Right fetal cardiac axis: clinical significance and associated findings

A basic aspect of the neuronal control of bipedal stance and gait represents the antigravity function of leg extensors. Proprioceptive reflexes involved in the maintenance of body equilibrium depend on the presence of contact forces opposing gravity. Extensor load receptors are thought to signal changes of the projection of the body's centre of mass with respect to the feet. According to recent observations in the spinal cat, this afferent input probably arises from Golgi tendon organs and represents a newly discovered function of these receptors in the regulation of stance and gait. In humans, evidence for a significant contribution of the load receptor to leg muscle activation has come from immersion experiments. Compensatory leg muscle activation depends on the actual body weight. Furthermore, recent experiments in paraplegic patients showed that the beneficial effects of a locomotor training critically depends on the initial degree of body unloading and reloading during the course of the training period.     

Treatment of cardiac arrhythmias during pregnancy: safety considerations

Adult spinal cats were trained to perform bipedal hindlimb locomotion on a treadmill for 6-12 wk. After each animal acquired the ability to step, locomotor training was withheld, and stepping was reexamined 6 and 12 wk after training ended. The performance characteristics, hindlimb muscle electromyographic activity patterns, and kinematic characteristics of the step cycle that were acquired with training were largely maintained when training was withheld for 6 wk. However, after 12 wk without training, locomotor performance declined, i.e., stumbling was more frequent, and the ability to consistently execute full weight-bearing steps at any treadmill speed decreased. In addition, the height that the paw was lifted during the swing phase decreased, and a smaller range of extension in the hindlimbs occurred during the E3 phase of stance. When three of the spinal cats underwent 1 wk of retraining, stepping ability was regained more rapidly than when trained initially. The finding that stepping ability in trained adult spinal cats can persist for 6 wk without training provides further evidence that training-induced enhancement of stepping is learned in the spinal cats and that a memory of the enhanced stepping is stored in the spinal networks. However, it appears that the spinal cord can forget how to consistently execute stepping if that task is not practiced for 12 wk. The more rapid learning that occurred with retraining is also consistent with a learning phenomenon. These results in conjunction with our earlier findings suggest that the efficacy of the neural pathways that execute a motor task is highly dependent on the periodic activation of those pathways in a sequence compatible with that motor task.     

Automated high-performance liquid chromatographic determination of hydroxylysylpyridinoline and lysylpyridinoline in urine using a column-switching method

17 right-handed males volunteered for an experiment that compared task-related patterns of electromyographic (EMG) activation with data from muscle biopsy on proportion of slow-twitch ((ST) aerobic) to fast-twitch ((FT) anaerobic) muscle fibers. The biopsy was taken from the right-leg gastrocnemius muscle after EMG measurement from that area of the leg muscle. EMG was also recorded from the left forearm flexor carpi radialis area. Recordings were obtained from pre- and post-task resting periods and during 150 s of video-task performance when the right hand operated a joy-stick. The results showed a highly significant tonic EMG activation in the leg muscle of subjects with predominance of ST fibers, and this relationship generalized to the EMG from the 'passive' forearm. The proportion of ST to FT fibers is genetically defined and not altered by exercise. Therefore, our results lend support to a genetic differentiation between individuals with high vs. low probability of unintended build-up of muscle tension during perceptual-motor task performance.     

Locomotor-like movements evoked by leg muscle vibration in humans

We attempted to elicit automatic stepping in healthy humans using appropriate afferent stimulation. It was found that continuous leg muscle vibration produced rhythmic locomotor-like stepping movements of the suspended leg, persisting up to the end of stimulation and sometimes outlasting it by a few cycles. Air-stepping elicited by vibration did not differ from the intentional stepping under the same conditions, and involved movements in hip and knee joints with reciprocal electromyogram (EMG) bursts in corresponding flexor and extensor muscles. The phase shift between evoked hip and knee movements could be positive or negative, corresponding to 'backward' or 'forward' locomotion. Such an essential feature of natural human locomotion as alternating movements of two legs, was also present in vibratory-evoked leg movements under appropriate conditions. It is suggested that vibration evokes locomotor-like movements because vibratory-induced afferent input sets into active state the central structures responsible for stepping generation.     

