Role of primate flocculus during rapid behavioral modification of vestibuloocular reflex. II. Mossy fiber firing patterns during horizontal head rotation and eye movement

1978 ◽  
Vol 41 (3) ◽  
pp. 764-777 ◽  
Author(s):  
S. G. Lisberger ◽  
A. F. Fuchs
Keyword(s):  
Firing Rate ◽  
Eye Movement ◽  
Head Rotation ◽  
Quantitative Comparison ◽  
Eye Position ◽  
Head Velocity ◽  
Firing Rates ◽  
Steady Fixation ◽  
Discharge Patterns ◽  
P Cells

1. Extracellular recordings were obtained from 113 mossu fibers (MFs) in the flocculus of alert monkeys trained to perform a visual tracking task during sinusoidal, horizontal head rotation. The analysis of MF discharge patterns was designed to allow quantitative comparison of the discharge properties of flocculus MFs with brain stem cell populations from which the MFs might originate and with flocculus Purkinje cells (P-cells). Based on their firing patterns, MFs were divided into two classes. Vestibular MFs discharged in relation to head velocity and, in some cases, also in relation to eye movement. Eye movement MFs discharged only in relation to one or more components of eye movement. 2. Vestibular MFs were subdivided into three classes. Vestibular-only MFs (n = 15) displayed a modulation in firing rate during head rotation but exhibited no relationship to spontaneous eye movements. Vestibular-plus-saccade MFs (n = 14) displayed a modulation in firing rate during head rotation that quantitatively resembled the modulation in vestibular-only MFs. In addition, a pause in firing rate interrupted the vestibular modulation during saccades in one or more directions. Vestibular-plus-position MFs (n = 4) exhibited steady firing rates that were linearly related to horizontal eye position in the absence of vestibular stimulation. Sinusoidal head rotation evoked a modulation ofiring rate above and below the firing rate set by the eye position. 3. during sinusoidal head rotation, vestibular MF firing rate led head velocity by an average of 24 degrees. The amplitude of MF firing-rate modulation increased as a function of the frequency of head rotation and, hence, maximum head velocity. Since these characteristics are similar to those displayed by P-cells during suppression of the VOR, vestibular MFs probably transmit the head velocity component of P-cell firing rate to the flocculus. Based on evidence from other mammals and a quantitative comparison of population discharge characteristics, it is likely that vestibular MFs originate from the vestibular nerve and from cells in the medial vestibular nucleus. 4. Based on their discharge patterns, eye movement MFs were also subdivided into three classes. Burst MFs (n = 14) emitted a high-frequency burst of spikes prior to and during saccades in one or more direction, but were silent during steady fixation. Burst-tonic MFs (n = 53) emitted a burst of spikes prior to saccades in a preferred ("on") direction, ceased firing during saccades in the opposite ("off") direction, and exhibited steady firing rates that increased as steady gaze shifted in the on direction. Tonic MFs (n = 13) displayed steady firing rates that increased as the position of steady gaze shifted in the on direction, and either paused or exhibited step changes in firing rate during saccades. 5. During steady fixation, 64% of tonic and burst-tonic MFs were recruited into maintained firing within +/- 10 degrees of the primary direction of gaze...

Role of primate flocculus during rapid behavioral modification of vestibuloocular reflex. I. Purkinje cell activity during visually guided horizontal smooth-pursuit eye movements and passive head rotation

1978 ◽  
Vol 41 (3) ◽  
pp. 733-763 ◽  
Author(s):  
S. G. Lisberger ◽  
A. F. Fuchs
Keyword(s):  
Eye Movements ◽  
Firing Rate ◽  
Eye Movement ◽  
Smooth Pursuit ◽  
Head Rotation ◽  
Head Velocity ◽  
Rate Modulation ◽  
Cell Firing ◽  
Eye Velocity ◽  
P Cells

