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At least 811 records · Page 45Linked to original sources
PubMed2000

Stimulation of the locus coeruleus suppresses trigeminal sensorimotor function in the rat.

The nucleus locus coeruleus (LC) has been implicated in the modulation of the spinal sensorimotor function. The aim of the present study was to examine the effect of electrical stimulation of the LC on sensorimotor function in the trigeminal system. The following two cases of sensorimotor behaviors mediated by the trigeminal brainstem sensory nuclear complex were examined: (1) the activity of the masseter muscle evoked by pressure on the region of the temporomandibular joint (TMJ); and (2) the activity of the digastric muscle evoked by electrical stimulation of the tooth pulp, resulting in the jaw-opening reflex. In the first case, LC stimulation at 10, 30 and 50 microA resulted in a 70%, 68% and 55% reduction in the magnitude of electromyogram (EMG) activity of the masseter muscle compared with the control (without LC stimulation), respectively. The threshold intensity for the onset of masseter EMG activity increaced to 106%, 111% and 121% of the control with 10, 30 and 50 microA LC stimulation, respectively. In the second case, EMG magnitude in response to the digastric muscle decreased to 42% of the control when 30 microA of LC stimulation was delivered. These results suggest that descending influences from the LC can act in suppression of the trigeminal sensorimotor function.

Animals↗
PubMed2003

Sensorimotor integration in movement disorders.

Although current knowledge attributes movement disorders to a dysfunction of the basal ganglia-motor cortex circuits, abnormalities in the peripheral afferent inputs or in their central processing may interfere with motor program execution. We review the abnormalities of sensorimotor integration described in the various types of movement disorders. Several observations, including those of parkinsonian patients' excessive reliance on ongoing visual information during movement tasks, suggest that proprioception is defective in Parkinson's disease (PD). The disturbance of proprioceptive regulation, possibly related to the occurrence of abnormal muscle-stretch reflexes, might be important for generating hypometric or bradykinetic movements. Studies with somatosensory evoked potentials (SEPs), prepulse inhibition, and event-related potentials support the hypothesis of central abnormalities of sensorimotor integration in PD. In Huntington's disease (HD), changes in SEPs and long-latency stretch reflexes suggest that a defective gating of peripheral afferent input to the brain might impair sensorimotor integration in cortical motor areas, thus interfering with the processing of motor programs. Defective motor programming might contribute to some features of motor impairment in HD. Sensory symptoms are frequent in focal dystonia and sensory manipulation can modify the dystonic movements. In addition, specific sensory functions (kinaesthesia, spatial-temporal discrimination) can be impaired in patients with focal hand dystonia, thus leading to a "sensory overflow." Sensory input may be abnormal and trigger focal dystonia, or defective "gating" may cause an input-output mismatch in specific motor programs. Altogether, several observations strongly support the idea that sensorimotor integration is impaired in focal dystonia. Although elemental sensation is normal in patients with tics, tics can be associated with sensory phenomena. Some neurophysiological studies suggest that an altered "gating" mechanism also underlies the development of tics. This review underlines the importance of abnormal sensorimotor integration in the pathophysiology of movement disorders. Although the physiological mechanism remains unclear, the defect is of special clinical relevance in determining the development of focal dystonia.

Animals↗
PubMed1992

A neural network model rapidly learning gains and gating of reflexes necessary to adapt to an arm's dynamics.

Effects of dynamic coupling, gravity, inertia and the mechanical impedances of the segments of a multi-jointed arm are shown to be neutralizable through a reflex-like operating three layer static feedforward network. The network requires the proprioceptively mediated actual state variables (here angular velocity and position) of each arm segment. Added neural integrators (and/or differentiators) can make the network exhibit dynamic properties. Then, actual feedback is not necessary and the network can operate in a pure feedforward fashion. Feedforward of an additional load can easily be implemented into the network using "descendent gating", and a negative feedback control loop added to the feedforward control reduces errors due to external noise. A training, which combines a least squared error based simultaneous learning rule (LSQ-rule) with a "self-imitation algorithm" based on direct inverse modeling, enables the network to acquire the whole inverse dynamics, limb parameters included, during one short training movement. The considerations presented also hold for multi-jointed manipulators.

Animals↗
PubMed1995

Mechanoreceptors in intervertebral discs. Morphology, distribution, and neuropeptides.

