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PubMedDate not supplied

Measuring eye movements during locomotion: filtering techniques for obtaining velocity signals from a video-based eye monitor.

Video-based eye-tracking systems are especially suited to studying eye movements during naturally occurring activities such as locomotion, but eye velocity records suffer from broad band noise that is not amenable to conventional filtering methods. We evaluated the effectiveness of combined median and moving-average filters by comparing prefiltered and postfiltered records made synchronously with a video eye-tracker and the magnetic search coil technique, which is relatively noise free. Root-mean-square noise was reduced by half, without distorting the eye velocity signal. To illustrate the practical use of this technique, we studied normal subjects and patients with deficient labyrinthine function and compared their ability to hold gaze on a visual target that moved with their heads (cancellation of the vestibulo-ocular reflex). Patients and normal subjects performed similarly during active head rotation but, during locomotion, patients held their eyes more steadily on the visual target than did subjects.

Adult↗
PubMed1985

Cardiopulmonary blood volume and plasma renin activity in normal and hypertensive humans.

Plasma renin activity (PRA) and systemic and forearm hemodynamics were studied during acute changes in cardiopulmonary blood volume and central venous pressure in 20 subjects, including 9 normotensive controls and 11 essential hypertensive patients of the same age. Changes in cardiopulmonary blood volume and central venous pressure were induced by a "head-down" tilt and thigh-cuff inflation. Blood pressure, pulse pressure, and heart rate did not change during cardiopulmonary blood volume variations, whereas significant changes in cardiac output, forearm blood flow, and PRA were observed. A significant negative correlation between cardiopulmonary blood volume (CPBV) and PRA existed, and slope of this correlation of delta PRA/delta CPBV was estimated as a sensitivity index of control of renin release. Sensitivity of neural control of renin release was not statistically different in normal subjects and hypertensive patients. In two groups, sensitivity of this reflex mechanism similarly decreased with age. Aging seems to be an important factor influencing the sensitivity of neural control of renin release, both in normal and essential hypertensive humans.

Adult↗
PubMed1996

Force dependent response reversal mediated by low- and high-threshold afferents from the same mechanoreceptor in a crayfish leg.

1. The reflex responses initiated by cuticular stress detector one (CSD1) afferents in anterior levator motor neurnons in the fifth walking leg of crayfish were studied in an in vitro preparation by means of intracellular recordings. 2. The response in the anterior levator reversed with strong mechanical stimulation. Inhibitory responses were correlated with the activation of low-threshold CSD1 units, excitatory responses with the activation of high-threshold CSD1 units. Two opposing reflexes thus originate from the same sense organ at different levels of stimulation. 3. Some low-threshold units were inactive at stimulus strengths that activated the high-threshold units. Other low-threshold units remained active. Their reflex effects were reduced by either pre- or postsynaptic mechanisms. 4. Functionally, this force dependent response reversal could be important in switching from postural/locomotor responses to defensive responses such as limb autotomy.

Animals↗
PubMed1994

Acceleration registrography of head movement during alternating inclination of the support platform.

The righting reflex, essential for maintaining equilibrium, keeps the head and trunk in a state of balance with regard to gravity. Because patients suffering from vestibular disorders almost always complain of dizziness during everyday movements such as rising and walking, the righting reflex should be evaluated within the context of these dynamic states. A new method of acceleration registrography was designed to enable the testing of this reflex as the subject stands upon a moving platform. Participating in the study were 49 normal control subjects and 80 patients with peripheral vestibular disorders. The test we devised proved to be more successful in detecting labyrinthine righting reflex dysfunction in patients than the tests of righting reflex and deviation evaluations used thus far, such as Romberg's, Mann's and the stepping test, and to more accurately represent the disequilibrium and/or dizziness experienced by patients in everyday movements.

Acceleration↗
PubMed1996

Control of locomotion in the decerebrate cat.