Evidence for a spinal stepping generator in man. Electrophysiological study

We present some evidence favouring the presence of a spinal stepping generator in humans. Electrophysiological studies have shown that the spinal cord even deprived of supraspinal influence can generate rhythmic activity, and that some elements of the spinal circuitry on which the generation of stepping rhythmic relies in lower vertebrates exist in man. Moreover, comparison of the variations of the polysynaptic spinal flexor reflex in normal subjects and paraplegic patients brought about some evidence that normal subjects use a spinal locomotor center. Nevertheless, these studies do not absolutely prove the existence of a central pattern generator in man.     

Tail pinching-induced hindlimb movements are suppressed by clonidine in spinal cord injured mice.

Experiments in completely spinal cord transected (Tx) cats have provided compelling evidence that clonidine combined with tail stimulation can promote locomotor function recovery. However, clonidine has generally failed to induce locomotor activity in other comparable animal models suggesting the existence of species- or condition-specific effects. This study aimed at investigating the effects of clonidine administered (0.25 or 5.0 mg/kg, i.p.) in mice during tail pinching in early (6-7 days post-Tx) or late (41-42 days post-Tx) paraplegic animals (Th9/10 level). Comparisons were made with the effects induced by 8-OH-DPAT (1.0 mg/kg, i.p.), a 5-HT1A/7 receptor agonist known to display prolocomotor effects. Clonidine with or without tail pinching failed to induce hind limb movements and even suppressed the frequency of spontaneously occurring nonlocomotor (NLM) and locomotor-like movements (LM) whereas tail pinching alone (prior to clonidine administration) increased the frequency of spontaneous movements specifically in late chronic animals. In turn, 8-OH-DPAT clearly induced hind limb movements that remained relatively unchanged during tail pinching. Altogether, the results suggest that the prolocomotor effects of clonidine reported elsewhere must depend upon stimuli or factors that remain to be identified. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Human lumbosacral spinal cord interprets loading during stepping

Studies suggest that the human lumbosacral spinal cord can generate steplike oscillating electromyographic (EMG) patterns, but it remains unclear to what degree these efferent patterns depend on the phasic peripheral sensory information associated with bilateral limb movements and loading. We examined the role of sensory information related to lower-extremity weight bearing in modulating the efferent motor patterns of spinal-cord-injured (SCI) subjects during manually assisted stepping on a treadmill. Four nonambulatory subjects, each with a chronic thoracic spinal cord injury, and two nondisabled subjects were studied. The level of loading, EMG patterns, and kinematics of the lower limbs were studied during manually assisted or unassisted stepping on a treadmill with body weight support. The relationships among lumbosacral motor pool activity [soleus (SOL), medial gastrocnemius (MG), and tibialis anterior (TA)], limb load, muscle-tendon length, and velocity of muscle-tendon length change were examined. The EMG mean amplitude of the SOL, MG, and TA was directly related to the peak load per step on the lower limb during locomotion. The effects on the EMG amplitude were qualitatively similar in subjects with normal, partial, or no detectable supraspinal input. Responses were most consistent in the SOL and MG at load levels of < 50% of a subject's body weight. The modulation of the EMG amplitude from the SOL and MG, both across steps and within a step, was more closely associated with limb peak load than muscle-tendon stretch or the velocity of muscle-tendon stretch. Thus stretch reflexes were not the sole source of the phasic EMG activity in flexors and extensors during manually assisted stepping in SCI subjects. The EMG amplitude within a step was highly dependent on the phase of the step cycle regardless of level of load. These data suggest that level of loading on the lower limbs provides cues that enable the human lumbosacral spinal cord to modulate efferent output in a manner that may facilitate the generation of stepping. These data provide a rationale for gait rehabilitation strategies that utilize the level of load-bearing stepping to enhance the locomotor capability of SCI subjects.     

