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PubMed1990

Focal dystonia following soft tissue injury: three case reports with long-term outcome.

Three cases of focal dystonia are described which followed upper extremity injuries. Each patient developed a dystonic posturing in that limb; two patients improved when their initial condition was addressed. Various authors have proposed that focal dystonia represents a limited form of generalized dystonia, which is believed to result from a disturbance of striatopallidal-thalamic input to the supplementary motor area (SMA)--a vital executive area for motor control. An alternative hypothesis is offered; that is, a similar dysfunction of the SMA could be the result of altered sensory information from a painful limb disturbing the crucial integration between sensory input and motor performance. The following three examples of such integration are provided: (1) the long loop or transcortical reflex, (2) input of distinctive somatosensory neurons to the SMA, and (3) the projection of proprioceptive and tactile sensory input into peripheral receptive fields of the motor cortex.

Adolescent↗
PubMed1997

Sensori-sensory afferent conditioning with leg movement: gain control in spinal reflex and ascending paths.

Studies are reviewed, predominantly involving healthy humans, on gain changes in spinal reflexes and supraspinal ascending paths during passive and active leg movement. The passive movement research shows that the pathways of H reflexes of the leg and foot are down-regulated as a consequence of movement-elicited discharge from somatosensory receptors, likely muscle spindle primary endings, both ipsi- and contralaterally. Discharge from the conditioning receptors in extensor muscles of the knee and hip appears to lead to presynaptic inhibition evoked over a spinal path, and to long-lasting attenuation when movement stops. The ipsilateral modulation is similar in phase to that seen with active movement. The contralateral conditioning does not phase modulate with passive movement and modulates to the phase of active ipsilateral movement. There are also centrifugal effects onto these pathways during movement. The pathways of the cutaneous reflexes of the human leg also are gain-modulated during active movement. The review summarizes the effects across muscles, across nociceptive and non-nociceptive stimuli and over time elapsed after the stimulus. Some of the gain changes in such reflexes have been associated with central pattern generators. However, the centripetal effect of movement-induced proprioceptive drive awaits exploration in these pathways. Scalp-recorded evoked potentials from rapidly conducting pathways that ascend to the human somatosensory cortex from stimulation sites in the leg also are gain-attenuated in relation to passive movement-elicited discharge of the extensor muscle spindle primary endings. Centrifugal influences due to a requirement for accurate active movement can partially lift the attenuation on the ascending path, both during and before movement. We suggest that a significant role for muscle spindle discharge is to control the gain in Ia pathways from the legs, consequent or prior to their movement. This control can reduce the strength of synaptic input onto target neurons from these kinesthetic receptors, which are powerfully activated by the movement, perhaps to retain the opportunity for target neuron modulation from other control sources.

Animals↗
PubMed1988

Inspiratory muscle activity during unloaded and obstructed rebreathing in dogs.

Moving-average electromyogram (EMG) of the diaphragm (DI), scalenes, and cranial and caudal parasternals was assessed in anesthetized, supine, and head-up dogs during rebreathing. The shape of EMG trajectory was similar for all muscles and conditions; activation of different muscles could be thus compared on the basis of changes in peak activity. In intact dogs changes in peak activity were greater for the scalenes and cranial parasternals than for the caudal parasternals and greater for the inspiratory thoracic muscles (ITM) than for the DI. Posture, vagotomy, and cordotomy at C7-T1 did not affect the rate of rise of DI activity. The relations between peak activity of ITM did not change because of posture, vagotomy, and phrenicotomy. Vagotomy selectively depressed the rate of rise of ITM activity, but relative changes in peak ITM activity for a given change in peak DI activity were independent of intact vagi. Differences in the pattern of activation between inspiratory muscles with rebreathing are largely independent of proprioceptive inputs and likely reflect properties of central control mechanisms. However, airway occlusion at end expiration caused a reflex fall of DI activity and reflex increase of ITM activity in intact and vagotomized dogs. Cordotomy at C7-T1 did not change DI response, whereas reduction of ITM activity occurred after phrenicotomy, indicating that both facilitatory and inhibitory segmental inputs are involved in ITM response to loading.