Many of the general concepts regarding the control of walking were described years ago by: Sherrington (1906) Integrative Actions of the Nervous System. Yale University Press: New Haven, CT; Sherrington (1910a) Remarks on the reflex mechanism of the step, Brain 33, 1-25; Sherrington (1910b) Flexor-reflex of the limb, crossed extension reflex, and reflex stepping and standing (cat and dog), J. Physiol. (Lond.) 40, 28-121; Sherrington (1931) Quantitative management of contraction in lowest level coordination, Brain 54, 1-28; Graham-Brown (1912) The intrinsic factors in the act of progression in the mammal, Proc. R. Soc. Lond. 84, 308-319; Graham-Brown (1914) On the nature of the fundamental activity of the nervous centres; together with an analysis of the conditioning of rhythmic activity in progression, and a theory of the evolution of function in the nervous system, J. Physiol. 49, 18-46; Graham-Brown (1915) On the activities of the central nervous system of the unborn foetus of the cat, with a discussion of the question whether progression (walking, etc.) is a 'learnt' complex, J. Physiol. 49, 208-215; Graham-Brown (1922) The physiology of stepping, J. Neur. Psychopathol. 3, 112-116. Only in recent years, however, have the mechanisms been analyzed in detail. Quite a few of these mechanisms have been described using the decerebrate cat. Locomotion is initiated in decerebrate cats by activation of the mesencephalic locomotor region (MLR) that activates the medial medullary reticular formation (MRF) which in turn projects axons to the spinal cord which descend within the ventrolateral funiculus (VLF). The MRF region regulates as well as initiates the stepping pattern and is thought to be involved in interlimb coordination. Afferent feedback from proprioceptors and exteroceptors can modify the ongoing locomotor pattern. Recently, the types of afferents responsible for signaling the stance to swing transition have been identified. A general rule states that if the limb is unloaded and the leg is extended, then swing will occur. The afferents that detect unloading of the limb are the Golgi tendon organs and stimulation of these afferents (at group I strengths) prolongs the stance phase in walking cats. The afferents that detect the extension of the leg have been found to be the length- and velocity-sensitive muscle afferents located in flexor muscles. Plasticity of locomotor systems is discussed briefly in this article. Descerebrate animals can adapt locomotor behaviors to respond to new environmental conditions. Oligosynaptic reflex pathways that control locomotion can be recalibrated after injury in a manner that appears to be functionally related to the recovery of the animal.

Animals↗
PubMed1987

Enhanced vagal activity and normal arginine vasopressin response in carotid sinus syndrome: implications for a central abnormality in carotid sinus hypersensitivity.

The relation between arginine vasopressin and vagal activity in carotid sinus syndrome was studied in 10 patients and 17 age matched controls using head up tilt as a stimulus. Of the controls, seven had unexplained syncope and 10 were healthy elderly subjects with no previous history of syncope. Subjects were studied supine for 45 min and thereafter during 120 min head up tilt to 40 degrees. Phasic arterial pressure and heart rate were monitored throughout. Serum was sampled at frequent intervals to measure arginine vasopressin, noradrenaline, and adrenaline concentrations. Seventy per cent of carotid sinus patients had vasovagal syncope at (mean(SD)) 25(4) min after tilt compared with 43% of subjects with unexplained syncope and one healthy elderly control. The maximum (mean(SD)) fall in systolic blood pressure and heart rate was 70(20) mmHg and 20(7) beats.min-1 (p less than 0.001 and p less than 0.01 respectively). Arginine vasopressin, noradrenaline, and adrenaline concentrations rose significantly in syncopal subjects (p less than 0.001, p less than 0.01, and p less than 0.05 respectively). Changes in systolic blood pressure, heart rate, and hormone concentrations were similar for patients with carotid sinus syndrome and control subjects. For those who completed the tilt period without the development of symptoms, systolic blood pressure and arginine vasopressin and adrenaline concentrations were unchanged, whereas noradrenaline concentrations and heart rate rose significantly. Vasovagal activity is thus appreciably increased in carotid sinus syndrome. Furthermore, the afferent limb of the carotid sinus reflex appears to be intact in patients with carotid sinus syndrome since the pattern of arginine vasopressin release was not different from controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed2001

Stereopsis outweighs gravity in the control of the eyes.

