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At least 883 records · Page 49Linked to original sources
PubMed1999

Smoothness of human jaw movement during chewing.

Human limb movements are successfully modeled based on the assumption that the central nervous system controls the movements by maximizing movement smoothness. Movement smoothness is quantified by means of a time integral of squared jerk (jerk-cost), where jerk is defined as the rate of change in acceleration. This study was performed to investigate whether the control of human masticatory vertical jaw movements can also be explained by a minimum-jerk (maximum-smoothness) model. Based on the assumption that minimum-jerk models account for vertical jaw-opening and -closing movements during chewing, the actual time profile of the movement trajectory was simulated by the model. The simulated jerk-costs and peak velocities were compared with those obtained by actual measurements of jaw movements during chewing. Jerk-costs and peak velocities of the jaw movements during chewing were significantly correlated with those predicted by minimum-jerk models (P < 0.0001, r between 0.596 and 0.799). The minimum-jerk models predicted closing movement trajectories more accurately than opening movement trajectories (jaw opening, root-mean-square error = 1.19 mm; jaw closing, 0.52 mm, t = 4.375, P < 0.0001). The results indicated that the vertical jaw movement control during chewing was represented by the minimum-jerk control model and that the vertical jaw-closing movement is smoother than the opening movement during gum-chewing.

Adult↗
PubMed1991

Duration, amplitude and shape of accelerations in relation to fetal body movements in behavioral state 2F.

The relationship between fetal movements and fetal heart rate accelerations was analyzed in 34 healthy near term fetuses. Periods of coincidence 2F (C2F) with a mean duration of 34 +/- 6 minutes per fetus were selected, with a total of 463 accelerations. Nineteen percent of single body movements and 71% of compilations of movements were accompanied by an acceleration. The minimal duration of single movements associated with accelerations was 4-5 seconds. Movements with associated accelerations differed significantly in duration from movements without accelerations. The duration of accelerations was strongly correlated with the duration of movements. The amplitude of accelerations was not clearly correlated with the duration of movements, but depended on the type of movement. The shape of accelerations appeared to be dependent on the timing of the various fetal movements. In 77%, the number of notches in the accelerations was equal to the number of pauses in the movement complications. A discrepancy between notches in accelerations and pauses in movements could be explained in the majority of cases when the timing of the various movements in relation to one another was considered, or by the presence of fetal mouth movements.

Computers↗
PubMed1991

[Studies on features of fetal movement and development of human fetus with use of fetal actogram].

In 167 normal fetuses at 26 to 41 weeks of gestation, features of fetal movement and fetal development were investigated with use of actocardiograph in connection with a microcomputer system. The signals of fetal movement obtained by actocardiograph were stored in a floppy disc every 250 ms for 5 minutes through an AD-converter, and were analyzed every 5 minutes with the computer to reveal 3-dimensional (3-D) histograms. The 3-D histogram of fetal movement was composed of number, amplitude and interval of the signals in 11 voltage steps between 0.05 and 0.55V. The histogram clearly indicated state of fetal behavior, being either resting or active state. Fetal movement such as rolling movement, breathing movement and hiccup could be also identified with the computer analysis. In 68 normal fetuses at 14 to 41 weeks of gestation, the cross-correlation between fetal movement and fetal heart rate (FHR) were examined with the computer analysis. Finally fetal responses to acoustic and light stimulation were evaluated with use of pure-tone generator and flashlight. Acoustic stimulation was carried out in 53 normal fetuses at 28 to 41 weeks and light stimulation was performed in 116 normal fetuses at 18 to 41 weeks of gestation. The fetal responses were evaluated with actocardiogram. As a result, 1) Frequency in active state decreased and resting state increased as gestational weeks advanced, and then the frequencies of both state remained constant after 37 weeks of gestation. Duration of resting state also increased from 26 weeks to 37 weeks. These observations may suggest that fetal behavior can be established by 37 weeks of gestation. 2) Frequency in rolling movement decreased until 37 weeks of gestation, and then the movement increased during 38-41 weeks. Frequency in breathing movement increased to 33 weeks of gestation, then it remained constant. Hiccup occurred most frequently at 30-33 weeks, and it decreased thereafter. The function in fetal respiratory movement may be accomplished by 33 weeks of gestation. 3) Positive cross-correlation between fetal movement and FHR was observed as gestational weeks advanced. The correlation coefficient increased from 14 weeks up to 41 weeks. Acceleration of FHR following fetal movement eventually occurred in fetuses at 16 weeks, but the onset of acceleration delayed than normally occurred in developed fetuses. The delay was shortened in fetuses at 24 weeks and this was comparable to the delay in developed fetuses. These results suggest that the linkage of the acceleration of FHR with fetal movement is established at 24 weeks of gestation.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1990

