Search PubMed⌕ Search

Biomedical subjects

R M Jell

Publications and source records attributed to R M Jell.

At least 19 recordsLinked to original sources
PubMed1994

Human vertical optokinetic nystagmus and after-response, and their dependence upon head orientation with respect to gravity.

Characteristics of human vertical optokinetic nystagmus (VOKN) and afternystagmus (VOKAN) were examined by electro-oculography in 18 normal human subjects by means of the analysis of slow phase velocity (SPV) and area under the regression curve of the VOKAN decay. Under normal gravity, subjects were tested in upright and left ear down (90 degrees roll) positions, respectively, using a hemisphere onto which stripes were projected at a velocity of 40 degrees/s in left, right, up and down directions. Analysis of the VOKN and VOKAN revealed a significant asymmetry of vertical eye movements in the subjects' sagittal plane, ie, stronger upward SPV than downward in both VOKN and VOKAN decay. This asymmetry became even more prominent when the head was in the 90 degrees roll position. It is postulated that the asymmetry of VOKN and VOKAN in humans, as in animals, is due to the asymmetrical storage capability of the vertical velocity storage mechanism which mainly contributes to upward eye movements. In addition, it is postulated that the vertical storage mechanism is modified by the action of gravity on the otolith organs. However, only two out of our 18 subjects demonstrated cross-coupling, as reported in animals, from the horizontal to the vertical mode of storage when the head was tilted away from the spatial vertical.

Adult↗
PubMed1992

Stimulus velocity dependence of human vertical optokinetic nystagmus and afternystagmus.

Stimulus velocity dependence of human VOKN and VOKAN was investigated using 20 degrees, 40 degrees, 60 degrees, and 80 degrees/s optokinetic stimulation. In our experimental conditions, 40 degrees/s was found to be the most appropriate stimulus velocity for inducing reliable VOKN and VOKAN based on the analysis of SPV, gain, and the area under the VOKAN decay curve. There was a clear trend toward up/down asymmetry of VOKN gain, with higher upward OKN SPV than downward at 40 degrees/s. VOKAN with both short and long time constant components was induced in 5 of 11 subjects, but only when the stimulus was upgoing. Stimulation at 20 degrees/s in either direction produced a decay with only a short time constant. VOKN-SPV and the area under VOKAN decay curve at 40 degrees/s showed no significant difference from the corresponding values at 60 degrees/s or 80 degrees/s, indicating that following and the velocity storage mechanism had saturated at 40 degrees/s. However, the gain at 60 degrees/s and 80 degrees/s became low and eye movement regularity was poor. Stimulation at 20 degrees/s may activate mainly the vertical pursuit mechanism, as it did not produce up/down asymmetry. It is proposed that, as in the horizontal case, two kinds of mechanisms are involved in vertical stripe-following eye movements, which represent smooth pursuit and optokinetic systems respectively.

Adult↗
PubMed1988

Convergent effects from vestibulospinal tract and primary cutaneous afferent fibers on motoneurons to proximal lower limb flexor and extensor muscles in humans.

In human subjects, the latency and magnitude of cutaneomuscular test reflexes, evoked by stimulation of the sural nerve in the contralateral and ipsilateral quadricep and hamstring muscles, were investigated during static tilts in the pitch axis. The ANOVA demonstrated a highly significant, tilt-dependent modulation of the magnitude of the test reflex for the initial phase of both ipsilateral quadriceps and ipsilateral hamstrings. These results are consistent with results from a similar study on human ankle muscles and provide further evidence that the tilt-dependence of these cutaneomuscular reflexes originates from activity in the otolith receptors.

Afferent Pathways↗
PubMed1988

Concussion. Acceleration limits causing concussion.

Among the many features common to all species of the animal kingdom is the transient loss of function of the nervous system as the result of a jarring blow, a phenomenon known as concussion. Understanding of concussion has been hampered by the lack of a uniform definition, with many authors including cases with gross, irreversible changes. The phenomenon occurs only with a blow that significantly accelerates and thus is best defined as "a transient disturbance of neuronal function as a result of acceleration." There must be a threshold beneath which no loss of function occurs and a ceiling beyond which changes are not reversible. Experiments with nonanesthetized frogs revealed that at 33 g only the occasional frog would be stunned. From 50 to 230 g, consciousness was always lost but rapidly regained and retained, while beyond, the loss was not always reversible. The time of functional loss was increasingly proportional to acceleration.

Acceleration↗
PubMed1988

Effect of active head movements about the pitch, roll, and yaw axes on human optokinetic afternystagmus.

