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PubMed1979

Somatosensory evoked potential of the stretch-reflex (T-reflex).

Averaging of EEG recorded monopolarly from C3, contralateral to the activated limb, in the stretch reflex shows the presence of somatosensory evoked potential (SSEP) with characteristic shape: four constant waves--P29, N84, P202 and N294, and four inconstant waves--N31, P74, P99 and N123. Comparison of this SSEP with the SSEP in children, evoked in the stretch reflex, shows shorter latencies of the waves in adults. On the basis of data from the different series of experiments, it is assumed that kinesthetic signalization plays a dominant role in the genesis of SSEP of the T-reflex. Studies have shown that SSEP of the T-reflex is succeptible to habituation upon long repetition of the stretch reflex.

Achilles Tendon↗

PubMed1982

Recovery cycle of the reflex-evoked muscle potential (H reflex): excitability of spinal motor neurons in the healthy dog.

The recovery cycle for a reflex-evoked muscle potential has been demonstrated in the healthy dog, using the ulnar nerve-interosseous muscle preparation. The amplitude of a test response, at various time intervals (2 to 1,000 ms) after a conditioning response, was compared with the amplitude of the unconditioned response. The resulting ratio was plotted as a function of interstimulus interval. The curve was shown to consist of 3 distinct phases. The 1st phase, called the phase of early responsiveness, lasted from 2 to 20 ms and was characterized by a rapid decrease in amplitude of the test response. The 2nd phase, the phase of unresponsiveness, was characterized by a reduced response, and eventually no response which occurred between 20 and 80 ms. The 3rd phase, the phase of late responsiveness, began with a small test reflex amplitude at 80 ms and increased to 200 ms where it plateaued thereafter. Between 200 and 1,000 ms, there was no significant change in amplitude. Only at 2 ms, where the conditioning and test responses were so close together that they fused, did the mean amplitude of the test response exceed the mean unconditioned response. The reflex-evoked muscle potential recovery curve provides additional proof that the reflex is the equivalent of the H-reflex, and it provides a quantitative measure of spinal cord lower motor neuron excitability in the dog.

Animals↗

PubMedDate not supplied

Admittance values associated with the acoustic reflex and reflex decay.

Acoustic stapedial reflexes were elicited from 10 normal S's in each of three age groups. Susceptance and conductance values were measured for each subject in both the unreflexed and reflexed states and at 10-sec intervals during a continuous, reflex-sustaining stimulation with pure tones. Percentage of reflex decay over time was noted for each group and as a function of stimulus frequency and measurement mode. No significant age group differences were noted. Significant stimulus frequency and measurement mode differences were presented to represent "normal" reflex decay.

Adult↗

PubMedDate not supplied

Interactions between homogeneous conditioned motor reflexes during conditioned reflex switching: transfer of learning and interference.

Studies in rabbits of the time course of the formation of conditioned reflex switching of homogeneous reflexes showed that learning involved three main stages, characterized by the extent of stability of the conditioned reflexes, their interaction, and the level of switching. Formation of conditioned reflex switching was found to involve transfer of motor learning and interference of motor reflexes.

Animals↗

PubMed2001

Medial prefrontal lesions attenuate conditioned reflex facilitation but do not affect prepulse modification of the eyeblink reflex in rabbits.

Conditioned reflex facilitation occurs when the amplitude of the eyeblink (EB) unconditioned reflex (UR) is increased as a result of prior pavlovian conditioning. Prepulse modification of the EB reflex is produced by preceding the unconditioned stimulus (US) by a brief low-level neutral stimulus. This study examined both conditioned EB facilitation and prepulse modification in rabbits with either medial prefrontal (mPFC) lesions or sham lesions. Conditioned reflex facilitation was assessed by comparing EB UR amplitude prior to and after pavlovian EB conditioning. Animals that received CS/US paired presentations showed evidence of conditioned reflex facilitation, but animals with unpaired training did not. However, this increase in EB UR magnitude in the paired groups was smaller in animals with mPFC lesions, compared to those with sham lesions. In two subsequent experiments different groups of sham and lesion animals received an intense burst of white noise preceded by tones with different interstimulus interval durations to assess prepulse modification. Unlike conditioned facilitation, prepulse modification was unaffected by mPFC lesions.

Acoustic Stimulation↗

PubMed1990

Electrically and mechanically elicited blink reflexes in infants and children--maturation and recovery curves of blink reflex.

