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PubMed2001

The neurophysiological substrate for the cervico-ocular reflex in the squirrel monkey.

Passive rotation of the trunk with respect to the head evoked cervico-ocular reflex (COR) eye movements in squirrel monkeys. The amplitude of the reflex varied both within and between animals, but the eye movements were always in the same direction as trunk rotation. In the dark, the COR typically had a gain of 0.3-0.4. When animals fixated earth-stationary targets during low-frequency passive neck rotation or actively tracked moving visual targets with head movements, the COR was suppressed. The COR and vestibulo-ocular reflex (VOR) summed during passive head-on-trunk rotation producing compensatory eye movements whose gain was greater than 1.0. The firing behavior of VOR-related vestibular neurons and cerebellar flocculus Purkinje cells was studied during the COR. Passive neck rotation produced changes in firing rate related to neck position and/or neck velocity in both position-vestibular-pause neurons and eye-head-vestibular neurons, although the latter neurons were much more sensitive to the COR than the former. The neck rotation signals were reduced or reversed in direction when the COR was suppressed. Flocculus Purkinje cells were relatively insensitive to COR eye movements. However, when the COR was suppressed, their firing rate was modulated by neck rotation. These neck rotation signals summed with ocular pursuit signals when the head was used to pursue targets. We suggest that the neural substrate that produces the COR includes central VOR pathways, and that the flocculus plays an important role in suppressing the reflex when it would cause relative movement of a visual target on the retina.

Action Potentials↗

PubMed2005

Elucidation of a potentially destabilizing control strategy in ACL deficient non-copers.

PURPOSE: The purpose was to differentiate the dynamic knee stabilization strategies of potential copers (individuals who have the potential to compensate for the absence of an ACL without episodes of giving way after return to pre-injury activities) and non-copers (those who have knee instability following ACL rupture with return to pre-injury activities). METHODS: Twenty subjects with ACL rupture were assigned to potential coper (n=10) and non-coper (n=10) groups via a screening examination. Ten active people without lower extremity injury were also tested. Knee angle, tibial position and muscle activity data were collected while subjects stood in unilateral stance on a platform that moved horizontally in an anterior direction. Analysis included the preparation for platform movement; and monosynaptic, intermediate reflex and voluntary response intervals after platform movement. RESULTS: Non-copers showed greater knee flexion than uninjured subjects, and had a posterior tibial position and altered hamstring recruitment compared to the other groups. Potential copers demonstrated greater medial quadriceps activity while maintaining knee kinematics similar to uninjured subjects. Both potential copers and non-copers had greater co-contraction between medial hamstrings and quadriceps than uninjured subjects. All excitatory muscle activation occurred in the intermediate reflex interval. DISCUSSION AND CONCLUSIONS: Non-copers displayed aberrant muscle recruitment that may contribute to knee instability. Potential copers maintained normal tibial position using a strategy that permits quadriceps activation without excessive anterior tibial translation. Muscle recruitment in the intermediate reflex interval suggests neuromuscular training may influence the strategies.

Adaptation, Physiological↗

PubMed1995

Extraocular muscle proprioception and eye position.

In the lamb, acute unilateral section of the ophthalmic branch induced in the ipsilateral eye occasional oscillations of the resting position and misalignment of the horizontal vestibulo-ocular reflex (HVOR) with respect to the stimulus. Additional electrolytic lesion of the cells innervating the proprioceptors of the medial rectus muscle, or of the lateral rectus muscle in the contralateral semilunar ganglion, provoked a 4 degrees-7 degrees consensual eye deviation towards and away from the lesioned side, respectively. The optokinetic beating field was similarly deviated. Under these experimental conditions, HVOR showed enhanced gain and marked misalignment in both eyes. Therefore, the selective suppression of muscular proprioceptive input deviated both eyes towards the direction opposite to the muscle whose gangliar proprioceptive representation has been destroyed.

Animals↗

PubMed1997

The effects of chronic effusion on knee joint proprioception: a case study.

Knee joint effusion has been shown to cause a reflex inhibition of the quadriceps musculature. However, the effect of effusion on knee joint proprioception has not been thoroughly investigated. This issue is further clouded by the debate surrounding the role of the muscle spindle and joint mechanoreceptors in providing afferent feedback to the central nervous system. This case study examines the effects of a chronic effusion on knee joint proprioception. Possible suggestions for the results are discussed, and areas for further study are offered.

Arthroscopy↗

PubMedDate not supplied

[Effect of stimulation of the spinal cord on phasic and tonic reflexes in patients with central motor neuron damage].

