Modification of central vestibular neuron response by conflicting visual-vestibular stimulation.
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Abducens Nerve↗
Biomedical subjects
W Precht
Publications and source records attributed to W Precht.
Vestibular mechanisms.
It is apparent from this and other reviews of the subject that our knowledge of vestibular function is most complete for the primary canal and otolithic afferents. Relatively little progress has been made in the understanding of receptor mechanisms and the functional importance of the efferent vestibular system. Since most of it has been summarized previously the latter were not considered here. Considerably more knowledge has accumulated in the field of central vestibular mechanisms, particularly those related to eye movements. Recent advances in functional synaptology of direct and indirect vestibuloocular pathways are described. It appears that the indirect pathways are essential for the central integration of the peripheral head velocity into a central eye position signal. Candidates for the neural integrator are presented and discussed and their connectivity described both for the horizontal and the relatively poorly studied vertical eye movement system. This field will certainly be studied extensively during the next years. Another interesting field is the role of the cerebellum in the control the vestibuloocular reflex. Recent data and hypotheses, including the problem of cerebellar plasticity, are summarized and evaluated. That the vestibular nuclei are by no means a simple relay system for specific vestibular signals destined for other sensory or motor centers is evidenced in this review by the description of multiple canal-canal, canalotolith, and visual-vestibular convergence at the nuclear level. Canal-otolith and polysensory convergence in vestibular neurons enables them to correct for the inherent inadequacies of the peripheral canal system in the low frequency range. The mechanisms of polysensory interaction in the central vestibular system will undoubtedly be an important and interesting field for future research.
Abducens Nerve↗
Adaptive modification of central vestibular neurons in response to visual stimulation through reversing prisms.
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Action Potentials↗
Response characteristics of semicircular canal and otolith systems in cat. I. Dynamic responses of primary vestibular fibers.
1. The activity of cat semicircular canal and otolith afferents was studied during yaw and roll rotations, respectively, to examine their dynamic behavior. 2. A sinusoidal analysis of the canal afferent activities showed that their dynamic characteristics are similar to those of second order vestibular neurons, except for a two to three-fold lower absolute gain. This agrees with earlier studies using angular acceleration steps. 3. Both divisions of the eighth nerve were sampled so as to examine afferents from both the utriculus and sacculus. Within the range of inputs used (+/- 25 degrees lateral tilt), the presumed sacular afferents (inferior division) showed either a gamma- or beta-response. However, the gain of their response was generally much less than for the afferents of the superior division (mostly utricular). This behavior is to be expected on the basis of receptor orientations and the components of gravity acting upon the macular receptors. 4. In response to ramp changes in angular position, some otolith units showed a phasic-tonic response pattern, i.e., an overshoot followed by an adaptation to a new steady state level of activity. The majority of units showed predominantly tonic responses proportional to displacement. 5. During sinusoidal rotations the predominantly tonic units showed small phase leads of 0 to 15 degrees at 0.025 Hz which remained constant or decreased to 0 to -15 degrees at 1.0 Hz. The gains were flat or increased by up to 2 fold. The phasic-tonic units showed greater phase leads, 10 to 50 degrees, and gains which increased from 2 to 8 fold. 6. This behavior of otolith afferents suggests that they can provide information about both the magnitude and the rate of change of linear acceleration stimuli.
Acoustic Maculae↗
Response characteristics of semicircular canal and otolith systems in cat. II. Responses of trochlear motoneurons.
1. The electrical activity of single trochlear motoneurons (TMns) and axons of second order vestibular neurons presumably terminating on these motoneurons were studied during natural stimulation of semicircular canals and otolith organs in cats anesthetized with Ketamine. 2. Null point analysis showed that TMns received an excitatory canal input from the contralateral posterior canal, and labyrinthine lesion experiments suggested that the functionally synergistic, ipsilateral anterior canal provides an inhibitory input. A small number of motoneurons showed orthogonal canal convergence. 3. In addition to the canal projections most TMns received an otolithic input. Firing rate was proportional to lateral head tilt and was of the beta type. Most units also responded to pitch with an increase and decrease in firing rate on nose-up and nose-down positioning, respectively. Lesion experiments indicated that the otolith responses are the results of reciprocal innervation of TMns by contralateral (excitatory) and ipsilateral (inhibitory) otolith projections. 4. During sinusoidal rotation in yaw (canal only stimulation) the mean phase lag re acceleration of the response of TMns increased from 60 degrees at 0.025 Hz to 126 degrees at 1.0 Hz. In roll (canal plus otolith stimulation) the phase lag of TMn responses measured 180 degrees and 130 degrees at 0.025 and 1.0 Hz, respectively. Phase-lags measured in Vi and Vc axons were less by ca. 15 degrees. 5. The otolith contribution to TMn responses in roll was calculated by vectorial subtraction of the yaw from the roll responses: A phase lag of 10 (0.025 Hz) to 90 degrees (0.5 Hz) re. displacement was noted and gain was constant over the same range. Similar lag dynamics were revealed in TMns when studied during ramp displacement of the head. 6. The possible functional role of central canal-otolith convergence and the differences between the response of primary vestibular afferents and secondary vestibular neurons and TMns will be discussed.
