysis of congenital mirror movements in a single subject.

Mirror movements are involuntary movements executed by one side of the body that occur with voluntary activation of homologous muscles of the other side. Although such movements have been described qualitatively and with surface EMG recordings, the spatial and temporal characteristics of these movements remain relatively unexplored. We studied selected simple and complex upper limb movements in a 20-yr.-old woman with congenital mirror movements and no other neurological disorder. Movements were digitized in three-dimensional space, reconstructed computergraphically, and analyzed numerically and graphically. Mirror movements had smaller amplitudes than did the corresponding voluntary movements, and there was, in general, temporal coupling between mirror and voluntary movements. Nonetheless, mirror movements were not always a perfect mirror image of the corresponding voluntary movements and sometimes differed in timing and trajectory shape from the original movement. Substantially larger mirror movements were elicited by distal than by proximal movements, and mirror movements were enhanced when loads were applied to the hand executing the voluntary movement. These data support the proposal that congenital mirror movements are produced by a partial failure of decussation of the pyramidal tract. We suggest that the variability in the extent to which mirror movements correspond to the voluntary movements is due to propriospinal and descending extrapyramidal input.

Adult↗
PubMed1994

Accuracy of planar reaching movements. I. Independence of direction and extent variability.

This study examined the variability in movement end points in a task in which human subjects reached to targets in different locations on a horizontal surface. The primary purpose was to determine whether patterns in the variable errors would reveal the nature and origin of the coordinate system in which the movements were planned. Six subjects moved a hand-held cursor on a digitizing tablet. Target and cursor positions were displayed on a computer screen, and vision of the hand and arm was blocked. The screen cursor was blanked during movement to prevent visual corrections. The paths of the movements were straight and thus directions were largely specified at the onset of movement. The velocity profiles were bell-shaped, and peak velocities and accelerations were scaled to target distance, implying that movement extent was also programmed in advance of the movement. The spatial distributions of movement end points were elliptical in shape. The major axes of these ellipses were systematically oriented in the direction of hand movement with respect to its initial position. This was true for both fast and slow movements, as well as for pointing movements involving rotations of the wrist joint. Using principal components analysis to compute the axes of these ellipses, we found that the eccentricity of the elliptical dispersions was uniformly greater for small than for large movements: variability along the axis of movement, representing extent variability, increased markedly but nonlinearly with distance. Variability perpendicular to the direction of movement, which results from directional errors, was generally smaller than extent variability, but it increased in proportion to the extent of the movement. Therefore, directional variability, in angular terms, was constant and independent of distance. Because the patterns of variability were similar for both slow and fast movements, as well as for movements involving different joints, we conclude that they result largely from errors in the planning process. We also argue that they cannot be simply explained as consequences of the inertial properties of the limb. Rather they provide evidence for an organizing mechanism that moves the limb along a straight path. We further conclude that reaching movements are planned in a hand-centered coordinate system, with direction and extent of hand movement as the planned parameters. Since the factors which influence directional variability are independent of those that influence extent errors, we propose that these two variables can be separately specified by the brain.

Adult↗
PubMed2002

The breakdown of Fitts' law in rapid, reciprocal aiming movements.

