scholarly journals Commissural Inputs to Secondary Vestibular Neurons in Alert Cats After Canal Plugs

2003 ◽  
Vol 89 (6) ◽  
pp. 3351-3353 ◽  
Author(s):  
Karl Farrow ◽  
Dianne M. Broussard
Keyword(s):  
Brain Stem ◽  
Head Movements ◽  
Excitatory Synapses ◽  
Vestibular Loss ◽  
Horizontal Semicircular Canal ◽  
Vestibular Neurons ◽  
Discharge Rates ◽  
Alert Cats ◽  
Change In Mean ◽  
Stimulation Of

Gaze is stabilized during head movements primarily by the vestibuloocular reflex (VOR). After a unilateral canal plug, the VOR's response is reduced. Recovery of the VOR may be brought about by changes in the efficacy of brain stem synapses or by other mechanisms. We measured the responses of horizontal secondary vestibular neurons (HSNs) to stimulation of the contralateral labyrinth. HSN responses in normal alert cats were compared with those in cats that had recovered from unilateral horizontal semicircular canal (HSCC) plugs. After recovery, excitatory commissural inputs to HSNs on the plugged side elicited significantly smaller responses than in normal cats with no change in mean discharge rates. However, mean discharge rates tended to be higher after recovery for cells receiving inhibitory commissural inputs. The change in resting rate invalidates any direct comparison of inhibitory inputs. These results are interpreted in terms of possible mechanisms for recovery from unilateral vestibular loss by the VOR neural network. We conclude that after unilateral HSCC plugs, changes in brain stem excitatory synapses and/or excitability of secondary vestibular neurons may participate in the restoration of normal vestibular reflexes.

Firing Behavior of Vestibular Neurons During Active and Passive Head Movements: Vestibulo-Spinal and Other Non-Eye-Movement Related Neurons

1999 ◽  
Vol 82 (1) ◽  
pp. 416-428 ◽  
Author(s):  
Robert A. McCrea ◽  
Greg T. Gdowski ◽  
Richard Boyle ◽  
Timothy Belton
Keyword(s):  
Electrical Stimulation ◽  
Eye Movement ◽  
Head Rotation ◽  
Head Movements ◽  
Whole Body ◽  
Body Rotation ◽  
Firing Behavior ◽  
Vestibular Neurons ◽  
Gaze Saccades ◽  
Stimulation Of

The firing behavior of 51 non-eye movement related central vestibular neurons that were sensitive to passive head rotation in the plane of the horizontal semicircular canal was studied in three squirrel monkeys whose heads were free to move in the horizontal plane. Unit sensitivity to active head movements during spontaneous gaze saccades was compared with sensitivity to passive head rotation. Most units (29/35 tested) were activated at monosynaptic latencies following electrical stimulation of the ipsilateral vestibular nerve. Nine were vestibulo-spinal units that were antidromically activated following electrical stimulation of the ventromedial funiculi of the spinal cord at C1. All of the units were less sensitive to active head movements than to passive whole body rotation. In the majority of cells (37/51, 73%), including all nine identified vestibulo-spinal units, the vestibular signals related to active head movements were canceled. The remaining units ( n = 14, 27%) were sensitive to active head movements, but their responses were attenuated by 20–75%. Most units were nearly as sensitive to passive head-on-trunk rotation as they were to whole body rotation; this suggests that vestibular signals related to active head movements were cancelled primarily by subtraction of a head movement efference copy signal. The sensitivity of most units to passive whole body rotation was unchanged during gaze saccades. A fundamental feature of sensory processing is the ability to distinguish between self-generated and externally induced sensory events. Our observations suggest that the distinction is made at an early stage of processing in the vestibular system.