We studied the electrically and mechanically elicited blink reflexes in 2 groups of subjects, i.e., 237 newborn infants, 25-41 weeks of conceptional age, and 74 children, 1 month-12 years of age. In infants after 25 weeks of conceptional age we could usually induce the early response (R1) and ipsilateral late response (R2), while the contralateral late response (R2') of the electrical blink reflex became apparent after 33 weeks of conceptional age and the frequency of the appearance of R2' reached more than 60% after 38 weeks of conceptional age. After 7 months of age, R2' was usually observed. The R1 latency in full-term newborns was close to adult values, while the R2 and R2' latencies reached adult values at 7-12 years. After 1 year of age the latency of the R2 mechanical blink reflex had a tendency to be shorter than that of the electrical blink reflex. Under 35 weeks of conceptional age, the recovery curves of the blink reflex were considerably different from those of full-term infants, and premature infants showed little or no evidence of inhibition. These results indicate the absence of inhibitory interneurones in premature infants.

Blinking↗

PubMed2004

Artificial autonomic reflexes: using functional electrical stimulation to mimic bladder reflexes after injury or disease.

Autonomic reflexes controlling bladder storage (continence) and emptying (micturition) involve spinal and supraspinal nerve pathways, with complex mechanisms coordinating smooth muscle activity of the lower urinary tract with voluntary muscle activity of the external urethral sphincter (EUS). These reflexes can be severely disrupted by various diseases and by neurotrauma, particularly spinal cord injury (SCI). Functional electrical stimulation (FES) refers to a group of techniques that involve application of low levels of electrical current to artificially induce or modify nerve activation or muscle contraction, in order to restore function, improve health or rectify physiological dysfunction. Various types of FES have been developed specifically for improving bladder function and while successful for many urological patients, still require substantial refinement for use after spinal cord injury. Improved knowledge of the neural circuitry and physiology of human bladder reflexes, and the mechanisms by which various types of FES alter spinal outflow, is urgently required. Following spinal cord injury, physical and chemical changes occur within peripheral, spinal and supraspinal components of bladder reflex circuitry. Better understanding of this plasticity may determine the most suitable methods of FES at particular times after injury, or may lead to new FES approaches that exploit this remodeling or perhaps even influence the plasticity. Advances in studies of the neuroanatomy, neurophysiology and plasticity of lumbosacral nerve circuits will provide many further opportunities to improve FES approaches, and will provide "artificial autonomic reflexes" that much more closely resemble the original, healthy neuronal regulatory mechanisms.

Animals↗

PubMedDate not supplied

Changes of reflexes in vasoconstrictor neurons supplying the cat hindlimb following chronic nerve lesions: a model for studying mechanisms of reflex sympathetic dystrophy?

The generic term 'reflex sympathetic dystrophy' describes a clinical syndrome which sometimes develops after traumata at the extremities with lesions of nerves or --more rarely--after other events. The syndrome consists of the following components: pain (hyperpathia, allodynia), trophic changes of skin and deep tissues, dysregulation of sweating and cutaneous blood flow of the extremity concerned. It is assumed that all symptoms are produced by abnormal sympathetic activity. Interruption of the sympathetic activity to the affected extremity abolishes most of the pain and may lead to remission of the trophic changes. The hypothesis is that the trauma with lesion of the primary afferent axons leads subsequently to an abnormal state of the primary afferent neurons and to distorted processing of information in the spinal cord. As a consequence of this abnormal central state the activity in the sympathetic (vasomotor and sudomotor) supply to the affected extremity is distorted. The results are pain, trophic changes and dysregulations of autonomic effector organs. In some yet unknown way a vicious circle between periphery and spinal cord is established (afferent leads to spinal cord leads to sympathetic leads to afferent). This hypothesis was the starting point for analysis of the reflex pattern in postganglionic vasoconstrictor neurons supplying the cat hindlimb after chronic nerve lesions performed in the same limb (cutting and ligating a skin nerve; suturing the central stump of a skin nerve to the peripheral stump of a muscle nerve). The results obtained show that the reciprocity of the reflex pattern which is normally observed between cutaneous and muscle vasoconstrictor neurons is lost in many animals. Cutaneous vasoconstrictor neurons are very similar to muscle vasoconstrictor neurons in their reactions to stimulation of arterial baroreceptors and chemoreceptors. If the same sequence of events also occurs in patients with reflex sympathetic dystrophy, it could explain the dysregulation of blood flow through skin and also the occurrence of trophic changes in the limb.