Spinal cord stimulation (SCS) is a method enabling the control of increased muscle tonus to be achieved in various spinal cord injuries. Polyelectromyographic (PEMG) methods were used for neurophysiological assessment of the degree of cord damage and persistent spinal reflexes as well as supramedullary influences. The analysed material comprised 40 PEMG records in 19 patients with spastic paraparesis or paraplegia after cord injury, cord tumour or multiple sclerosis. In 15 cases tentative epidural cord stimulation was done and 11 patients received implantation of a system for long-term stimulation. In most cases the epidural electrodes were implanted below the damaged segment, usually in the thoracic part of the cord. Before and after SCS beginning PEMG was done with a 16-channel Mingograph Siemens Elema with simultaneous recording of the responses from the symmetric muscles: quadriceps, semitendinous, adductor femoris, anterior tibialis and triceps surae. The effect of SCS was analysed on exteroceptive and proprioceptive reactions during testing of knee and ankle reflexes, and on the response of the muscles to vibration. In most patients a reduction was observed of the intensity of tendon reflexes, particularly the spread of the reflex to the contralateral extremity was no longer seen. The vibration reflex had a tonic character persisting in 48% of the studied muscles, even in patients with clinically complete transsection of the cord. The change of the character of monosynaptic reflexes and the presence of the vibration reflex suggest that SCS modifies the proprioceptive segmental spinal reactions.

Adult↗

PubMed1988

Human jaw muscle motor behaviour. II. Reflex and receptor mechanisms.

The stretch reflex is much more complicated than the simple tendon jerk with a monosynaptic reflex pathway. Muscle stretch is not a necessary prerequisite to elicit the short latency EMG excitatory response. Long latency EMG responses are probably of greater functional importance. The silent period (SP) following the jaw jerk is prolonged in patients with symptoms of mandibular dysfunction. In the individual case, however, measurement of the SP may not be of diagnostic value. The Golgi tendon organs are highly sensitive tension receptors which play a much larger role in the proprioceptive regulation of muscle tension than has been believed in the past. So-called type P mechanoreceptors which like a large part of the periodontal receptors have their cells of origin in the mesencephalic nucleus V, have been found in the hard palate. The majority of periodontal mechanoreceptors are slowly adapting and thus able to respond with sustained discharge to long lasting stimulation, as during chenching or bruxing. The postural position has been assigned great clinical significance. It has been assumed that this position is constant throughout life. It has, however, been observed that the postural position rapidly adapts to changes of the vertical occlusal dimension.

Electromyography↗

PubMed1974

Disturbances in the voluntary recruitment order of anterior tibial motor units in spastic paraparesis upon fatigue.

The recruitment order of motor units in the tibialis anterior muscle upon fatigue of tonic voluntary contraction was studied in 20 patients with severe spastic paraparesis. An electromyographic technique for secure identification of single motor units was used. Before fatigue the recruitment order is stable and low-frequency units are recruited before high-frequency units; this recruitment pattern agrees with that in normal voluntary activity. When fatigue appears, however, the recruitment order becomes indefinite and high-frequency units can be recruited before low-frequency units; this recruitment pattern agrees with that in normal phasic voluntary activity. Finally, all voluntary activation power disappears, even in the case of units which have never been active. Contraction ability and original recruitment order are restored upon rest but also upon tonic reflex support of the voluntary drive. Whether the fatigue reaction may be due to insufficient gamma motoneurone innervation and whether it is related to spasticity are discussed. The practical physiotherapeutic implications are reviewed.

Electromyography↗

PubMed2005

Smooth pursuit rather than visual signals mediate short-term adaptation of the cervico-ocular reflex in humans.

Cervical stimulation in the horizontal plane induces small and variable eye movements in normal human adults [cervico-ocular reflex (COR)]. In patients with bilateral vestibular loss, the slow COR component increases in amplitude and is thought to contribute to gaze stabilization during head movements, as it is directed opposite to head-on-trunk excursions. The procedures underlying COR slow phase gain enhancement in the compensatory direction remain unclear. We studied the horizontal COR during passive trunk oscillations of +/-16 degrees under the stationary head at 0.1 Hz in ten normal subjects, aged 24-30 years, before and immediately after the application of an adaptation procedure engaging various combinations of sinusoidal neck-proprioceptive, pursuit and retinal slip signals. The duration of this adaptation period was 40 min. A significant gain increase and phase modulation in the compensatory direction were observed in four out of eight subjects after exposing them to neck-proprioceptive stimulation, while pursuing a spot moving in-phase with their trunk. In contrast, staring at the rotating optokinetic pattern or fixating at a stationary spot, while being subjected to combined cervical and optokinetic stimulation, failed to result in any significant modification of the subjects' COR gain and phase. Conceivably, the contribution of the pursuit system was greatly reduced in the paradigm using optokinetic stimulation, while full engagement of retinal slip signals, in the absence of any pursuit contribution, was obtained in the latter adaptation paradigm. These results indicate that motor responses of target tracking rather than simply sensory signals of retinal slip may represent the 'error signal' modifying the COR in humans.