According to Fitts' law, there is speed-accuracy trade-off in a wide variety of discrete aiming movements. However, it is unknown whether the same law applies to cyclic aiming movements. In the present study, a comparison is made between discrete versus cyclic aiming movements. A group of 24 healthy participants made graphical pen movements in 12 different aiming tasks in which successive finger and wrist movements were emphasized, consecutively executed as discrete and cyclic movements and varying in three target widths. In the cyclic condition, aiming movements consisted of back-and-forth movements that were performed in immediate succession for 20 s. In the discrete condition, back-and-forth aiming movements were drawn as 20 single strokes, starting after a go signal and stopping after reaching the target area. The targets had various levels of spatial accuracy and the movements had different directions (from lower left to upper right; from lower right to upper left) elicit either predominantly wrist or finger movements. The amount of information processed per unit of time (bits per second; index of performance, IP), tangential velocity, the pen pressure, and the ratio of peak-over-mean velocity were studied to gain understanding about the differences in control between discrete and cyclic movements. It was found that the IP and movement velocity were almost twice as large in cyclic versus discrete movements. In contrast, the axial pen pressure and the ratios of peak-over-mean velocity were much lower in cyclic movements (1.24 N versus 0.94 N; 2.26 N versus 1.81 N). The results of our study indicate that the predicted constant IP does not hold for rapid cyclic aiming movements and that speed-accuracy trade-off is different. It is concluded that cyclic movements exploit the energetic and physiological properties of the neuromotor system. Expected differences in brain activity related to discrete and cyclic aiming movements are discussed as well as several neurophysiological mechanisms, which predict more economic force recruitment and information processing in cyclic than in discrete movements.

Adult↗
PubMed2001

The timing of control signals underlying fast point-to-point arm movements.

It is known that proprioceptive feedback induces muscle activation when the facilitation of appropriate motoneurons exceeds their threshold. In the suprathreshold range, the muscle-reflex system produces torques depending on the position and velocity of the joint segment(s) that the muscle spans. The static component of the torque-position relationship is referred to as the invariant characteristic (IC). According to the equilibrium-point (EP) hypothesis, control systems produce movements by changing the activation thresholds and thus shifting the IC of the appropriate muscles in joint space. This control process upsets the balance between muscle and external torques at the initial limb configuration and, to regain the balance, the limb is forced to establish a new configuration or, if the movement is prevented, a new level of static torques. Taken together, the joint angles and the muscle torques generated at an equilibrium configuration define a single variable called the EP. Thus by shifting the IC, control systems reset the EP. Muscle activation and movement emerge following the EP resetting because of the natural physical tendency of the system to reach equilibrium. Empirical and simulation studies support the notion that the control IC shifts and the resulting EP shifts underlying fast point-to-point arm movements are gradual rather than step-like. However, controversies exist about the duration of these shifts. Some studies suggest that the IC shifts cease with the movement offset. Other studies propose that the IC shifts end early in comparison to the movement duration (approximately, at peak velocity). The purpose of this study was to evaluate the duration of the IC shifts underlying fast point-to-point arm movements. Subjects made fast (hand peak velocity about 1.3 m/s) planar arm movements toward different targets while grasping a handle. Hand forces applied to the handle and shoulder/elbow torques were, respectively, measured from a force sensor placed on the handle, or computed with equations of motion. In some trials, an electromagnetic brake prevented movements. In such movements, the hand force and joint torques reached a steady state after a time that was much smaller than the movement duration in unobstructed movements and was approximately equal to the time to peak velocity (mean difference < 80 ms). In an additional experiment, subjects were instructed to rapidly initiate corrections of the pushing force in response to movement arrest. They were able to initiate such corrections only when the joint torques and the pushing force had practically reached a steady state. The latency of correction onset was, however, smaller than the duration of unobstructed movements. We concluded that during the time at which the steady state torques were reached, the control pattern of IC shifts remained the same despite the movement block. Thereby the duration of these shifts did not exceed the time of reaching the steady state torques. Our findings are consistent with the hypothesis that, in unobstructed movements, the IC shifts and resulting shifts in the EP end approximately at peak velocity. In other words, during the latter part of the movement, the control signals responsible for the equilibrium shift remained constant, and the movement was driven by the arm inertial, viscous and elastic forces produced by the muscle-reflex system. Fast movements may thus be completed without continuous control guidance. As a consequence, central corrections and sequential commands may be issued rapidly, without waiting for the end of kinematic responses to each command, which may be important for many motor behaviours including typing, piano playing and speech. Our study also illustrates that the timing of the control signals may be substantially different from that of the resulting motor output and that the same control pattern may produce different motor outputs depending on external conditions.