Control of voluntary trunk movements in man. Mechanisms for postural equilibrium during standing.

The relatively large mass of the upper body and its elevated position in relation to the area of support during standing accentuate the importance of an accurate control of trunk movements for the maintenance of equilibrium. This fact has often been emphasized but never studied in detail. In this thesis the kinematics and motor patterns of simple voluntary trunk movements are investigated during standing. The analysis integrates neurophysiology and biomechanics using electromyographic (EMG) and optoelectronic techniques. Both the voluntary (primary movement) and the involuntary (associated postural adjustment) components of the movement are considered. The results demonstrate how the central nervous system (CNS) in its control of equilibrium utilizes biomechanical principles such as mechanical leverage of the different muscles and the interaction of active (muscle force) and passive forces (e.g. gravity and forces in stretched ligaments and/or muscles). Both primary and associated movements were found to be controlled by task specific and flexible muscle synergies which adapt to the mechanical demands of the situation. These task specific synergies were related to the amplitude, velocity and direction of the movement. Slow movements were often initiated through the action of gravity after a decrease or cessation of activity in postural muscles. Fast movements, however, were always initiated by a marked burst of activity in the agonist muscles. Significant relationships were observed between kinematical parameters (amplitude, duration and velocity) of fast trunk movements and temporal aspects of the EMG pattern. Multiple regression analysis indicated that the time to onset of muscle activity braking the ongoing trunk movement contained more information regarding the amplitude of the movement than did the duration of the initiating burst of activity in the prime mover. This supports the view that the initiating agonist burst is preprogrammed, whereas the braking antagonist burst may be influenced by peripheral feedback such as from muscle stretch receptors. In the early phase of a fast trunk flexion an unexpected flexion of the knees was observed. It is suggested that this knee flexion is a fast postural adjustment passively initiated as a mechanical consequence of the activation of muscles controlling the primary movement. This mechanism, which for anatomical reasons cannot act during an extension of the trunk, simplifies the feed-forward control of equilibrium during voluntary trunk flexion movements. For fast trunk extension movements a preactivation of ankle muscles occurred which resulted in a delay in the onset of the prime mover muscles when measured during a simple reaction time task.(ABSTRACT TRUNCATED AT 400 WORDS)

Humans↗
PubMed1989

Movement disorder of premature infants with severe bronchopulmonary dysplasia: a new syndrome.

A previously unrecognized, striking movement disorder has been observed in 10 premature infants with severe bronchopulmonary dysplasia. Chronic hypoxemia, hypercarbia, bronchospasm, and inadequate nutrition were present in all. The movement disorder developed from approximately the third postnatal month. The dominant movements involve the limbs, neck, trunk, and oral-buccal-lingual structures. The limb movements were most prominent distally and consisted of rapid, random, jerky movements (similar to chorea) and "restless" movements (similar to akathisia). Similar movements of the neck and face were observed; tongue movements had a "darting" quality. The oral-buccal-lingual movements were similar to the dyskinesia of older patients. Movements were exacerbated during episodes of respiratory failure and attenuated during sleep. All infants exhibited feeding disorders, largely due to tongue movements. In 3 infants treated with clonazepam, there was striking improvement in motor function, including feeding. The natural history was partial or complete resolution or a static course. Thus, of the 7 surviving infants, the movements were absent (without therapy) at 15, 18, and 30 months of age. In the remaining 4 infants (3 of whom receive clonazepam), the movements, though attenuated, persisted at 6, 12, 15 and 21 months of age, respectively. Neuropathologically, 1 infant showed neuronal loss with astrocytosis in caudate, putamen, globus pallidus, and thalamus. These data defined a previously unrecognized extrapyramidal movement disorder of infants with severe bronchopulmonary dysplasia; pathogenesis may be related to chronic hypoxemia.