Animals↗

PubMed1986

Ventilation and the oculocardiac reflex. Prevention of oculocardiac reflex during surgery for squints: role of controlled ventilation and anticholinergic drugs.

A randomised prospective study was carried out in children undergoing surgery for squint correction, to determine the value of controlled ventilation as a prophylaxis against the occurrence of the oculocardiac reflex. One hundred patients anaesthetised with nitrous oxide/oxygen and halothane were randomly assigned to either ventilated or spontaneously breathing groups of 50 each. Half the patients in each group received glycopyrronium 7.5 micrograms/kg intravenously at the time of induction of anaesthesia. Heart rate, rhythm, blood pressure and end tidal CO2 concentration were monitored throughout. A positive oculocardiac reflex, defined as a fall in heart rate of 20% or more and/or the occurrence of dysrhythmias, was observed in 72% of spontaneously breathing patients and in 100% of ventilated patients not receiving prophylactic intravenous glycopyrronium. The incidence of a positive reflex in patients receiving glycopyrronium was 10% (4 and 16% respectively in spontaneously breathing and ventilated patients). It is concluded that controlled ventilation is of no value as a preventive measure against the occurrence of the oculocardiac reflex in patients undergoing squint surgery and that prophylaxis is safely achieved with the use of intravenous glycopyrronium.

Adolescent↗

PubMedDate not supplied

The Hoffmann reflex (H-reflex) in senile dementia of the Alzheimer's type--preliminary results.

The Hoffmann reflex (H-reflex) and direct motor response (M) were investigated (latency, amplitude and excitability curves were analyzed) in patients with senile dementia of the Alzheimer's type (SDAT). M responses had similar latencies in SDAT patients and old control subjects. H reflex latencies were similar in SDAT patients and old control subjects but longer than in younger controls. The H max/M max ratio was also lower in SDAT patients and old control subjects than in younger controls. The excitability curve of the H-reflex (using a double shock procedure) in SDAT patients was lower than in non-demented old controls for all values of the interstimulus intervals.

Aged↗

PubMed1976

[Descending long-loop reflexes in the human spinal cord I. Facilitation of the triceps surae H reflex following stimulation of forelimb afferences (author's transl)].

The H reflex in the triceps surae muscle was elicited by just supraliminal stimulation of the tibial nerve. It was conditioned by paired impulses to the brachial plexus or the forelimb nerves and in some cases to other sites of the body. With a conditioning test interval of 32-47 msec a facilitation occurred which reached its maximum at about 80 msec and lasted for about 400 msec. The facilitation evoked by ipsilateral conditioning had a shorter latency than that from contralateral (ipsilateral: 32-42 msec, contralateral; 37-47 msec). The facilitation at the optimum interval (about 80 msec) ranged between 1;5 and 11.3 times of the control values. Ipsilateral conditioning was slightly more effective than the contralateral one (Fig. 1, 2). Stimulation of different forelimb nerves at an interval of 80 msec showed only insignificant differences in the amount of facilitation but was more effective than skin stimulation in the most cases (Fig. 3). Varying the intensity of the conditioning stimulus showed that facilitation occurred with just perceptable stimuli but it became more pronounced as soon as pain threshold (2-3 time of perception threshold) was exceeded (Fig. 3). This suggests that facilitation was mainly due to activation of nociceptor afferents. From the onset of facilitation and the conduction velocities of the respective forelimb and hindlimb afferents (cf. 6) a central reflex lantency of about 43 msec was calculated. To get further insight into the central connections of the reflex loop the H reflex was conditioned by paravertebral stimulation at C5 and L1 level. Both stimuli caused a distinct facilitation. However, the latency of the onset was 10-15 msec shorter with lumbar stimulation than with cervical stimulation. This and the similar time course of facilitation seen in animal experiments (12) suggest that an early part of facilitation is mediated via a descending propriospinal pathway. The major part, however, is supposed to be mediated via supraspinal pathways and seems to be related to a startle response.

Animals↗

PubMed1996

Axon reflexes or ephaptic responses simulating blink reflex R1 after XII-VII nerve anastomosis.