Epaxial and limb muscle activity during swimming and terrestrial stepping in the adult newt, Pleurodeles waltl

We have investigated the patterns of activation of epaxial musculature during both swimming and overground stepping in an adult newt (Pleurodeles waltl) with the use of electromyographic (EMG) recordings from different sites of the myomeric muscle dorsalis trunci along the body axis. The locomotor patterns of some limb muscles have also been investigated. During swimming, the epaxial myomeres are rhythmically active, with a strict alternation between opposite myomeres located at the same longitudinal site. The pattern of intersegmental coordination consists of three successively initiated waves of EMG activity passing posteriorly along the anterior trunk, the midtrunk, and the posterior trunk, respectively. Swimming is also characterized by a tonic activation of forelimb (dorsalis scapulae and extensor ulnae) and hindlimb (puboischiotibialis and puboischiofemoralis internus) muscles and a rhythmic activation of muscles (latissimus dorsi and caudofemoralis) acting both on limb and body axis. The latter matched the activation pattern of epaxial myomeres at the similar vertebral level. During overground stepping, the midtrunk myomeres express single synchronous bursts whereas the myomeres of the anterior trunk and those of the posterior trunk display a double bursting pattern in the form of two waves of EMG activity propagating in opposite directions. During overground stepping, the limb muscles and muscles acting on both limb and body axis were found to be rhythmically active and usually displayed a double bursting pattern. The main conclusion of this investigation is that the patterns of intersegmental coordination during both swimming and overground stepping in the adult newt are related to the presence of limbs and that they can be considered as hybrid lampreylike patterns. Thus it is hypothesized that, in newt, a chain of coupled segmental oscillatory networks, similar to that which constitutes the central pattern generator (CPG) for swimming in the lamprey, can account for both trunk motor patterns if it is influenced by limb CPGs in a way depending on the locomotor mode. During swimming, the segmental networks located close to the girdles receive extra tonic excitation coming from the limb CPGs, whereas during stepping, the axial CPGs are entrained to some extent by the limb oscillators.     

Effects of dopamine on postural control in parkinsonian subjects: scaling, set, and tone

1. This study investigates the effects of parkinsonism and of dopamine replacement therapy (levodopa) on scaling the magnitude of automatic postural responses based on sensory feedback and on predictive central set. Surface reactive torques and electromyographic (EMG) activity in response to backward surface translations were compared in patients with parkinsonism ON and OFF levodopa and in elderly control subjects. Correlations between the earliest postural responses [initial rate of change of torque and integrated EMG (IEMG)] and translation velocity provided a measure of postural magnitude scaling using somatosensory feedback. Correlations of responses with expected translation amplitude provided a measure of scaling dependent on predictive central set because the responses preceded amplitude completion. 2. Parkinsonian EMG responses in six leg and trunk muscles were not later than in elderly control subjects. In fact, quadriceps antagonist latencies were earlier than normal, resulting in coactivation at the knee not present in control subjects. EMG activation was fragmented, with short burst durations and high tonic levels that often returned to baseline with multiple bursts. In addition, parkinsonian responses showed smaller-than-normal agonist extensor bursts and larger-than-normal activation in tibialis and rectus femorus antagonist flexors. 3. Although parkinsonian subjects scaled postural responses to both displacement velocities and amplitudes, their torque response were smaller than those of elderly controls, especially in response to the largest displacement amplitudes. The gain (slope) of postural response magnitude scaling to displacement velocity was similar for parkinsonian and control subjects, although parkinsonian subjects had smaller torques. Parkinsonian subjects were also able to use prediction to scale responses to small expected displacement amplitudes, but many patients did not generate the larger plantarflexion torques required at larger displacement amplitudes. Reduced torque at large amplitudes was associated with less agonist gastrocnemius IEMG, increased tibialis antagonist burst responses, and increased tibialis tonic background activity. 4. Levodopa further reduced the already low magnitude of initial torque and IEMG responses to displacement velocities and amplitudes in parkinsonian patients. The ability to scale postural responses to velocity feedback was not affected by levodopa, but the ability to scale responses to large displacement amplitudes based on central set was worsened by levodopa. Levodopa also significantly reduced the tonic, background levels of EMG, particularly the distal gastrocnemius and tibialis activity. 5. High baseline muscle tone was apparent in parkinsonian subjects from their high background EMG activity in quiet stance, especially in tibialis and quadriceps, and the slow initial velocity of center of mass falling in response to displacements. By reducing tone, levodopa reduced passive stiffness to perturbations without increasing EMG burst magnitudes, resulting in less resistance to external displacements and thus faster center of body mass (COM) displacements. 6. The biggest postural deficit in parkinsonian subjects was not in response latency, pattern, or reactive or predictive scaling of response magnitude, but in quickly generating an adequate level of postural force. Dopamine improved tonic background postural tone but further weakened automatic postural responses to external displacements. Thus the basal ganglia may participate in postural control by regulating appropriate levels of background postural tone and by enabling adequate force generation for resisting external displacements.     