Adult↗
PubMed2002

Dopaminergic and cholinergic stimulation of the ventrolateral striatum elicit rat jaw movements that are funnelled via distinct efferents.

It has been reported that two distinct types of jaw movements can be elicited by bilateral injections of drugs into the ventrolateral striatum: (1) dopamine receptor-mediated jaw movements that are elicited by a mixture of (+/-)-6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol (SKF 82958; 5 microg) and quinpirole (10 microg), and (2) acetylcholine receptor-mediated jaw movements that are elicited by carbachol (2.5 microg). In the present study, electromyographic analysis was used to characterise these movements: the dopamine receptor-mediated jaw movements were marked by a dominant digastric activity during jaw opening and a dominant masseter activity during jaw closing (digastric/masseter type), whereas the acetylcholine receptor-mediated jaw movements were marked by a dominant digastric activity during jaw opening without any significant change in masseter activity during jaw closing (digastric type). The main goal was to (in)validate the hypothesis that these two types of jaw movements are funnelled via distinct gamma-aminobutyric acid (GABA)ergic output channels. Bilateral injections of both muscimol (25 and 50 ng/0.2 microl per side) and bicuculline (50 and 150 ng/0.2 microl per side) into the ventral pallidum, entopeduncular nucleus or dorsolateral part of the substantia nigra pars reticulata essentially inhibited dopamine receptor-mediated jaw movements to various degrees. In contrast, acetylcholine receptor-mediated jaw movements were inhibited by muscimol given into the entopeduncular nucleus and dorsolateral part of the substantia nigra pars reticulata, whereas these movements were enhanced by bicuculline. The acetylcholine receptor-mediated jaw movements were not affected by muscimol injections into the ventral pallidum, but were inhibited by bicuculline injections. Studies on such injections into the ventral pallidum, entopeduncular nucleus or dorsolateral part of the substantia nigra pars reticulata of naive rats revealed that jaw movements of the digastric/masseter type were elicited either by muscimol injections into the dorsolateral part of the substantia nigra pars reticulata or by combined injections of muscimol and bicuculline into the entopeduncular nucleus, and that jaw movements of the digastric type were elicited only by combined injections of muscimol and bicuculline into the entopeduncular nucleus. Together, the data allow the conclusion that dopamine receptor-mediated and acetylcholine receptor-mediated jaw movements are two distinct types of jaw movements that are funnelled via separate GABAergic output channels. It is suggested that the three different profiles of responses to GABAergic drugs in animals showing either dopamine receptor-mediated or acetylcholine receptor-mediated jaw movements reflect the involvement of three distinct types of output neurons of the striatum, namely: type I neurons with collateralised axons to the ventral pallidum, entopeduncular nucleus and dorsolateral part of the substantia nigra pars reticulata, mediating the dopamine receptor-mediated jaw movements; type II neurons with collateralised axons to the globus pallidus that, in turn, project to the entopeduncular nucleus and the dorsolateral part of the substantia nigra pars reticulata, mediating directly the acetylcholine receptor-mediated jaw movements; and type III neurons with a single axon to the ventral pallidum, mediating indirectly the acetylcholine receptor-mediated movements. It is evident that future studies are required to provide direct evidence in favour of the latter hypothesis.

Animals↗
PubMed2000

Neurophysiological aspects of eye and eyelid movements during blinking in humans.