Adaptation, Physiological↗

PubMed1995

Imaginary gaze effects on eye movements induced by linear acceleration: involvement of vestibular induced smooth pursuit eye movement.

We investigated smooth eye movements elicited i) by linear acceleration in a space-fixed imaginary gaze condition (smooth component of eye movement induced by linear motion: LSEM) and ii) during acoustic pursuit of a moving sound source (smooth component of eye movement induced by acoustic pursuit of a sound source: SSPEM). The two conditions were examined using the same test subjects. LSEM and SSPEM performance was found to be positively correlated across the subject population. From the comparison of LSEM and SSPEM we propose the following hypothesis: LSEM consists not only of a pure translational vestibular-ocular reflex (tVOR) component but also of a component based on the perception of otolithic information. Accordingly, this second component is instrumental in the pursuit of an imaginary visual target during linear self-motion.

Acceleration↗

PubMed1994

Propofol infusion and the suppression of consciousness: dose requirements to induce loss of consciousness and to suppress response to noxious and non-noxious stimuli.

We have defined the infusion dose requirements of propofol to suppress consciousness and response to a variety of graded non-noxious and noxious stimuli in 52 unpremedicated patients aged 16-40 yr and 32 patients aged 41-65 yr. They were allocated to receive one of five loading dose-infusion schemes designed to establish stable conditions covering the range from wakefulness, through sedation, to loss of consciousness and anaesthesia. At 10 and 20 min after the loading dose, each patient's response to a graded series of stimuli was recorded. Probit analysis was used to derive mean values (95% confidence interval) for the ED50 and ED95 (as final infusion rate) for loss of response to verbal command at 4.9 (4.7-5.1) mg kg-1 h-1 and 7.9 (7.3-8.8) mg kg-1 h-1, respectively, in the young group and 4.2 (4.0-4.4) mg kg-1 h-1 and 5.8 (5.4-6.4) mg kg-1 h-1, respectively, in the older group. In both groups the dose-response curves for suppression of proprioception, finger counting and perception of light touch in conscious patients were shifted to the left of the curves for loss of consciousness and eyelash reflex. Dose-response curves for noxious stimuli were shifted to the right of those for loss of consciousness.

Adolescent↗

PubMed2005

Central suppression of regenerated proprioceptive afferents.

Long after a cut peripheral nerve reinnervates muscle and restores force production in adult cats, the muscle does not respond reflexively to stretch. Motivated by the likelihood that stretch areflexia is related to problems with sensing and controlling limb position after peripheral neuropathies, we sought to determine the underlying mechanism. Electrophysiological and morphological measurements were made in anesthetized rats having one of the nerves to the triceps surae muscles either untreated or cut and immediately rejoined surgically many months earlier. First, it was established that reinnervated muscles failed to generate stretch reflexes, extending observations of areflexia to a second species. Next, multiple elements in the sensorimotor circuit of the stretch reflex were examined in both the PNS and CNS. Encoding of muscle stretch by regenerated proprioceptive afferents was remarkably similar to normal, although we observed some expected abnormalities, e.g., increased length threshold. However, the robust stretch-evoked sensory response that arrived concurrently at the CNS in multiple proprioceptive afferents produced synaptic responses that were either smaller than normal or undetectable. Muscle stretch failed to evoke detectable synaptic responses in 13 of 22 motoneurons, although electrical stimulation generated monosynaptic excitatory postsynaptic potentials that were indistinguishable from normal. The ineffectiveness of muscle stretch was not attributable therefore to dysfunction at synapses made between regenerated Ia afferents and motoneurons. Among multiple candidate mechanisms, we suggest that centrally controlled neural circuits may actively suppress the sensory information encoded by regenerated proprioceptive afferents to prevent recovery of the stretch reflex.

Afferent Pathways↗

PubMed2006

Stretch reflex and Hoffmann reflex responses to osteopathic manipulative treatment in subjects with Achilles tendinitis.

