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Two versions of the hypothesis that discrete movements are produced by shifts in the system's equilibrium point are considered. The first suggests that shifts are monotonic and end near the peak velocity of movement, and the second presumes that they are nonmonotonic ("N-shaped") and proceed until the end of movement. The first version, in contrast to the second, predicts that movement time may be significantly reduced by opposing loads without changes in the control pattern. The purpose of the present study was to test the two hypotheses about the duration and shape of the shift in the equilibrium point based on their respective predictions concerning the effects of perturbations on kinematic and EMG patterns in fast elbow flexor movements. Subjects performed unopposed flexions of about 55-70 degrees (control trials) and, in random test trials, movements were opposed by spring-like loads generated by a torque motor. Subjects had no visual feedback and were instructed not to correct arm deflections in case of perturbations. After the end of the movement, the load was removed leading to a secondary movement to the same final position as that in control trials (equifinality). When the load was varied, the static arm positions before unloading and associated joint torques (ranging from 0 to 80-90% of maximum voluntary contraction) had a monotonic relationship. Test movements opposed by a high load (80-90% of maximal voluntary contraction) ended near the peak velocity of control movements. Phasic and tonic electromyographic patterns were load-dependent. In movements opposed by high loads, the first agonist burst was significantly prolonged and displayed a high level of tonic activity for as long as the load was maintained. In the same load conditions, the antagonist burst was suppressed during the dynamic and static phases of movement. The findings of suppression of the antagonist burst does not support the hypothesis of an N-shaped control signal. Equally, the substantial reduction in movement time by the introduction of an opposing load cannot be reconciled in this model. Instead, our data indicate that the shifts in the equilibrium point underlying fast flexor movements are of short duration, ending near the peak velocity of unopposed movement. This suggests that kinematic and electromyographic patterns represent a long-lasting oscillatory response of the system to the short-duration monotonic control pattern, external forces and proprioceptive feedback.
The response discharges of precentral motor cortical cells to brief trains of vibration applied to the tendon of biceps brachii were analyzed in two alert but passive monkeys. The activity of 20 phasic-tonic and 6 tonic cells was analyzed. All had functional linkages with flexor muscles during a preceding flexion task and responded to passive movement of the elbow. Taking as a reference the stereotyped reflex response in the stretched muscle, the effect of changes in the amplitude of a constant frequency vibration (4 vibrations at 58 Hz) was quantified statistically in peristimulus histograms of the cortical cell discharges. All cells were transiently influenced by low vibration amplitudes. Most responses (71%) were excitatory and occurred at a mean latency of 24 ms, which is consistent with cells activated by input from stretch receptors. Excitatory, reproducible responses to the lowest vibration amplitudes were more frequent in phasic-tonic than in pure tonic cells. Large-amplitude vibrations always excited the motor cortical cells. The sign of the responses to vibration matched that to passive elbow movements for most cells. These findings show that elbow-related motor cortical cells are very sensitive to proprioceptive input from primary spindle afferents.
OBJECTIVE: To test the hypothesis that motoneuron excitability in stroke subjects is influenced by peripheral sensory input through passive exercise to the hemiplegic upper extremity. DESIGN: Case-control prospective study. SETTING: Physical medicine and rehabilitation inpatient and outpatient clinic at a tertiary Veterans Affairs medical center. PARTICIPANTS: Nineteen hemiplegic adult subjects with a history of a cerebrovascular event. INTERVENTION: A standardized passive exercise program was performed on the right upper extremity by using a robotic arm. Nerve conduction study of the median nerve was obtained before and after the exercise. Maximum onset and peak amplitudes of the Hoffmann reflex (Hmax) and motor response (Mmax) wave were recorded. MAIN OUTCOME MEASURES: Hmax, Mmax, and Hmax/Mmax ratio. RESULTS: Immediately after passive exercise, there was no significant alteration in the Hmax (P=.94), Mmax (P=.60), or Hmax/Mmax ratio (P=.53) as compared with pre-exercise evoked responses. CONCLUSIONS: Peripheral proprioceptive input with passive exercise does not cause appreciable change in the Hmax/Mmax ratio, suggesting that motoneuron excitability of the affected upper extremity in stroke subjects is not influenced by passive robotic intervention.