The neural relationships between eyelid movements and eye movements during spontaneous, voluntary, and reflex blinking in a group of healthy subjects were examined. Electromyographic (EMG) recording of the orbicularis oculi (OO) muscles was performed using surface electrodes. Concurrently, horizontal and vertical eye positions were recorded by means of the double magnetic induction (DMI) ring method. In addition, movement of the upper eyelid was measured by a specially designed search coil, placed on the upper eyelid. The reflex blink was elicited electrically by supraorbital nerve stimulation either on the right or the left side. It is found that disconjugate oblique eye movements accompany spontaneous, voluntary as well as reflex blinking. Depending on the gaze position before blinking, the amplitude of horizontal and vertical components of the eye movement during blinking varies in a systematic way. With adduction and downward gaze the amplitude is minimal. With abduction the horizontal amplitude increases, whereas with upward gaze the vertical amplitude increases. Unilateral electrical supraorbital nerve stimulation at low currents elicits eye movements with a bilateral late component. At stimulus intensities approximately two to three times above the threshold, the early ipsilateral blink reflex response (R(1)) in the OO muscle can be observed together with an early ipsilateral eye movement component at a latency of approximately 15 ms. In addition, during the electrical blink reflex, early ipsilateral and late bilateral components can also be identified in the upper eyelid movement. In contrast to the late bilateral component of upper eyelid movement, the early ipsilateral component of upper eyelid movement appears to open the eye to a greater degree. This early ipsilateral component of upper eyelid movement occurs more or less simultaneously with the early eye movement component. It is suggested that both early ipsilateral movements following electrical stimulation do not have a central neural origin. Late components of the eye movements slightly precede the late components of the eyelid movement. Synchrony between late components of eyelid movements and eye movements as well as similarity of oblique eye movement components in different types of blinking suggest the existence of a premotor neural structure acting as a generator that coordinates impulses to different subnuclei of the oculomotor nucleus as well as the facial nerve nucleus during blinking independent from the ocular saccadic and/or vergence system. The profile and direction of the eye movement rotation during blinking gives support to the idea that it may be secondary to eyeball retraction; an extra cocontraction of the inferior and superior rectus muscle would be sufficient to explain both eye retraction and rotation in the horizontal vertical and torsional planes.

Adult↗
PubMedDate not supplied

A neural model of cortico-cerebellar interactions during attentive imitation and predictive learning of sequential handwriting movements.

Much sensory-motor behavior develops through imitation, as during the learning of handwriting by children. Such complex sequential acts are broken down into distinct motor control synergies, or muscle groups, whose activities overlap in time to generate continuous, curved movements that obey an inverse relation between curvature and speed. How are such complex movements learned through attentive imitation? Novel movements may be made as a series of distinct segments, but a practiced movement can be made smoothly, with a continuous, often bell-shaped, velocity profile. How does learning of complex movements transform reactive imitation into predictive, automatic performance? A neural model is developed which suggests how parietal and motor cortical mechanisms, such as difference vector encoding, interact with adaptively timed, predictive cerebellar learning during movement imitation and predictive performance. To initiate movement, visual attention shifts along the shape to be imitated and generates vector movement using motor cortical cells. During such an imitative movement, cerebellar Purkinje cells with a spectrum of delayed response profiles sample and learn the changing directional information and, in turn, send that learned information back to the cortex and eventually to the muscle synergies involved. If the imitative movement deviates from an attentional focus around a shape to be imitated, the visual system shifts attention, and may make an eye movement, back to the shape, thereby providing corrective directional information to the arm movement system. This imitative movement cycle repeats until the cortico-cerebellar system can accurately drive the movement based on memory alone. A cortical working memory buffer transiently stores the cerebellar output and releases it at a variable rate, allowing speed scaling of learned movements which is limited by the rate of cerebellar memory readout. Movements can be learned at variable speeds if the density of the spectrum of delayed cellular responses in the cerebellum varies with speed. Learning at slower speeds facilitates learning at faster speeds. Size can be varied after learning while keeping the movement duration constant (isochrony). Context-effects arise from the overlap of cerebellar memory outputs. The model is used to simulate key psychophysical and neural data about learning to make curved movements, including a decrease in writing time as learning progresses; generation of unimodal, bell-shaped velocity profiles for each movement synergy; size and speed scaling with preservation of the letter shape and the shapes of the velocity profiles; an inverse relation between curvature and tangential velocity; and a Two-Thirds Power Law relation between angular velocity and curvature.