It has been claimed that functional recovery of the blink reflex occurs after hypoglossal-facial nerve anastomosis. This has been explained through central nervous system plasticity and reorganization of neuronal connections. In 5 patients with reinnervated facial muscles after hypoglossal-facial nerve anastomosis we observed "R1-like" responses that fulfilled criteria for facial nerve axon reflexes or ephapses. First, displacement of the stimulating electrode from the supraorbital to zygomatic area shortened the latency of the evoked response. Second, these responses were stable (jitter mean consecutive difference < 25 microsec) and they had complex potential shapes unmodified by high-frequency stimulation. Finally, collision techniques demonstrated antidromic conduction of impulses in the facial nerve from supraorbital to zygomatic points. Therefore, these "R1-like" responses are not the early component of a functionally recovered blink reflex but motor axon reflexes or ephaptic responses similar to the short latency responses observed following facial nerve regeneration or from sutured nerves in human forearms.

Adolescent↗

PubMed1994

Exteroceptive reflexes in dystonia: a study of the recovery cycle of the R2 component of the blink reflex and of the exteroceptive suppression of the contracting sternocleidomastoid muscle in blepharospasm and torticollis.

The recovery cycle of the R2 component of the blink reflex and the exteroceptive suppression of EMG activity in the contracting sternocleidomastoid muscle produced by electrical stimulation of the supraorbital nerve were studied in normal subjects and in patients with either blepharospasm or torticollis. The latencies of the reflexes were normal, suggesting that the neural structures that mediated them were intact. However, the recovery of the R2 component of the blink reflex was enhanced in patients with either blepharospasm or torticollis. Also, the size of the exteroceptive suppression of the sternocleidomastoid muscle was reduced in both groups of patients. Our results are indicative of abnormalities of interneurons mediating exteroceptive reflexes in patients with craniocervical dystonia that are not restricted to the systems controlling the muscle involved in the dystonia.

Adult↗

PubMed1998

Choledochosphincter inhibitory reflex: identification of the reflex in dogs and its significance.

BACKGROUND: The sphincter of Oddi (SO) may undergo functional disorders. The mechanism of action of this sphincter is as yet not fully explored; the current study aims at studying some aspects of this mechanism. METHODS: Twelve mongrel dogs (mean weight 15.3 +/- 2. 9 SD kg, 8 male, 4 female) were studied. Under general anesthesia, the abdomen was opened and the gall bladder, common bile duct (CBD), and duodenum were exposed. Through separate punctures in the CBD, a balloon-tipped 2F catheter was introduced into the CBD and a 2F manometric catheter was placed within the SO. The positioning of the catheters was controlled fluoroscopically. The pressure response of the CBD and SO to CBD balloon distension with CO2, without and with separate anesthetization of either the CBD or SO, was recorded. RESULTS: Upon CBD distension by 0.5 ml of CO2, the pressure in the CBD rose (P < 0.001) and in the SO dropped (P < 0.01). The SO pressure drop was momentary and did not change significantly (P > 0. 05) with increase in the volume of CBD distension. The pressure response was blocked on separate anesthetization of the CBD and SO. CONCLUSIONS: The SO opening on CBD distension is suggested to be reflex and not hydromechanical. It seems to be mediated through a reflex which we call "choledochosphincter inhibitory reflex." Derangement of this reflex might result in functional disorders of the SO.

Anesthesia↗

PubMed1989

Studies on the rectoanal reflex in children and in experimental animals: an evaluation of neuronal control of the rectoanal reflex.

A single-chamber pressure probe for rectal electromanometry was developed which seems to be superior to the complicated multichamber systems not only for clinical but also for experimental purposes. Measurements of rectoanal reflex were carried out in 268 cases with abnormal bowel function, in 103 cases following operation for Hirschsprung's disease, and in 61 cases of imperforate anus to assess postoperative continence. Experimental studies were performed in 36 dogs, 27 of which were used for short-term and 9 for long-term studies. The results of clinical and experimental studies are described and discussed, with accompanying literature. From clinical and experimental studies, the neuronal pathways of the rectoanal reflex are schematized. The normal rectoanal reflex is mediated by both the sacral cord and the myenteric neurons. It is concluded that measurements of the anal resting pressure and the rectoanal reflex constitute a valuable method to distinguish between normal and pathological sacral and myenteric innervation.

Anal Canal↗

PubMed1999

Evidence suggesting that a transcortical reflex pathway contributes to cutaneous reflexes in the tibialis anterior muscle during walking in man.

