scholarly journals Vestibular Reflexes: Evaluation and Relevance in Microgravity

2016 ◽  
Author(s):  
Wg Cdr (Dr) Himanshu Swami ◽  
Keyword(s):  
Vestibular Reflexes

Dynamics of neck-to-forelimb reflexes in the decerebrate cat

1983 ◽  
Vol 50 (3) ◽  
pp. 688-695 ◽  
Author(s):  
K. Ezure ◽  
V. J. Wilson
Keyword(s):  
Head Rotation ◽  
Longitudinal Axis ◽  
Triceps Brachii ◽  
Vestibular Reflexes ◽  
Sinusoidal Analysis ◽  
Low Frequencies ◽  
Decerebrate Cat ◽  
Splenius Capitis ◽  
Response Phase ◽  
Stimulation Of

We have studied the neck-to-forelimb reflex evoked by head rotation around the longitudinal axis (roll) in the long and medial heads of triceps brachii of decerebrate, acutely labyrinthectomized cats. Reflexes were measured by recording mass electromyogram (EMG). As expected from the work of others, they were reciprocal in the two limbs, with excitation in the limb toward which the chin rotates. The reflex was sufficiently linear for a sinusoidal analysis. Although there was sometimes adaptation at stimulus frequencies of 0.1 Hz and below, response phase at these frequencies was usually in phase with position, and gain was flat. At higher frequencies there was some sensitivity to the velocity of the stimulus: gain increased with a slope of 10 dB/decade and phase advanced in some cats but not in others. Gain at low frequencies of head rotation, expressed as percent modulation of EMG, was typically 1%/deg or less. Reflexes evoked by head rotation in triceps and in the neck extensor splenius capitis have different dynamics. It remains to be determined whether this difference is due to activation of different receptors. We compared the dynamics of roll reflexes evoked by stimulation of neck receptors with those of vestibular reflexes evoked by tilt of the whole animal (23). Taking into account dynamics and gain, the two reflexes should cancel at low frequencies, as predicted by others. Above 0.2 Hz, cancellation becomes less effective.

Extracting phase-dependent human vestibular reflexes during locomotion using both time and frequency correlation approaches

2011 ◽  
Vol 111 (5) ◽  
pp. 1484-1490 ◽  
Author(s):  
Jean-Sébastien Blouin ◽  
Christopher J. Dakin ◽  
Kees van den Doel ◽  
Romeo Chua ◽  
Bradford J. McFadyen ◽  
...  
Keyword(s):  
Vestibular Stimulation ◽  
Time Dependent ◽  
Medial Gastrocnemius ◽  
Electromyographic Activity ◽  
Step Cycle ◽  
Vestibular Reflexes ◽  
Time Frequency ◽  
Dynamic Modulation ◽  
Frequency Decomposition ◽  
Heel Contact

Daily activities, such as walking, may require dynamic modulation of vestibular input onto motoneurons. This dynamic modulation is difficult to identify in humans due to limitations in the delivery and analysis of current vestibular probes, such as galvanic vestibular stimulation. Stochastic vestibular stimulation, however, provides an alternative method to extract human vestibular reflexes. Here, we used time-dependent coherence and time-dependent cross-correlation, coupled with stochastic vestibular stimulation, to investigate the phase dependency of human vestibular reflexes during locomotion. We found that phase-dependent activity from the medial gastrocnemius muscles is correlated with the vestibular signals over the 2- to 20-Hz bandwidth during the stance phase of locomotion. Vestibular-gastrocnemius coherence and time-dependent cross-correlations reached maximums at 21 ± 4 and 23 ± 8% of the step cycle following heel contact and before the period of maximal electromyographic activity (38 ± 5%). These results demonstrate 1) the effectiveness of these techniques in extracting the phase-dependent modulation of vestibulomuscular coupling during a cyclic task; 2) that vestibulomuscular coupling is phasically modulated during locomotion; and 3) that the period of strongest vestibulomuscular coupling does not correspond to the period of maximal electromyographic activity in the gastrocnemius. Therefore, we have shown that stochastic vestibular stimulation, coupled with time-frequency decomposition, provides an effective tool to assess the contribution of vestibular ex-afference to the muscular control during locomotion.

Ataxia telangiectasia: a “disease model” to understand the cerebellar control of vestibular reflexes

2011 ◽  
Vol 105 (6) ◽  
pp. 3034-3041 ◽  
Author(s):  
Aasef G. Shaikh ◽  
Sarah Marti ◽  
Alexander A. Tarnutzer ◽  
Antonella Palla ◽  
Thomas O. Crawford ◽  
...  
Keyword(s):  
Ataxia Telangiectasia ◽  
Disease Model ◽  
Head Rotation ◽  
Vestibular Evoked Myogenic Potentials ◽  
Electromyographic Activity ◽  
Vestibular Reflexes ◽  
Healthy Humans ◽  
Motor Strategy ◽  
Eye Rotation ◽  
Cerebellar Cortical Degeneration

Experimental animal models have suggested that the modulation of the amplitude and direction of vestibular reflexes are important functions of the vestibulocerebellum and contribute to the control of gaze and balance. These critical vestibular functions have been infrequently quantified in human cerebellar disease. In 13 subjects with ataxia telangiectasia (A-T), a disease associated with profound cerebellar cortical degeneration, we found abnormalities of several key vestibular reflexes. The vestibuloocular reflex (VOR) was measured by eye movement responses to changes in head rotation. The vestibulocollic reflex (VCR) was assessed with cervical vestibular-evoked myogenic potentials (cVEMPs), in which auditory clicks led to electromyographic activity of the sternocleidomastoid muscle. The VOR gain (eye velocity/head velocity) was increased in all subjects with A-T. An increase of the VCR, paralleling that of the VOR, was indirectly suggested by an increase in cVEMP amplitude. In A-T subjects, alignment of the axis of eye rotation was not with that of head rotation. Subjects with A-T thus manifested VOR cross-coupling, abnormal eye movements directed along axes orthogonal to that of head rotation. Degeneration of the Purkinje neurons in the vestibulocerebellum probably underlie these deficits. This study offers insights into how the vestibulocerebellum functions in healthy humans. It may also be of value to the design of treatment trials as a surrogate biomarker of cerebellar function that does not require controlling for motivation or occult changes in motor strategy on the part of experimental subjects.

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