1. Extracellular recordings were obtained from 124 Purkinje cells (P-cells) in the flocculus of alert monkeys. P-cell simple spike-firing rate was analyzed quantitatively during various combinations of smooth-pursuit eye movement and passive head rotation. 2. During sinusoidal smooth eye movements, 80% of the P-cells displayed increased firing rate during ipsilateral and 20% during contralateral eye movement. Over the frequency range 0.3--1.4 Hz, firing-rate modulation was proportional to and in phase with maximum eye velocity. During the steady state of triangle-wave tracking, firing rate increased monotonically as a function of eye velocity. Since firing rate was uncorrelated with retinal-error velocity, one component of P-cell firing rate was related to eye velocity. 3. During the transient phase of triangle-wave tracking, when an instantaneous change in the direction of target movement caused a large retinal-error velocity, 40% of the P-cells were related only to eye velocity. Sixty percent of the P-cells displayed an overshoot or undershoot in firing rate, indicating a relationship to either retinal-error velocity or eye acceleration as well as to eye velocity. 4. During the vestibuloocular reflex (VOR), evoked by head rotation in the dark, P-cell firing rate was only weakly modulated. In contrast, when the monkey suppressed the VOR by fixating a target that rotated with him, P-cell rate was deeply modulated. Since the modulation was proportional to and in phase with maximum head velocity, another component of P-cell firing rate was related to head velocity. 5. Of 36 P-cells tested, 35 displayed firing-rate modulation during both suppression of the VOR and smooth-pursuit eye movement. P-cells that reached peak firing rate during ipsilateral head rotation also reached peak firing rate during ipsilateral smooth eye rotation. Average population sensitivitites to head velocity and eye velocity were equal. In three conditions in which eye and head velocity were elicited simultaneously, P-cell firing rate could be predicted by the linear, vector addition of the separate eye and head velocity components of firing rate. Therefore, the relatively weak modulation of P-cell firing rate during the VOR in the dark can be accounted for by the cancellation of equal but opposite head and eye velocity components. 6. The connections of flocculus P-cells to interneurons in the brain stem VOR pathways have been established in other mammals. In the context of those connections, P-cell firing patterns were appropriate to facilitate the eye movements the monkey was required to make. We conclude that the flocculus is important for sustaining any smooth eye movements that are different from those evoked by head rotation in the dark. The eye velocity component may represent an efference copy signal that sustains ongoing eye velocity during smooth pursuit.

Discharge patterns in nucleus prepositus hypoglossi and adjacent medial vestibular nucleus during horizontal eye movement in behaving macaques

1992 ◽  
Vol 68 (1) ◽  
pp. 319-332 ◽  
Author(s):  
J. L. McFarland ◽  
A. F. Fuchs
Keyword(s):  
Eye Movements ◽  
Eye Movement ◽  
Smooth Pursuit ◽  
Vestibular Nucleus ◽  
Medial Vestibular Nucleus ◽  
Eye Position ◽  
Head Velocity ◽  
Firing Rates ◽  
Prepositus Hypoglossi ◽  
Eye Velocity