Bronchopulmonary Dysplasia↗
PubMed1986

Step-tracking movements of the wrist in humans. I. Kinematic analysis.

We have examined the kinematics of the initial trajectory of step-tracking movements performed by human subjects. Each subject tracked a target that required 5-30 degrees of radial or ulnar deviation of the wrist. All movements were to be performed as accurately as possible. Speed instructions were given before each trial. When subjects performed different amplitude movements following the same speed instruction, the peaks of velocity, acceleration, and jerk were linearly related to peak displacement. The peaks of velocity, acceleration, and jerk also changed when the speed instruction was altered. Thus, for any given movement, the peak values of the derivatives of displacement were dependent on both movement amplitude and intended speed. As a result, the peak values of the derivatives cannot be used by themselves to control or monitor peak displacement. When subjects performed different amplitude movements following the same speed instruction, movement duration tended to remain constant. In contrast, movement duration changed when the speed instruction was altered. Movements performed when subjects intended to move slowly had longer durations than when subjects intended to move quickly. These results suggest that subjects volitionally alter intended speed by selecting different movement durations. When both movement amplitude and intended speed were varied, the peak displacement of a step-tracking movement was linearly related to the product of 2 kinematic variables: the initial peak of a derivative of displacement (either velocity, acceleration, or jerk) and movement duration. On the basis of our observations, we propose that central commands generate step-tracking movements of different amplitudes and intended speeds by adjusting both the magnitude and duration of a derivative of displacement.

Adult↗
PubMed1993

Cerebellar nuclei: rapid alternating movement, motor somatotopy, and a mechanism for the control of muscle synergy.

Monkeys were trained to make rapid alternating flexion and extension movements seriatim at each of five body parts--foot (toe grasp and release), shoulder, elbow, wrist, and thumb. "Facial movements"--mouth, tongue, jaw and pharynx--were also made to drink the fruit juice reward. Movement at a given joint could be performed simply by alternate activation of the prime mover muscle groups, and EMG analysis indicated that these primary muscles were active during movement of that joint. No muscle within any one large body part (leg or arm) was strongly active in relation to movement of another body part. Yet, within a body part (arm), synergist muscles were often more active than the primaries during movement of a given joint, only to become less active during movement of the joint at which their action was primary. Neurons in dentate and interpositus discharged in relation to these movements. In the antero-posterior dimension of both dentate and interposed nuclei, there was a significant tendency for neural modulation to be somatotopically arranged according to the preferred movement: hindlimb anteriormost, forelimb in the middle, and head posteriorly. In the medio-lateral dimension, no such localization was seen for the different movements of the upper limb. Like muscle activity, neural discharge modulation usually occurred in strong relation to a number of movements in a single body part (arm), but not to the movements of different body parts (leg, face). Lesion of the middle third of dentate and of a portion of lateral interpositus had little effect upon the movements at the single joints, and thus upon the prime movers. However, the pattern of activity of agonist, antagonist, and synergist muscles was changed. These results are consistent with the view that the dentate controls muscle synergy and movement coordination more than the prime movers per se.

Animals↗
PubMed2006

Phase II jaw movements and masseter muscle activity during chewing in Papio anubis.

