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PubMed2005

Corticospinal excitability is lower during rhythmic arm movement than during tonic contraction.

Humans perform rhythmic, locomotor movements with the arms and legs every day. Studies using reflexes to probe the functional role of the CNS suggest that spinal circuits are an important part of the neural control system for rhythmic arm cycling and walking. Here, by studying motor-evoked potentials (MEPs) in response to transcranial magnetic stimulation (TMS) of the motor cortex, and H-reflexes induced by electrical stimulation of peripheral nerves, we show a reduction in corticospinal excitability during rhythmic arm movement compared with tonic, voluntary contraction. Responses were compared between arm cycling and tonic contraction at four positions, while participants generated similar levels of muscle activity. Both H-reflexes and MEPs were significantly smaller during arm cycling than during tonic contraction at the midpoint of arm flexion (F = 13.51, P = 0.006; F = 11.83, P = 0.009). Subthreshold TMS significantly facilitated the FCR H-reflex during tonic contractions, but did not significantly modulate H-reflex amplitude during arm cycling. The data indicate a reduction in the responsiveness of cells constituting the fast, monosynaptic, corticospinal pathway during arm cycling and suggest that the motor cortex may contribute less to motor drive during rhythmic arm movement than during tonic, voluntary contraction. Our results are consistent with the idea that subcortical regions contribute to the control of rhythmic arm movements despite highly developed corticospinal projections to the human upper limb.

Adaptation, Physiological↗

PubMed2006

Central resetting of neuromuscular steady states may underlie rhythmical arm movements.

Changing the steady-state configuration of the body or its segments may be an important function of central pattern generators for locomotion and other rhythmical movements. Thereby, muscle activation, forces, and movement may emerge following a natural tendency of the neuromuscular system to achieve the current steady-state configuration. To verify that transitions between different steady states occur during rhythmical movements, we asked standing subjects to swing one or both arms synchronously or reciprocally at approximately 0.8 Hz from the shoulder joints. In randomly selected cycles, one arm was transiently arrested by an electromagnetic device. Swinging resumed after some delay and phase resetting. During bilateral swinging, the nonperturbed arm often stopped before resuming swinging at a position that was close to either the extreme forward or the extreme backward arm position observed before the perturbation. Oscillations usually resumed when both arms arrived at similar extreme positions when a synchronous bilateral pattern was initially produced or at the opposite positions if the initial pattern was reciprocal. Results suggest that a central generator controls both arms as a coherent unit by producing transitions between its steady state (equilibrium) positions. By controlling these positions, the system may define the spatial boundaries of movement. At these positions, the system may halt the oscillations, resume them at a new phase (as observed in the present study), or initiate a new motor action. Our findings are relevant to locomotion and suggest that walking may also be generated by transitions between several equilibrium configurations of the body, possibly accomplished by modulation and gating of proprioceptive reflexes.

Acoustic Stimulation↗

PubMed1981

Evidence for pattern generator control of the effects of spindle afferent input during rhythmical jaw movements.

The following recordings were made during spontaneous rhythmic jaw movements in the anesthetized guinea pig: jaw movement in the vertical plane, electromyograms from the digastric muscle (a jaw opener), and intracellular recordings from motoneurons and spindle afferent fibers of the jaw-closer muscles. The rapid jaw-opening phase of these rhythmic movements is characterized by a marked increase in activity in the spindle afferent fibers of the jaw-closer muscles and a coincident pronounced hyperpolarization of the membranes of the jaw-closer motoneurons. It is proposed that the excitatory spindle afferent input evoked by passive stretch of the jaw-closer muscles resulting from a centrally programmed contraction of the jaw-opener muscles impinges upon closer motoneurons that have been hyperpolarized as part of te central program. The hyperpolarization inhibits the motoneurons and nullifies the effect of the spindle afferent input thereby assuring relaxation of the closer muscles and an unimpeded rapid jaw-opening movement.

Animals↗

PubMed2006

Loading the limb during rhythmic leg movements lengthens the duration of both flexion and extension in human infants.