The eyes are controlled by multiple brain circuits, some phylogenetically old and some new, whose aims may conflict. Old otolith reflexes counterroll the eyes when the head tilts relative to gravity. Newer vergence mechanisms coordinate the eyes to aid stereoptic vision. We show that counterroll hinders stereopsis, weakly when you look into the distance but strongly when you look near. The resolution of this conflict is that counterroll virtually vanishes when monkeys look close, i.e., stereopsis overrides gravity-driven reflexes but only on near gaze. This balance between gyroscopic and stereoptic mechanisms explains many other puzzling features of primate gaze control, such as the weakness of our otolith-ocular reflexes even during far viewing and the strange geometry of the primate counterpitch reflex, which rolls the eyes clockwise when monkeys look leftward while their heads are tipped nose up, but rolls them counterclockwise when the monkeys look rightward, and reverses this pattern when the head is tipped nose down.

Animals↗
PubMed1993

A multidimensional model of the effect of gravity on the spatial orientation of the monkey.

A "sensory conflict" model of spatial orientation was developed. This mathematical model was based on concepts derived from observer theory, optimal observer theory, and the mathematical properties of coordinate rotations. The primary hypothesis is that the central nervous system of the squirrel monkey incorporates information about body dynamics and sensory dynamics to develop an internal model. The output of this central model (expected sensory afference) is compared to the actual sensory afference, with the difference defined as "sensory conflict." The sensory conflict information is, in turn, used to drive central estimates of angular velocity ("velocity storage"), gravity ("gravity storage"), and linear acceleration ("acceleration storage") toward more accurate values. The model successfully predicts "velocity storage" during rotation about an earth-vertical axis. The model also successfully predicts that the time constant of the horizontal vestibulo-ocular reflex is reduced and that the axis of eye rotation shifts toward alignment with gravity following postrotatory tilt. Finally, the model predicts the bias, modulation, and decay components that have been observed during off-vertical axis rotations (OVAR).

Animals↗
PubMed1983

Evaluation of calcium-mediated vasoconstriction in chronic congestive heart failure.

Intercellular vascular smooth muscle calcium results in vasoconstriction and is therefore a potentially adverse mechanism of increased afterload in chronic congestive heart failure. Therefore, an evaluation was made of supine and tilt hemodynamic data, sympathetic reflexes, and the hormonal response to calcium channel antagonism after administration of nifedipine in nine patients with severe chronic congestive heart failure. After a 10 mg oral dose, the peak hemodynamic response occurred at 30 minutes and was characterized primarily by afterload reduction, improvement of systemic flow, and reduction of pulmonary hypertension. Despite reduction of supine blood pressure, there was no orthostatic hypotension during head-up tilt at the same time of peak response. Reflex responses to sympathetic stimulation (cold pressor test) were improved but still attenuated when compared with normal responses. Plasma renin activity increased significantly, but a dissociation of the aldosterone response was observed. Plasma catecholamine levels were not significantly altered. In summary, calcium antagonism resulted in significant afterload reduction and hemodynamic improvement in chronic congestive heart failure. This was associated with improved reflex responsiveness and, potentially, altered other vasoconstrictor hormones independently of the hemodynamic response. Calcium antagonism may provide a means to further understand vasoconstrictor mechanisms in heart failure and enhance therapy in appropriate patient subsets.

Adult↗
PubMed1979

Breathing responses of unanesthetized man and guinea pigs to increased transrespiratory pressure.

We compared the breathing responses of unanesthetized men and guinea pigs to externally imposed shifts in lung volume produced by steady pressures applied to the body surface while the mouth remained near atmospheric pressure. Lung inflation caused no consistent or significant changes either in frequency or end-tidal CO2 in the three men. In contrast, during lung inflation the guinea pigs breathed at low frequencies and smaller tidal volumes and showed consistent increases in arterial PCO2 lasting up to 10 min. The changes seen immediately on application of pressure, namely apneic periods followed by breathing in which inspiratory duration was shortened while expiratory duration was substantially increased, indicates that conscious guinea pigs have active inflation reflexes. We concluded that the reflex responses rather than mechanical factors probably account for the underventilation in the guinea pigs and that guinea pigs are not nearly as well equipped as is man to defend gas exchange in the face of nonmetabolic shifts in lung volume.

Animals↗
PubMed1986

Otolith stimulation evokes compensatory reflex eye movements of high velocity when linear motion of the head is combined with concurrent angular motion.