It was proposed that the power stroke in primates has two distinct periods of occlusal contact, each with a characteristic motion of the mandibular molars relative to the maxillary molars. The two movements are called phase I and phase II, and they occur sequentially in that order (Kay and Hiiemae [1974] Am J. Phys. Anthropol. 40:227-256, Kay and Hiiemae [1974] Prosimian Biology, Pittsburgh: University of Pittsburgh Press, p. 501-530). Phase I movement is said to be associated with shearing along a series of crests, producing planar phase I facets and crushing on surfaces on the basins of the molars. Phase I terminates in centric occlusion. Phase II movement is said to be associated with grinding along the same surfaces that were used for crushing at the termination of phase I. Hylander et al. ([1987] Am J. Phys. Anthropol. 72:287-312; see also Hiiemae [1984] Food Acquisition and Processing, London: Academic Press, p. 257-281; Hylander and Crompton [1980] Am J. Phys. Anthropol. 52:239-251, [1986] Arch. Oral. Biol. 31:841-848) analyzed data on macaques and suggested that phase II movement may not be nearly as significant for food breakdown as phase I movement simply because, based on the magnitude of mandibular bone strain patterns, adductor muscle and occlusal forces are likely negligible during movement out of centric occlusion. Our goal is to better understand the functional significance of phase II movement within the broader context of masticatory kinematics during the power stroke. We analyze vertical and transverse mandibular motion and relative activity of the masseter and temporalis muscles during phase I and II movements in Papio anubis. We test whether significant muscle activity and, by inference, occlusal force occurs during phase II movement. We find that during phase II movement, there is negligible force developed in the superficial and deep masseter and the anterior and posterior temporalis muscles. Furthermore, mandibular movements are small during phase II compared to phase I. These results suggest that grinding during phase II movement is of minimal importance for food breakdown, and that most food breakdown on phase II facets occurs primarily at the end of phase I movement (i.e., crushing during phase I movement). We note, however, that depending on the orientation of phase I facets, significant grinding also occurs along phase I facets during phase I.

Animals↗
PubMed1997

The relevance of sensory input for the cerebellar control of movements.

The performance of a motor task not only requires subjects to plan, prepare, and initiate but also to monitor how a movement is performed. We used positron emission tomography to examine to what extent the human cerebellum is involved in controlling motor output or sensory input from movements in normal subjects. In the first study, we compared the active performance of a motor task (flexion and extension of the right elbow) to the passive execution of the same movements. Passive movements were driven by a motor with the arm fixed in a guide hinge. Active movements (compared to rest) elicited increases of rCBF mainly in the ipsilateral neocerebellar hemisphere and vermis of the posterior lobe. During passive movements, almost identical parts of the cerebellar hemispheres and vermis were activated (compared to the rest condition). The direct comparison of active and passive movement conditions revealed a small activation of the neocerebellar hemisphere of the posterior lobe and cerebellar nuclei ipsilateral to the movement. Approximately 90% of cerebellar neuronal activity was related to sensory input. In the second study, we compared the execution of a free selection joystick movement task to a condition in which subjects simply imagined the movements. The execution of movements (compared to rest) was associated with increases of rCBF in the ipsilateral neocerebellar hemisphere and vermis of the posterior lobe. During movement imagination, a small part of the ipsilateral cerebellar hemisphere and vermis of the posterior lobe was activated (compared to rest). The increase of rCBF during movement imagination accounted for only 20% of the signal seen during movement execution. Our results indicate that the neocerebellum may be much more concerned with sensory information processing than has been considered previously.

Adult↗
PubMed2002

The preparation and execution of self-initiated and externally-triggered movement: a study of event-related fMRI.

Studies of functional brain imaging in humans and single cell recordings in monkeys have generally shown preferential involvement of the medially located supplementary motor area (SMA) in self-initiated movement and the lateral premotor cortex in externally cued movement. Studies of event-related cortical potentials recorded during movement preparation, however, generally show increased cortical activity prior to self-initiated movements but little activity at early stages prior to movements that are externally cued at unpredictable times. In this study, the spatial location and relative timing of activation for self-initiated and externally triggered movements were examined using rapid event-related functional MRI. Twelve healthy right-handed subjects were imaged while performing a brief finger sequence movement (three rapid alternating button presses: index-middle-index finger) made either in response to an unpredictably timed auditory cue (between 8 to 24 s after the previous movement) or at self-paced irregular intervals. Both movement conditions involved similar strong activation of medial motor areas including the pre-SMA, SMA proper, and rostral cingulate cortex, as well as activation within contralateral primary motor, superior parietal, and insula cortex. Activation within the basal ganglia was found for self-initiated movements only, while externally triggered movements involved additional bilateral activation of primary auditory cortex. Although the level of SMA and cingulate cortex activation did not differ significantly between movement conditions, the timing of the hemodynamic response within the pre-SMA was significantly earlier for self-initiated compared with externally triggered movements. This clearly reflects involvement of the pre-SMA in early processes associated with the preparation for voluntary movement.