Sensory input is critical for adapting motor outputs to meet environmental conditions. A ubiquitous force on all terrestrial animals is gravity. It is possible that when performing rhythmic movements, animals respond to load-related feedback in the same way by prolonging the muscle activity resisting the load. We hypothesized that for rhythmic leg movements, the period (extension or flexion) experiencing the higher load will be longer and vary more strongly with cycle period. Six rhythmic movements were studied in human infants (aged 3-10 mo), each providing different degrees of load-related feedback to the legs during flexion and extension of the limb. Kicking in supine provided similar loads (inertial) during flexion and extension. Stepping on a treadmill, kicking in supine against a foot-plate, and kicking in sitting loaded the legs during extension more than flexion, whereas air-stepping and air-stepping with ankle weights did the opposite. Video, electrogoniometry, surface electromyography, and contact forces were recorded. We showed that load-related feedback could make either the duration of flexion or extension longer. Within the tasks of stepping and kicking against a plate, infants who exerted lower forces showed shorter extensor durations than those who exerted higher forces. Because older babies tend to step with greater force, we wished to rule out the contribution of age. Eight babies (>8 mo old) were studied during stepping, in which we manipulated the amount of weight-bearing. The same effect of load was seen. Hence, the degree of loading directly affects the duration of extension in an incremental way.

Aging↗

PubMed1984

Neural substrates of two different rhythmical vibrissal movements in the rat.

Normal rats show two types of rhythmical vibrissal movement, one synchronized precisely with alpha waves (about 9 Hz) of the thalamocortical system, and the other often synchronized with theta waves (about 7 Hz) of the septohippocampal system. The alpha-synchronized vibrissal movements appear while the rat stands still with a slow respiratory pattern, and are of small amplitude (a fine tremor). The theta-synchronized vibrissal movements appear during exploratory sniffing behavior, and are of large amplitude. Thus, a group of facial motoneurons which constitute the final common pathway for vibrissal movement apparently receive input convergently from these two neural systems. In the present study, we observed the following: (1) the two types of movement rarely, if ever, appeared simultaneously and the same was true of the two brain wave patterns. Topographically, the predominant appearance of the alpha waves was in the frontal (sensorimotor) cortex, whereas that of the theta waves was in the occipital cortex and hippocampus. (2) Bilateral ablation of either the entire neocortex or just its anterior (but not posterior) half eliminated the vibrissal alpha-tremor movement while leaving vibrissal theta-sniffing movement normal. In anterior decorticate rats, the tremor movements started to recover by 1-4 months, and were abolished again by the removal of the remaining posterior cortex. (3) Lesions of the medial septum or the fornix eliminated hippocampal theta waves, but had no effect on vibrissal sniffing movement or alpha wave-vibrissal tremor. (4) Cerebellectomy and, to a lesser extent, pharmacological lesions of the inferior olive slowed, but did not block, alpha waves. In addition, vibrissal tremor movement became intermittent and less vigorous. The same manipulations, however, did not affect theta wave-vibrissal sniffing movement. (5) Harmaline (30 mg/kg, i.p.) did not induce alpha-tremor, which, in combination with the results with cerebellectomy and inferior olive lesions, indicates that alpha-tremor is generated by a neural mechanism that is different from that for harmaline-induced generalized tremor of 10 Hz. These findings confirmed that there exist two patterns of synchrony between vibrissal movement and rhythmical brain activity in the rat, i.e. alpha wave-vibrissal tremor movement and theta wave-vibrissal sniffing movement, and suggest that the two patterns reflect a rhythmical mode of functioning of two different neural systems, probably the thalamocortical and the septohippocampal system, respectively.

Animals↗

PubMed1991

Genioglossus EMG activity during rhythmic jaw movements in the anesthetized guinea pig.

The electromyograph (EMG) activity of the left anterior digastric and the genioglossus muscles was studied in ketamine-anesthetized guinea pigs under 3 separate jaw movement paradigms. The first paradigm has been previously named spontaneous rhythmic jaw movements. These jaw movements occur 1-2 h after the onset of ketamine anesthesia. After spontaneous rhythmic jaw movements began, a single dose of apomorphine caused a new, second jaw movement paradigm to occur, apomorphine-induced rhythmic jaw movements. The final paradigm, cortically-evoked rhythmic jaw movements, was elicited by electrical stimulation of the masticatory area of the cerebral cortex. Genioglossus EMG activity was complex and highly variable in spontaneous rhythmic jaw movements; however, apomorphine-induced jaw movements were characterized by simultaneously occurring rhythmic EMG bursts of approximately 230 ms duration in both the digastric and genioglossus muscles. In 4 of 5 animals, genioglossus muscle activity onset preceded digastric muscle activity onset by approximately 20 ms. These results support the hypothesis that apomorphine-induced rhythmic jaw movements are an analog of lapping in the awake animal. In cortically-evoked rhythmic jaw movements, both digastric and genioglossus EMG activity were time-locked to the cortical electrical stimulation, with an onset latency of approximately 11 ms for the digastric EMG activity and of 16 ms for the genioglossus EMG activity. These results support the hypothesis that both trigeminal and hypoglossal motoneuron pools are closely coupled in certain coordinative movement patterns.