Is backward stepping over obstacles achieved through a simple temporal reversal of forward stepping?

The main purpose of the study was to examine whether backward stepping over obstacles was a simple temporal reversal of kinematic and muscle activation patterns found in forward obstacle avoidance. Obstacle avoidance was used as a probe to represent one aspect of walking over variable terrain. Kinematics, trajectories and muscle activation profiles for forward versus backward stepping over obstacles revealed that the simple reversal of locomotor patterns observed for level walking cannot be applied to obstacle avoidance. However, key kinematic data and limb trajectories for backward leading limb stepping were found to be similar to existing forward trailing limb data. Therefore, it appears that stepping over obstacles requires a complex upper level reorganization of the basic locomotor pattern based on biomechanical and sensory feedback.     

Areas of sinusoidal surface hepatocyte nuclear predominance in type C chronic hepatitis

It has been suggested that the coordination of the activity of multiple muscles results from the comparison of the actual configuration of the body with a referent configuration specified by the nervous system so that the recruitment and gradation of the activity of each skeletal muscle depend on the difference between these two configurations. Active movements may be produced by the modification of the referent configuration. The hypothesis predicts the existence of a global minimum in electromyographic (EMG) activity of multiple muscles during movements involving reversals in direction. This prediction was tested in five subjects by analysing movements resembling the act of reaching for an object placed beyond one's reach from a sitting position. In such movements, initially sitting subjects raise their body to a semi-standing position and then return to sitting. Consistent with the hypothesis is the observation of a global minimum in the surface EMG activity of 16 muscles of the arm, trunk and leg at a specific phase of the movement. When the minimum occurred, EMG activity of each muscle did not exceed 2-7% of its maximal activity during the movement. As predicted, global EMG minima occurred at the phase corresponding to the reversal in movement direction, that is, during the transition from raising to lowering of the body. The global EMG minimum may represent the point at which temporal matching occurs between the actual and the referent body configurations. This study implies a specific link between motor behavior and the geometric shape of the body modified by the brain according to the desired action.     

Step-tracking movements of the wrist. IV. Muscle activity associated with movements in different directions