Adult↗
PubMed1996

Vacuous jaw movements induced by acute reserpine and low-dose apomorphine: possible model of parkinsonian tremor.

Coadministration of the monoamine-depleting agent reserpine with a low dose of apomorphine has been shown to result in high levels of vacuous jaw movements in rats. Two experiments were conducted to study the pharmacologic and motoric characteristics of the vacuous jaw movements induced by 5.0 mg/kg reserpine plus 0.1 mg/kg apomorphine. The first experiment was undertaken to determine whether the vacuous jaw movements induced by reserpine plus apomorphine could be reduced by coadministration of the muscarinic antagonist scopolamine. Injections of scopolamine produced a dose-related decrease in vacuous jaw movements induced by reserpine plus apomorphine, with the two highest doses (0.5 and 1.0 mg/kg scopolamine) producing significant differences relative to the control group that received reserpine plus apomorphine. In the second experiment, a slow-motion videotape system was used to study the temporal characteristics of the vacuous jaw movements induced by reserpine and apomorphine, and to study the effects of 1.0 mg/kg scopolamine on these movements. Most of the vacuous jaw movements shown by rats treated with reserpine and apomorphine occurred in rapid bursts of jaw movement. Analysis of the interresponse times (i.e., time between each jaw movement) showed that most of the jaw movements had a local frequency in the range of 2.86-6.67 Hz. Cotreatment with scopolamine significantly affected several measures of jaw movements. Thus, the vacuous jaw movements induced by reserpine plus apomorphine can be reversed by anticholinergic treatment, and these movements tend to occur as periodic oscillations of the lower jaw with a frequency of 3-7 Hz. Vacuous jaw movements in rats share some characteristics with parkinsonian symptoms and may represent an animal model of parkinsonian tremor.

Animals↗
PubMed1988

Head movement co-ordination in the African chameleon.

Chameleon head movement was studied to learn how information from more than one sensory system can be co-ordinated to produce a single motor behavior. In this study, the co-ordination of visual, vestibular, and kinesthetic senses was examined by: (1) moving a cricket back and forth in front of a hungry chamelon, (2) moving the body of an alert chameleon or the body of an anesthetized chameleon, and (3) moving both a cricket and the body of an alert chameleon. During cricket movement, the chameleon locked both eyes straight forward in their orbits and followed the cricket movement with a visually guided head movement. During movement of the body of an alert chameleon, the vestibulo-collic reflex kept the chameleon's head relatively stationary in space. During movement of the body of an anesthetized chameleon, there was no measurable movement of the head relative to the body. Thus, during the body movements used in this study, passively induced kinesthetic stimulation was negligible. It was hypothesized that during movement of both a cricket and the body of an alert chameleon, the visually guided head movement and the vestibulo-collic reflex were additive. This hypothesis was supported by demonstrating that in this situation, the vestibulo-collic reflex was not suppressed. It is suggested that the vestibulo-collic reflex compensated for the passive head movement produced by body movement without canceling active, visually guided head movement. This may have been accomplished by the use of an efference copy system associated with the motor commands that produce visually guided head movement.

Afferent Pathways↗
PubMed2004

Towards an understanding of gait control: brain activation during the anticipation, preparation and execution of foot movements.

While a detailed understanding of brain activity with hand movements has developed, less is known about the functional anatomy of motor control for foot movements. Here we have used fMRI to define brain activity associated with unilateral foot extension and flexion, component movements of gait. We studied brain responses to visually cued active and passive movements and periods of either preparation (before active movement) or anticipation (before passive movement) with a pseudo-randomized block design. A mixed-effects (n = 12) contrast of the active movement condition vs. rest identified brain activation in regions including the medial wall of the primary sensorimotor cortex, consistent with expected somatotopy. Medial wall activation during passive movement vs. rest was less intense and localized to the same region. Frontal and association cortices were more active during preparation or anticipation periods than during the movements themselves. A contrast of preparation to move vs. active movement showed significant activation in the medial frontal and frontopolar gyri and the precuneus. Contrast of the anticipation of movement with the passive movement condition revealed activation in the dorsal premotor cortex and precuneus. Our study thus provides evidence for somatotopy in multiple functional regions in the motor control network. The anterior prefrontal activity is involved in the preparation for cued movement with distinct regions of the medial motor cortex (including SMA and CMA) preferentially involved in motor program planning and execution. This direct characterization of brain activation patterns associated with foot movements promises use of fMRI for the functional analysis of pathologies of gait.