Previous investigations have failed to find significant compensatory eye movements in response to linear motion of the head. However, the fact that visual acuity is essentially preserved during natural head movements, which combine both linear and angular components, is evidence that there must be compensation for linear translation. Hence we examined the lateral eye movements produced by angular oscillation, in the dark, in yaw at 0.5 and 1.5 Hz, 80 degrees/s peak, with the head both centred and positioned 30 cm eccentric from the axis of rotation in order to produce an additional linear acceleration acting tangentially. The combined stimuli produced high velocities of eye movement which were much greater than those produced by angular motion alone. The findings are evidence or a linear-compensatory reflex which is probably otolithic. The dependency of otolithic eye movements on concurrent stimulation of the semicircular canals is a possible explanation of positional nystagmus in neuro-otological disease in which it may be released by a pathological imbalance of canal function.

Adult↗
PubMed1985

Acute and chronic effects of the converting enzyme inhibitors enalapril and lisinopril on reflex control of heart rate in normotensive man.

The effects of enalapril maleate and its lysine analogue, lisinopril, on reflex control of heart rate after acute and chronic administration were examined in 10 normotensive males. Both drugs reduced blood pressure without change in heart rate after acute dosing and after seven days. Both drugs impaired the vagally mediated early cardiac acceleration associated with lying down (standing to lying test). A similar effect was observed following edrophonium. After lisinopril bradycardia induced by facial immersion (diving reflex) was significantly attenuated. Edrophonium similarly attenuated the bradycardia. Both these reflexes are parasympathetically mediated. Neither drug altered heart rate or blood pressure changes following Valsalva's manoeuvre and the cold pressor test. Plasma noradrenaline was unchanged. Absence of reflex tachycardia with blood pressure reduction by converting enzyme inhibitors may be related to increased parasympathetic activity either centrally or peripherally without impairment of baroreflexes or sympathetic function.

Adult↗
PubMed1992

Clinical observations on the on-off effect of the acoustic stapedius reflex.

The on-off effect of the acoustic stapedius reflex was found in association with several kinds of ear disease: otosclerotic stapes fixation, incudostapedial dislocation and sensorineural hearing loss. One fifth (8/40) of the patient group with an on-off effect and sensorineural hearing loss showed the typical symptoms of Ménière's syndrome.

Adult↗
PubMed1996

The stretch reflex response in the normal and spastic ankle: effect of ankle position.

OBJECTIVE: The influence of stretch of the gastrocnemiussoleus muscle on the stretch reflex activity was studied, by varying the ankle angle in steps from 10 degrees of plantarflexion (PF) to 5 degrees of dorsiflexion (DF). DESIGN: Nonrandomized control trial. SETTING: Department of Rehabilitation Medicine of a university medical center. PATIENTS: Sixteen subjects with and 16 subjects without spasticity. MAIN OUTCOME MEASURES: The passive elastic stiffness and active reflex response, expressed by the total and elastic path lengths, were determined at each ankle angle as a sinusoidal displacement of 5 degrees was applied to the joint at frequencies from 3 to 12 Hz. RESULTS: The elastic stiffness showed no difference between the spastic and normal subjects for all ankle angles (p > .05). The elastic stiffness increased linearly similarly in both groups when the ankle was dorsiflexed. The reflex response was significantly greater in the spastic group for all positions (p < or = .01). The total and elastic path lengths showed a linear increase in both groups when the ankle angle was varied from PF to DF. The spastic group, however, had a significantly faster increase (p < or = .005). Between-group comparison showed a significant quadratic trend in the elastic path length for the spastic group (p < or = .05), with a maximum at 2.5 degrees of DF. CONCLUSIONS: This study showed that the stretch reflex activity varies with the ankle position. This must be considered when performing spasticity tests subsequent to an intervention that has changed the available range of motion and when comparing subjects measured at different ankle positions.

Adult↗
PubMed2002

Anticipatory and reflexive neck muscle activities during voluntary rapid jaw opening and passive jaw depression in humans.

