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At least 145 records · Page 8Linked to original sources
PubMed1971

Apparent movement and real movement detection in the pigeon: stimulus generalization.

Pigeons were trained to discriminate apparent movement and real movement in visual displays showing horizontal movement. Generalization testing on the dimension of directional movement yielded gradients that sloped as movement changed from horizontal to vertical. Evidence of generalization between apparent movement and real movement was found in equivalent response rates to training displays of either type. Extremely low response rates to training displays pulsating but showing no movement eliminated flicker as the basis of the discrimination.

Animals↗
PubMed1987

Sinusoidal movement of a grating across the monkey's fingerpad: representation of grating and movement features in afferent fiber responses.

Gratings of alternating grooves and ridges were moved sinusoidally back and forth across the monkey's fingerpad. Each grating was completely specified by its spatial period and the movement by its peak speed: together these determined the peak temporal frequency at which grating ridges passed over the skin. Responses of cutaneous, mechanoreceptive afferents innervating the fingerpad were characterized in terms of these 3 parameters. Slowly adapting afferents (SAs), rapidly adapting afferents (RAs), and Pacinian afferents (PCs) had different characteristics. The responses (mean cyclic discharge rates) of the SAs increased when the spatial period of the grating increased (and peak speed of movement remained constant) but did not change with changes in the peak speed of the movement (while the spatial period of the grating remained constant). Conversely, the responses of the PCs increased when the peak speed of movement increased (and the spatial period remained constant) but were relatively insensitive to changes in the spatial period of the grating (while the peak speed remained constant). The responses of the RAs increased as the spatial period of the grating increased (and peak speed remained constant) and also increased as the peak speed of movement increased (and the grating spatial period remained constant). When the peak temporal frequency of the grating ridges was held constant, the responses of all 3 afferent groups changed with changes in the grating spatial period or in the peak speed of movement. Information about the spatial features of the grating, independent of the peak speed of movement, was present in the SA population response and in the ratios of the RA and PC population responses. Information about the peak speed of movement, independent of the spatial period of the grating, was present in the PC population response and could be extracted from the RA population response.

Action Potentials↗
PubMed1987

Eye movement responses to combined linear and angular head movement.

Lateral eye movements evoked by linear head motion were evaluated in human subjects by subtracting the eye movement responses to head-centred angular oscillation in the dark, about a vertical axis, from the responses evoked by similar oscillation with the head displaced 30 cm eccentrically from the axis. The centred oscillation gave a purely angular stimulus whereas the eccentric oscillation gave an additional tangential linear acceleration acting laterally to the head. The stimuli used were relatively unpredictable, enveloped sinewaves at 0.02 to 1.2 Hz, 60 degrees/s peak angular velocity, 0.004 to 0.24 g peak tangential acceleration, and subjects were either given no instructions or were told to imagine fixating on targets at 60 cm or 5 m distance. Eye movements of significantly higher velocity were evoked in the eccentric position, particularly at the higher frequencies and when subjects imagined near targets. The increase in velocity of eye movement was attributed to the linear stimulus and probably derives from stimulation of the otolith organs. The frequency response of the gain (degree/s/g) of these movements gave an approximate slope of -1, indicating that the eye velocity bears a constant proportionality to linear head velocity. The findings are in accord with the theoretical prediction that eye movements compensating for linear head motion should only be required for viewing near targets. These otolithic influences on eye movements could either the mediated by a direct "otolith-ocular reflex" which is subservient to viewing conditions, or, alternatively, the otolith signals may modify the activity of other oculomotor mechanisms.

Acceleration↗
PubMed1998

Differences between 'congenital mirror movements' and 'associated movements' in normal children: a neurophysiological case study.