Adult↗
PubMed2001

The preparation and execution of saccadic eye and goal-directed hand movements in patients with Parkinson's disease.

The oculomotor and manual motor systems were studied in a two-segment movement task in a group of patients with Parkinson's disease and in age matched normal controls. In order to avoid reflexive motor movements the selection of the correct motor sequence was derived from the interpretation of symbolic (coloured) cues. The latencies and dynamics of eye and hand (pointing) movements performed during the first (fixed) movement segment were measured and the planning and execution processes were manipulated by varying the complexity of the second movement segment relative to the first (with regard to direction and amplitude). The results showed that the eye and hand movements made by patients with Parkinson's disease were not impaired in the initiation of the first movement segment. Interestingly, both Parkinson's patients and controls showed increased eye and hand reaction time latencies for the first movement when the second movement was in the direction opposite to the first. This indicates that the complexity of the second movement influences the execution of the first movement, and importantly that complexity affects motor initiation and execution processes in both normal subjects and in patients with Parkinson's disease. The execution of hand movements was found to be impaired in patients with Parkinson's disease as indicated by a reduced peak velocity of manual pointing responses when compared to age matched controls. By contrast, no differences were found in the dynamics of saccadic eye movements. This dissociation is consistent with the notion that the skeletomotor loop passes through the functionally corresponding portions of the basal ganglia independently of the oculomotor loop. Together, these results demonstrate that Parkinson's patients are able to generate multiple non-reflexive eye and hand movements and that the observed (manual) motor deficits are specific to the processes of motor execution.

Aged↗
PubMedDate not supplied

Aging and rapid aiming arm movement control.

The authors explored the motor control of target-oriented arm movements across 3 age groups: 20 20- to 30-year-olds, 2 groups (n = 38) of older adults (54 to 64, and 65 to 80). Each individual completed 2 arm movement tasks that had the same movement difficulty but different movement directions. A mixed design was used to examine the differences among age groups and movement directions in reaction time (RT), variability in RT, movement time (MT), timing variability, and inter-segment-interval (ISI). Comparing to the young participants, the senior adults initiated movement tasks slower (RT) and with more RT variability, and executed the arm movements slower and less consistently. The two older groups had greater timing variability in their movements, showed more delays (longer ISI) when reversing arm movement direction, and had lower correlations among segments of the movements than the younger group. The quality of the elderly's control of rapid aiming arm movements showed a regression, which suggests a lack of movement planning, resulting in greater use of visual feedback during movement execution.

Adult↗
PubMed1991

Motor function of the monkey globus pallidus. 2. Cognitive aspects of movement and phasic neuronal activity.

In order to study the role of the basal ganglia (BG) in cognitive aspects of movement, we recorded extracellularly from pallidal neurons in conscious monkeys while they performed a sequential wrist movement task consisting of a series of holds and ballistic jumps. The movement sequence had to be performed within specified time restraints and was predictable. We recorded the activity of 297 neurons whose discharges were related to the movement task. The movement-related response was found to be influenced by the contextual setting and by the degree of difficulty of the task in a subgroup of 82 neurons with a clear response to the first ballistic movement. Predictable and easy movements were usually represented by more prominent movement-related responses in 46% of these neurons; 35% of neurons from a different subset of 105 neurons also demonstrated a second phasic response just before the end of the final hold period of the task. This response was also found to be influenced by the predictability of the final hold period, both in its time duration and also by the direction of the following ballistic movement in double jump tasks. These findings were in keeping with a cognitive role for the BG in movement performance. In particular we suggest that the phasic neuronal activity was an internal cue generated by the BG for predictable movements of a subconscious nature which signals the end of a component of movement in a movement sequence. This cue is appropriately timed to terminate sustained neuronal activity in the SMA and to allow the next movement in the sequence to be executed.