Head Impulses After Unilateral Vestibular Deafferentation Validate Ewald’s Second Law1

1991 ◽  
Vol 1 (2) ◽  
pp. 187-197
Author(s):  
G.M. Halmagyi ◽  
I.S. Curthoys ◽  
P.D. Cremer ◽  
C.J. Henderson ◽  
M. Staples
Keyword(s):  
Head Rotation ◽  
Normal Subjects ◽  
Head Movements ◽  
Afferent Neurons ◽  
Horizontal Semicircular Canal ◽  
Ocular Reflex ◽  
Vestibulo Ocular Reflex ◽  
Unilateral Vestibular Deafferentation ◽  
Head Impulses ◽  
Stimulation Of

To determine the relative contributions of ampullofugal (AF) and ampullopetal (AP) stimulation of the horizontal semicircular canal (HSCC) to the horizontal vestibulo-ocular reflex (HVOR), 12 patients were studied 1 year after total unilateral vestibular deafferentation (UVD). Compensatory eye movement responses to impulses of horizontal head rotation were studied using magnetic search coils. The head impulses were rapid (up to 3000 deg/sec/sec) passive, unpredictable, step displacements of horizontal angular head position with respect to the trunk. Tbe results from these 12 patients were compared with results from 30 normal subjects. An HVOR deficit was found to each side. The HVOR in response to head impulses toward the deafferented side, a response generated exclusively by ampullofugal stimulation of the single functioning HSCC, was severely deficient with an average gain of 0.25; the HVOR in response to head impulses toward the intact side, a response generated exclusively by ampullopetal stimulation of the single functioning HSCC, was mildly but significantly deficient compared with normal subjects. These results show that rapid, unpredictable head movements, unlike slow, predictable head movements, do demonstrate the AP-AF HVOR asymmetry, which could be expected from consideration of the behavior of single vestibular afferent neurons, an asymmetry that is expressed by Ewald’s 2nd Law.

Integration of Vestibular and Head Movement Signals in the Vestibular Nuclei During Whole-Body Rotation

1999 ◽  
Vol 82 (1) ◽  
pp. 436-449 ◽  
Author(s):  
Greg T. Gdowski ◽  
Robert A. McCrea
Keyword(s):  
Eye Movement ◽  
Head Rotation ◽  
Vestibular Nuclei ◽  
Head Movements ◽  
Whole Body ◽  
Body Rotation ◽  
Horizontal Semicircular Canal ◽  
Head Velocity ◽  
Vestibular Neurons ◽  
Single Unit Recordings

Single-unit recordings were obtained from 107 horizontal semicircular canal-related central vestibular neurons in three alert squirrel monkeys during passive sinusoidal whole-body rotation (WBR) while the head was free to move in the yaw plane (2.3 Hz, 20°/s). Most of the units were identified as secondary vestibular neurons by electrical stimulation of the ipsilateral vestibular nerve (61/80 tested). Both non–eye-movement ( n = 52) and eye-movement–related ( n = 55) units were studied. Unit responses recorded when the head was free to move were compared with responses recorded when the head was restrained from moving. WBR in the absence of a visual target evoked a compensatory vestibulocollic reflex (VCR) that effectively reduced the head velocity in space by an average of 33 ± 14%. In 73 units, the compensatory head movements were sufficiently large to permit the effect of the VCR on vestibular signal processing to be assessed quantitatively. The VCR affected the rotational responses of different vestibular neurons in different ways. Approximately one-half of the units (34/73, 47%) had responses that decreased as head velocity decreased. However, the responses of many other units (24/73) showed little change. These cells had signals that were better correlated with trunk velocity than with head velocity. The remaining units had responses that were significantly larger (15/73, 21%) when the VCR produced a decrease in head velocity. Eye-movement–related units tended to have rotational responses that were correlated with head velocity. On the other hand, non–eye-movement units tended to have rotational responses that were better correlated with trunk velocity. We conclude that sensory vestibular signals are transformed from head-in-space coordinates to trunk-in-space coordinates on many secondary vestibular neurons in the vestibular nuclei by the addition of inputs related to head rotation on the trunk. This coordinate transformation is presumably important for controlling postural reflexes and constructing a central percept of body orientation and movement in space.