In this study we analysed how far physiological associated movements in normal children (which may be present up to the age of 10 years) share the same physiological mechanism with clinically apparent mirror movements. Transcranial magnetic stimulation (TMS) and kinematic movement analysis were applied in a 4-year-old child with congenital mirror movements (CMM). The results were compared with a normative data base of clinically normal children. In the child with CMM focal TMS of one motor cortex induced bilaterally symmetrical responses in distal and proximal upper extremities muscles with identical ipsi- and contralateral latencies. Also kinematic analysis showed a precise symmetrical onset of intended and unintended contralateral movements, whereas normal children with associated movements showed a variable movement onset delay between extremities. The data suggest a different physiological mechanism underlying these two varieties of elementary associated motor activity in childhood.

Biomechanical Phenomena↗
PubMed2001

Conversion in the requirement of coat protein in cell-to-cell movement mediated by the cucumber mosaic virus movement protein.

Plant viruses have movement protein (MP) gene(s) essential for cell-to-cell movement in hosts. Cucumber mosaic virus (CMV) requires its own coat protein (CP) in addition to the MP for intercellular movement. Our present results using variants of both CMV and a chimeric Brome mosaic virus with the CMV MP gene revealed that CMV MP truncated in its C-terminal 33 amino acids has the ability to mediate viral movement independently of CP. Coexpression of the intact and truncated CMV MPs extremely reduced movement of the chimeric viruses, suggesting that these heterogeneous CMV MPs function antagonistically. Sequential deletion analyses of the CMV MP revealed that the dispensability of CP occurred when the C-terminal deletion ranged between 31 and 36 amino acids and that shorter deletion impaired the ability of the MP to promote viral movement. This is the first report that a region of MP determines the requirement of CP in cell-to-cell movement of a plant virus.

Bromovirus↗
PubMed2001

Discrepancy between dysmetric centrifugal movements and normometric centripetal movements in psychogenic ataxia.

A method to unravel an aberrant motor behaviour in psychogenic ataxia is reported. The kinematic features of fast reaching movements in the vertical plane are described in a patient presenting a psychogenic ataxia. The procedure compared centrifugal and centripetal movements. Path ratios were computed for each phase, as well as the ratios of the paths for centrifugal and centripetal directions. Trajectories of centrifugal phases were erratic but centripetal movements were very regular, whereas both centripetal and centrifugal movements were irregular in patients presenting an organic cerebellar syndrome. A similar incongruity between movements in opposite directions is also shown for a second patient exhibiting psychogenic ataxia. Discrepancies between the centrifugal phase and the centripetal phase of multi-joint reaching movements support the diagnosis of a psychogenic movement disorder.

Adult↗
PubMed1981

[A comparison between orienting rapid eye movements accompanying active or passive head movement in the cat].

Gaze is shifted by means of eye saccades which, in most instances, are synchronized with head rotations. During eye-head movements performed by cats in the dark, most of the rapid eye movements start after the head has begun to move (mean time lag was 45 msec). This pattern resembles that observed when the cat, as a whole, is suddenly rotated passively and consists of a short lasting vestibularly induced slow phase component followed by a rapid eye movement that takes the eye in the same direction as the head. We have compared the passively and actively induced eye-head movements. The rapid eye movements are similar in both cases in that they terminate at a fixed position ("goal") in the orbit irrespective of the eye's starting position. They differ primarily in the fact that the eccentricity of the "goal" during active head rotations increases much more rapidly with velocity than it does during the passive condition. The results suggest that the rapid eye movement that accompanies an active head movement in the dark is not simply a vestibularly induced quick phase.

Animals↗
PubMed1995

A kinematic theory of rapid human movements. Part II. Movement time and control.

This paper describes how a synergy made up of a pair of agonist and antagonist systems involved in the production of a rapid movement can control movement time. A quadratic law is derived to predict the movement time as a function of the various parameters describing the neuromuscular synergy. Conditions for a simplified description of the process, using a power law, are also presented. It is predicted that movement time can be controlled at the input level by the ratio of the agonist to antagonist commands or at the system level by modifying the total log-time delay or the log-response time of the agonist or antagonist neuromuscular networks. Adapting this approach to the specific case of movements executed under different spatial accuracy demands, it is found that movement time is linked to the inverse of the relative spatial error by similar laws. The whole approach is used to explain within a single framework all the observations that have been reported concerning speed/accuracy trade-offs. Strategies for controlling movement amplitude and duration are analyzed, and other predictions dealing with EMG, acceleration patterns, load effects and changes in the asymmetry of the velocity profile are also discussed.

