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At least 703 records · Page 39Linked to original sources
PubMed1999

Characteristics of slow and fast phases of the optocollic reflex (OCR) in head free pigeons (Columba livia): influence of flight behaviour.

The effect of behavioural context on the properties of slow and fast phases of the horizontal optocollic reflex (OCR) were investigated in head free pigeons for two situations, i.e.: (i) animals were hung in a harness ('resting condition'); (ii) animals were additionally submitted to a frontal airflow that provoked a flight posture ('flying condition') [Bilo and Bilo (1983) J. Comp. Physiol., 153, 111]. A 'transient flight' was also provoked in the 'resting condition' by tapping the breastbone region. Stimuli consisted either of velocity steps (30-300 degrees/s) or of an increasing velocity stimulus (0-300 degrees/s). The amplitude of nystagmic beats and the OCR gain increased in the 'flying condition' and during 'transient flight' as compared to the 'resting condition'. The OCR working range was considerably extended toward high velocities by the flying behaviour. In the 'resting condition', spontaneous head oscillations generally triggered a high-gain OCR, close to that obtained in the 'flying condition'. One-third of the animals showed a higher gain in response to an increasing velocity stimulus than with step stimuli, in the high velocity range. The linear relation between amplitude and peak velocity of OCR fast phases was independent of the stimulation velocity in the 'resting condition', whereas the amplitude and peak velocity increased with the stimulation velocity in the 'flying condition'. In this condition, the fast phase velocity was correlated with the slow phase velocity, but not with the retinal slip velocity. Thus, both the slow and fast phases of the OCR are dependent on the behavioural context.

Animals↗
PubMed1976

The grasp reflex of the foot and related phenomena in the absence of other reflex abnormalities following cerebral commissurotomy.

The grasp reflex of the foot and related pheonomena were examined in six subjects with no abnormalities of deep tendon or plantar (and related) reflexes 6 to 10 years after cerebral comissurotomy. In all subjects they were more marked on the same side as the more damaged hemisphere. These tonic phenomena seem to be facillitated by sitting and standing postures. Practical and theoretical implications of the tonic foot responses in the absence of similar phenomena of the hand are discussed.

Adult↗
PubMed1986

Position dependence of stretch reflex dynamics at the human ankle.

The purpose of this study was to examine the effect of ankle position on the human ankle stretch reflexes during tonically-maintained contractions over most of the range of motion. The ankle was placed at randomly selected mean positions. Target levels of triceps surae (TS) or tibialis anterior (TA) tonic contractions were generated while the ankle was displaced by small amplitude, stochastic perturbations. System identification techniques were used to identify the stretch reflex dynamics at each combination of tonic level and ankle angle. As shown previously, the TS stretch reflex was characterized by an unidirectional, velocity-sensitive impulse response function whereas the TA stretch reflex was characterized by a linear impulse response function between ankle velocity and TA EMG. TS stretch reflexes showed a strong dependence on ankle position while TA stretch reflexes did not. Thus the TS stretch reflex magnitude increased greatly as the ankle was progressively dorsiflexed. In contrast, ankle mean position had only a minor effect on the TA stretch reflex magnitude. Our results indicate that the position-dependent facilitation of the TS stretch reflex is not due to changes in the level of skeletal motoneuron excitability. Rather, this effect may be accounted for by mechanisms that modulate the efficacy of the stochastic ankle perturbation. Such mechanisms could include position-induced: modulation of monosynaptic and polysynaptic afferent inputs to skeletal motoneurons, alterations in the extent of fusimotor drive and changes in the transmission of the joint perturbation to spindle receptors. Such mechanisms are discussed in terms of the differences between TS and TA stretch reflexes. Finally, the functional significance of position-dependent reflex responses are considered.

Adult↗
PubMed1977

Modulation of hindlimb reflexes by tonic neck positions in cats.