We examined the patterns of muscle activity associated with multiple directions of step-tracking movements of the wrist in humans and monkeys. Human subjects made wrist movements to 12 different targets that required varying amounts of flexion-extension and radial-ulnar deviation. Wrist muscles displayed two patterns of electromyographic (EMG) modulation as movement direction changed: amplitude graded and temporally shifted. The amplitude-graded pattern was characterized by modulation of the quantity of muscle activity that occurred during two distinct time periods, an agonist burst interval that began before movement onset and an antagonist burst interval that began just after movement onset. The timing of muscle activity over the two intervals showed little variation with changes in movement direction. For some directions of movement, EMG activity was present over both time intervals, resulting in "double bursts." Modulation of activity during the agonist burst interval was particularly systematic and was well fit by a cosine function. In contrast, the temporally shifted pattern was characterized by a gradual change in the timing of a single burst of muscle activity. The burst occurred at a time intermediate between the agonist and antagonist burst intervals. The temporally shifted pattern was seen less frequently than the amplitude-graded pattern and was present only in selected wrist muscles for specific directions of movement. Monkeys made wrist movements to 8-16 different targets that required varying amounts of flexion-extension and radial-ulnar deviation. These movements were performed more slowly than those of human subjects. The wrist muscles of the monkeys we examined displayed the amplitude-graded pattern of activity but not the temporally shifted pattern. Stimulation of individual wrist muscles in monkeys resulted in wrist movements that were markedly curved, particularly for the wrist extensors. These results indicate that step-tracking movements of the wrist are generated mainly by using the amplitude-graded pattern to modulate muscle activity. We propose that this pattern reflects a central process that decomposes an intended movement into an agonist, "propulsive" component and an antagonist, "braking" component. Separate bursts of muscle activity then are generated to control each component. On the other hand, we argue that the temporally shifted pattern may function to reduce the amount of movement curvature associated with the activation of wrist muscles.     

Coupling Between "Hand" Primary Sensorimotor Cortex and Lower Limb Muscles After Ulnar Nerve Surgical Transfer in Paraplegia.

Previous neuroimaging evidence revealed an "invasion" of "hand" over "lower limb" primary sensorimotor cortex in paraplegic subjects, with the exception of a rare patient who received a surgical motor reinnervation of hip-thigh muscles by the ulnar nerve. Here, the authors show that a functional reorganization of cortico-muscular and cortico-cortical oscillatory coupling was related to the recovery of the rare patient, as a paradigmatic case of long-term plasticity in human sensorimotor cortex after motor reinnervation of paraplegic muscles. This conclusion was based on electroencephalographic and electromyographic data collected while the patient and normal control subjects performed isometric muscle contraction of the left hand or lower limb. Cortico-muscular and cortico-cortical coupling was estimated by electroencephalographic-electromyographic coherence and directed transfer function of a multivariate autoregressive model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The activation of back muscles during locomotion in the developing rat

The development of posture during locomotion was studied in rats from the 11th day until adulthood. The EMGs were recorded and analyzed of the left and right longissimus muscles at caudal, intermediate and rostral levels as well as of the gastrocnemius, the tibialis and the vastus medialis muscles and movements were simultaneously recorded on videotape. Results indicate that from the 12th day of life, burst activity occurs in the longissimus muscles which is phase-related to the stepcycle. Until the 21st day these muscles are most strongly activated during burst activity in the gastrocnemius muscle in the contralateral hindleg but thereafter this activation coincides with bursts in the ipsilateral gastrocnemius muscle. At adult age such activation in the LL is restricted to fast walking or to accelerations. Latencies between bursts in the longissimus muscles and the gastrocnemius muscles vary around 100 ms until the 25th day, but thereafter they decrease to adult values of less than 10 ms. The large variations in these phase-relations at all ages suggest that supraspinal influences and afferent input are important factors in this coupling. The shift from a contra- to an ipsilateral coupling between bursts in the longissimus and in the gastrocnemius muscles might indicate that an ontogenetically older pattern of locomotion with the trunk muscles playing a major role in propulsion, is replaced by a newer pattern, mainly effected by extremity movements.     

Absence of tonic electromyographic activity during sleep in normal and spastic nonmimetic skeletal muscles in man

An electromyographic study of nonmimetic skeletal muscles was carried out in 8 normal adults and 4 patients with spastic hemiparesis during all stages of sleep for a total of 21 nights. All normal subjects showed absence of tonic electromyographic activity in all nonmimetic skeletal muscles in all stages of sleep. Also, during quiet, relaxed wakefulness, tonic muscle discharges disappeared in the normal subjects. Three patients with upper motor neuron spasticity demonstrated results during sleep similar to those obtained in the normal subjects. In the fourth patient, tonic muscle discharges persisted into stage 2 non-REM sleep, disappeared within 30 to 240 seconds following the onset of stage 2 sleep, and were absent during stages 3 and 4 sleep and REM sleep.     