Airway Obstruction↗
PubMedDate not supplied

The clinical neurology of scrapie in Irish sheep.

One hundred twenty-nine sheep with scrapie were identified from 20 flocks in which scrapie previously had been confirmed. Physical and neurologic examinations were performed on all animals. Videotape recordings were made and reviewed to assess gait. These procedures were repeated in 46 sheep at 2- to 3-week intervals until recumbency or inappetence necessitated euthanasia. Confirmation of scrapie was made by histopathologic and immunohistochemical examinations of brain tissue. The clinical signs most frequently recorded in the 129 animals on initial presentation were hindlimb ataxia (71%), head tremor (61%), altered mental status (57%), positive nibble reflex (51%), crouching posture (51%), teeth grinding (44%), low head carriage (38%), body condition score (BCS) < 1.5 (38%), and conscious proprioceptive deficits of the hindlimbs (36%). Progression of the disease was characterized by an increase in the frequency and severity of ataxia, weakness and hypermetria of the hindlimbs, a decreasing sway response, a decreasing extensor response to thoracolumbar pressure, and a reduction in the BCS. No effect of farm of origin on the clinical presentation could be shown. The presence of a nibble reflex was strongly associated (P < .0005) with prion protein (PrP) genotypes AA136RR154QH171 and AA136RR154QQ171. Logistic regression modeling of groups with associated clinical signs showed that animals with a crouching posture (odds ratio [OR], 20.036) and an abnormal yield to thoracolumbar pressure (OR, 7.117) were at increased risk of ataxia. Pruritus (OR, 0.168) was negatively associated with ataxia. Pruritus (OR, 4.974) and teeth grinding (OR, 4.279) were associated with a positive nibble reflex.

Animals↗
PubMed1978

Movement epilepsy in the monkey with an experimental motor focus.

In the monkey with an alumina focus in the primary motor area, proprioceptive afferents are crucial in triggering or modulating seizures. The reversible exclusion of these afferents by curarization results, depending on the level of activity of the focus, either in regularization of spontaneous seizure frequency and duration (recorded from the cortex), or in their subtotal suppression. In the last case, muscular stimulation is still able to elicit seizures. The triggering modality is highly specific: if it is possible to induce seizures with acoustic or cutaneous stimuli in normal conditions, this is no longer possible under curare. It may then be assumed that exteroceptive stimulation is effective through the startle reaction or flexion reflex that they elicit; in other words, the actual trigger would take origin in the indirect involvement of proprioceptive afferents. Physiological mechanisms and relations with human clinical features are discussed.

Animals↗
PubMed2003

Brain stem pursuit pathways: dissociating visual, vestibular, and proprioceptive inputs during combined eye-head gaze tracking.

Eye-head (EH) neurons within the medial vestibular nuclei are thought to be the primary input to the extraocular motoneurons during smooth pursuit: they receive direct projections from the cerebellar flocculus/ventral paraflocculus, and in turn, project to the abducens motor nucleus. Here, we recorded from EH neurons during head-restrained smooth pursuit and head-unrestrained combined eye-head pursuit (gaze pursuit). During head-restrained smooth pursuit of sinusoidal and step-ramp target motion, each neuron's response was well described by a simple model that included resting discharge (bias), eye position, and velocity terms. Moreover, eye acceleration, as well as eye position, velocity, and acceleration error (error = target movement - eye movement) signals played no role in shaping neuronal discharges. During head-unrestrained gaze pursuit, EH neuron responses reflected the summation of their head-movement sensitivity during passive whole-body rotation in the dark and gaze-movement sensitivity during smooth pursuit. Indeed, EH neuron responses were well predicted by their head- and gaze-movement sensitivity during these two paradigms across conditions (e.g., combined eye-head gaze pursuit, smooth pursuit, whole-body rotation in the dark, whole-body rotation while viewing a target moving with the head (i.e., cancellation), and passive rotation of the head-on-body). Thus our results imply that vestibular inputs, but not the activation of neck proprioceptors, influence EH neuron responses during head-on-body movements. This latter proposal was confirmed by demonstrating a complete absence of modulation in the same neurons during passive rotation of the monkey's body beneath its neck. Taken together our results show that during gaze pursuit EH neurons carry vestibular- as well as gaze-related information to extraocular motoneurons. We propose that this vestibular-related modulation is offset by inputs from other premotor inputs, and that the responses of vestibuloocular reflex interneurons (i.e., position-vestibular-pause neurons) are consistent with such a proposal.

