Dynamics of adaptive change in vestibulo-ocular reflex direction. I. Rotations in the horizontal plane

Horizontal and vertical vestibulo-ocular reflex (VOR) eye movements were recorded in alert cats before and after adaptation to vertical optokinetic motion coupled with horizontal rotation at 0.05, 0.25 or 1.0 Hz. Within 15-30 min, the VOR measured in darkness acquired a vertical component; the maximal directional change in the VOR occurred at the frequency of the adapting stimulus. At other frequencies the gain was less and there were phase leads or lags for higher or lower frequencies, respectively. Adaptive VOR was stable for at least 14 h in unrestrained animals with no visual input and decayed within 30 min during rotation in a stationary visual world.     

Dependence of cat vestibulo-ocular reflex direction adaptation on animal orientation during adaptation and rotation in darkness

Four series of experiments investigated how adaptive changes in direction of the cat's vestibulo-ocular reflex (VOR) vary with position of the animal during adaptive training and postadaptive testing. In all experiments VOR was measured electrooculographically during rotations about earth-horizontal and vertical axes in the dark before and after 2 h of adaptation in which 0.25 Hz sinusoidal whole body rotation about a horizontal/vertical axis was paired with synchronous 0.25 Hz rotation of a visual pattern about a vertical/horizontal axis, respectively. In upright sagittal (US) experiments, coupling of pitch rotation with visual pattern rotation about an earth vertical axis yielded an adaptive horizontal VOR response to pitch rotation whose gain had a local maximum at 0.25-0.5 Hz plus a sustained rise for frequencies below 0.1 Hz. When post-tests were done with the animal rolled 90 degrees onto its side and rotated about the earth vertical axis (pitch relative to the cat), the low frequency rise was eliminated and the 0.25 Hz peak was reduced. In on side sagittal (SS) experiments, where training was done in the latter (on side) position, training produced only the 0.25 Hz peak without the low frequency rise, indicating that the rise is due to coupling of otolith input to horizontal VOR. Again the 0.25 Hz peak was reduced when testing was done with the cat oriented 90 degrees from the training position (in the US position). This indicates that the cross-coupled canal-ocular reflex response is modulated or gated by the position of the animal with respect to gravity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamics of adaptive change in vestibulo-ocular reflex direction. II. Sagittal plane rotations

Alert cats were rotated sinusoidally (0.25 Hz) in their sagittal plane while viewing optokinetic motion in their horizontal plane. Vertical and horizontal vestibulo-ocular reflex (VOR) was measured in the dark before and after 2 h of these adaptation stimuli in upright or onside orientation of the cat. Onside exposure produced maximal adaptive horizontal VOR at the training frequency. Upright exposure produced highest gain at lower frequencies. A cat with inoperative vertical canals adapted only to upright exposure. We conclude that in the presence of horizontal image rotation either vertical canal or otolith stimulation can produce adaptation in VOR direction and stimulation of both produces complex adaptation dynamics.     

MIDDLE-FINGER REFLEX

A new reflex is described: middle-finger extensor reflex elicited by percussion of tendon insertion of musculus extensor digitorum communis in forearm. Following percussion using a reflex hammer, two EMG responses from the belly of the muscle were recorded: a short latency monosynaptic reflex with a latency of 31.4 ± 1.5 ms (M1), and a long-latency middle-finger reflex with a mean latency of 64.8 ± 6.31 ms (M2), the former being a monosynaptic extensor reflex, and the latter belonging to a spino-cortico-spinal reflex circuitry. It was suggested that the middle-finger extensor reflex elicited by radial nerve afferents and efferents (C7–C8) would be of clinical and theoretical importance.     

Topodiagnostic value of brain stem reflexes

The masseter and medial pterygoid stretch reflexes, the masseter inhibitory reflexes, and the blink reflexes are useful diagnostic tools for evaluation of brain stem disorders. The structures mediating these reflexes are largely known. Characteristic changes of the normal response patterns due to various lesions have been described. Distinct reflex abnormalities indicate lesions at specific sites. Multireflex testing improves the accuracy with which localization can be made. A number of lesions suspected on clinical data may be confirmed by reflex findings only and not by imaging studies. Reflex testing can be utilized to demonstrate multiple lesions evoked by a single vascular event and evaluate dissemination of central nervous involvement in multiple sclerosis patients. © 1994 John & Sons, Inc.     