The characteristics of head movement during voluntary rapid jaw opening movement and passive jaw depression were investigated using accelerometers and electromyographs (EMG) on eight healthy examinees. Passive depressions were executed by means of load on the lower jaw, initiated either by examinees themselves or an experimenter. In the depression initiated by examinees, a head-extension movement that preceded the load to the lower jaw and anticipatory activities in the nuchal region of the trapezius muscle were observed. In the depression initiated by the experimenter, the anticipatory activities were not observed. In both of these cases, stretch reflexes were induced in the trapezius muscle. During voluntary rapid jaw opening, a head-extension movement nearly synchronized with the opening movement in the lower jaw acceleration, and dorsal-neck muscle activities accompanying the synchronized movement were observed. The peak timing of these neck-muscle activities preceded the latencies of the stretch-reflex activities observed in the jaw-depressed tasks, but no anticipatory activities were observed in the dorsal-neck muscles. We conclude that neither the anticipatory activities nor the reflex activities observed in the passive depressions have effects on the initial part of the dorsal-neck muscle activities, which are related to the head-extension synchronized with the voluntary lower-jaw opening movement.

Adult↗
PubMed2006

Influence of the behavioural context on the optocollic reflex (OCR) in pigeons (Columba livia).

We investigated the effects of several behavioural conditions on the properties of the horizontal optocollic reflex (OCR) in pigeons. The head reflex was triggered by rotating the visual surroundings at different velocities (stimuli steps of 30-300 deg. s(-1)) and the characteristics of the slow and fast phases of the OCR were analysed during, (i) the 'resting condition', in which animals were hung in a harness, (ii) the 'standing condition', in which animals were freely standing, (iii) the 'walking condition', in which animals were walking on a treadmill at different velocities, and (iv) the 'flying condition', in which animals were hung in a harness and subjected to a frontal air-stream, provoking a flying posture. In the 'resting' condition, irregularities were observed in the amplitude of nystagmic beats, in the beating field and in the slow phase velocity (SPV) of the OCR. These irregularities diminished progressively when the behavioural condition changed from 'standing' to 'walking', and disappeared in the 'flying' condition. Correlatively, the working range of the OCR (evaluated by its gain at the plateau of SPV) was progressively extended toward higher stimulation velocities. The velocity of the fast phases of the OCR (measured for all the conditions except the 'walking condition') also increased in correlation with the SPV. The walking speed did not influence the OCR in the treadmill velocity range of 0.20-0.40 m s(-1). The presence of a frontal airstream in the 'standing condition' did not change the OCR properties. This fact (and other observations discussed in the paper) suggests that the adaptation of the OCR to the behavioural context is mediated by internal signals generated by each behavioural condition.

Analysis of Variance↗
PubMedDate not supplied

[Changes in vestibular reflex activity during orthostatic tests].

This paper presents data on vestibular responses of healthy test subjects, aged 18 to 33 years, to active and passive orthostatic loads. Standing and tilting orthostatic tests led to a decline of vestibular activity caused by decreases in cerebral and labyrinthine blood flow as well as somatic and visceral afferentation that converged on the vestibular centers of stem bulbar formations and supratentorial vestibular structures.

Adolescent↗
PubMed2003

Vestibular testing abnormalities in individuals with motion sickness.

HYPOTHESIS: The goal of this study was to compare the results of vestibular testing in individuals with motion sickness to a group of control subjects. BACKGROUND: Studying motion sickness is difficult, because no animal model has been developed and symptoms rarely occur outside motion environments. Tests that can be performed in normal laboratory settings, which help to identify individuals with motion sickness, may be valuable in characterizing this disorder. METHODS: Twenty active duty military individuals with well-documented motion sickness were tested. The test battery included sinusoidal rotational chair testing to calculate vestibulo-ocular reflex function, step-velocity testing to calculate vestibular time constants, and posturography testing to assess vestibulo-spinal reflex status. The results of this test battery were compared with a set of age- and sex-matched controls without motion sickness. RESULTS: Vestibular test abnormalities were demonstrated in individuals with motion sickness. Vestibulo-spinal reflex function on posturography was normal in the control group but abnormal in 70% of the individuals with motion sickness. In addition, 5% of the control group demonstrated a minimal shortening of the absolute time constant, whereas 60% of the individuals with motion sickness had abnormal absolute time constants. CONCLUSION: A significant percentage of individuals with motion sickness demonstrate abnormalities in their time constant or vestibulo-spinal reflex function. These abnormalities can be detected using standard, land-based vestibular tests. These preliminary results have implications in understanding the etiology of motion sickness and may provide outcome measures to be used in treating motion sickness.

Adult↗