STUDY DESIGN: The present study investigated the occurrence and morphology of mechanoreceptors in human and bovine intervertebral discs and longitudinal ligaments. OBJECTIVE: To determine the type and frequency of mechanoreceptors present in intervertebral discs and anterior longitudinal ligaments in two patient groups, those with low back pain and those with scoliosis. Bovine coccygeal discs were examined. SUMMARY OF BACKGROUND DATA: Nerves have been described in intervertebral tissues, but there is little information on the endings of these nerves and their receptors, stimulation of which can cause a nerve impulse. METHODS: The presence of mechanoreceptors were investigated by immunolocalization of nerves and neuropeptides. By examining sequential sections, the frequency of receptors was assessed. RESULTS: Immunoreactivity to neural antigens showed mechanoreceptors in the anulus fibrosus and longitudinal ligaments of bovine and human specimens. Their morphology resembled Pacinian corpuscles, Ruffini endings, and, most frequently, Golgi tendon organs. They were found in 50% of discs investigated from patients with low back pain and in 15% of those with scoliosis. CONCLUSIONS: Mechanoreceptors were found in the outer 2-3 lamellae of the human intervertebral disc and anterior longitudinal ligament. Physiologic studies in other tissues indicate that these provide the individual with sensation of posture and movement, and in the case of Golgi tendon organs, of nociception. In addition to providing proprioception, mechanoreceptors are thought to have roles in maintaining muscle tone and reflexes. Their presence in the intervertebral disc and longitudinal ligament can have physiologic and clinical implications.

Adolescent↗
PubMed1998

A cortico-spinal model of reaching and proprioception under multiple task constraints.

A model of cortico-spinal trajectory generation for voluntary reaching movements is developed to functionally interpret a broad range of behavioral, physiological, and anatomical data. The model simulates how arm movements achieve their remarkable efficiency and accuracy in response to widely varying positional, speed, and force constraints. A key issue in arm movement control is how the brain copes with such a wide range of movement contexts. The model suggests how the brain may set automatic and volitional gating mechanisms to vary the balance of static and dynamic feedback information to guide the movement command and to compensate for external forces. For example, with increasing movement speed, the system shifts from a feedback position controller to a feedforward trajectory generator with superimposed dynamics compensation. Simulations of the model illustrate how it reproduces the effects of elastic loads on fast movements, endpoint errors in Coriolis fields, and several effects of muscle tendon vibration, including tonic and antagonist vibration reflexes, position and movement illusions, effects of obstructing the tonic vibration reflex, and reaching undershoots caused by antagonist vibration.

Computer Simulation↗
PubMed1999

Role of proprioceptive signals from an insect femur-tibia joint in patterning motoneuronal activity of an adjacent leg joint.

Interjoint reflex function of the insect leg contributes to postural control at rest or to movement control during locomotor movements. In the stick insect (Carausius morosus), we investigated the role that sensory signals from the femoral chordotonal organ (fCO), the transducer of the femur-tibia (FT) joint, play in patterning motoneuronal activity in the adjacent coxa-trochanteral (CT) joint when the joint control networks are in the movement control mode of the active behavioral state. In the active behavioral state, sensory signals from the fCO induced transitions of activity between antagonistic motoneuron pools, i.e., the levator trochanteris and the depressor trochanteris motoneurons. As such, elongation of the fCO, signaling flexion of the FT joint, terminated depressor motoneuron activity and initiated activity in levator motoneurons. Relaxation of the fCO, signaling extension of the FT joint, induced the opposite transition by initiating depressor motoneuron activity and terminating levator motoneuron activity. This interjoint influence of sensory signals from the fCO was independent of the generation of the intrajoint reflex reversal in the FT joint, i.e., the "active reaction," which is released by elongation signals from the fCO. The generation of these transitions in activity of trochanteral motoneurons barely depended on position or velocity signals from the fCO. This contrasts with the situation in the resting behavioral state when interjoint reflex action markedly depends on actual fCO stimulus parameters, i.e., position and velocity signals. In the active behavioral state, movement signals from the fCO obviously trigger or release centrally generated transitions in motoneuron activity, e.g., by affecting central rhythm generating networks driving trochanteral motoneuron pools. This conclusion was tested by stimulating the fCO in "fictive rhythmic" preparations, activated by the muscarinic agonist pilocarpine in the otherwise isolated and deafferented mesothoracic ganglion. In this situation, sensory signals from the fCO did in fact reset and entrain rhythmic activity in trochanteral motoneurons. The results indicate for the first time that when the stick insect locomotor system is active, sensory signals from the proprioceptor of one leg joint, i.e., the fCO, pattern motor activity in an adjacent leg joint, i.e., the CT joint, by affecting the central rhythm generating network driving the motoneurons of the adjacent joint.