Interaction of tonic labyrinth and neck reflexes in man

Interaction of tonic labyrinth and neck reflexes was studied in 3 healthy volunteers by analyzing changes in Soleus H-Reflex (SHR) area in relation to both lateral tiltings and neck rotations. By using a Kermath chair each subject was tilted laterally from the vertical to the left and to the right up 15° in steps of 5° and at the same time the longitudinal body axis, keeping the head fixed, was rotated to the right and to the left up to 15° in steps of 5°. All combinations of lateral tiltings and neck rotations were tested. Each test position was followed by a return to 0° for both rotation and tilting (control position). Twelve H-reflexes of right soleus muscle were recorded in each test and control position and the changes in RSHR area were expressed as percentage variations from the mean value absorved in the pretest and post-test control position. Out data indicate that in man, as in animals, labyrinth and neck reflexes act in the opposite direction, and that in the static condition their contribution to postural stabilization is equal.

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Sommario Al fine di studiare nell'uomo le interazioni reciproche dei riflessi tonici labirintici e tonici del collo abbiamo analizzato le variazioni dell'area del riflesso H del muscolo soleo indotte da diverse combinazioni di rotazione del collo ed inclinazioni laterali dell'asse corporeo su 3 soggetti volontari sani. Dalla posizione verticale venivano inclinati lateralmente verso destra e verso sinistra di 5° in 5° fino ad un massimo di 15° e contemporaneamente veniva ruotato l'asse corporeo, tenendo il capo fisso, di 5° in 5° fino ad un massimo di 15°. In ciascun soggetto venivano studiate tutte le possibili combinazioni di inclinazioni e rotazioni. Ogni posizione test veniva fatta seguire da una posizione di controllo a 0° (capo in posizione primaria ed asse corporeo verticale). In ciascuna posizione test e di controllo venivano registrati 12 riflessi H e di ciascuno si misurava l'area. I valori ottenuti nelle diverse posizioni test venivano espressi come percentuale della media dei valori osservati nella corrispondente posizione di controllo precedente e successiva. I risultati così ottenuti indicano che nell'uomo, come nell'animale, i riflessi tonici labirintici e tonici del collo agiscono esercitando sul tono estensorio dell'arto inferiore azioni opposte e di entità sovrapponibile.

     

Identification of stapedius muscle motoneurons in squirrel monkey and bush baby

The location of brainstem neurons which mediate the stapedius reflex was identified by injecting horseradish peroxidase into the stapedius muscle of squirrel monkeys and bush babies. Retrogradely labeled neurons, arranged in a one- to three-cell column, were found medial to the main facial motor nucleus in squirrel monkeys and ventral to it in bush babies. Nissl, protargol, and acetylcholinesterase stains were subsequently used to identify and describe this unique column of cells. It was found that staining characteristics, as well as shape, size, and location, distinguish stapedius muscle motoneurons from closely associated cell groups. Furthermore, stapedius muscle motoneurons are morphologically similar to periolivary cells and morphologically dissimilar to cells within the facial motor nucleus.     

Separation of the medullo-spinal descending pathway for somatic and autonomic outflow in the cat

The present study investigated differences between vestibulo-somatic and vestibulo-sympathetic reflexes, along with differences between somatic and autonomic spino-bulbo-spinal (SBS) reflexes in chloralose-urethane anesthetized cats. Electrical stimulation was applied to the vestibular nerve (V) for a duration of 0.3 ms. The potential responses in the sympathetic renal nerve (RN) and somatic lumbar nerve were recorded simultaneously. Responses were recorded for a variety of conditioning stimulus to testing stimulus intervals, and the results were plotted to form a recovery curve. The recovery curve for the test response from the somatic nerve was very different from that of the sympathetic nerve. Following transection of the lateral part of the thoracic cord, in the case of the sympathetic renal nerve, recorded responses were still present on vestibular and lumbar nerve stimulation, whereas in the case of the vestibulo-somatic and somatic SBS reflexes, the reflex response had disappeared after transection. These findings suggest that sympathetic and somatic reactions as a result of vestibular stimulation have different descending pathways in the spinal cord, and that their physiological characteristics are different.     