Altered efficacy, from change in receptor discharge with different positions of the knee, was investigated in a heteronymous Ib reflex of the human leg. The electrical stimulus was low threshold, to the common peroneal nerve. The divergence of the group I afferents was studied in the electromyograms (EMGs) of ipsilateral and contralateral thigh muscles. The stimulus evoked ipsilateral, short latency, excitation in the three quadriceps muscles studied and inhibition in the knee flexor semitendinosus (ST), with prior contraction of target muscles. This excitation and inhibition did not alter when studied over the range of the knee joint. The stimulus did not evoke responses in contralateral thigh muscles, contracted or relaxed. It is concluded that (1) any change in convergence from discharge of receptors, during extension of the limb, is small and sub-threshold, and (2) this spinal proprioceptive level of neural control appears to be directed primarily to the single limb.
Microgravity provides unique, though experimentally challenging, opportunities to study motor control. A traditional research focus has been the effects of linear acceleration on vestibular responses to angular acceleration. Evidence is accumulating that the high-frequency vestibulo-ocular reflex (VOR) is not affected by transitions from a 1 g linear force field to microgravity (<1 g); however, it appears that the three-dimensional organization of the VOR is dependent on gravitoinertial force levels. Some of the observed effects of microgravity on head and arm movement control appear to depend on the previously undetected inputs of cervical and brachial proprioception, which change almost immediately in response to alterations in background force levels. Recent studies of post-flight disturbances of posture and locomotion are revealing sensorimotor mechanisms that adjust over periods ranging from hours to weeks.
Rheumatoid arthritis is considered to represent a disease of the synovial membrane, osteoarthritis of the hyaline articular cartilage, and osteoporosis of the bone. It can be questioned to what extent this is true and to what extent these diseases could be considered to be due to extra-articular, extra-skeletal pathology related to the neuroendocrine system. Pain is the main symptom in arthritis. This is related to prostaglandin-mediated sensitization of the primary afferent nociceptive nerves. Accordingly, nonsteroidal anti-inflammatory drugs are used in symptomatic treatment, occasionally together with opioids and tricyclic antidepressants. The midline symmetry and involvement of the richly innervated, small peripheral joints in rheumatoid arthritis have raised speculation about the role of neurogenic inflammation and neuropeptides in its pathogenesis. In contrast to the free nerve endings, the role of the proprioceptive sensors is to provide information of our actual motor performance (the afferent copy of our movements) compared to the efferent motor program, which is activated by our will to move. These include proprioceptors in the skin (e.g., Meissner corpuscles), muscles (annulospiral and flower-spray endings of the muscle spindles), Golgi tendon organs, and Ruffini end organs and Pacinian corpuscles in the superficial and deep layers of the joint capsule. Elderly people may have slow reflexes, lax joints, joint incongruity, and loss of muscle power; obesity, alcohol and medicinal use, and joint pain can be combined with poor/nonexisting capacity for repair and remodeling of the musculoskeletal tissues. Impaired biomechanics contributes to increased joint tenderness, accumulation of minor trauma (secondary osteoarthritis), and falls (osteoporotic fractures). More attention needs to be paid to aging of proprioception, not only to the terminal disease target.