CONTEXT: Irvin M. Korr, PhD, hypothesized that sensitivity of the monosynaptic stretch reflex (ie, deep tendon reflex) plays a major role in the restriction-of-motion characteristic of somatic dysfunction, and that restoration of range of motion through osteopathic manipulative treatment (OMT) could be achieved by resetting of the stretch receptor gain. OBJECTIVE: To test Korr's hypothesis in the context of Achilles tendinitis, examining whether OMT applied to patients with Achilles tendinitis reduces the strength of the stretch reflex. METHODS: Subjects were recruited through public advertisements and referrals from healthcare professionals. There were no recruitment restrictions based on demographic factors. Amplitudes for stretch reflex and H-reflex (Hoffmann reflex) in the triceps surae muscles (the soleus together with the lateral and medial heads of the gastrocnemius) were measured in subjects with diagnosed Achilles tendonitis (n=16), both before and after OMT. These measurements were also made in asymptomatic control subjects (n=15) before and after sham manipulative treatment. RESULTS: As predicated on the concepts of the strain-counterstrain model developed by Lawrence H. Jones, DO, the use of OMT produced a 23.1% decrease in the amplitude of the stretch reflex of the soleus (P<.05) in subjects with Achilles tendinitis. Similarly significant responses were measured in the lateral and medial heads of the gastrocnemius in OMT subjects. The H-reflex was not significantly affected by OMT. In control subjects, neither reflex was significantly affected by sham manipulative treatment. By using a rating scale on questionnaires before treatment and daily for 7 days posttreatment, OMT subjects indicated significant clinical improvement in soreness, stiffness, and swelling. CONCLUSION: The reduction of stretch reflex amplitude with OMT, together with no change in H-reflex amplitude, is consistent with Korr's proprioceptive hypothesis for somatic dysfunction and patient treatment. Because subjects' soreness ratings also declined immediately after treatment, decreased nociceptor activity may play an additional role in somatic dysfunction, perhaps by altering stretch reflex amplitude.

Achilles Tendon↗

PubMed1993

Proprioception after rupture of the anterior cruciate ligament. An objective indication of the need for surgery?

Failure of conservative treatment is the usual indication for the reconstruction of a knee with deficiency of the anterior cruciate ligament (ACL) and this depends on subjective judgement. The ability of muscles to protect the subluxing joint by reflex contraction could provide an objective measurement. We have studied 30 patients with unilateral ACL deficiency by measuring the latency of reflex hamstring contraction. We found that the mean latency in the injured leg was nearly twice that in the unaffected limb (99 ms and 53 ms respectively). There was a significant correlation between the differential latency and the frequency of 'giving way' indicating that functional instability may be due, in part, to loss of proprioception. Measures of proprioception, including reflex hamstring latency, may be useful in providing an objective assessment of the efficacy of conservative treatment and the need for surgery.

Adult↗

PubMed2005

Effect of quadriceps contraction on upper limb position sense errors in humans.

Short-length muscle contraction (hold-short conditioning) causes limb position sense errors after the muscle returns to its intermediate length; this is due to intrafusal muscle thixotropy, which raises the muscle spindle sensitivity. In humans, contraction of muscles in the upper body (referred to as the Jendrassik manoeuvre) reinforces tendon reflexes in the lower limbs. However, it is unclear whether such a reinforcement manoeuvre enhances thixotropic position sense errors. We studied the effect of quadriceps contraction on upper limb position sense errors induced by hold-short conditioning of the biceps in 12 healthy men. Quadriceps contraction increased the tonic vibration reflex of the biceps, suggesting that quadriceps contraction has a reinforcing effect similar to that of the Jendrassik manoeuvre. After hold-short conditioning of the right biceps, subjects perceived that the conditioned forearm was placed in a more extended position than it actually was. Such position sense errors were enhanced during quadriceps contraction and the degree of error was increased with the intensity of the quadriceps contraction. These results suggest that limb position sense is affected by remote muscle contraction.

Adult↗

PubMed2006

Scaling of the fore-aft vestibulo-ocular reflex by eye position during smooth pursuit.

An eye position signal scales the amplitude of compensatory eye velocity in the translational vestibulo-ocular reflex (TVOR). To investigate the origin of such a modulatory signal, we studied the kinematics of the fore-aft TVOR as rhesus monkeys pursued a horizontally moving target at velocities between 0.5 and 30 degrees /s. We found that the "V-shaped" curve of the fore-aft TVOR amplitude as a function of eye position was shifted opposite to the direction of pursuit eye movement. As a result, the tip of the V-shaped curve that occurred close to zero eye position during steady-state fixation was shifted to the right during leftward pursuit and to the left during rightward pursuit eye movements. The faster the pursuit velocity the larger the observed shift. These results suggest that the scaling of the TVOR can precede actual eye position changes by several tens of milliseconds, which averaged 169 +/- 87 ms in three rhesus monkeys. Thus, central motor commands, rather than low-level efference copy or proprioceptive information, may be the signals scaling TVOR amplitude.