Animals↗
PubMed1986

Activity of dentate neurons during arm movements triggered by visual, auditory, and somesthetic stimuli in the monkey.

Single-unit recordings were obtained from 404 neurons in the dentate and interposed nuclei in two monkeys trained to perform simple movements of the elbow in response to three different sensory cues: a light, a tone, and a small, brief perturbation of the trained forearm. Both flexion and extension movements were investigated. Those dentate neurons that showed a clear modulation before the onset of movement (149 of 318 cells recorded) were classified as stimulus related or movement related on the basis of an analysis of the timing of the initial change in discharge. Seventy-one percent of these dentate neurons (106/149) were classified as stimulus related, and 21% (31/149) were classified as movement related. Within the stimulus-related group 87% responded selectively to only one or two of the sensory cues (selective stimulus-related neurons), most often the teleceptive cues, whereas the remaining 13% responded nonselectively to all three cues (nonselective stimulus-related neurons). Interposed neurons, in contrast, showed principally movement-related discharge, and this represented the initial change in discharge in 89% of the neurons. Eleven percent of the interposed cells showed a selective response to the somesthetic cue. The discharge of 28 out of 91 dentate neurons tested with both flexion and extension movements varied with the direction of movement. Few dentate neurons (9%) were found to display any direction sensitivity when considering the discharge preceding the onset of movement, and none of these showed a reciprocal pattern. The discharge of a greater proportion of neurons (24%) was direction sensitive during movement and was occasionally reciprocal. In the same monkeys, however, 78% of the neurons in the neighboring interposed nucleus were direction sensitive, and one-quarter of these displayed reciprocal patterns of discharge. Thus, the discharge of dentate neurons, occurring well in advance of a conditioned movement, cannot specify direction in this simple reaction-time (RT) task. The sensory responses of selective stimulus-related dentate cells ended near the onset of movement but were time locked to the stimulus and not to the movement. When a neuron was responsive to two of the cues the response did not vary with the modality of the stimulus apart from changes in the latency. The initial sensory response was usually followed by later "secondary" changes in discharge that were temporally related to the movement.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2001

Gaze anchoring to a pointing target is present during the entire pointing movement and is driven by a non-visual signal.

A well-coordinated pattern of eye and hand movements can be observed during goal-directed arm movements. Typically, a saccadic eye movement precedes the arm movement, and its occurrence is temporally correlated with the start of the arm movement. Furthermore, the coupling of gaze and aiming movements is also observable after pointing initiation. It has recently been observed that saccades cannot be directed to new target stimuli, away from a pointing target stimulus. Saccades directed to targets presented during the final phase of a pointing movement were delayed until after pointing movement offset ("gaze anchoring"). The present study investigated whether ocular gaze is anchored to a pointing target during the entire pointing movement. In experiment 1, new targets were presented at various times during the duration of a pointing movement, triggered by the kinematics arm moment itself (movement onset, peak acceleration/velocity/deceleration, and offset). Subjects had to make a saccade to the new target as fast as possible while maintaining the pointing movement to the initial target. Saccadic latencies were increased by an amount of time that approximately equaled the remaining pointing time after saccadic target presentation, with the majority of saccades executed after pointing movement offset. The nature of the signal driving gaze stabilization during pointing was investigated in experiment 2. In previous experiments where ocular gaze was anchored to a pointing target, subjects could always see their moving arm, thus it was unknown whether a visual image of the moving arm, an afferent (proprioceptive) signal or an efferent (motor control related) signal produced gaze anchoring. In experiment 2 subjects had to point with or without vision of the moving arm to test whether a visual signal is used to anchor gaze to a pointing target. Results indicate that gaze anchoring was also observed without vision of the moving arm. The findings support the existence of a mechanism enforcing ocular gaze anchoring during the entire duration of a pointing movement. Moreover, such a mechanism uses an internally generated, or proprioceptive, nonvisual signal. Possible neural substrates underlying these processes are discussed, as well as the role of selective attention.

Adolescent↗