Effects of active head movements about the pitch, roll, or yaw axes on horizontal optokinetic afternystagmas (OKAN) were examined in 16 subjects to test the hypothesis that otolith organ mediated activity induced by a change in head position can couple to the horizontal velocity storage in humans. Active head movements about the pitch axis, forwards or backwards, produced significant OKAN suppression. Pitch forward head movements exerted the strongest effect. Active head movements about the roll axis towards the right also produced OKAN suppression but only if the tilted position was sustained. No suppression was observed following sustained yaw. However, an unsustained yaw left movement after rightward drum rotation significantly enhanced OKAN. Sustained head movement trials did not significantly alter subsequent control trials. In contrast, unsustained movements about the pitch axis, which involve more complex interactions, exerted long-term effects on subsequent control trials. We conclude that otolith organ mediated activity arising from pitch or roll head movements couples to the horizontal velocity storage in humans, thereby suppressing ongoing OKAN. Activity arising from the horizontal canals during an unsustained yaw movement (observed mainly with yaw left), following drum rotation in a direction contralateral to the movement, may also couple to the velocity storage, resulting in increased activity instead of suppression.

Adolescent↗
PubMed1988

The influence of active versus passive head oscillation, and mental set on the human vestibulo-ocular reflex.

We compared passive (manual) whole body, and active head oscillation in normal human subjects attempting mentally to influence the vestibulo-ocular reflex (VOR). Our objective was to establish simple procedural guidelines for vestibular test procedures in clinical settings. Using a head-fixed target, both methods of oscillation yielded virtually zero gain. Using an Earth-fixed target, active oscillation gain was unity, while passive gain was slightly less than 1. Using an imagined Earth-fixed target in the dark, both active and passive gains were reduced considerably, but passive gain was reduced more. Using an imagined head-fixed target in the dark, VOR gain was near zero at low frequencies but increased as frequency increased. Again, passive gain was less than active gain. At frequencies above 1 Hz, VOR gain in all conditions approached a value between 0.7 and 0.9. We conclude that active and manual passive rotation are simple and effective methods to test the VOR, but emphasize that visual and mental influences must be carefully controlled.

Adult↗
PubMed1987

Convergent effects from vestibulospinal tract and primary cutaneous afferent fibers on motoneurons to ankle extensor and flexor muscles in humans.

The latency and magnitude of cutaneomuscular reflexes, evoked by stimulation of the sural nerve in the contralateral and ipsilateral tibialis anterior and soleus, were investigated in normal human subjects during static tilts in the pitch axis. For all subjects the test reflex consisted of oscillating sequences of excitation and inhibition, each muscle exhibiting a characteristic pattern defined by its latency and sign of the initial phase. The latency of the various components and the sign of the initial phase did not vary with angle of tilt. However, the results of an ANOVA demonstrate a highly significant tilt-dependent modulation of the amplitude of the test reflex for the initial inhibitory phase of the contralateral tibialis anterior. We propose that this tilt-dependent effect on the crossed cutaneomuscular reflex originates from activity in the otolith organ receptors.

Adult↗
PubMed1985

Initiation of locomotion from the mesencephalic locomotor region: effects of selective brainstem lesions.

The effects of selected brainstem lesions on controlled treadmill locomotion produced by stimulation of the mesencephalic locomotor region (MLR) in postmamillary cats were determined in these experiments. The importance for the initiation of locomotion of projections from the MLR to rostral brainstem structures, described in a preceding paper, were examined by selective lesioning or by adjusting the level of the decerebration. The role played by the lateral vestibulospinal tract (LVST) in the initiation of locomotion was examined by lesioning Deiters' nucleus bilaterally. Contrary to previous claims, the results of the present experiments show that areas of the brainstem rostral to the MLR are not required for the initiation of locomotion by MLR stimulation. This finding eliminates the ventral tegmental area of Tsai and the substantia nigra, both implicated in the initiation of locomotion, as required participants in MLR stimulated locomotion. Bilateral Deiters' nucleus (DN) lesions did not significantly affect the initiation of locomotion from the MLR, nor did such lesions alter in a systematic fashion the amplitude or timing of EMG activity in flexor or extensor muscles of the hindlimb during MLR evoked walking. Joint angle changes during the locomotor cycle were also essentially unaltered by DN lesions. The significance of these findings regarding the brainstem structures which must be involved in the initiation of locomotion are discussed.

Animals↗
PubMed1984

Reversible cooling of the brainstem reveals areas required for mesencephalic locomotor region evoked treadmill locomotion.

The evidence suggests that the mesencephalic locomotor region (MLR) may not be a unitary region since anatomical and functional variations in the descending projections are clearly indicated. Reversible cooling of midline reticular structures can effectively block locomotion evoked by stimulation of lateral MLR (L3.5-4) sites while not significantly affecting the locomotion evoked from more medial MLR (L2-2.5) sites. In contrast, locomotion evoked by stimulation of the medial MLR sites is blocked by cooling of the ipsilateral lateral brainstem region which corresponds to the pontomedullary strip (PLS). Ipsilateral PLS cooling was not effective for blocking lateral MLR evoked locomotion, and contralateral PLS cooling was not effective for blocking either medial or lateral MLR evoked stepping. The evidence indicates that the lateral MLR relays through medial reticular nuclei while the medial MLR sites relay largely through the lateral brainstem structures often referred to as the PLS.

Animals↗
PubMed1984

Symmetrical optokinetic after-nystagmus loss in Wallenberg's syndrome and multiple sclerosis.