Action Potentials↗
PubMed2006

The effects on sensorimotor performance and balance with Tai Chi training.

OBJECTIVES: To compare the effects of short-term and long-term Tai Chi training on the sensorimotor and balance performance of able-bodied subjects. DESIGN: A nonrandomized cross-sectional controlled trial. SETTING: Sport laboratory. PARTICIPANTS: Forty-eight healthy subjects, 16 with 3 months of experience in Tai Chi training, 16 with 1 to 3 years of experience in Tai Chi training, and 16 with no experience in Tai Chi training. INTERVENTION: Experimental. MAIN OUTCOME MEASURES: The reflex contraction latencies (reaction time) of medial hamstrings and gastrocnemius after perturbation, the active knee joint angle-repositioning error, and the balance time on a tilt board were measured and analyzed with 1-way analysis of covariance. Significant results were further analyzed with post hoc linear contrasts. RESULTS: Long-term Tai Chi practitioners had a significantly faster reflex reaction time in hamstrings (P<.000) and gastrocnemius (P=.043) muscles and a longer balance time on a tilt board (P<.000) than short-term Tai Chi practitioners and nonpractitioners. Both long- and short-term Tai Chi practitioners had significantly less knee joint angle-repositioning error than nonpractitioners (P=.001 and P=.027, respectively). CONCLUSIONS: Tai Chi training of more than 1 year might have the benefits of faster hamstrings and gastrocnemius reflex reaction and improved knee joint position sense (JPS). These changes might be associated with an improved dynamic standing balance. Better knee JPS was shown in subjects with 3 months of Tai Chi practice, but this had not led to a significant improvement in balance.

Adult↗
PubMed2003

Attenuation of human neck muscle activity following repeated imposed trunk-forward linear acceleration.

It has been suggested that, after a passive linear acceleration of a seated subject which resembles a small, rear-end car impact, sensory information from proprioceptive, vestibular, and visual systems elicit stabilizing neck muscular responses. These neck muscular responses are presumably reflex based and are modified with the magnitude of the perturbation. A key issue that remains is to determine whether the neck and head postural responses can be modulated by a previous experience of the acceleration and not only by the magnitude of the acceleration. This question is of interest because, contrary to cadaver studies, one could expect that humans apprehending a rapid trunk acceleration would adopt a bracing behavior to minimize head movements. The aim of the present experiment was to verify whether neck-muscle activities can be modulated when prior knowledge about whole-body acceleration onset, direction, and magnitude are unknown compared with when only acceleration onset is unknown. Nine seated subjects were submitted to 11 imposed, forward linear accelerations (1.1 g). For the first trial, subjects were completely unaware of the platform acceleration characteristics (onset, direction, amplitude, and acceleration magnitude). For the subsequent ten trials, subjects knew they would be submitted to a forward linear acceleration, but the onset of the acceleration was unknown. Head kinematics and EMG responses of the neck muscles to the first perturbation were similar for all subjects (6.2 degrees head extension, EMG activity starting from 55 to 72 ms after platform onset). Following the first trial, however, all subjects showed a decreased neck EMG activity. Moreover, subjects responded in one of two ways across trials: one group of subjects ( n=5) maintained a constant head angular position and velocity, whereas the other group ( n=4) showed an increased head angular position (up to 12.6 degrees ) and velocity. This suggests that the first perturbation trial revealed a completely reactive response. After this initial trial, the responses observed may present a mixture of feedforward and feedback control. It is likely that whiplash injuries occur under conditions resembling those observed for the first trial only. If this is the case, the behavior for the following trials cannot be representative of injury mechanisms occurring in whiplash-like motion. Altogether, our results strongly suggest that, following repeated trunk linear accelerations of a constant magnitude, the nervous system prefers to minimize muscle stress instead of adopting a bracing strategy.