We reviewed 153 episodes of cobalamin deficiency involving the nervous system that occurred in 143 patients seen over a recent 17-year period at 2 New York City hospitals. Pernicious anemia was the most common underlying cause of the deficiency. Neurologic complaints, most commonly paresthesias or ataxia, were the first symptoms of Cbl deficiency in most episodes. The median duration of symptoms before diagnosis and treatment with vitamin B12 was 4 months, although long delays in diagnosis occurred in some patients. Diminished vibratory sensation and proprioception in the lower extremities were the most common objective findings. A wide variety of neurologic symptoms and signs were encountered, however, including ataxia, loss of cutaneous sensation, muscle weakness, diminished or hyperactive reflexes, spasticity, urinary or fecal incontinence, orthostatic hypotension, loss of vision, dementia, psychoses, and disturbances of mood. Multiple neurologic syndromes were often seen in a single patient. In 42 (27.4%) of the 153 episodes, the hematocrit was normal, and in 31 (23.0%), the mean corpuscular volume was normal. Neutropenia and thrombocytopenia were unusual even in anemic patients. In nonanemic patients in whom diagnosis was delayed, neurologic progression frequently occurred although the hematocrit remained normal. In 27 episodes, the serum cobalamin concentration was only moderately decreased (in the range of 100-200 pg/ml) and in 2 the serum level was normal. Neurologic impairment, as assessed by a quantitative severity score, was judged to be mild in 99 episodes, moderate in 39 and severe in 15. Severity of neurologic dysfunction before treatment was clearly related to the duration of symptoms prior to diagnosis. In addition, the hematocrit correlated significantly with severity, independent of the longer duration of symptoms in nonanemic patients. Four patients experienced transient neurologic exacerbations soon after beginning treatment with cyanocobalamin, with subsequent recovery. Followup evaluation was adequate to assess the neurologic response to vitamin B12 therapy in 121 episodes. All patients responded, and in 57 (47.1%), recovery was complete, with no remaining symptoms or findings on examination. The severity score was reduced by 50% or greater after treatment in 91% of the episodes. Residual long-term moderate or severe neurologic disability was noted following only 7 (6.3%) episodes. The extent of neurologic involvement after treatment was strongly related to that before therapy as well as to the duration of symptoms. The percent improvement over baseline neurologic status after treatment was inversely related to duration of symptoms and hematocrit. Some evidence of response was always seen during the first 3 months of treatment.(ABSTRACT TRUNCATED AT 400 WORDS)
Single-case, longitudinal studies of the three-dimensional vestibulo-ocular response (VOR) were conducted with two spaceflight subjects over a 180-day mission. For reference, a control study was performed in the laboratory with 13 healthy volunteers. Horizontal, vertical and torsional VOR was measured during active yaw, pitch and roll oscillations of the head, performed during visual fixation of real and imaginary targets. The control group was tested in the head-upright position, and in the gravity-neutral, onside and supine positions. Binocular eye movements were recorded throughout using videooculography, yielding eye position in Fick co-ordinates. Eye velocity was calculated using quaternion algebra. Head angular velocities were measured by a head-mounted rate sensor. Eye/head velocity gain and phase were evaluated for the horizontal, vertical and torsional VOR. The inclination of Listing's plane was also calculated for each test session. Control group gain for horizontal and vertical VOR was distributed closely around unity during real-target fixation, and reduced by 30-50% during imaginary-target trials. Phase was near zero throughout. During head pitch in the onside position, vertical VOR gain did not change significantly. Analysis of up/down asymmetry indicated that vertical VOR gain for downward head movement was significantly higher than for upward head movement. Average torsional VOR gain with real-target fixation was significantly higher than with imaginary-target fixation. No difference in phase was found. In contrast to vertical VOR gain, torsional VOR gain was significantly lower in the gravity-neutral supine position. Spaceflight subjects showed no notable modification of horizontal or vertical VOR gain or phase during real-target fixation over the course of the mission. However, the up/down asymmetry of vertical VOR gain was inverted in microgravity. Torsional VOR gain was clearly reduced in microgravity, with some recovery in the later phase. After landing, there was a dip in gain during the first 24 h, with subsequent recovery to near baseline over the 13-day period tested. Listing's plane appeared to remain stable throughout the mission. The findings reflect various functions of the otolith responses. The reduced torsional VOR gain in microgravity is attributed to the absence of the gravity-dependent, dynamic stimulation to the otoliths (primarily utricles). On the other hand, the reversal of vertical VOR up/down gain asymmetry in microgravity is attributed to the off-loading of the constant 1-g bias (primarily to the saccules) on Earth. The observed increase in torsional VOR gain from the 1st to the 6th month in microgravity demonstrates the existence of longer-term adaptive processes than have previously been considered. Likely factors are the adaptive reweighting of neck-proprioceptive afferents and/or enhancement of efference copy.