In cats with the head fixed in a stereotactic frame a slight facilitation of the gastrocnemiussoleus (GS) monosynaptic reflexes in the ipsilateral hindlimb, accompanied by an inhibition of the monosynaptic reflex of the antagnostic deep peroneal nerve (DP), occurs following lateral flexion and rotation around the body axis at an angle of 25 degrees. Following dorsiflexion of the body a moderate inhibition of the extensor reflexes (GS) up to 10% and a reciprocal slight excitation in the same range of the monosynaptic reflexes of flexor muscles (DP) is recorded. On the other hand after ventriflexion of the body there is a marked inhibition in the range of 50% of all the monosynaptic extensor and flexor reflexes for all the stimulus intensities used. This inhibition can already be demonstrated in ventriflexion of 10 degrees-15 degrees. All these patterns of reflex modulation are similar in cortically intact, ischemically decorticated and precollicularly decerebrated cats. Furthermore these patterns are not essentially influenced by cerebellectomy, although all reflex amplitudes are reduced. However, the spinal reflexes can not be modulated by these body movements after acute spinalization.

Afferent Pathways↗
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↗
PubMed1986

[Cardiovascular reflex evaluation for detecting autonomic neuropathy in chronic dialysis patients].

3 cardiovascular reflexes were tested in 25 patients on regular haemodialysis: measurement of the beat-to-beat variation in heart rate in the supine position and during deep breathing, measurement of heart rate response to change in posture (30:15 ratio). 8 patients (32%) had abnormal results in at least two of the tests, 3 patients (12%) had abnormal results in all 3 tests. Beat-to-beat variation was found to be the most sensitive test, the heart rate difference during deep breathing showing a direct correlation to the nerve conduction velocity of the peroneal nerve. Hence, a common cause can be postulated in the pathogenesis of the autonomic lesions and the sensorimotor polyneuropathy in the patients under investigation. Furthermore, the group with the most severe radiological calcification due to Mönckeberg's medial sclerosis had a significantly lower mean heart rate difference during deep breathing than the group with no radiological calcification. A similar correlation between autonomic neuropathy and Mönckeberg's medial sclerosis has recently been described in diabetic patients.

Adolescent↗
PubMedDate not supplied

[Effect of electric stimulation of the hypothalamus and limbic formations on vestibular-somatic reflexes].

Chronic experiments on rabbits which had electrodes implanted into the hypothalamus, amygdalar area and hyppocampus have shown that electrostimulation of these brain structures which brought about different emotional and behavioral reactions during preliminary test produces a distinct modulating effect on the vestibular (rotatory and post-rotatory) nystagmus and labyrinthine posture-tonic reflexes.

Acceleration↗
PubMedDate not supplied

Effect of labyrinthine dysfunction upon head oscillation and gaze during stepping and running.

Head oscillations and eye movements when stepping and running were studied in normal subjects and in patients with labyrinthine dysfunctions. In normal subjects, whereas linear head oscillations in the horizontal plane were very limited during both stepping and running, a marked increase in the vertical linear displacement induced pitching motions of the head during running. Patients with unilateral and bilateral lesions complaining of oscillopsia manifested lateral and diffuse oscillations, respectively, in the horizontal plane during stepping. The ratio of eye amplitude to head amplitude in the vertical plane showed larger values in subjects with labyrinthine lesions than in normals. The present results suggested that oscillopsia during upright locomotion is closely related to linear head oscillations with irregular and high-frequency components, in addition to dysfunction of the vestibulo-ocular reflex.

Adult↗
PubMed1986

Orthostatic tolerance of normal Indians and those with suspected abnormal cardiovascular reflex status.