1. Monkeys were trained to perform a variety of horizontal eye tracking tasks designed to reveal possible eye movement and vestibular sensitivities of neurons in the medulla. To test eye movement sensitivity, we required stationary monkeys to track a small spot that moved horizontally. To test vestibular sensitivity, we rotated the monkeys about a vertical axis and required them to fixate a target rotating with them to suppress the vestibuloocular reflex (VOR). 2. All of the 100 units described in our study were recorded from regions of the medulla that were prominently labeled after injections of horseradish peroxidase into the abducens nucleus. These regions include the nucleus prepositus hypoglossi (NPH), the medial vestibular nucleus (MVN), and their common border (the “marginal zone”). We report here the activities of three different types of neurons recorded in these regions. 3. Two types responded only during eye movements per se. Their firing rates increased with eye position; 86% had ipsilateral “on” directions. Almost three quarters (73%) of these medullary neurons exhibited a burst-tonic discharge pattern that is qualitatively similar to that of abducens motoneurons. There were, however, quantitative differences in that these medullary burst-position neurons were less sensitive to eye position than were abducens motoneurons and often did not pause completely for saccades in the off direction. The burst of medullary burst position neurons preceded the saccade by an average of 7.6 +/- 1.7 (SD) ms and, on average, lasted the duration of the saccade. The number of spikes in the burst was well correlated with saccade size. The second type of eye movement neuron displayed either no discernible burst or an inconsistent one for on-direction saccades and will be referred to as medullary position neurons. Neither the burst-position nor the position neurons responded when the animals suppressed the VOR; hence, they displayed no vestibular sensitivity. 4. The third type of neuron was sensitive to both eye movement and vestibular stimulation. These neurons increased their firing rates during horizontal head rotation and smooth pursuit eye movements in the same direction; most (76%) preferred ipsilateral head and eye movements. Their firing rates were approximately in phase with eye velocity during sinusoidal smooth pursuit and with head velocity during VOR suppression; on average, their eye velocity sensitivity was 50% greater than their vestibular sensitivity. Sixty percent of these eye/head velocity cells were also sensitive to eye position. 5. The NPH/MVN region contains many neurons that could provide an eye position signal to abducens neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Responses during eye movements of brain stem neurons that receive monosynaptic inhibition from the flocculus and ventral paraflocculus in monkeys

1994 ◽  
Vol 72 (2) ◽  
pp. 909-927 ◽  
Author(s):  
S. G. Lisberger ◽  
T. A. Pavelko ◽  
D. M. Broussard
Keyword(s):  
Eye Movements ◽  
Firing Rate ◽  
Brain Stem ◽  
Eye Movement ◽  
Head Rotation ◽  
Eye Position ◽  
Eye Motion ◽  
Ventral Paraflocculus ◽  
Straight Ahead ◽  
Stimulation Of

1. We have identified a group of brain stem cells called “flocculus target neurons” (or FTNs) because they are inhibited at monosynaptic latencies by stimulation of the flocculus and the ventral paraflocculus with single electrical pulses. We report the responses of FTNs, as well as those of other brain stem cells, during horizontal eye movements with the head stationary and during natural vestibular stimulation in monkeys. 2. FTNs discharged primarily in relation to eye movements. The majority (71%) showed increased firing for eye movement away from the side of the recording (“contraversive”), which is consistent with their inhibition by Purkinje cells that show increased firing for eye movement toward the side of recording. However, a significant and surprisingly large percentage (29%) of FTNs showed increased firing for eye movement toward the side of recording (“ipsiversive”). 3. The firing rate of FTNs showed strong modulation during pursuit of sinusoidal target motion with the head stationary and during the compensatory eye movements evoked by fixation of an earth-stationary target with sinusoidal head rotation. In addition, firing rate was related to eye position during steady fixation at different positions. Of the FTNs that showed increased firing for contraversive eye motion during pursuit with the head stationary, most had an infection in the relationship between firing rate and eye position so that the sensitivity to eye position was low for eye positions ipsilateral to straight-ahead gaze and high for eye positions contralateral to straight-ahead gaze. 4. When the monkey canceled the vestibuloocular reflex (VOR) by tracking a target that moved exactly with him during sinusoidal head rotation, the firing rate of FTNs was modulated much less strongly than during pursuit with the head stationary. In the FTNs that showed increased firing for contraversive eye motion during pursuit, firing rate during cancellation of the VOR increased for contraversive head motion during sinusoidal vestibular rotation at 0.4 Hz but was only weakly modulated during rotation at 0.2 Hz. 5. The position-vestibular-pause cells (PVP-cells), previously identified as interneurons in the disynaptic VOR pathways, were not inhibited by stimulation of the flocculus and ventral paraflocculus and had response properties that were different from FTNs. The majority (69%) showed increased firing for contraversive eye motion during pursuit and for ipsiversive head motion during cancellation of the VOR, whereas some (31%) showed the opposite direction preferences under both conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamics of rabbit vestibular nucleus neurons and the influence of the flocculus