Algorithms↗
PubMed1979

Apparent movement and appearance of periodic stripes during eye movements across a stroboscopically illuminated random dot pattern.

When the eyes follow a small target moving across a stationary random dot pattern illuminated stroboscopically at 3--45 flashes . s-1, the structure of the random dot pattern is seen as moving in the direction of the eye pursuit movements (sigma-movement). At flash frequencies above 9.5 flashes . s-1, periodic stripes oriented perpendicularly to the direction of the pursuit eye movements appear and are also seen as moving in the direction of the eye pursuit movement. The period Ps of the apparent stripes depended on the flash frequency fs and the angular speed of the eyes Ve: Formula: see text. Apparent sigma-movement and apparent stripes were also seen when eye pursuit movements were initiated outside of the random dot pattern and they continued autonomously without a moving target across the pattern. The angular velocity of the sigma-pursuit movement across the random dot pattern depended on the flash frequency and the angular velocity of the initiating target. With the eyes stationary but a moving random dot pattern, the apparent stripes also appeared at flash frequencies fs greater than or equal to 9.5 flashes . s-1. Eq. (1) was valid when Ve was replaced by the target angular velocity Vs (k = 1).

Adult↗
PubMed1983

Finger movement versus toe movement-related potentials: further evidence for supplementary motor area (SMA) participation prior to voluntary action.

The cerebral potentials associated with voluntary, self-paced rapid flexions of (1) right fingers, (2) left fingers, (3) right toes, and (4) left toes were compared in the same experiment using 32 right- and left-handed subjects. The Bereitschaftspotential (BP) or readiness potential was, in the first half of the foreperiod, bilaterally symmetrical for both finger and toe movements of either side. In the later foreperiod there were differences: Finger movements showed two maxima, an early one at Cz and a late one, which was lateralized toward the contralateral precentral region. With toe movements, the maximum BP amplitude was always at Cz and not lateralized and was twice as large as with finger movements. The data are compatible with the view that two principal sources of different spatial and temporal characteristics are active in the foreperiod of a voluntary movement. The early generator is probably the supplementary motor area (SMA) on the mesial surface of the hemispheres; the later is the primary motor cortex (MI) which is lateralized for finger but not for toe movements. In lateral leads, rather remote from the mesial source, the BP for toe movements showed a small but significant ipsilateral preponderance, which is obviously due to the fact that dipole sources located on the mesial surface of the hemispheres point to the opposite direction as compared to those on the convexity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed2004

Posture-based or trajectory-based movement planning: a comparison of direct and indirect pointing movements.

Various models have been proposed in the literature to explain the control of human arm movements. To make a quantitative comparison between the predictions of various models, we tested subjects for movements to targets on a vertical screen in various conditions. Subjects were asked to move directly from one target to another, or to move by a via-point, at various movement velocities and in a condition with a weight of 0.6 kg attached to the forearm. This set of experimental data was used for comparison with the predictions by various posture-based and trajectory-based models on 3-D movement planning and control. Small but significant effects of starting position and path towards the target were found on the torsion of the arm at the end of the movement. No effects of movement velocity and weight attached to the forearm were found. The experimental results differed significantly from the predictions by any of the models considered. Of the models considered, Donders' law best predicts the experimental data. Our data indicate that future tests of models for motor control (1) should compare the predictions of not just one, but several models to a data set, and (2) should include not only planar, but rather 3-D movements in such a comparison.

Acceleration↗
PubMed2004

Keeping with the beat: movement trajectories contribute to movement timing.