There were 143 healthy Indian males subjected to 70 degrees headup tilt (HUT) for 20 min on 166 occasions to evaluate their cardiovascular response. They responded with a significant rise in heart rate, diastolic pressure, and mean arterial pressure. Pulse pressure fell significantly. Heart rate and diastolic pressure during the tilt were significantly (p less than 0.05) and positively correlated to the height of the subjects. None of the subjects had syncope, which has been reported in normal individuals elsewhere. Of the 57 subjects with suspected abnormality of the cardiovascular reflex status, who were also investigated by the tilt test, 13 (22.8%) developed various degrees of orthostatic intolerance. Of these 13 subjects, 10 had had syncope in the past. In view of these observations, it is concluded that 70 degrees head-up tilt is an important clinicophysiological investigation in the assessment of subjects with a suspected abnormality of their cardiovascular reflex status.

Adult↗
PubMed1996

Motor profile of patients in minimally responsive and persistent vegetative states.

The purpose of this descriptive clinical study is to document the motor characteristics of patients in minimally responsive and persistent vegetative states. Twelve subjects, presenting a prolonged altered state of consciousness (x = 7.82 years, range 2-27), aged 27-78 years (x = 50, SD = 15.26) were evaluated, using standardized protocols, on the following variables: passive range of motion, observed movements, reflexes, tonus, postural status and reactions. The subjects' level of awareness and responsivity were measured with the Coma/Near Coma (CNC) scale at each of the three data collection sessions. While group CNC scores were stable over the three sessions, fluctuations in the level of awareness of individual subjects was recorded, confirming the heterogeneity of this clientele. Abnormal primitive reflexes were present in all subjects, with the flexor withdrawal (75%), the tonic labyrinthine (36%) and the body-on-body righting reaction (25%) being the most frequently observed. All subjects presented altered tonus, considerable posturing and varied degrees of reduced range of joint motion. A range of abnormal (e.g. chewing, clonus) and normal patterned (e.g. bridging, scratching) movement behaviours was recorded, but these did not translate into functional use, such as rolling. Collectively, the findings stress the complexity of the motor profile of patients in minimally responsive and vegetative states, and suggest the need for physiotherapists to become more actively involved in the evaluation and treatment of this clientele.

Adult↗
PubMed1991

Modulation of human short latency reflexes between standing and walking.

Inhibition of the magnitude of soleus muscle homonymous (H) reflexes occurs in humans when walking, compared to standing. The current study asked, (1) was the task modulation of Ia reflexes limited to soleus muscle, (2) was there support for attributing a presynaptic source to the inhibition in humans and (3) did an oligosynaptic short latency reflex show similar task modulation? In 3 subjects, H reflexes were evoked in vastus medialis and soleus, at 4 levels of contraction in the target muscle, with constant stimulus intensity when walking and standing. The reflex magnitudes in both muscles were significantly inhibited during the contractions for walking, compared to standing. Such inhibition also occurred in H reflexes of tibialis anterior muscle. An excitatory oligosynaptic reflex was then evoked in vastus medialis, through low intensity stimulation of the common peroneal nerve during walking and standing. The mean amplitudes of this reflex were not significantly different (P less than 0.05) between the two conditions, at any contraction level. The depression of quadriceps H reflexes, compared to the oligosynaptic reflexes through the same quadriceps motoneuronal pool in the same task, strongly suggested that the inhibition of H reflexes arose at other sites besides the motoneuronal cell body and proximal dendrites. We conclude that Ia H reflexes of various leg muscles of humans are inhibited when walking but that this does not generalize to the oligosynaptic short latency reflex between the anterior shank and thigh.

Adult↗
PubMed1984

Axonal branching in the projections from the paramedian reticular nucleus to the cerebellar cortex.

Injections of fluorescent tracers into cat cerebellar cortex gave evidence of collateral axonal branching of neurons situated in the paramedian reticular nucleus. These branched reticulocerebellar projections were distributed to opposing sides of the cerebellum, in particular the anterior lobe and the ansiform lobule. No topographical organization was observed in the PRN. Less than 30% of ipsilaterally projecting reticulocerebellar fibers had contralaterally directed collateral branches. These results are in keeping with a bilateral fastigial projection to the PRN forming a feedback loop circuit through which orthostatic reflexes may be mediated.

Animals↗