Attention↗
PubMed1992

Role of primate basal ganglia and frontal cortex in the internal generation of movements. I. Preparatory activity in the anterior striatum.

The purpose of these studies was to investigate neuronal activity in the basal ganglia and frontal cortex in relation to the internal generation of goal-directed movements. Monkeys performed goal-directed arm movements at a self-chosen moment in the absence of phasic stimuli providing external temporal reference. They were rewarded with a small morsel of food for each movement, although automatic or repetitive behavior was not reinforced. For reasons of comparison, animals were also trained in a delayed go no-go task in which visual cues instructed them to perform or refrain from an arm movement reaction to a subsequent trigger stimulus. This report describes the activity of neurons in the head of the caudate nucleus and rostral putamen preceding self-initiated arm movements and compares it with instruction-induced preparatory activity preceding movements in the delay task. A total of 497 caudate and 354 putamen neurons were tested in the delay task. Two types of preparatory activity were observed: (1) transient responses to the instruction cue, and (2) sustained activity preceding the trigger stimulus or movement onset. Transient responses were found in 48 caudate and 50 putamen neurons, occurring twice as often in movement ('go') as compared to no-movement ('no-go') trials, but rarely in both. These responses may code the information contained in the instruction relative to the forthcoming behavioral reaction. Sustained activity began after instruction onset and lasted until the trigger stimulus or the arm movement occurred, this being for periods of 2-7 s, 12-35 s, or up to 80 s, depending on the task requirements. This activity was seen in 47 caudate and 45 putamen neurons, was largely confined to go trials, and was unrelated to the preparation of saccadic eye movements. In some cases, this activity began as direct responses to the instruction stimulus, but in the majority of cases developed more gradually before the movement. Thus, both transient and sustained activations appear to be related to the preparation of movements. A total of 390 caudate and 293 putamen neurons were tested during self-initiated movements. Activity preceding earliest movement-related muscle activity was found in 32 caudate and 42 putamen neurons. This premovement activity began 0.5-5.0 s before movement onset (median 1160 ms), increased slowly, reached its peak close to movement onset, and subsided rapidly thereafter. It was unrelated to the preparation of saccadic eye movements. Comparisons between the two tasks were made on 53 neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Rapid goal-directed elbow flexion movements: limitations of the speed control system due to neural constraints.

In rapid goal-directed elbow flexion movements the influence of both movement amplitude and inertial load on the three-burst pattern and the consequences on movement time were studied. Subjects performed visually guided, self-paced movements as rapidly and as accurately as possible. An increase of both the movement amplitude and the inertial load were found to be interacting factors for the modulation of the three-burst-pattern and movement time. The first biceps burst progressively increased in duration and amplitude for larger movements, resulting in prolonged movement times. Surplus inertial loads further prolonged the agonist burst for large, but not for small movement amplitudes. The activity of the antagonist burst, in contrast, was largest in small movements and successively decreased at increasing movement amplitudes. Its duration, however, remained fairly constant. As was similarly observed for the agonist burst, surplus inertial loads lead to a prolongation of antagonist burst duration and an small movement amplitudes. It is suggested that in elbow flexion movements the programming of fastest goal-directed movements must take into account neural constraints and biomechanical characteristics of the agonist muscle and the antagonist muscle. Due to neural constraints of the biceps muscle, in contrast to finger movements, the concept of movement time invariance does not hold for elbow movements. Furthermore, neural constraints of the antagonist muscle lead to a limited force production of the agonist muscle at small movement amplitudes in order to avoid an overload of the braking process.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1997

Pallidal discharge related to the kinematics of reaching movements in two dimensions.