Visual-Vestibular Interaction Hypothesis for the Control of Orienting Gaze Shifts by Brain Stem Omnipause Neurons

2007 ◽  
Vol 97 (2) ◽  
pp. 1149-1162 ◽  
Author(s):  
Mario Prsa ◽  
Henrietta L. Galiana
Keyword(s):  
Brain Stem ◽  
Head Movements ◽  
Gaze Control ◽  
Gaze Shifts ◽  
Gaze Shift ◽  
Switching Mechanism ◽  
Interaction Hypothesis ◽  
Visual Vestibular Interaction ◽  
Motor Error ◽  
Gaze Position

Models of combined eye-head gaze shifts all aim to realistically simulate behaviorally observed movement dynamics. One of the most problematic features of such models is their inability to determine when a saccadic gaze shift should be initiated and when it should be ended. This is commonly referred to as the switching mechanism mediated by omni-directional pause neurons (OPNs) in the brain stem. Proposed switching strategies implemented in existing gaze control models all rely on a sensory error between instantaneous gaze position and the spatial target. Accordingly, gaze saccades are initiated after presentation of an eccentric visual target and subsequently terminated when an internal estimate of gaze position becomes nearly equal to that of the target. Based on behavioral observations, we demonstrate that such a switching mechanism is insufficient and is unable to explain certain types of movements. We propose an improved hypothesis for how the OPNs control gaze shifts based on a visual-vestibular interaction of signals known to be carried on anatomical projections to the OPN area. The approach is justified by the analysis of recorded gaze shifts interrupted by a head brake in animal subjects and is demonstrated by implementing the switching mechanism in an anatomically based gaze control model. Simulated performance reveals that a weighted sum of three signals: gaze motor error, head velocity, and eye velocity, hypothesized as inputs to OPNs, successfully reproduces diverse behaviorally observed eye-head movements that no other existing model can account for.

Neck Muscle Responses to Stimulation of Monkey Superior Colliculus. II. Gaze Shift Initiation and Volitional Head Movements

2002 ◽  
Vol 88 (4) ◽  
pp. 2000-2018 ◽  
Author(s):  
Brian D. Corneil ◽  
Etienne Olivier ◽  
Douglas P. Munoz
Keyword(s):  
Superior Colliculus ◽  
Neck Muscles ◽  
Head Movements ◽  
Emg Activity ◽  
Neck Muscle ◽  
Gaze Shift ◽  
Antagonist Muscles ◽  
Agonist And Antagonist ◽  
Agonist And Antagonist Muscles ◽  
Stimulation Of

We report neck muscle activity and head movements evoked by electrical stimulation of the superior colliculus (SC) in head-unrestrained monkeys. Recording neck electromyography (EMG) circumvents complications arising from the head's inertia and the kinetics of muscle force generation and allows precise assessment of the neuromuscular drive to the head plant. This study served two main purposes. First, we sought to test the predictions made in the companion paper of a parallel drive from the SC onto neck muscles. Low-current, long-duration stimulation evoked both neck EMG responses and head movements either without or prior to gaze shifts, testifying to a SC drive to neck muscles that is independent of gaze-shift initiation. However, gaze-shift initiation was linked to a transient additional EMG response and head acceleration, confirming the presence of a SC drive to neck muscles that is dependent on gaze-shift initiation. We forward a conceptual neural architecture and suggest that this parallel drive provides the oculomotor system with the flexibility to orient the eyes and head independently or together, depending on the behavioral context. Second, we compared the EMG responses evoked by SC stimulation to those that accompanied volitional head movements. We found characteristic features in the underlying pattern of evoked neck EMG that were not observed during volitional head movements in spite of the seemingly natural kinematics of evoked head movements. These features included reciprocal patterning of EMG activity on the agonist and antagonist muscles during stimulation, a poststimulation increase in the activity of antagonist muscles, and synchronously evoked responses on agonist and antagonist muscles regardless of initial horizontal head position. These results demonstrate that the electrically evoked SC drive to the head cannot be considered as a neural replicate of the SC drive during volitional head movements and place important new constraints on the interpretation of electrically evoked head movements.

scholarly journals Electrical stimulation of the auditory brain stem structure in deafened adults

1987 ◽  
Vol 24 (3) ◽  
pp. 9 ◽  
Author(s):  
Laurie S. Eisenberg ◽  
Albert A. Maltan ◽  
Franco Portillo ◽  
Phil Mobley ◽  
William F. House
Keyword(s):  
Electrical Stimulation ◽  
Brain Stem ◽  
Auditory Brain Stem ◽  
Stem Structure ◽  
Stimulation Of
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