We have demonstrated abolition of OKAN in either horizontal direction with retention of caloric responses in 3 patients with unilateral brain stem infarcts. In one further patient with diffuse brain stem disease, we have been able to show bilateral loss of horizontal OKAN in the acute phase, with recovery during remission. These findings support the conclusion that the velocity storage mechanism or connections to it, are permanently disabled by unilateral medullary infarcts and may be temporarily disabled by demyelinating disease. Retention of caloric responses in the absence of OKAN would appear to be of assistance in the differential diagnosis between peripheral and central vestibular pathway lesions.

Humans↗
PubMed1983

Spinal-cord concussion in frogs. A study of reflex changes.

A reliable experimental model of the spinal frog, employing the flexor withdrawal reflex to a noxious stimulus, has been used to study the response to single and repeated concussing blows over the spinal column. It is evident that caudally placed blows depress the reflex response, whereas more cephalad blows facilitate the response. The results of studies using repeated concussing blows support the concept that neuronal units may completely lose their function without suffering permanent structural damage.

Animals↗
PubMed1982

Optokinetic after-nystagmus in man after loss or reduction of labyrinthine function - a preliminary report.

Horizontal optokinetic after-nystagmus (OKAN) was studied in normal volunteers and in patients with either unilateral or bilateral loss of labyrinthine function. Optokinetic stimulation in normal volunteers produced OKAN in the same direction as preceding optokinetic nystagmus (OKN) with a duration of 45-90 seconds and a slowly decreasing slow phase eye velocity. Similar stimulation in the bilateral labyrinthine loss group produced markedly diminished or no OKAN. In the unilateral group when the optokinetic stimulus produced OKN with fast phase to the affected ear, OKAN was markedly diminished or absent and replaced by a nystagmus which was reversed in direction to the preceding OKN. The opposite stimulus produced OKAN similar to the volunteer group. The above results support the observation that in human beings, the production of normal OKAN depends on an intact bilateral peripheral vestibular input and further demonstrates that the technique has lateralizing value in unilateral vestibular disease. These results also suggest that separate storage mechanisms are responsible for producing OKAN in the two directions, and that these storage mechanisms are decoupled from each other.

Dark Adaptation↗
PubMed1982

The vestibulo-ocular reflex in man during voluntary head oscillation under three visual conditions.

The vestibulo-ocular reflex (VOR) generated by voluntary head movements keyed to a tone varying sinusoidally in pitch was studied in 13 men. Modulation of pitch at frequencies ranging from 0.1-5.0 Hz yielded systematic variation in head movement frequencies, although above 2 Hz head frequencies fell below requested frequencies. Three conditions of visual stimulation were used. When an Earth-fixed visual target was visible, VOR gain (maximum eye velocity/maximum head velocity) was slightly but significantly greater than VOR gain in darkness at all frequencies except 0.1 Hz. With a head-fixed target, VOR gain was substantially less than VOR gain in darkness at all requested frequencies below 2.0 Hz. The finding that visual suppression becomes ineffective at frequencies above 1.0 Hz parallels results obtained in other laboratories during passive whole-body oscillation. Results indicate that the procedures are feasible for further evaluation as part of a clinical test battery.

Acceleration↗
PubMed1981

Spinal cord concussion.

A reliable experimental model using decerebrate frogs has been developed by which a measured cutaneous stimulus to the right forelimb produces a single electrical response from the left sciatic nerve. Using this model, the minimal concussing force necessary to abolish the propagation of the nerve impulse down the spinal cord was established by trial and error. The mean recovery time was 31.2 seconds, with a standard deviation of 1.32 seconds. Recovery of function of the spinal cord, as measured this method, was complete following single and multiple concussions.

Animals↗
PubMed1981

Visual-vestibular interactions: the directional component of visual background movement.

Legibility of a head-fixed display and visual suppression of the vestibulo-ocular reflex (VOR) were found to be superior when vestibular stimuli and optokinetic stimuli were of like direction (i.e. would produce the same directions of nystagmus) and inferior when they were opposite in direction. Velocities (relating to the head) of peripheral optokinetic stimuli ranging between -18 degrees/s and +180 degrees/s interacted effectively with vestibular stimuli to influence visibility of a head-fixed display. This indicates that peripheral optokinetic stimulation can influence visual suppression of the VOR at velocities that far surpass effective production of optokinetic nystagmus.

Electronystagmography↗
PubMed1979

Visual-vestibular interactions: I. Influence of peripheral vision on suppression of the vestibulo-ocular reflex and visual acuity.

Legibility of head-fixed displays in some motion environments is partially dependent upon visual suppression of the vestibuloocular reflex (VOR). This study investigates the effects of differing relationships between peripheral background movement and whole-body motion on the VOR and on visual performance. The purpose of the study is to explore factors in motion environments that influence performance limits and to develop procedures of potential usefulness in evaluating interacting visual and vestibular function. Visual performance and visual suppression of the VOR were markedly different, depending upon the relative direction of peripheral background movement. Visual suppression of the VOR, and visual performance, were disrupted far more when vestibular inputs and peripheral optokinetic inputs were discordant than when they were concordant. Results have potential implications for head-up displays and suggest a procedure for evaluating visual/vestibular function.

Acceleration↗