Previous studies of paced repetitive movements with respect to an external beat have either emphasised (a) the form of movement trajectories or (b) timing errors made with respect to the external beat. The question of what kinds of movement trajectories assist timing accuracy has not previously been addressed. In an experiment involving synchronisation or syncopation with an external auditory metronome we show that the nervous system produces trajectories that are asymmetric with respect to time and velocity in the out and return phases of the repeating movement cycle. This asymmetry is task specific and is independent of motor implementation details (finger flexion vs. extension). Additionally, we found that timed trajectories are less smooth (higher mean squared jerk) than unpaced ones. The degree of asymmetry in the flexion and extension movement times is positively correlated with timing accuracy. Negative correlations were observed between synchronisation timing error and the movement time of the ensuing return phase, suggesting that late arrival of the finger is compensated by a shorter return phase and conversely for early arrival. We suggest that movement asymmetry in repetitive timing tasks helps satisfy requirements of precision and accuracy relative to a target event.

Acoustic Stimulation↗
PubMed1985

Movement related slow potentials. II. A contrast between finger and foot movements in left-handed subjects.

Finger and foot movement related potentials (MRPs) were recorded over the frontal, central and parietal areas of both hemispheres in 20 left-handed subjects. A unilateral flexion of the index finger and a plantar flexion of the foot were studied on either side. MRPs were larger preceding foot movements than preceding finger movements, their onset being earlier also. Prior to a finger flexion amplitudes were larger over the hemisphere contralateral to the movement than over the ipsilateral hemisphere. Preceding a foot movement, however, amplitudes were larger over the ipsilateral hemisphere. These results indicate differently localized sources of the MRPs in the two kinds of movement, in accordance with data obtained in right-handed subjects. No indication of a hemisphere effect, possibly related to motor dominance, was found in left-handers. This is in contrast to a slight hemisphere effect found with foot movements in right-handed subjects in the former study.

Adolescent↗
PubMed1995

Movement-related cortical potentials in persistent mirror movements.

Mirror movements (MMs) are involuntary movements executed on one side of the body during voluntary movements of the contralateral homologous body parts which may abnormally persist into adulthood. In 6 subjects affected by persistent MM with autosomal dominant inheritance, movement-related cortical potentials (MRCPs) during self-paced, voluntary extensions of either the left or right middle finger were recorded from 30 EEG electrodes simultaneously with the electromyogram (EMG) of both extensor digitorum communis muscles. The negative potentials before and during EMG onset were evaluated statistically for the two electrodes next to the cortical hand areas. A comparison with 7 normal subjects revealed no marked differences for the Bereitschaftspotential (BP) and the negative slope (NS'). Only in the periods around EMG onset (from -50 to +50 msec) a significant difference between both groups was found. The MM subjects showed fairly symmetric potentials over the right and left hemispheres, whereas the potentials of the control subjects were lateralized to the hemisphere contralateral to the intended movement. No difference was found for the amplitude of the maximum negative peak of MRCP following EMG onset. Our data showed no evidence for a different type of movement preparation in MM subjects as compared to normals. We propose that the additional ipsilateral cortical activation around movement onset may be the cortical mechanism, which compensates for abnormal ipsilateral corticospinal pathways in subjects with persistent MM.

Adolescent↗
PubMed2005

Prefrontal cortex activity in self-initiated movements is condition-specific, but not movement-related.

Activity of the prefrontal cortex (PFC) has been observed in previous block-design brain imaging studies of self-initiated movements. However, the meaning of these activations remained unclear. A functional MRI experiment was carried out, which utilized an epoch and an event-related analysis approach to the data. We hypothesized that event-related activity of the PFC would argue for a contribution to movement preparation. In contrast, epoch-, but not event-related activity pointed to tonic activations, probably reflecting enhanced attentional states or working memory processing. Twenty-one subjects were examined with 845 T2*-weighted images. During active phases, subjects were instructed to perform self-initiated movements of the right index finger with intertrial intervals of about 8 s. On single subject level, epoch- and event-related regressors were entered into a combined model, estimating the exclusive contribution of either regressor. For statistical inference on multisubject level, random effects analyses were performed. For the epoch regressor, activity within the right dorso- and ventrolateral prefrontal cortex, the bilateral insula, and the right inferior parietal lobe was observed. The event-related regressor detected activity within the right inferior parietal lobe, ventral from the activity found with the epoch regressor. The present results indicate a condition-, but not a movement-related function of the PFC in self-initiated movements. Furthermore, anatomically distinct regions within the inferior parietal cortex seem to be involved in condition-specific and movement-related processes. The observed condition-specific activations are suggested to reflect attentional or working memory processes, supervising task performance, rather than movement preparation or initiation.