Action Potentials↗
PubMed1981

Gait apraxia in communicating hydrocephalus.

Apraxia of gait in patients with communicating hydrocephalus appears in the context of a generalised motor disorder that includes defective righting reflexes, generalised increased tone to passive movements, grasp reflexes, difficulty with serial movements of the hands and defective smooth pursuit eye movements. The inability to walk does not appear to be due to a motor disorder but to release of proprioceptive supporting reactions. This mechanism is triggered by proprioceptive stimuli.

Apraxias↗
PubMed1996

Loop gain of reflexes controlling human standing measured with the use of postural and vestibular disturbances.

1. In this study we measured the loop gain of postural reflexes in standing human subjects. Reflex activity is conventionally described in terms of the muscle activation arising from a perturbation, but in this study the ability of the evoked muscle activity to correct the perturbation was also measured, and the behavior of the entire feedback loop is described. 2. A weak continuous random perturbation was applied at waist level to standing subjects. The effects of the perturbation on body sway and soleus electromyogram (EMG) were identified by cross-correlation, and spectral analysis was used to estimate the open-loop reflex transmission characteristics (i.e., sway to EMG). Under the same conditions, activity in the leg muscles was evoked by galvanic vestibular stimulation with the use of a continuous randomly varying current. The effects on soleus EMG and the subsequent body sway were identified by cross-correlation. This allowed calculation of the open-loop muscle and load behavior (i.e., EMG to sway). From these open-loop reflex and muscle and load transfer functions, the loop gain and phase were calculated. 3. In addition to the gain of the feedback loop, the study describes the transmission characteristics of reflex responses in the leg muscles associated with body sway and the effects of excluding visual and proprioceptive contributions to the response; the transfer function of human soleus with a stimulus that preserves the normal recruitment of motoneurons, including the effects of different load conditions on the muscle; and the transmission characteristics of vestibular pathways that evoke responses in the leg muscles during standing in situations that might modify the reflexes. 4. When standing, the loop gain of reflex feedback is approximately unity and is unchanged by eye closure and stability of support. Reflex transmission introduced a marked phase advance, and this served to offset most of the phase lag introduced by muscle and load. The residual phase lag could explain the frequency of tremor observed during standing (6-8 Hz). 5. The gain of the feedback loop (approximately 1) is higher than suggested by both previous estimates and theoretical considerations, but is still insufficient to explain the stability of normal human standing. This implies that, although sensory information is used to control posture, it does not do so exclusively through a negative feedback control process. The experimental findings are consistent with a reflex response based on a feed-forward process, and this would result in prediction of the response necessary to counteract a postural disturbance.

Adult↗
PubMedDate not supplied

Role of the sensory innervation of the extraocular muscles in habituation of vestibulo-oculomotor responses.

The role of the sensory innervation of the extraocular muscles in extinction of reflex nystagmus induced by periodic rotation with standard angular acceleration was studies in experiments on rabbits. Limitation or complete abolition of the motor activity of the extraocular muscles and also passive forced movements of the eyes were used. Comparison of results obtained with intact animals and animals with abolition of motor activity of the extraocular muscles showed no difference between them. In both cases the dynamics of extinction of nystagmus was the same. On the other hand, repeated forced movements of the eyes had no effect on reflex nystagmus of the eyes. It is concluded from the results that the proprioceptive efferent innervation of the extraocular muscles plays no part in habituation of vestibulo-oculomotor responses.

Animals↗
PubMed1987

Effects of methylmercury on the motor and sensory innervation of the rat extensor digitorum longus muscle.

This histochemical study examined the effects of chronic methylmercury (MeHg) intoxication on the motor and sensory innervation of extensor digitorum longus muscles. Light microscopic examination of silver-stained axons in the intramuscular nerve bundles of MeHg-treated rats showed Wallerian-like degeneration and a reduction in the number of nerve fibers. Disrupted axons were predominantly sensory because 22.2% of spindle afferents (Ia) and 90.0% of Golgi tendon organ (Ib) sensory fibers were completely degenerated whereas less than 1% of motor endings were totally destroyed. Partial disruption occurred in the cholinesterase and motor terminals of 13.7% of endplates. Our results demonstrated greater vulnerability of sensory nerves than of motor nerves to MeHg-induced degeneration. Thus, the abnormal reflexes, ataxia, and muscle weakness following MeHg poisoning appear related to reduction of proprioceptive feedback from muscles and tendons in addition to the documented lesions in the central nervous system.