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It has been shown in previous investigations that the recruitment order of motor units is different in tonic and in phasic voluntary activity. The significance of the pre-existing state of facilitation in the motoneurone pool for the recruitment of units is studied, using the phasic flexion reflex in the anterior tibial muscle as test reflex. It is shown that the recruitment order of units in a series of reflexes (1) is unstable if the subject does not expect the stimulus; (2) is stable and identical with that in tonic activity if the subject subliminally facilitates the motoneurone pool before the reflex activation; (3) is stable and almost identical with that in tonic activity if the subject expects the stimulus and therefore involuntarily influences the motoneurone pool; (4) is stable and similar to that in phasic voluntary activity if the subject inhibits the motoneurone pool before the activation and the stimulus strength thus consequentially is increased; and (5) is influenced by blockade of the proprioceptive afferent impulses from the muscle. It is concluded that normal man can select in advance the recruitment order of motor units most appropriate for the work intended.
The neural histology of the anterior band of the inferior glenohumeral ligament (IGHL) was studied in 11 fresh shoulder specimen using a special silver impregnation technique. Between the collagen fibers small myelinated and unmyelinated dendrites could be detected. The appearance of neurovascular structures in the adjacent synovial layer clearly exceeded the typical supply to soft tissues. Analysing about 11,000 sections Ruffini mechanoreceptors that are known to be slow adapting were found on the humeral insertion of the band. The sections containing these neural end organs were identified by means of transillumination and reflection-contrast microscopy and reconstructed using three-dimensional image processing. The presence of neural structures including Ruffini corpuscles in these most important passive stabilizers of the shoulder joint shows that these ligaments function also as an active safety device. There slow adaption is a prerequisite for muscular reflexes counteracting the tensile stresses to which the passive stabilizing structures of the shoulder are exposed. A disruption of the continuity of these structures by mechanical forces or surgery can reduce the biofeedback and proprioceptive quality and thus lead to a decrease of shoulder function and/or stability. These observations should be taken into account when planning surgical interventions involving the IGHL. Procedures like capsule shifts or plications may affect mechanoreceptor orientation and concentrations, thereby affecting the interaction between these structures and the synergistic muscles. When possible, these intervention should avoid receptor-dense regions while attempting to restore normal anatomical orientation and tissue tension.
When moving an object, the motor system estimates the dynamic properties of the object and then controls the movement using a combination of predictive feedforward control and proprioceptive feedback. In this study, we examined how the feedforward and proprioceptive feedback processes depend on the expected movement task. Subjects made fast elbow flexion movements from an initial position to a target. The experimental protocol included movements made over a short and a long distance against an expected light or heavy inertial load. In each task in a few randomly chosen trials, a motor applied an unexpected viscous load that produced a velocity error, defined as the difference between the expected and unexpected velocities, and electromyographic (EMG) responses. The EMG responses appeared not earlier than 170-250 ms from the agonist EMG onset. Our main finding is that the onset of the EMG responses was correlated with the expected time of peak velocity, which increased for longer distances and larger loads. An analysis of the latency of the EMG responses with respect to the velocity error suggested that the EMG responses were due to segmental reflexes. We conclude that segmental reflex gains are centrally modulated with the time course dependent on the expected movement task. According to this view, the control of fast point-to-point movement is feedforward from the agonist EMG onset until the expected time of peak velocity after which the segmental reflex feedback is briefly facilitated.
Cervically induced eye movements consist of a nystagmus and a deviation of the mean eye position (shift). They show in relation to different neck torsion velocities maximum reactions at slow velocities. The clinical significance of these cervico-ocular reactions is discussed controversially. Therefore we investigated 40 healthy subjects without any neurootological findings, who, in addition, underwent a manual examination. The neck torsion test was performed automatically with quantifiable stimulus parameters and a complete head fixation by means of individual dental casts. It could be shown that at a constant chair velocity of 5 degrees/s every healthy subject exhibits cervical nystagmus and/or shift deviations. In comparison a group of 30 patients with an upper cervical spine syndrome also showed similar cervico-ocular reactions without significant difference. It can be concluded that a muscle hypertonus in the deep neck region does not lead to pathological, cervically induced eye movements and that the cervical nystagmus itself is not a pathognomonic sign for cervical, proprioceptive vertigo.