Movement-related discharge of neurons in the internal and external segments of the globus pallidus (GPi and GPe, respectively) of two monkeys was studied during reaching movements in a two-dimensional work-space. Discharge was studied during movements to targets in eight directions and at three distances from the starting position under three behavioral conditions that manipulated target visibility and movement triggering. A total of 73 neurons (57 in GPe and 18 in GPi) with changes in discharge in concert with arm movements were included in a quantitative analysis. Of these, 83% also changed their discharge during manipulation of the contralateral arm outside of the task. Although 73% of changes in discharge began before the initiation of movement, they seldom preceded the initial activity of the antagonist muscles. Decreases in discharge were more common than reported previously, constituting 40% of the changes in discharge detected. In GPi neurons, decreases also tended to begin earlier than increases. Changes in discharge in GPe neurons were of larger magnitude than those in GPi, and increases in discharge were larger than decreases. Onsets of changes in discharge were temporally linked to movement onset in 69% of neurons. Time locking of neural onset to trigger presentation and movement termination was found in only 30 and 1% of neurons, respectively. Direction of movement influenced the magnitude of changes in discharge in 78% of cells. Directional modulations were broadly tuned and preferred directions were uniformly distributed across the range of directions. When directional modulations were large, preferred directions were consistent for different amplitudes of movement and for different behavioral conditions. Amplitude of movement influenced the magnitude of changes in discharge in 78% of cells, and in 80% of cases that relation had a significant linear component. Amplitude effects were not more common or stronger for movements in directions close to a cell's preferred direction. Linear relations to movement amplitude were more common and accounted for more of the trial-to-trial variance in discharge rate than relations to either average velocity or movement duration. The relation to movement amplitude was consistent for two behavioral conditions when the change in discharge was scaled strongly with movement amplitude. Movement-related changes in discharge of neurons in the skeletomotor portions of both pallidal segments reflect the kinematics of movement. This information, encoded in combination with sensory and contextual information, may play an on-line role in the selective facilitation and suppression of different frontal thalamocortical circuits.

Action Potentials↗
PubMed1998

Motor subcircuits mediating the control of movement velocity: a PET study.

The influence of changes in the mean velocity of movement on regional cerebral blood flow (rCBF) was studied using positron emission tomography (PET) in nine healthy right-handed adults while they performed a smooth pursuit visuomanual tracking task. Images of relative rCBF were obtained while subjects moved a hand-held joystick to track the movement of a target at three different rates of a sinusoidal displacement (0.1, 0.4, and 0.7 Hz). Significant changes in rCBF between task conditions were detected using analysis of variance and weighted linear contrasts. The kinematics of arm and eye movements indicated that subjects performed tasks in a similar manner, particularly during the faster two tracking conditions. Significant increases in rCBF during arm movement (relative to an eye tracking only control condition) were detected in a widespread network of areas known for their involvement in motor control. The activated areas included primary sensorimotor (M1S1), dorsal and mesial premotor, and dorsal parietal cortices in the left hemisphere and to a lesser extent the sensorimotor and superior parietal cortices in the right hemisphere. Subcortically, activations were found in the left putamen, globus pallidus (GP), and thalamus, in the right basal ganglia, and in the right anterior cerebellum. Within the cerebral volume activated with movement, three areas had changes in rCBF that correlated positively with the rate of movement: left M1S1, left GP, and right anterior cerebellum. No movement-related sites had rCBF that correlated negatively with the rate of movement. Regressions of mean percent change (MPC) in rCBF onto mean hand velocity yielded two nonoverlapping subpopulations of movement-related loci, the three sites with significant rate effects and regression slopes steeper than 0.17 MPC.cm-1.s-1 and all other sites with nonsignificant rate effects and regression slopes below 0.1 MPC.cm-1. s-1. Moreover, the effects of movement per se and of movement velocity varied in magnitude independently. These results confirm previous reports that movement-related activations of M1S1 and cerebellum are sensitive to movement frequency or some covarying parameter of movement. The activation of GP with increasing movement velocity, not described in previous functional-imaging studies, supports the hypothesis that the basal ganglia motor circuit may be involved preferentially in controlling or monitoring the scale and/or dynamics of arm movements. The remaining areas that were activated equally for all movement rates may be involved in controlling higher level aspects of motor control that are independent of movement dynamics.