1995 ◽  
Vol 73 (4) ◽  
pp. 1396-1413 ◽  
Author(s):  
J. S. Stahl ◽  
J. I. Simpson
Keyword(s):  
Eye Movements ◽  
Transfer Function ◽  
Firing Rate ◽  
Eye Movement ◽  
Vestibular Nucleus ◽  
Head Rotation ◽  
Medial Vestibular Nucleus ◽  
Eye Position ◽  
Abducens Nucleus ◽  
Nucleus Neuron

1. We recorded single vestibular nucleus neurons shown by electrical stimulation to receive floccular inhibition [flocculus receiving neurons (FRNs)] and/or to project toward midbrain motoneuronal pools [midbrain projecting neurons (MPNs)] in awake, head-fixed rabbits during compensatory eye movements. Stimuli included head rotation in the light, head rotation in the dark, and rotation of an optokinetic drum about the animal. We employed sinusoidal and triangular position profiles in the 0.05- to 0.8-Hz frequency band. We also examined transient responses to step changes in eye position. 2. We found identified vestibular nucleus cells (i.e., FRN/non-MPNs, FRN/MPNs, and non-FRN/MPNs) in the parvocellular and magnocellular portions of the medial vestibular nucleus, at the rostrocaudal level of the dorsal acoustic stria. 3. All identified vestibular nucleus neurons were excited during ipsilateral (relative to side of recording) head rotation and contralateral eye rotation. 4. The neuronal firing rates could be related to eye position and its time derivatives, and that relationship could be approximated by a two-pole, one-zero linear transfer function. As with abducens neurons, a more detailed approximation requires inclusion of two nonlinearities-a hysteresis and a variable sensitivity term that increases as eye movement amplitude decreases. 5. When the vestibuloocular reflex is suppressed by a conflicting full-field visual stimulus [visual vestibular conflict condition (VVC)], vestibular nucleus neuron modulation is largely suppressed. The remaining modulation is motoric in nature, because it can be related to the residual eye movements. Cells with "sensory vestibular signals," i.e., cells whose modulation during VVC correlates better with head rotation than eye movement, were not encountered. 6. We examined the dependence of firing rate parameters on stimulus modality. All neurons exhibited increased phase lead with respect to abducens nucleus neurons during stimuli involving head rotation. This finding could indicate that vestibular-derived inputs are inhomogeneously distributed on premotor neurons and that the studied premotor population receives a stronger vestibular input than another premotor group, not recorded in the current experiments. 7. FRNs and non-FRNs were similar in their qualitative response to the fast phases, the applicability of the two-pole, one-zero transfer function, hysteresis, and the amplitude nonlinearity. 8. FRNs differed from non-FRNs in having a phase advanced firing rate at all stimulus frequencies during visual and vestibular stimuli. The phase difference suggests that one role of the rabbit flocculus is to regulate phase of the net premotor signal.

Quantitative Analysis of Abducens Neuron Discharge Dynamics During Saccadic and Slow Eye Movements

1999 ◽  
Vol 82 (5) ◽  
pp. 2612-2632 ◽  
Author(s):  
Pierre A. Sylvestre ◽  
Kathleen E. Cullen
Keyword(s):  
Eye Movements ◽  
Firing Rate ◽  
Eye Movement ◽  
Neuronal Activity ◽  
Smooth Pursuit ◽  
Slow Phase ◽  
Vestibular Nystagmus ◽  
Firing Rates ◽  
Rapid Eye Movements ◽  
Eye Velocity