Anesthesia, General↗

PubMed1992

Kinematic adaptations to perturbations as a function of practice in rhythmic drawing movements.

Kinematic adaptations in multijoint rhythmic drawing movements were investigated under unexpected perturbations in friction levels between stylus and writing surface. Changes in coupling and stability properties were assessed as a function of practice level by applying perturbations to subjects' dominant and nondominant limbs. Under nonperturbation and perturbation conditions, joint motions of right-handed subjects were highly coupled in the nondominant limb and uncoupled in the dominant limb. Stability analyses of the kinematic responses in the phase plane showed a relatively higher intrajoint resistance to perturbations in the nondominant limb as compared to the dominant limb for the elbow joint. indicating a decrease in global joint stiffness with practice. These changes in joint coupling and stiffness with practice were not observed for left-handed subjects. In addition, the stability to perturbations in the end-effector (stylus) kinematics was related to the amount of joint coupling in the nondominant limb, whereas in the dominant limb there existed no such coupling. It was concluded that (a) practice changes the responses to perturbations from anatomically specific early in practice to task-specific late in practice, and (b) this shift is related to the stability in the joint phase-plane dynamics, degree of coupling between joint angles, and the decoupling of the dynamics in the intrinsic and extrinsic control spaces.

Journal Article↗

PubMed1996

Autonomy versus forcing in the organization of human rhythmic forearm movements.

In biological systems, obviously dissipative, some injection of muscle force is required in order to sustain rhythmic movement. As the movement frequency increases, the way the muscle-force-to-movement relationship evolves (in timing and amplitude) can be used to characterize some fundamental control properties, including whether the observed system is autonomous or forced. In the case of a simple rhythmic, biological movement (single-joint horizontal forearm movement), this question can be addressed by assuming that the processed electromyographic activity (EMG) is related to the muscle torques. In this case, 2 interesting phenomena can be observed as the frequency increases. The first is that the phase lag between the force and movement remains constant (40 degrees), and the second is that the co-contraction of the agonist and antagonist muscle groups increases with the square of the frequency. These results showed that the contribution of muscle forces to movement organization cannot be regarded in terms of an escapement in an autonomous system, nor in terms of a forcing function in a forced system.

Adult↗

PubMed1984

Masticatory muscle activities during rhythmic jaw movement associated with tooth contact in lightly anesthetized rats.

Rhythmic jaw movements were observed in lightly anesthetized rats when a bitable object was placed between the maxillary and mandibular incisors. To elicit the jaw movements, an initiating stimulus was required. A successful stimulus was to push on the mandible at the incisors in both opening and posterior directions. This may be a suitable movement for studying mastication because of the following properties: (i) The rhythmic jaw movements could not continue without tooth contact. (ii) The timing pattern of the electromyographic activity of the masseter and digastric muscles and the tooth contact was similar to that of human mastication. (iii) Frequency of the movements was independent of hardness of the object placed between the incisors, though oral stimulation easily stopped the movement as did a noxious stimulus applied around the oral cavity. We conclude that peripheral activation, which may be generated by tooth contact, is as essential to the rhythmic jaw movement as central activation.

Anesthesia, General↗

PubMed1996

Resonance Tuning in Rhythmic Arm Movements.

The hypothesis was tested that the preferred frequency of rhythmic movement corresponds to the resonant frequency of the muscle-limb system, as proposed by the hybrid spring-pendulum model (Kugler Turvey, 1987). In contrast to previous studies, the resonant frequency and stiffness of the system were estimated independently, which permitted quantitative predictions of the preferred frequency to be made. Human subjects (N = 5) were asked to oscillate their forearms in the vertical plane at their preferred frequency under conditions of added mass and external spring loading. Subjects also oscillated their arms at frequencies below and above the preferred frequency, which enabled the investigators to estimate the resonant frequency and stiffness of the elbow joint by using the phase transfer method (Viviani, Soechting, Terzuolo, 1976). The preferred frequency corresponded to the resonant frequency of the muscle-limb system under each condition, as predicted. The oscillation amplitude varied inversely with the preferred frequency, which was also predicted. Finally, the internal joint stiffness was modulated so that it matched the impedance of the external springs but was unaffected by added mass. The results are consistent with an autonomous oscillator model that incorporates proprioception about the dynamics of the periphery.