Effects of intrathecal alpha1- and alpha2-noradrenergic agonists and norepinephrine on locomotion in chronic spinal cats

Noradrenergic drugs, acting on alpha adrenoceptors, have been found to play an important role in the initiation and modulation of locomotor pattern in adult cats after spinal cord transection. There are at least two subtypes of alpha adrenoceptors, alpha1 and alpha2 adrenoceptors. The aim of this study was to investigate the effects of selective alpha1 and alpha2 agonists in the initiation and modulation of locomotion in adult chronic cats in the early and late stages after complete transection at T13. Five cats, chronically implanted with an intrathecal cannula and electromyographic (EMG) electrodes were used in this study. Noradrenergic drugs including alpha2 agonists (clonidine, tizanidine, and oxymetazoline) and an antagonist, yohimbine, one alpha1 agonist (methoxamine), and a blocker, prazosin, as well as norepinephrine were injected intrathecally. EMG activity synchronized to video images of the hindlimbs were recorded before and after each drug injection. The results show differential effects of alpha1 and alpha2 agonists in the initiation of locomotion in early spinal cats (i.e., in the first week or so when there is no spontaneous locomotion) and in the modulation of locomotion and cutaneous reflexes in the late-spinal cats (i.e., when cats have recovered spontaneous locomotion). In early spinal cats, all three alpha2 agonists were found to initiate locomotion, although their action had a different time course. The alpha1 agonist methoxamine induced bouts of nice locomotor activity in three spinal cats some hours after injection but only induced sustained locomotion in one cat in which the effects were blocked by the alpha1 antagonist prazosin. In late spinal cats, although alpha2 agonists markedly increased the cycle duration and flexor muscle burst duration and decreased the weight support or extensor activity (effects blocked by an alpha2 antagonist, yohimbine), alpha1 agonist increased the weight support and primarily the extensor activity of the hindlimbs without markedly changing the timing of the step cycle. Although alpha2 agonists, especially clonidine, markedly reduced the cutaneous excitability and augmented the foot drag, the alpha1 agonist was found to increase the cutaneous reflex excitability. This is in line with previously reported differential effects of activation of the two receptors on motoneuron excitability and reflex transmission. Noradrenaline, the neurotransmitter itself, increased the cycle duration and at the same time retained the cutaneous excitability, thus exerting both alpha1 and alpha2 effects. This work therefore suggests that different subclasses of noradrenergic drugs could be used to more specifically target aspects of locomotor deficits in patients after spinal injury or diseases.     

Nuclear magnetic resonance evidence of different muscular adaptations after resistance training

OBJECTIVE: To evaluate muscle bioenergetics, muscle cross-sectional area (CSA), and soreness when the gastrocnemius was subjected to concentric and concentric/eccentric resistance training modes. DESIGN: Prospective study, before and after training. The subjects served as their own controls. SETTING: Rehabilitation center and nuclear magnetic resonance spectroscopy unit of a university hospital. PARTICIPANTS: Sixteen healthy young volunteers from the local physiotherapist school. INTERVENTION: Two distinct resistive training programs were evaluated on the gastrocnemius: a protocol consisting of concentric contractions only and a mixed concentric/eccentric program. MAIN OUTCOME MEASURES: Maximal isometric resistance was measured after each training session. Before and after training, muscle CSA was appreciated using magnetic resonance imaging, whereas changes in muscle pH, phosphorus metabolite ratios, maximal oxidative power (Pmax), and oxidative phosphorylation were studied using 31P nuclear magnetic resonance spectroscopy at rest and during an incremental exercise protocol. RESULTS: Magnetic resonance imaging revealed a significant increase (7.1%) in the gastrocnemius CSA in the concentric-eccentric group only. The PCr/Pi (8.3 +/- 0.9 vs 10.4 +/- 1.7) and PCr/ATP (3.68 +/- .36 vs 4.07 +/- .27) resting ratios increased significantly (p = .008) after concentric-eccentric resistance training. Pmax was significantly improved in the concentric-eccentric group (7.0 +/- 2.1W vs 8.4 +/- 1.8W: p < .02). This mixed protocol also reduced the incidence of muscular soreness. CONCLUSION: The data suggest that the improved oxidative mechanical power output could be due mainly to a greater muscle cross-section in the concentric-eccentric group, with circumstantial evidence suggesting a relatively higher type IIa fiber activity.     