Acceleration↗
PubMedDate not supplied

Urodynamic evaluation of 12 ataxic subjects: neurophysiopathologic considerations.

Twelve ataxic subjects (seven with Friedreich's heredo-ataxia and five with a cerebellar vascular or traumatic lesion) were examined by way of urodynamic evaluation. The results explain the role the cerebellum plays in the modulation of the micturition reflex and confirm the importance of bilateral encephalic damage in causing vesico-sphincteral malfunctioning and the important role of the lateral myelon cords in transporting bladder proprioceptive sensitivity.

Adult↗
PubMed1996

Inhibition of the soleus H-reflex during dorsiflexion is dependent on individual differences in maximal soleus H-reflex as a test reflex.

The quantitative differences among individuals in the natural reciprocal inhibition of the soleus H-reflex during dorsiflexion were examined, in conjunction with the maximal H-reflex as the test reflex size in each individual. Maximal H-reflex was expressed relative to the maximal M-response (H(max)) when compared among individuals. Analysis showed that with increases in H(max) at rest in each individual, the inhibitory effect was first enhanced, then reached a peak, and was finally alleviated. This pattern was similar to the intraindividual pattern of the inhibitory effect induced by specific conditioning stimulus as a function of the test reflex size.

Adolescent↗
PubMedDate not supplied

Cobalamine deficiency associated with neuropathy and oral mucosal melanosis in untreated gluten-sensitive enteropathy.

A 32-year-old woman was admitted with complaints of difficulty in walking and hypoaesthesia and tingling in her legs. She had short stature and brown-black hyperpigmentation, cheliosis, dental irregularities and scars in the axillary regions. Neurological examination revealed mild, symmetric, predominantly distal weakness of the legs; deep tendon reflexes were depressed. There was glove-and-stocking decrease in pinprick and temperature perception but proprioception and light touch were normal. Investigations established a diagnosis of celiac disease; her neurological features improved on gluten-free diet, but oral pigmentation persisted.

Adult↗
PubMed1995

Visual accommodation as a cue for size.

Accommodation micropsia is examined in the general context of ocular accommodation as a cue for object size. The nature and limits of accommodation micropsia and arguments dealing with the possible contribution of accommodation to the perception of size are reviewed. Literature on the anomalous myopias, the intermediate-resting hypothesis, and theories of ciliary muscle innervation is examined critically in so far as it bears on the accommodation-micropsia hypothesis. The anomalous myopias and evidence for the intermediate-resting hypothesis are well documented, but without a mechanism for proprioceptive feedback from the ciliary complex about the state of accommodation it can only be concluded that such feedback would have to be indirect, either via the reflex link with vergence, or possibly through the agency of efference-copy neurones.

Accommodation, Ocular↗
PubMed1999

Mechanosensory pegs constitute stridulatory files in grasshoppers.

Stridulatory files on the inner face of hindleg femora were shown to consist of mechanosensory pegs in males and females of Syrbula montezuma (Saussure) and in males of Chorthippus biguttulus (L.). Females of Chorthippus had stiff protuberances on their stridulatory files, with an innervated tubercle instead of pegs. Pegs and tubercles of adult grasshoppers were shown to develop from innervated tubercular hairs present from the first instar onward in Chorthippus. In adults of Chorthippus, two sensory cells innervated each peg of males and each tubercle of females. Central projections of these afferents from the stridulatory files were very similar to those of the neighboring tactile hairs on the femur. The afferents from pegs in Syrbula responded to deflection and pressure introduced via the widened cuticular cap. In both species, selective stimulation of femoral cuticular receptors elicited antagonistic reflex responses in a coxal retractor muscle: pegs inhibited and neighboring hairs raised the efferent tonic discharges. Apparently, in these two distantly related grasshopper species, stridulatory files function as both sound-producing and proprioceptive organs.

Afferent Pathways↗
PubMed2005

Intrinsic musculoskeletal properties stabilize wiping movements in the spinalized frog.