Journal Article↗

PubMed1984

Rhythmic circumnutation movement of the shoots in Phaseolus vulgaris L.

The apex of growing stems in twining plants describes a rhythmic movement in space called circumnutation. By the method of orthogonal projections, the position in space of the apex can be determined constantly. The mathematical analysis of data allowed us to determine that for Phaseolus vulgaris L. (cv. Mangetout Blanc de Juillet) grown under constant illumination and temperature (25 degrees C) the period is about 100 min. This movement has been related to rhythmic changes in the osmotic potential of the cells located in the bending zone of the stem for a constant period. These variations are longitudinally and laterally coordinated. Treatment with a solution of LiCl at 7 X 10(-3) M supplied to the root system induces a lengthening of the period. The effect of the treatment is reversed by K+ ions. From these results we deduce that rhythmic changes of the membranes are implicated in the circumnutation movements of twining plants.

Chlorides↗

PubMed1982

The neuromuscular basis of rhythmic struggling movements in embryos of Xenopus laevis.

Xenopus embryos struggle when restrained. Struggling involves rhythmic movements of large amplitude, in which waves of bending propagate from the tail to the head. Underlying this, electrical activity in myotomal muscles occurs in rhythmic bursts that alternate on either side of a segment. Bursts in ipsilateral segments occur in a caudo-rostral sequence. Curarized embryos can generate motor nerve activity in a struggling pattern in the absence of rhythmic sensory stimulation; the pattern is therefore produced by a central pattern generator.

Animals↗

PubMed1986

Comparison of mandibular movement trajectories and associated patterns of oral muscle electromyographic activity during spontaneous and apomorphine-induced rhythmic jaw movements in the guinea pig.

Vertical and horizontal movements of the lower jaw (mandible) of ketamine-anesthetized guinea pigs were recorded in association with electromyographic (EMG) activity in the anterior digastric, lateral pterygoid, medial pterygoid, and deep masseter muscles during spontaneously occurring rhythmic jaw movements (SRJMs) and during rhythmical jaw movements induced by the intravenous administration of apomorphine (ARJMs). Both ARJMs and SRJMs were near periodic and occurred at frequencies in the 2- to 5-Hz range. However, the profiles of the mandibular movements and associated patterns of jaw muscle EMG activity differed dramatically for SRJMs versus ARJMs. SRJMs were characterized by prominent lateral excursions of the mandible that occurred in association with both the jaw opening and closing movements. The lateral excursions were directed to the left side on some SRJM cycles and to the right side on others. The direction of the lateral component alternated irregularly, but no more than three consecutive cycles with horizontal movements to the same side were observed at any time. Each SRJM cycle was generated by the occurrence of one of two coordinated sequences of EMG activity. One sequence produced right-sided cycles, the other produced left-sided cycles. Each sequence was initiated by an EMG burst in the digastric muscle ipsilateral to the direction of the horizontal excursion of the mandible, followed by EMG bursts in the contralateral digastric, lateral pterygoid, and medial pterygoid muscles. The EMG bursts in the digastrics and contralateral lateral pterygoid muscles were associated with jaw opening and the initial stage of lateral movement. EMG activity in the contralateral medial pterygoid muscle was associated with the onset of closing and a second stage of lateral movement. Masseter muscle activity was also observed during SRJMs, but only in a subset of the animals tested (3 of 12). When present, the masseter activity began well after the onset of jaw closing. No significant horizontal mandibular movements were observed during ARJMs. The mandibular trajectories during opening and closing always remained close to the midline. The opening phase of ARJM cycles was associated with bilaterally synchronized activity in the digastric and lateral pterygoid muscles. The closing phase was associated with bilaterally symmetric activity in the masseter muscles. The medial pterygoid muscles displayed little or no EMG activity during ARJMs. The durations of the EMG bursts recorded in the masseter muscle were correlated with cycle time during SRJMs, as were the burst durations of the digastric and lateral pterygoid muscles during ARJMs.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

The muscle activity paradox during circular rhythmic leg movements.