Adult↗
PubMed2005

Cell wall localization of Red clover necrotic mosaic virus movement protein is required for cell-to-cell movement.

The Red clover necrotic mosaic virus movement protein (MP) is essential for cell-to-cell movement. Eight previously characterized alanine-scanning mutants of the MP were fused to the green fluorescent protein (GFP) and expressed from viral infectious transcripts. Inoculated plants were assayed for movement and intracellular accumulation of MP by confocal laser-scanning microscopy. A strict correlation was observed between the targeting to the cell wall (presumably the plasmodesmata) and cell-to-cell movement. Complementation of dysfunctional MP mutants with either wild-type MP or other null mutants in some cases rescued intracellular targeting and movement. The data suggest the presence of distinct domains in the MP for virus movement (near residues 27-31), complementarity (near residues 122 and 128), and intracellular localization (near residue 161). These data support a model of MP interacting cooperatively with itself to bind viral RNA, localize to and modify plasmodesmata and effect virus movement.

Amino Acid Sequence↗
PubMed2000

The role of the supplementary motor area in externally timed movement: the influence of predictability of movement timing.

A significant role in the planning and preparation for voluntary movement has been ascribed to secondary motor areas located on the medial wall of the cerebral hemispheres, and in particular to the supplementary motor area (SMA). Within the SMA, rostral and caudal subdivisions have been described, and differential roles have been attributed to these regions in relation to movement planning, preparation and execution. We have used functional magnetic resonance imaging (fMRI) to investigate the role of the SMA in the timing of movement execution, by recording the fMRI signal from mesial pre-motor areas and primary sensorimotor cortex (SM1) during the execution of a simple motor task externally cued at predictable (regular) and unpredictable (irregular) time intervals. The mean rate of movement was matched in both experiments. There was a greater activation of caudal than rostral SMA with both predictably and unpredictably cued movements, and a doubling of the signal when the timing of the motor response was unpredictable. In contrast, there was no difference in the activation of primary sensorimotor cortex with the two tasks. The data demonstrate that the caudal SMA has an important role in the execution of externally cued movements. The results also suggest a greater role for this region in the performance of unpredictably timed compared with predictably timed movements, however a model is proposed (based on electrophysiological data) which shows how the difference in functional signal in these two situations can be explained on the basis of a difference in the time course of neuronal activation in the SMA, rather than in the overall degree of activation.

Adult↗
PubMed1997

Sensory feedback contributes to early movement-evoked fields during voluntary finger movements in humans.

Neuromagnetic field changes accompanying voluntary movement in humans ('movement-evoked fields' or MEFs) were recorded over the scalp using a whole-head MEG system during the performance of self-paced finger movements in order to determine the contribution of sensory feedback to the generation of these brain responses. It was found that cooling the subject's arm resulted in delays of 8 ms or more in the latency of the early movement-evoked field component (MEFI). These delays were attributed to increases in conduction times in the afferent pathways as confirmed by electrically evoked somatosensory responses and suggest a peripheral origin of the MEFI. In a second experiment, we demonstrated the effects of sensory input to the contralateral hand during a simple button pressing task in 4 subjects. The results indicated that responses over the hemisphere ipsilateral to the side of movement which resembled previously reported ipsilateral MEFs can be elicited by the spread of mechanical stimulation to opposite side of the body when a mechanical trigger is used. These experiments provide further evidence that early movement-evoked fields produced by unilateral finger movements are observed primarily over the contralateral somatosensory cortex and represent sensory feedback to the somatosensory cortex from the periphery.

Arm↗