Cutaneous silent periods – Part 1: Update on physiological mechanisms

Testing of exteroceptive electromyographic modulation of ongoing voluntary muscle activity is of interest in normal human physiology and in diagnostic clinical neurophysiology in normal and pathological conditions. The cutaneous silent period (CSP) is a robust and reproducible nociceptive EMG suppression, mediated at the spinal level by small-diameter A-delta afferents. This critical review surveys the literature on applied stimulation and recording techniques, physiological principles, involved fiber types, spinal circuitry, supraspinal modulation, neurotransmitters and pharmacology of CSPs. Understanding the principles of CSP testing is fundamental for a valid and thoughtful clinical application of CSPs (reviewed in part 2) (Kofler et al., 2019).     

A Quantitative Model of the Hoffmann Reflex

Abstract

Electrical stimulation of the human posterior tibial nerve elicits two separate electromyographic responses. The shorter latency response results from electrical activation of motor axons and is termed the direct motor (M) response, while the longer latency response results from activation of stretch receptor afferents of the monosynaptic reflex arc and is termed the Hoffmann (H) reflex. At high stimulus intensities, the H reflex is either greatly reduced in size or completely extinguished, presumably by antidromic impulses elicited by stimulation of the motor nerve. In most subjects, a simple quantitative model appears to account for this extinction. In this model: (1) the M response is used to estimate the number of antidromic impulses; (2) the H reflex is used to estimate the number of orthodromic impulses which escape collision; (3) the maximum size of the M response is used to indicate the size of the motoneuron pool; and (4) it is assumed ,that antidromic impulses collide in a random fashion with orthodromic impulses in the motor nerve.     

Clinical and electromyographic deep tendon reflexes in polyneuropathy: diagnostic value and prevalence*

Background – Evidence is accumulating that patients with polyneuropathy may present with normal clinical deep tendon reflexes (C‐DTR). There are few studies that assessed the diagnostic utility of electromyographically recorded DTR (Er‐DTR) in patients with polyneuropathy. Objectives – The objectives of this study were twofold: (i) to evaluate the prevalence of preserved C‐DTR in polyneuropathy; (ii) diagnostic value of Er‐DTR latency measurement in patients with polyneuropathy. Methods – We prospectively studied 38 controls and 185 patients with polyneuropathy. All subjects had evaluation of C‐DTR, Er‐DTR obtained from right biceps brachii (BR), right patellar (PR) and bilateral ankle reflexes (AR). Results – Of these 185 patients, 118 (63.8%) had chronic axonal neuropathy (CAN), 49 (26.5%) demyelinating polyradiculoneuropathy (DPN) and 18 (9.7%) small fiber neuropathy (SFN). The C‐DTR were normal in 65 patients whereas 39 of these 65 (60%) patients had abnormalities of Er‐DTR at one or more sites. Er‐DTR latencies in patients with polyneuropathies were prolonged at all sites compared with controls (P < 0.01). Among patients with various types of polyneuropathies the Er‐DTR, mean latencies at all the sites and latency indicative of demyelination (>150% of the normal mean) were higher in patients with DPN than that of CAN or SFN (P < 0.01). Conclusions – We conclude that C‐DTR are preserved in 35.1% of the patients with polyneuropathies and Er‐DTR should be performed in such patients in order to provide electrophysiological evidence of a polyneuropathy. Er‐DTR are useful in distinguishing axonal from demyelinating disorders of peripheral nerve, and detection of subclinical involvement of large fibers in SFN.     

Somatovesical and vesicovesical excitatory reflexes in urethane-anaesthetized rats

The effect of spinal cord transection on excitatory somato- and vesicovesical micturition reflexes have been investigated in urethane-anaesthetized rats. In adult rats, 3 distinct types of excitatory reflexes to the bladder may be observed: a somatovesical reflex organized at spinal level and two vesicovesical reflexes organized at spinal and supraspinal level, respectively. In agreement with results of lesion experiments (Neurosci. Lett., 8 (1978) 27-33), bladder voiding is abolished following spinal cord transection although both somato- and vesicovesical reflexes may be demonstrated in acute spinal rats. Occurrence of the spinal vesicovesical reflex during the collecting phase of the cystometrogram appears to be inhibited by a supraspinal inhibitory pathway.     