Aged↗
PubMed1997

Training and generalized production of wh- and NP-movement structures in agrammatic aphasia.

The present research examines production of "complex" sentences, which involve movement of noun phrases (NPs), in 2 agrammatic aphasic subjects. According to linguistic theory (Chomsky, 1991, 1993), such sentences are derived using one of two movement operations, either wh- or NP-movement, subsumed under the general rule "move alpha." In this experiment recovery of both wh- and NP-movement derived sentences was investigated using a treatment research paradigm. Subjects were sequentially trained to produce either wh-movement (i.e., who questions, object clefts) or NP-movement (i.e., passives, subject-raising structures) derived sentences. Throughout training, generalization to untrained sentences relying on both types of movement was tested. The influence of training on aspects of narrative discourse also was examined. Results showed generalization patterns constrained to type of movement. Training wh-movement structures resulted in generalized production of untrained wh-movement structures without influencing production of NP-movement structures. Similarly, training of NP-movement structures resulted in generalization only to other sentence types also relying on NP-movement. Aspects of sentence production in narrative contexts also was improved with treatment. These data indicate that movement to an argument (A) position as in NP-movement is distinct from movement to a non-argument (A-bar) position, required in wh-movement. The site where movement terminates in the s-structure of noncanonical sentences appears to influence sentence production. These findings show that linguistic properties of sentences influence sentence production breakdown and recovery in aphasia.

Aphasia, Broca↗
PubMed1998

A fiberscopic analysis of velopharyngeal movement before and after primary palatoplasty in cleft palate infants.

There have been few studies done on the abnormal function of velopharyngeal muscles in unrepaired cleft palate infants. To examine and assess velopharyngeal movement before primary palatoplasty offers supposedly any valuable information for the successful operation and the restoration of excellent velopharyngeal function. We designed to investigate and analyze velopharyngeal movement before and after primary palatoplasty in 26 cleft palate infants with a fine nasopharyngeal fiberscope. We found three different patterns of velopharyngeal movement in unrepaired cleft palate infants when crying or strangulation reflex occurred: (1) posterior movement type (10 cases, 38.5 percent), where the soft palates moved only posteriorly and cephalically and did not move medially; (2) medial movement type (10 cases, 38.5 percent), where the soft palates moved only medially and did not move posteriorly or cephalically; and (3) posteromedial movement type (6 cases, 23.0 percent), where the soft palates moved both posteriorly and cephalically as well as medially. Postoperative velopharyngeal closure was classified into three patterns: (1) the soft palate type, in which the soft palate mainly operates; (2) the lateral wall type, in which compensational medial movement of the lateral pharyngeal wall is mainly observed; and (3) the mixed type, in which both the soft palate and the lateral pharyngeal wall operate. Also, we demonstrated a close relationship between velopharyngeal movement before and after primary palatoplasty in cleft palate infants. In total, 10 of 16 cleft palate infants with the posterior movement type or posteromedial movement type, in which posterior movement of the soft palates was observed before primary palatoplasty, postoperatively showed the soft palate type of velopharyngeal closure. On the other hand, only 2 of 10 cleft palate infants with the medial movement type, in which the soft palates did not move posteriorly but medially before primary palatoplasty, postoperatively showed the soft palate type of velopharyngeal closure. The Fisher's exact probability test clarified that cleft palate infants with the posterior movement type or posteromedial movement type were more likely to show postoperatively the soft palate type of the velopharyngeal closure compared with those with the medial movement type (p = 0.051). This is the first trial to examine velopharyngeal movement in unrepaired cleft palate infants. Our findings indicate the probability that velopharyngeal closure mechanism in repaired cleft palate infants is able to be predicted by velopharyngeal movement behavior before primary palatoplasty. Next, we must clarify a correlation between preoperative velopharyngeal movement and postoperative velopharyngeal function and speech outcome.

Cleft Lip↗