Animals↗
PubMed1999

An imposed oscillating electrical field improves the recovery of function in neurologically complete paraplegic dogs.

We show that an applied electric field in which the polarity is reversed every 15 minutes can improve the outcome from severe, acute spinal cord injury in dogs. This study utilized naturally injured, neurologically complete paraplegic dogs as a model for human spinal cord injury. The recovery of paraplegic dogs treated with oscillating electric field stimulation (OFS) (approximately 500 to 600 microV/mm; n = 20) was compared with that of sham-treated animals (n = 14). Active and sham stimulators were fabricated in West Lafayette, Indiana. They were coded, randomized, sterilized, and packaged in Warsaw, Indiana, and returned to Purdue University for blinded surgical implantation. The stimulators were of a previously unpublished design and meet the requirements for phase I human clinical testing. All dogs were treated within 18 days of the onset of paraplegia. During the experimental applications, all received the highest standard of conventional management, including surgical decompression, spinal stabilization (if required), and acute administration of methylprednisolone sodium succinate. A radiologic and neurologic examination was performed on every dog entering the study, the latter consisting of standard reflex testing, urologic tests, urodynamic testing, tests for deep and superficial pain appreciation, proprioceptive placing of the hind limbs, ambulation, and evoked potential testing. Dogs were evaluated before and after surgery and at 6 weeks and 6 months after surgery. A greater proportion of experimentally treated dogs than of sham-treated animals showed improvement in every category of functional evaluation at both the 6-week and 6-month recheck, with no reverse trend. Statistical significance was not reached in comparisons of some individual categories of functional evaluation between sham-treated and OFS-treated dogs (ambulation, proprioceptive placing); an early trend towards significance was shown in others (deep pain), and significance was reached in evaluations of superficial pain appreciation. An average of all individual scores for all categories of blinded behavioral evaluation (combined neurologic score) was used to compare group outcomes. At the 6-month recheck period, the combined neurologic score of OFS-treated dogs was significantly better than that of control dogs (p = 0.047; Mann-Whitney, two-tailed).

Animals↗
PubMed2006

Extraretinal signals in MSTd neurons related to volitional smooth pursuit.

Smooth pursuit (SP)-related neurons in the dorsal-medial part of medial superior temporal cortex (MSTd) carry extraretinal signals that may play a role in maintenance of SP once eye velocity matches target velocity. For example, it has not been determined whether the extraretinal signals reflect volitional SP commands or proprioception. The aim of this study was to test some potential sources of extraretinal signals in MSTd pursuit neurons. We tested 40 MSTd neurons during step-ramp SP with target blink conditions to show that they carried an extraretinal signal. To examine potential contributions from eye movements that might reflect proprioceptive feedback from eye muscles, we tested MSTd neurons during rotational vestibular ocular reflex in complete darkness (VORd). Vestibular stimulation was delivered in the earth horizontal plane to elicit reflex driven smooth eye movements that matched the speed and frequency of volitional SP. We also tested VOR in the light (VOR x 1) and cancellation of the VOR (VOR x 0). Our neurons were modulated during both SP and cancellation of the VOR. In contrast, MSTd smooth pursuit neurons with extraretinal signals were not significantly modulated during VORd (sensitivity < or = 0.10 spike/s/ degrees /s). This combination of properties is compatible with classifying these neurons as gaze-velocity related. Absence of modulation during VORd testing could be caused by cancellation of head and eye movement sensitivity or dependence of neuronal firing on volitional SP commands. Our results support the suggestion that modulation of SP-related MSTd neurons reflects volitional SP commands rather then eye movements generated by reflex pathways.

Animals↗
PubMed2006

Threshold control of motor actions prevents destabilizing effects of proprioceptive delays.