A cyclist's legs make a simple 360 degrees circular and rhythmic movement, activated by a simple flexion-extension function in a sagittal plane. However, because of the simultaneous combination of leg rotation in the hip, knee and ankle joint with translation of the upper body, the general motion becomes quite complex. This complexity is increased by the anatomical interpretations of EMG readings taken during the pedalling cycle, indicating a high activity of 'flexor' muscles during the downward 'extension' of the leg (0-90 degrees propulsion phase of the pedalling cycle). This calls for an anatomical paradox. In order to verify these interpretations, the activity of six lower limb muscles was measured under field circumstances on nine elite cyclists using a portable EMG data acquisition system and active surface electrodes allowing remote (non-telemetric) monitoring of the cyclists' muscle activity patterns. Measurements were made during a 1000 m submaximal but constant effort and during a 200 m sprint. Confirmation of the anatomical paradox was found in both test circumstances. Analyses of the normalized EMG in combination with torque values of both hip and knee during the pedalling cycle indicate a zero torque at 135 degrees for the knee, while at this same angle the overall extensor activity ends in one leg and starts simultaneously in the other leg (at 315 degrees). Since the propulsion does not continue until 180 degrees, the flexor muscles have to be activated before the extension activity ends in order to generate the continuation of the circular motion until (and beyond) the bottom dead centre (180 degrees).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2006

Modulation of cortically induced rhythmical jaw movements by stimulation of the red nucleus in the rat.

We study whether stimulation of the red nucleus (RN) can modulate rhythmical jaw movements in rats anesthetized by urethane. Rhythmical jaw movements were induced by repetitive electrical stimulation of the two cortical masticatory areas (area A: the orofacial motor cortex; area P: the insular cortex). Stimuli applied to the RN did influence rhythmical jaw movements induced by stimulation of the A-area. Stimuli applied in the jaw-closing phase increased the amplitude of the jaw-closing movement. Stimuli applied in the jaw-opening phase disturbed the rhythm of jaw movements and induced a small jaw-closing movement. Stimuli applied to the RN did not influence rhythmical jaw movements induced by stimulation of the P-area. These results indicate that the RN is involved in the modulation of rhythmical jaw movements induced by stimulation of the A-area.

Animals↗

PubMed1981

Paroxysmal, rhythmic lingual movements and chronic epilepsy.

Paroxysmal and rhythmic lingual movements were observed in three children during a study designed to investigate epileptiform movements of oropharyngeal muscles in patients with chronic epilepsy. The movements were confined to the tongue, occurred mainly during sleep, and were observed again in two children 7 and 18 months later. These movements corresponded to episodic desynchronization of the electroencephalogram and were attributed to an unusual form of subcortical seizures.

Adolescent↗

PubMed1979

Effect of vanadate on rhythmic leaflet movement in albizzia julibrissin.

Vanadate (Na(3)VO(4)) selectively and reversibly affects the rhythmic movement of Albizzia julibrissin leaflets. Leaflets floated on 1 millimolar vanadate open at the same rate or more rapidly than controls, but closure is inhibited. After 6 to 24 hours incubation, the inhibition can be reversed by a 24-to 48-hour period on water or control buffer. Recovery is complete in light-dark cycles, and it is almost complete under free-running conditions (prolonged darkness). Leaflets floated on 10 millimolar vanadate do not open in darkness, but they open at a reduced rate in light. Concentrations of 100 micromolar or less are ineffective.

Journal Article↗

PubMed1989

Angiotensin II-induced rhythmic jaw movements in the ketamine-anesthetized guinea pig.

The EMG activity of the left anterior digastric muscle as well as associated jaw movements were studied in ketamine-anesthetized guinea pigs that had received i.v. infusions of angiotensin II (ANG-II). Rhythmic jaw movements with two distinct movement profiles were associated with ANG-II infusion. One movement profile was typified by vertical jaw opening and closing movements with little or no associated horizontal movement. The second rhythmical jaw movement profile was unlike the first in that jaw closing was accompanied by a significant horizontal deflection of the jaw. Both jaw movement profiles were similar in that little or no horizontal movement occurred during jaw opening. Tongue protrusions were also observed during jaw opening in both cases. The results show that ANG-II induces rhythmic jaw movements in anesthetized guinea pigs. ANG-II-induced jaw movement profiles and digastric muscle EMG activity are similar to those seen after an i.v. injection of apomorphine in the anesthetized guinea pig, and to those associated with lapping in the awake animal.

Anesthesia↗