Experimental muscle pain does not cause long-lasting increases in resting electromyographic activity

The mutual links between muscle pain and resting electromyographic (EMG) activity are still controversial. This study described effects of experimental muscle pain on resting EMG activity in a jaw-closing muscle and a leg muscle. Pain was induced by injections of hypertonic saline into the muscles in 10 subjects. Injections of isotonic saline served as a control. The pain intensity was scored on visual analog scales (VAS) and surface and intramuscular wire EMGs were obtained from the resting muscles before, during, and after saline injections. EMG activity was analyzed in 30-s intervals and demonstrated, in both muscles, significant increases 30-60 s after injection of hypertonic saline, but not after injection of isotonic saline. In contrast to the transient increase in EMG activity, the pain sensation lasted up to 600 s after injection of hypertonic saline. It was concluded that acute muscle pain is unable to maintain longer-lasting resting muscle hyperactivity.     

Electromyographic activity of the cervical musculature during dynamic lateral bending

STUDY DESIGN: Electromyographic profiles from the neck muscles of five young, healthy men were obtained to study the muscular, activation patterns during dynamic external loading. OBJECTIVES: To examine the myoelectric activity of selected cervical muscles during dynamic loading, and to explore the reaction of the cervical muscles to different loading conditions. SUMMARY OF BACKGROUND DATA: The response of cervical muscles throughout dynamic external loading is not well understood. Electromyography provides information, within certain limitations, about the neural drive to various components of the musculature. Such information on activation, combined with geometric parameters of the musculoskeletal tissues, constitutes a tool for helping to understand the mechanism of head and neck impact-related injury. METHODS: Subjects were tested with the head and neck in the neutral and prebent positions. Dynamic loads were applied laterally to each subject by free-falling masses to create peak dynamic loads ranging from about 40 to 100 N. Force and electromyographic data were recorded, and cross-correlations from linear envelope electromyography were calculated. RESULTS: The peak electromyogram showed large differences between the two applied loads and between subjects. There were time delays (75-165 msec) between the peak applied force and the peak electromyogram. The muscles on the contralateral side demonstrated different electromyographic profiles between subjects. Within subjects, the electromyographic profiles from each muscle were consistent for the same trial conditions. CONCLUSIONS: Electromyographic profiles and the cross-correlator coefficients for cervical muscles have shown reproducible intrasubject muscle synergies, which were not sensitive to the magnitude of applied load and the posture of the head. Intersubject muscle activity patterns varied.     

Anticonvulsant and behavioural effects of bicuculline injected into the mesencephalic locomoter region of rats

Previous microinjection mapping studies in the mesencephalon established a significant association between the induction of locomotor activation and the suppression of tonic seizures in the electroshock model of epilepsy. The purpose of the present study was to see if this relationship also applies in an area of the brainstem commonly known as the mesencephalic locomotor region (MLR). The principal findings were the following. (i) Activation of extensive areas of the dorsal midbrain and tegmentum, including the MLR, by unilateral injections of the GABA antagonist bicuculline induced leg movements and suppressed the tonic component of electroshock-induced seizures. (ii) A highly significant correlation was observed between these two variables. (iii) In some cases, however, the induction of phasic leg movements was neither sufficient nor necessary for tonic seizure suppression. It is possible, therefore, that injection-elicited changes in tonic aspects of limb control may be more directly related to the suppression of tonic motor seizures in the electroshock model of epilepsy.