Animals↗
Persistence of visual response in vestibular nucleus neurons in cerebellectomized cat.
Responses to pure visual stimuli and visual-vestibular interactions similar to those reported in other vertebrates were found in single vestibular nucleus neurons in cat. Contrary to prevailing hypotheses, the cerebellum is not an essential part of the pathway mediating these visual responses.
Animals↗
Connections of behaviorally identified cat omnipause neurons.
The afferent and efferent connections of omnipause neurons involved in saccadic eye movements were studied electrophysiologically in ketamine anesthetized cats. Omnipause neurons were identified by their characteristic discharge pattern which was qualitatively unaltered by ketamine anesthesia.
Action Potentials↗
A mechanism for type III vestibular responses of frog cerebellar Purkinje cells.
Type III Purkinje cells (P-cells), which are excited with both directions of horizontal rotation, are found in high numbers in the frog auricular lobe and adjacent cerebellar areas. To examine the mechanisms underlying these responses, recordings were made from P-cells in curarized animals during rotational stimulation of the horizontal canals. The horizontal canal input to these cells was then modified unilaterally by VIIth nerve section, intraperilymphatic injection of local anesthetic, or by caloric stimulation. Control recordings were also obtained from peripheral canal neurons. Type III responses were abolished by unilateral lesions or reversible blockage of the VIIIth nerve with local anesthetic. The remaining responses were attributable only to the unaffected horizontal canal, ie. only type II or type I responses were observed upon interruption of the ipsi-or contralateral nerve, respectively. The level of spontaneous activity of cerebellar input fibers was low and during rotation produced 'cell silencing' response waveform asymmetries (facilitation greater than disfacilitation). When the level of peripheral resting activity was increased (warm water irrigation), thereby increasing horizontal canal response symmetry, type III responses were reduced in magnitude or abolished. Conversely, cold water irrigation, which decreases the resting rate and response symmetry of input fibers, enhanced type III response magnitudes. On the basis of these results, it is suggested that type III responses result from the fact that single P-cells receive a facilitatory input from both horizontal canals. Since these inputs are 180 degrees phase-reversed and their response waveforms asymmetrical, their resulting postsynaptic effect is a net excitation during both portions of the stimulus cycle.
Action Potentials↗
Modification of synaptic input following unilateral labyrinthectomy.
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Afferent Pathways↗
Functional organization of the vestibular input to the anterior and posterior cerebellar vermis of cat.
1. Responses evoked by electrical stimulation (auditory division of the VIIIth nerve sectioned chronically) and natural stimulation of the vestibular apparatus were recorded in the anterior and posterior cerebellar vermis of cats anesthetized with Ketamine or Nembutal. Under Ketamine the functional state of the cerebellar cortex was similar to that of the decerebrate or encéphale isolé preparation. 2. Vestibular-evoked responses were found bilaterally throughout the vermis (lob. I-X) and parts of pars intermedia and were, for the most part, mediated via the mossy fiber-granule cell pathway although natural stimulation occasionally evoked climbing fiber responses in Purkinje cells. 3. Lesion and stimulation experiments suggested that the polysynaptic potentials recorded in the dorsal folia of the anterior and parts of posterior vermis were mediated, at least in part, by the lateral reticular nucleus. Potentials recorded in the deeper folia often had shorter latencies and were probably mediated by primary and/or secondary vestibular fibers. Studies with horseradish peroxidase (injections in lob. V and VI) supported these notions. 4. An analysis of Purkinje cell responses to sinusoidal rotation and steps of angular acceleration or velocity indicated that P-cells in these regions signalled angular head velocity in the mid-frequency range. Single canal responses as well as multi-canal convergent P-cell responses were found. Purkinje cells also responded to static head displacement.
Animals↗
Response characteristics and vestibular receptor convergence of frog cerebellar purkinje cells. A natural stimulation study.