To investigate the role of localized, proprioceptive feedback in the regulation of interjoint coordination during locomotion, we substantially attenuated neural feedback from the triceps surae muscles in one hindlimb in each of four cats using the method of self-reinnervation. After allowing the recovery of motor innervation, the animals were filmed during level and ramp walking. Deficits were small or undetectable during walking on the level surface or up the ramp, behaviors that require a large range of forces in the triceps surae muscles. During walking down the ramp, when the triceps surae muscles normally undergo active lengthening, the ankle joint underwent a large yield and the coordination between ankle and knee was disrupted. The correlation of the deficit with the direction of length change and not muscle force suggested that a loss of feedback from muscle spindle receptors was primarily responsible for the deficit. These results indicate an important role for the stretch reflex and stiffness regulation during locomotion.
The tricyclic antidepressant, doxepin, has been reported to be a potent local anesthetic in rat sciatic nerve blockade. We hypothesized that topical doxepin has significantly longer antinociception compared with control and intrathecally compared with bupivacaine. Solutions of 0.3 mL of doxepin at 50, 75, and 100 mM and control (only the vehicle solution) were applied as a patch to the shaved dorsal skin of rats. After a 2-h contact interval, the patch was removed, and the rats were tested by three sets of six pinpricks. Inhibition of withdrawal to pain and cutaneous trunci muscle reflex were graded. In the second investigation, 60 muL of doxepin at 10, 20, and 50 mM was injected through intrathecal catheters implanted in the lumbar region of rats, which were evaluated for motor function, proprioception, and nociception. Topical doxepin at concentrations of 75 mM and 100 mM was significantly more effective than control (P < 0.05). Complete recovery for the 100-mM concentration occurred at 60 h, although two of five rats demonstrated erythema and scarring. Intrathecally, 20 mM of doxepin was not significantly different for motor and proprioceptive function from 23 mM (0.75%) bupivacaine; however, neurotoxicity (defined as persistent neurological deficit) commenced at 50 mM.
Phylogenesis, ontogenesis and anatomy explain the close relationship between temporo-mandibular joint and the middle ear and can therefore help understanding otologic symptoms such as: otalgia which often correspond to articular and muscular pain irradiation (coming from sterno-cleido-mastoid, lateral and medial pterygoid, deep layer of the masseter and temporal muscles); acouphens and ear block sensation that could be caused by a spasm extension of the manducatory (i.e. medial pterygoid) to levator and tympani tensors. These three muscles, which originate from the first branchial arch, have a proprioceptive sensitivity and share the same innervation. What is more tensor and levator veli exchange certain muscular fibers. Tensor tympani spasm can be held responsible both for a decrease or abolition of the Klockhoff's reflex, together with a decrease of the stapedian reflex, the latter due to tympani rigidity induced by a spasm of the tensor tympani.
The axis of head rotation is usually different from the axis of eye rotation. Geometrical considerations show that the eyes translate with respect to visual targets located near the head. In order to accurately stabilize retinal images against this translation, the vestibulo-ocular reflex (VOR) must be modulated inversely with the target's distance. The neural correlate of viewing distance used to modulate the VOR is not known. Since vergence angle is related inversely to viewing distance, an efference copy of instantaneous vergence angle or proprioceptive afferent information from extraocular muscles could be used to adjust the VOR. To examine this hypothesis, we compared the time-course of changes in the VOR with the time-course of changes in vergence angle. The VOR was induced by briefly rotating monkeys about a vertical axis at different times during the execution of vergence eye movements. We found that the amplitude of the VOR changed systematically during the course of a vergence eye movement. On average, the changes in the amplitude of vestibular induced eye movements anticipated changes in vergence angle by 50 msec, but in some instances, up to 200 msec of anticipation was observed. These data suggest that a central command signal rather than an afferent or efferent copy of vergence eye position was used to modulate the VOR.