Stimulation of cutaneous foot afferents has been shown to evoke a facilitation of the tibialis anterior (TA) EMG-activity at a latency of 70-95 ms in the early and middle swing phase of human walking. The present study investigated the underlying mechanism for this facilitation. In those subjects in whom it was possible to elicit a reflex during tonic dorsiflexion while seated (6 out of 17 tested), the facilitation in the TA EMG evoked by stimulation of the sural nerve (3 shocks, 3-ms interval, 2.0-2.5x perception threshold) was found to have the same latency in the swing phase of walking. The facilitation observed during tonic dorsiflexion has been suggested to be -- at least partly -- mediated by a transcortical pathway. To investigate whether a similar mechanism contributes to the facilitation observed during walking, magnetic stimulation of the motor cortex (1.2x motor threshold) was applied in the early swing phase at different intervals in relation to the cutaneous stimulation in 17 subjects. In 13 of the subjects, the motor potentials evoked by the magnetic stimulation (MEPs) were more facilitated by prior sural-nerve stimulation (conditioning-test intervals of 50-80 ms) than the algebraic sum of the control MEP and the cutaneous facilitation in the EMG when evoked separately. In four of these subjects, a tibialis anterior H-reflex could also be evoked during walking. In none of the subjects was an increase of the H-reflex similar to that for the MEP observed. In five experiments on four subjects, MEPs evoked by magnetic and electrical cortical stimulation were compared. In four of these experiments, only the magnetically induced MEPs were facilitated by prior stimulation of the sural nerve. We suggest that a transcortical pathway may also contribute to late cutaneous reflexes during walking.

Action Potentials↗

PubMed1975

Amygdala and masseteric reflex. II Mechanism of the diphasic modifications of the reflex elicited from the "defence reaction area". Role of the spinal trigeminal nucleus (pars oralis).

It has been demonstrated (Gary Bobo and Bonvallet 1975) that long-lasting stimulation of the "amygdaloid area for the defence reaction" (basal nucleus, pars magnocellularis) elicits, after an initial facilitation, a delayed inhibition of the monosynaptic masseteric reflex (MR), while stimulation of the amygdalofugal fibers running in the ansa lenticularis provokes an immediate inhibition of the reflex. In present study, the structure which mediates these inhibitions has been identified. Using combined techniques of limited transections, localized coagulations and localized stimulation and recording, it has been demonstrated that these ingibitions are mediated by the rostral portion of the spinal trigeminal nucleus, the subnucleus oralis (NO). After localized coagulation of this nucleus, or after lesions which interrupt slectively the connections between the NO and the masticatory nucleus, long-lasting stimulation of the basal nucleus elicits only well maintained facilitation of the MR. Hence, the delayed decrease in amplitude of the reflex, observed during stimulation of the basal nucleus in the preparations with intact brain, cannot be explained by the reversal of an initial facilitatory influence to an ingibitory one. The one ingibition of the reflex is due to the superimposition, on a background of sustained facilitation of the masseteric motoneurons, of the inhibitory influence exerted on the monosynaptic masseteric circuit by a trigeminal sensory nucleus, itself activated by delayed discharges of the basal nucleus. A tentative representation of the dual control exerted on the masseteric activity by the basal nucleus is given in Fig. 9. The functional implications of this dual control during the "defence reaction" are briefly discussed.

Amygdala↗

PubMed1993

Vesicolevator reflex. Description of a new reflex and its clinical significance.

A new reflex which I call "vesicolevator reflex" was studied in 21 healthy volunteers with a mean age of 36.3 years. The technique comprised the introduction of a catheter, with a balloon at its distal part, into the empty urinary bladder. A concentric needle electrode was inserted into the levator ani muscle. The vesical balloon was inflated with air in increments of 50 mL and the levator myoelectric activity recorded by a standard EMG apparatus. Vesical balloon was then removed, and levator EMG response to sudden suprapubic vesical compression was recorded with urinary bladder both empty and filled with saline in increments of 50 mL. Vesical balloon distention evoked levator muscle contraction; duration of contraction increased with increased vesical distention. Levator response to vesical distention did not occur when air-filling was below 50 mL air and when muscle was anesthetized. The latency of the reflex was calculated. Suprapubic manual compression of the empty urinary bladder did not cause levator contraction; yet, compression of distended bladder evoked the response. Compression should be sudden, while the patient is lying supine. Slow insidious compression did not evoke levator contraction. The vesicolevator reflex seems to play a role in the act of micturition, and hence could serve as a tool in investigating patients with micturition disorders.

Abdominal Muscles↗