1. The horizontal sinusoidal frequency response and the problem of vestibular receptor convergence in Purkinje cells (P-cells) of the auriculum, dorsal rim and corpus cerebelli were studied in curarized frogs with natural stimulation. 2. Primarily "simple" but also "complex" spikes were evoked by sinusoidal stimulation of the horizontal canals. P-cell "simple" spike activity could be grouped into types I-IV. Type I and II responses were directionally sensitive and thus were evoked at the stimulus frequency. Type III (and IV) cells, on the other hand, had response waveforms double that of the input frequency, with peak increases (or decreases) in discharge inphase with head velocity in the mid-frequency range. Except in the cerebellar midline regions where type III response waveforms were symmetrical, ipsilateral sinusoidal responses were larger in magnitude than those evoked during contralateral rotation. Despite the differences in magnitudes, ipsi- and contralateral response phase angles for one cell were approximately equal. "Complex" spikes were evoked with ipsi (type I) or contralateral (type II) horizontal rotation. Generally only 1-2 spikes were evoked per cycle with short (0-60 degrees) or long (120-150 degrees) phase-lags following acceleration. 3. A Bode analysis of type I "simple" spike activity in yaw indicates a slightly greater phase-lag and a 10-15 fold smaller P-cell gain in the range 0.05-0.5 Hz when compared to peripheral horizontal canal neurons. 4. Stimulation of the vertical canals and otolith organs also evoked "simple" and, to a lesser extent, "complex" P-cell spikes. "Simple" spikes were in most cases (85%) evoked by stimulation of several canal and/or otolithic receptors thus demonstrating a high degree of receptor convergence. "Complex" spikes, however, were only evoked by stimulation of one canal or otolith receptor. 5. Otolithic input to P-cells, examined statically and with low level constant velocity rolls, was mainly phasic or phasic-tonic in nature.
Animals↗
Responses of cat prepositus hypoglossi neurons to horizontal angular acceleration.
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Acceleration↗
Functional organization of vestibular and visual inputs to neck and forelimb motoneurons in the frog.
1. Intracellular responses in neck and forelimb motoneurons to electrical stimulation of the vestibular nerve, the optic tectum, and the optic nerve were studied in frog. 2. Stimulation of the anterior branch of the vestibular nerve typically produced EPSPs, bilaterally, in neck, shoulder (DOR), and forelimb extensor (TRI, RAD) motoneurons, and bilateral IPSPs in forelimb adductor (PED) and flexor (ULN, COR) motoneurons. 3. Latencies of PSPs recorded in neck, shoulder, and proximal extensor motoneurons (TRI) were mostly in the disynaptic range, whereas many of those recorded in distal extensor (RAD) and in adductor and flexor motoneurons involved three synapses. 4. Lesion of the vestibulospinal fibers greatly reduced the vestibular nerve-evoked field potentials in the spinal cord and the occurrence of PSPs in forelimb motoneurons. These results as well as the latency measurements suggest that the pathway linking vestibular nerve and forelimb motoneurons mainly consists of vestibulospinal fibers, though involvement of other structures for production of later PSPs could not be completely ruled out. Hemisection of the brain stem at its most caudal level showed that the pathway to the contralateral motoneurons crosses at the level of brain stem as well as in the spinal cord. 5. Stimulation of the optic tectum produced EPSPs, IPSPs, and a mixture of EPSPs and IPSPs in neck, shoulder, and forelimb motoneurons, bilaterally. Most frequently, a combination of an excitation and inhibition was observed. The pathway from the optic tectum to neck and limb motoneurons is at least dysnaptic in nature. 6. Stimulation of the optic nerve produced IPSPs and a mixture of EPSPs and IPSPs in neck and forelimb motoneurons. Impulses originating from the optic nerve descend as far as to lumbar motoneurons producing EPSP-IPSP sequences bilaterally. 7. Interaction studies suggested that the vestibular and optic pathways to neck and forelimb motoneurons are separate from each other so that the site of integration of vestibular and visual input occurs at the level of motoneurons. 8. Evidence for electronic coupling among forelimb motoneurons and electrical synaptic transmission in th pathway linking vestibular nerve and forelimb motoneurons is presented.
Animals↗
Responses of Purkinje cells in rabbit nodulus and uvula to natural vestibular and visual stimuli.
1. The responses of Purkinje cells and presumed mossy fibers to natural stimulation of the horizontal semicircular canals were recorded in the nodulus and uvula of rabbit vestibulocerebellum. Units responding to vestibular stimulation were also studied with visual stimulation. 2. The responses of presumed mossy fibers were of the Type I and Type II varieties and were characterized by a low threshold for angular acceleration and high sensitivity. 3. Purkinje cell responses were divided into two groups: The first group showed only modulation of simple spike activity during rotation. According to the directionality of their responses to rotation, Purkinje cells of the first group could be further subdivided into Types I, II or III; Type II was the most frequently encountered. The second group showed modulation of both simple spike and climbing fiber activity. The simple spike response most frequently encountered was of Type II while the climbing fiber activity in the same Purkinje cells responded in the Type I mode. In another population of Purkinje cells of this group, simple spike activity was modulated by rotation in one direction only. All Purkinje cell responses had relatively high thresholds and low sensitivities. 4. Some Purkinje cells responding to rotation showed direction-selective modulation of climbing fiber discharge in response to slowly moving visual patterns.