Algorithms↗

PubMed1992

Postural instability in Parkinson's disease.

Postural instability is one of the most disabling features of Parkinson's disease. Many factors contribute to balance impairment of Parkinson patients, including disturbed postural reflexes and poor control of voluntary movement. Additional factors which place Parkinson patients at risk for falls are side-effects of medication (dyskinesias), the poor response of postural instability to antiparkinsonian medication, orthostatic hypotension, gait abnormalities, muscular weakness in leg muscles and superimposed age-related changes such as reduced peripheral sensation. Future studies should not only investigate means of preventing falls in unstable patients, but should also be directed towards development of new treatment. Because accumulating evidence indicates that postural instability is at least partially related to non-dopaminergic lesions, these novel therapeutic approaches should be aimed at overcoming non-dopaminergic neurotransmitter deficiencies.

Humans↗

PubMed2002

Shoulder reflexes.

Dynamic shoulder stability is dependent on muscular coordination and sensory inputs. In the shoulder, mechanoreceptors are found in the coracoacromial ligament, the rotator cuff tendons, the musculotendinous junctions of the rotator cuff and in the capsule. The number of receptors in the capsule is small compared to the number in the other shoulder structures. Proprioceptive information from numerous receptors in muscles and tendons is mediated via fast conducting nervefibers and probably contribute more to kinaestethic sensation than information from capsule and ligaments. Therefore it seems likely that the joint receptors have a more distinct role for the kinaestethic sense than muscle receptors. In cats a direct reflex from the afferents innervating the shoulder to the muscles around the shoulder has been presented. The reflex had an extremely short latency (2.7-3.1 ms). In man, a very long latency (300 ms) excitatory reflex has been found when nerves in the capsule were stimulated electrically during shoulder surgery. In addition, when the anterior-inferior capsule was excited in conscious humans with modest amplitude electrical stimuli during muscle activity, a strong inhibition was found with an average latency of 33 ms. Stimulation of the sensory nerves in the coracoacromial ligament has also been found to modify muscle activity strongly. Even though our understanding of the control of shoulder motion is incomplete, it is clear that sensory inputs can strongly modify muscle activity around the shoulder. This has implications for rehabilitation and shoulder surgery.

Electric Stimulation↗

PubMed2002

Vestibuloocular reflex signal modulation during voluntary and passive head movements.

The vestibuloocular reflex (VOR) effectively stabilizes the visual world on the retina over the wide range of head movements generated during daily activities by producing an eye movement of equal and opposite amplitude to the motion of the head. Although an intact VOR is essential for stabilizing gaze during walking and running, it can be counterproductive during certain voluntary behaviors. For example, primates use rapid coordinated movements of the eyes and head (gaze shifts) to redirect the visual axis from one target of interest to another. During these self-generated head movements, a fully functional VOR would generate an eye-movement command in the direction opposite to that of the intended shift in gaze. Here, we have investigated how the VOR pathways process vestibular information across a wide range of behaviors in which head movements were either externally applied and/or self-generated and in which the gaze goal was systematically varied (i.e., stabilize vs. redirect). VOR interneurons [i.e., type I position-vestibular-pause (PVP) neurons] were characterized during head-restrained passive whole-body rotation, passive head-on-body rotation, active eye-head gaze shifts, active eye-head gaze pursuit, self-generated whole-body motion, and active head-on-body motion made while the monkey was passively rotated. We found that regardless of the stimulation condition, type I PVP neuron responses to head motion were comparable whenever the monkey stabilized its gaze. In contrast, whenever the monkey redirected its gaze, type I PVP neurons were significantly less responsive to head velocity. We also performed a comparable analysis of type II PVP neurons, which are likely to contribute indirectly to the VOR, and found that they generally behaved in a quantitatively similar manner. Thus our findings support the hypothesis that the activity of the VOR pathways is reduced "on-line" whenever the current behavioral goal is to redirect gaze. By characterizing neuronal responses during a variety of experimental conditions, we were also able to determine which inputs contribute to the differential processing of head-velocity information by PVP neurons. We show that neither neck proprioceptive inputs, an efference copy of neck motor commands nor the monkey's knowledge of its self-motion influence the activity of PVP neurons per se. Rather we propose that efference copies of oculomotor/gaze commands are responsible for the behaviorally dependent modulation of PVP neurons (and by extension for modulation of the status of the VOR) during gaze redirection.

Animals↗