The mechanical stability properties of hindlimb-hindlimb wiping movements of the spinalized frog were examined. One hindlimb, the wiping limb, was implanted with 12 electromyographic (EMG) electrodes and attached to a robot that both recorded its trajectory and applied brief force perturbations. Cutaneous electrical stimulation was applied to the other hindlimb, the target limb, to evoke the hindlimb-hindlimb wiping reflex. Kinematic and EMG data from both unperturbed trials and trials in which a phasic perturbation was applied were collected from each spinalized frog. In the perturbed behaviors, we found that the initially large displacement attributable to the perturbation was compensated such that the final position was statistically indistinguishable from the unperturbed final position in all of the frogs, thus indicating the dynamic stability of these movements. This stability was robust to the range of perturbation amplitudes and nominal kinematic variation observed in this study. In addition, we investigated the extent to which intrinsic viscoelastic properties of the limb and proprioceptive feedback play a role in stabilizing the movements. No significant changes were seen in the EMGs after the perturbation. Furthermore, deafferentation of the wiping limb did not significantly affect the stability of the wiping reflex. Thus, we found that the intrinsic viscoelastic properties of the hindlimb conferred robust stability properties to the hindlimb-hindlimb wiping behavior. This stability mechanism may simplify the control required by the frog spinal motor systems to produce successful movements in an unpredictable and varying environment.

Animals↗
PubMedDate not supplied

Spinal cord ischemia after cardiac arrest.

Subsequent to cardiac arrest, a 58-year-old man with intractable dysrhythmia and severe arteriosclerosis developed flaccid paraplegia, depressed deep tendon reflexes, and showed no pain or temperature sensation caudal to Th-7 in spite of completely intact proprioception and vibration sensation. An echocardiogram showed no clots or vegetation on the prosthetic valve and no thrombus in the left atrium or left ventricle. The patient's paraplegia was permanent, at least through a follow-up period of 2 years. These findings suggest that the etiology was spinal cord ischemia due to blood supply in the area of the anterior spinal artery (ASA); however, magnetic resonance T2-weighted imaging demonstrated signal abnormalities throughout the gray matter and in the adjacent center white matter. Somatosensory-evoked potentials (SEP) measure neural transmission in the afferent spinal cord pathway, which is located in the lateral and posterior columns of the white matter; these showed a delay in latency between Th-6 and Th-7. The spinal cord is as vulnerable to transient ischemia as the brain. Spinal cord ischemia after cardiac arrest results from principal damage in the anterior horn of the gray matter, the so-called ASA syndrome; however, the pathways of SEP and pathogenesis of the spinal cord ischemia need further investigation.

Evoked Potentials, Somatosensory↗
PubMed1994

Posterior column sensory impairment during ambulatory extradural analgesia in labour.

Ambulatory or "walking" extradural analgesia in labour has recently gained popularity because of preservation of motor function and subjective somatic sensation in the lower limbs, resulting in increased maternal satisfaction. This is produced by combining dilute concentrations (e.g. 0.1%) of bupivacaine with opioids. Detailed clinical neurological examination after mobile extradural analgesia has not been reported. We have investigated the effect of 0.1% bupivacaine 15 ml and fentanyl 2 micrograms ml-1 on motor and sensory function in the lower limbs in 50 primigravidae requesting extradural analgesia in labour. This was performed before and 30 min after confirming placement of a lumbar extradural catheter. While power, co-ordination and reflexes in all lower limb muscle groups remained within normal limits, 66% (n = 33) developed abnormal distal proprioception, 44% (n = 22) had a positive Romberg's sign and 38% (n = 19) had altered vibration sense. Moreover, 44% (n = 22) said that their legs felt different on standing and they did not feel confident walking unaccompanied. However, this subjective perception correlated poorly with the presence of posterior column sensory signs. Although there was a reduction in pain scores on a visual analogue scale after 30 min (mean 8.85 (SEM 0.3) vs 3.06 (0.32); P < 0.0001), pain increased within 60 min (5.77 (0.45); P < 0.001).

Analgesia, Epidural↗