Animals↗
Nystagmic modulation of neuronal activity in rabbit cerebellar flocculus.
1. The responses of neuronal elements in the flocculus of the awake, restrained rabbit were recorded during horizontal vestibular nystagmus in the dark. 2. Purkinje cells showed both vestibular (Types I and II) and eye movement modulation of simple spike activity. Type I Purkinje cells most commonly were inhibited in association with the ipsilaterally directed fast phase of nystagmus and excited during contralaterally directed fast phases. Type II Purkinje cells had a similar modulation but in the opposite direction. Variations on this pattern included an increase in firing during fast phases in both directions. 3. Presumed mossy fibers and granule cells also exhibited both vestibular and nystagmic modulation in various combinations. The nystagmic modulation often began during the fast phase and continued into the early part of the slow phase. Mossy fibers showing both vestibular and nystagmic modulation probably arise from the vestibular nuclei and/or the perihypoglossal nuclei. 4. Floccular control of brain stem nuclei utilizes not only vestibular but also eye movement signals and probably all sensory and internal signals involved in the regulation of gaze.
Animals↗
Functional characterization of primary vestibular afferents in the frog.
1. In order to more accurately identify the nature of the vestibular input to central neurons, the response properties of single semicircular canal and otolith units in the frog VIIth nerve were studied in curarized preparations. 2. An equation describing the response plane was calculated for each canal on the basis of null point measurements. These results show that the ipsilateral canal planes are orthogonal within 2-5 degrees, and the pairs of right-left synergists are essentially coplanar. A head position of 10-20 degrees maxilla nose up produces optimal horizontal canal and minimal vertical canal activation with horizontal rotation. 3. The frequency response of the horizontal canal was examined in the range 0.025-0.5 Hz. Comparatively shorter phase-lags and a 10 fold greater acceleration gain in this frequency range distinguish the frog from the mammalian species studied. 4. Otolithic responses were tonic, phasic-tonic, and phasic in nature. The preponderance of the latter two groups is stressed (94%). Tonic responses were proportional to the gravitational vector change. Phasic responses were proportional to velocity during transitions in head position and phase-led displacement (30-80%) with sinusoidal acceleration in roll and pitch. 5. Efferent vestibular neurons respond to rotation in the horizontal (usually Type III) as well as vertical planes. Responses in the vertical planes result from canal and/or otolithic input to these neurons indicating that the vestibular efferent system receives extensive multi-labyrinthine convergence.
Animals↗
Electrical properties of frog motoneurons in the in situ spinal cord.
Electrical properties of the spinal motoneurons of Rana temporaria and R. esculenta were investigated in the in situ spinal cord at 20-22 degrees C by means of intracellular recording and current injection. Input resistance values depended on the method of measurement in a given cell but were generally inversely related to axon conduction velocity. The membrane-potential response to a subthreshold current pulse was composed of at least two exponentials with mean time constants of 2.5 and 20 ms. The membrance potential reached by the peak of a spike depended on the mode of spike initiation and membrane potential. Preceding a suprathreshold depolarization by a hyperpolarizing pulse could delay and eliminate spike initiation, similar to effects reported in certain invertebrate neurons. Antidromic invasion frequently failed in motoneurons of normal resting potential. Antidromic spike components (m,IS, SD) were similar to those of cat motoneurons. The delayed depolarization and the long afterhyperpolarization following an antidromic spike had many properties in common with the analogous afterpotentials of cat motoneurons. The reversal potential of the short afterhyperpolarization occurring immediately after the spike varied with resting potential and could not be used to determine potassium equilibrium potential. Sustained rhythmic firing could be evoked by continuous synaptic drive or long pulses of injected current. The plot of firing rate versus current strength had a substantial linear region. Both steady firing and adaptation properties varied markedly with motoneuron input resistance.
Animals↗
Evidence for electrotonic coupling between frog motoneurons in the in situ spinal cord.
A recurrent EPSP was observed on antidromic stimulation of motoneurons in the in situ spinal cord of Rana temporaria and R. esculenta at 20-22C. The EPSP was finely graded and not refractory following full or partial antidromic spike components in a given neuron. The EPSP amplitude varied in parallel with the antidromic field potential under different conditions, suggesting transmission of the EPSP to the recorded motoneuron depended on invasion of the somadendritic membrane or neighboring motoneurons by the antidromic spike. The latency of the EPSP with respect to antidromic invasion of the local motoneuron pool was too short for the EPSP to be mediated by chemical transmission. It was concluded the EPSP was electrically transmitted between the somadendritic membranes of the motoneurons. Under certain conditions, the EPSP magnitude could be made to vary with membrane potential in a direction opposite to that expected from a chemical EPSP. Dendritic spikes were sometimes associated with the EPSP.
Animals↗