It is usually assumed that proprioceptive feedback comes to motoneurons too late to contribute to the initial activity of agonist muscles during fast arm movements, leading to the suggestion that this feedback is only efficient in slow movements and postural control. The argument does not take into account that the changes in the motoneuronal membrane potentials and the associated changes in the state of spinal neurons preceding the initial activity of muscles deeply affect, in a forward way, the state of reflex systems by shifting their thresholds, as suggested in the lambda model for motor control. As a result, the initial muscle activity emerges with full contribution of these systems so that the effects of reflex delays become negligible. We tested the hypothesis that threshold control of muscle activation may be instrumental in preventing destabilizing effects of proprioceptive delays in spinal and trans-cortical pathways to motoneurons. The analysis was made by recording fast elbow movements (peak velocity approximately 300-500 degrees/s) and simulating them in a dynamic model that incorporates the notion of threshold control of intrinsic and reflex muscle properties. The model was robust in reproducing experimental movement patterns (R (2)>0.95). It generated stable output despite substantial proprioceptive (up to 100 ms) and electromechanical (40 ms) delays. Stability was thus ensured for delays not only in segmental (about 25-50 ms) but also in trans-cortical loops (50-70 ms). Our study illustrates that a natural physiological process--threshold control--may manifest feed-forward properties hitherto attributed to hypothetical internal neural models.

Adult↗
PubMed1990

Hemicerebellectomy and motor behaviour in rats. I. Development of motor function after neonatal lesion.

This study was undertaken to determine the effect of a neonatal hemicerebellectomy (HCb) on the motor development of rats and to determine whether various aspects of motor behaviour were affected to a similar degree. Postnatal development of postural reflexes, locomotion and dynamic postural adjustments was examined during the first four months of life in normal and in neonatal HCbed rats. The results indicate that classes of motor responses are controlled by cerebellar networks to clearly different extents. Emergence of quadruped stance, placing reactions and swimming development were unaffected by neonatal cerebellar lesion. Righting reflexes, cliff avoidance and geotaxic reactions, pivoting and crawling all showed a delayed development although the subsequent recovery was almost complete. The complex postural adjustments required in crossing a narrow path or in suspending on a wire remained permanently impaired. Finally, some behaviours developed normally and only subsequently became defective. This "growing into a deficit" was displayed by the progressively reduced hindlimb grasping and the development of a vestibular drop response with a directional bias. An impressive finding was the shifting of postural asymmetries from the lesion side to the contralateral one occurring around the third postnatal week. These data providing a description of the effect of HCb on motor development are interpreted as indicating a progressive involvement of the archi- and neo-cerebellar structures in the motor function of the rat.

Animals↗
PubMed1990

Modulation of cutaneous flexor responses induced in man by vibration-elicited proprioceptive or exteroceptive inputs.

The effects of muscle tendon or skin vibration on the early and late components of polyphasic cutaneous responses elicited in the flexor carpi radialis by electrical stimulation of the radial nerve at the wrist were studied in the human, with all muscles at rest. Both early and late flexor responses were enhanced by flexor vibration and depressed by extensor vibration; facilitation was accompanied by a reduction of latency. Furthermore, when an "antagonist vibration response" was present, inhibition of the flexor reflexes was replaced by a facilitation. Palm skin vibration depressed both components of the flexor reflex, while dorsal or "back-hand" skin vibration induced either a facilitation or an inhibition. In addition, back-hand vibration modified the location of the sensations evoked by electrical stimulation of the nerve. In all cases, vibratory stimulus attenuated the perceived intensity of the electrical stimulus. These observations indicate that proprioceptive or exteroceptive information can modulate the gain of the cutaneous reflex loops in a flexible way, under supraspinal control. These data also suggest a possible impairment of the protective withdrawal reflex under vibratory environmental conditions at rest and eventually in active muscles.

Adaptation, Physiological↗
PubMed2006

A method to reversibly degrade proprioceptive feedback in research on human motor control.

In research on human motor skills, it is often desirable to manipulate proprioceptive feedback in order to determine its contribution towards subjects' performance. Here we evaluate an easy-to-use, non-invasive method to temporarily reduce proprioceptive responsiveness. Two physiotherapy vibrators contacted the distal end of the subjects' forearm on the flexor and extensor side; they were either turned off, or they vibrated at 80 Hz with an amplitude of 1mm. We found that vibration substantially impaired subjects' ability to use their hand in an angle matching, a force production and a haptic shape perception task. We also found that vibration strongly attenuated the H-reflex of the ipsilateral M. flexor carpi radialis. These results suggest that agonist-antagonist vibration is a useful method to degrade proprioceptive responsiveness for research on higher motor functions.

Adaptation, Physiological↗