Brainstem reflex excitability changes in patients with amyotrophic lateral sclerosis

Introduction: In this study we explored brainstem reflex excitability changes, blink reflex recovery cycles (BRRCs), and masseter inhibitory reflexes (MIRs) in patients with amyotrophic lateral sclerosis (ALS). Methods: Fourteen ALS patients and 14 healthy control subjects were recruited. The BRRC was examined at interstimulus intervals (ISIs) of 100, 200, 300, 400, 500, and 600 ms. The latencies and durations of silent period 1 (SP1) and silent period 2 (SP2) of the MIR were measured. Results: Decreased R2 area suppression was prominent in the ALS group at ISIs of 200, 300, and 400 ms (P < 0.02), whereas no significant differences between groups at 100, 500, and 600 ms ISIs (P > 0.05) were observed. SP2 duration was significantly prolonged in the ALS group compared with controls (P = 0.01). Conclusions: Brainstem inhibitory and excitatory interneuronal activity is altered in ALS, possibly brought about by physiological and morphological changes at the cortical or bulbar levels. Muscle Nerve 56 : 925–929, 2017     

The dynamic characteristics of the mouse horizontal vestibulo-ocular and optokinetic response

In the present study the optokinetic reflex, vestibulo-ocular reflex and their interaction were investigated in the mouse, using a modified subconjunctival search coil technique. Gain of the ocular response to sinusoidal optokinetic stimulation was relatively constant for peak velocities lower than 8°/s, ranging from 0.7 to 0.8. Gain decreased proportionally to velocity for faster stimuli. The vestibulo-ocular reflex acted to produce a sinusoidal compensatory eye movement in response to sinusoidal stimuli. The phase of the eye movement with respect to head movement advanced as stimulus frequency decreased, the familiar signature of the torsion pendulum behavior of the semicircular canals. The first-order time constant of the vestibulo-ocular reflex, as measured from the eye velocity decay after a vestibular velocity step, was 660 ms. The response of the vestibulo-ocular reflex changed with stimulus amplitude, having a higher gain and smaller phase lead when stimulus amplitude was increased. As a result of this nonlinear behavior, reflex gain correlated strongly with stimulus acceleration over the 0.1–1.6 Hz frequency range. When whole body rotation was performed in the light the optokinetic and vestibular system combined to generate nearly constant response gain (approximately 0.8) and phase (approximately 0°) over the tested frequency range of 0.1–1.6 Hz. We conclude that the compensatory eye movements of the mouse are similar to those found in other afoveate mammals, but there are also significant differences, namely shorter apparent time constants of the angular VOR and stronger nonlinearities.     

Conditioning of crossed extensor reflex pathways by independent natural stimulation of labyrinth, neck and elbow joint afferents

The present experiments demonstrated that labyrinth, neck and elbow joint afferents interact to influence the excitability of crossed extensor reflex pathways projecting to triceps brachii in decerebrate cats. Reflex excitability was dependent on head, neck and elbow position such that it was increased when the elbow was held at full flexion and either the head maintained side down or the neck rotated side up. Such interaction between these afferents is likely to be important in postural control.     

Consistency of the Babinski reflex and its variants

Background and purpose:  The Babinski Reflex, first described in 1896, is still an integral part of the neurological examination. Many have studied the consistency of this reflex, but none have compared the inter- and intra-observer consistency of the Babinski reflex and its variants.
Methods:  Thirty-four subjects were examined by six neurologists. The Babinski, Gordon, Chaddock, and Oppenheim reflexes were tested, and each neurologist concluded if the plantar response was flexor or extensor. Six subjects were re-tested 1 week later to determine intra-observer consistency.
Results:  The Babinski reflex had the highest interobserver consistency with a kappa value of 0.5491. The Chaddock, Oppenheim, and Gordon reflexes had kappa values of 0.4065, 0.3739, and 0.3515, respectively. For intra-observer consistency, Gordon was the most consistent with a kappa value of 0.6731. When reflexes were combined in pairs, the Babinski and Chaddock reflexes together were the most reliable.
Conclusions:  The Babinski reflex was shown to be the most consistent between examiners. The Gordon reflex had the highest intra-observer consistency; however, the small sample size should limit conclusions drawn from this calculation. Clinicians often utilize more than one reflex to examine the plantar response; the combination of the Babinski and Chaddock reflexes was the most reliable.     

The effect of elbow joint afferent discharge on transmission in forelimb flexion reflex pathways to biceps and triceps brachii in decerebrate cats

The present experiments were performed to investigate the influence of elbow joint afferent discharge on the excitability of reflex arcs mediating flexion withdrawal and crossed extensor reflexes in the forelimb muscles of decerebrate cats. The excitability of flexion withdrawal and crossed extensor reflexes in forelimb muscles was shown to be modulated by elbow joint position. Flexion withdrawal reflexes were most easily elicited when the elbow was extended and crossed extensor reflexes were most easily elicited when the elbow was flexed. This modulation of transmission was not confined to reflex pathways projecting to muscles acting at the elbow but also included pathways to muscles acting at the wrist and shoulder in addition to muscles in the contralateral forelimb. The changing excitability of reflex pathways caused by elbow movement was unaltered by degloving the skin covering the join and tenotomy of the medial head of triceps and the long head biceps. However, modulation of reflex excitability by joint movement was totally abolished by local anaesthesia of the joint in an otherwise intact limb. Thus, the present experiments indicate that transmission in forelimb flexion reflex pathways can be powerfully influenced by elbow joint afferent discharge.     

Vestibulo-ocular reflex (VOR), cervico-ocular reflex (COR) and its interaction in active head movements

Summary In normal adults the vestibulo-ocular reflex (VOR) and the cervico-ocular reflex (COR) were investigated during passive and active head or body movements, respectively. Sinusoidal rotations around the vertical axis of the body at frequencies of 0.05, 0.1, and 0.2 s^–1 and total amplitudes of 20°, 40°, 60°, or 80° were employed.The average eye deviations (Schlagfeld) during VOR were directed opposite to the direction of the head turning. During COR, however, slow eye deviations of higher amplitude were anticompensatory relative to the fixed head. During active head turnings the average eye deviations showed the same anticompensatory direction as in COR, but were still larger. They increased with stimulus amplitudes up to 60°.At least a weak cervical nystagmus was elicited in all subjects, with its fast phases beating in the direction of the relative head movement. Its gain reached marked values up to 0.5, but only for peak stimulus velocities below 25°/s. The nystagmus gain during active head turnings was only slightly higher than during VOR.With higher stimulus velocities, large anticompensatory saccades appeared just before the change of stimulus direction; these are typical for active head movements, but were also found during COR.Supported by Sonderforschungsbereich Hirnforschung und Sinnesphysiologie (SFB 70) der Deutschen Forschungsgemeinschaft (DFG)     

Reflexes elicited from cutaneous and mucosal trigeminal afferents in normal human subjects

It has been shown that in patients in whom the central stump of the hypoglossal nerve has been anastomosed to the peripheral stump of a lesioned facial nerve, supraorbital nerve stimulation can elicit a short-latency reflex (12.5±0.6 ms; mean±S.D.) in facial muscles similar to the R1 disynaptic blink reflex response, but not followed by an R2 blink reflex component⁴⁶. Thus in addition to replacing the facial neurons at peripheral synapses, these hypoglossal nerves contribute to a trigemino-hypoglossal reflex. The aim of this work was to study the type of reflex activities which can be elicited in both facial and tongue muscles by electrical stimulation of cutaneous (supraorbital nerve) or mucosal (lingual nerve) trigeminal (V) afferents in normal subjects. The results show that although stimulation of cutaneous V1 afferents elicits the well-known double component (R1–R2) blink reflex response in the orbicularis oculi muscles, it does not produce any detectable reflex response in the genioglossus muscle, even during experimental paradigms designed to facilitate the reflex activity. Conversely, stimulation of mucosal V3 afferents can elicit a single reflex response of the R1 type in the genioglossus muscle but not in the orbicularis oculi muscles, even during experimental paradigms designed to facilitate the reflex activity. These data are discussed in terms of two similar but separate circuits for the R1 responses of cutaneous (blink reflex) and mucosal (tongue reflex) origins. They suggest that in patients with hypoglossal-facial (XII–VII) nerve anastomosis, the short-latency trigemino-‘hypoglossal-facial' reflex of the R1 blink reflex type observed in facial muscles following supraorbital nerve stimulation could be due to changes in synaptic effectiveness of the central connectivity within the principal trigeminal nucleus where both cutaneous and mucosal trigeminal afferents project.