The mechanics of the eyeball and its surrounding tissues, which together form the oculomotor plant, have been shown to be the same for smooth pursuit and saccadic eye movements. Hence it was postulated that similar signals would be carried by motoneurons during slow and rapid eye movements. In the present study, we directly addressed this proposal by determining which eye movement–based models best describe the discharge dynamics of primate abducens neurons during a variety of eye movement behaviors. We first characterized abducens neuron spike trains, as has been classically done, during fixation and sinusoidal smooth pursuit. We then systematically analyzed the discharge dynamics of abducens neurons during and following saccades, during step-ramp pursuit and during high velocity slow-phase vestibular nystagmus. We found that the commonly utilized first-order description of abducens neuron firing rates (FR = b + kE + rE˙, where FR is firing rate, E and E˙ are eye position and velocity, respectively, and b, k, and r are constants) provided an adequate model of neuronal activity during saccades, smooth pursuit, and slow phase vestibular nystagmus. However, the use of a second-order model, which included an exponentially decaying term or “slide” (FR = b + kE + rE˙ + uË − c[Formula: see text]), notably improved our ability to describe neuronal activity when the eye was moving and also enabled us to model abducens neuron discharges during the postsaccadic interval. We also found that, for a given model, a single set of parameters could not be used to describe neuronal firing rates during both slow and rapid eye movements. Specifically, the eye velocity and position coefficients ( r and k in the above models, respectively) consistently decreased as a function of the mean (and peak) eye velocity that was generated. In contrast, the bias ( b, firing rate when looking straight ahead) invariably increased with eye velocity. Although these trends are likely to reflect, in part, nonlinearities that are intrinsic to the extraocular muscles, we propose that these results can also be explained by considering the time-varying resistance to movement that is generated by the antagonist muscle. We conclude that to create realistic and meaningful models of the neural control of horizontal eye movements, it is essential to consider the activation of the antagonist, as well as agonist motoneuron pools.

Discharge patterns and recruitment order of identified motoneurons and internuclear neurons in the monkey abducens nucleus

1988 ◽  
Vol 60 (6) ◽  
pp. 1874-1895 ◽  
Author(s):  
A. F. Fuchs ◽  
C. A. Scudder ◽  
C. R. Kaneko
Keyword(s):  
Firing Rate ◽  
Smooth Pursuit ◽  
Action Potentials ◽  
Medial Rectus ◽  
Eye Position ◽  
Oculomotor Nucleus ◽  
Abducens Nucleus ◽  
Position Sensitivity ◽  
Discharge Patterns ◽  
Eye Velocity

1. Single neurons in the abducens nucleus were recorded extracellularly in alert rhesus macaques trained to make a variety of eye movements. An abducens neurons was identified as a motoneuron (MN) if its action potentials triggered an averaged EMG potential in the lateral rectus muscle. Abducens internuclear neurons (INNs) that project to the oculomotor nucleus were identified by collision block of spontaneous with antidromic action potentials evoked with a stimulating electrode placed in the medial rectus subdivision of the contralateral oculomotor nucleus. 2. All abducens MNs and INNs had qualitatively similar discharge patterns consisting of a burst of spikes for lateral saccades and a steady firing whose rate increased with lateral eye position in excess of a certain threshold. 3. For both MNs and INNs the firing rates associated with different, constant eye positions could be described accurately by a straight line with slope, K (the eye position sensitivity in spikes.s-1.deg-1), and intercept, T (the eye position threshold for steady firing). For different MNs, K increased as T varied from more medial to more lateral values. In contrast, the majority of INNs already were active for values of T more medial than 20 degrees and showed little evidence of recruitment according to K. 4. During horizontal sinusoidal smooth-pursuit eye movements, both MNs and INNs exhibited a sinusoidal modulation in firing rate whose peak preceded eye position. From these firing rate patterns, the component of firing rate related to eye velocity, R (the eye velocity sensitivity in spikes.s-1.deg-1.s-1), was determined. The R for INNs was, on average, 78% larger than that for MNs. Furthermore, R increased with T for MNs, whereas INNs showed no evidence of recruitment according to R. If, as in the cat, the INNs of monkeys provide the major input to medial rectus MNs and if simian medial rectus MNs behave like our abducens MNs, then recruitment order, which is absent in INNs, must be established at the MN pool itself. 5. Unexpectedly, the R of MNs decreased with the frequency of the smooth-pursuit movement. Furthermore, the eye position sensitivity, K, obtained during steady fixations was usually less than that determined during smooth pursuit. Therefore, conclusions about the roles of MNs and premotor neurons based on how their R and K values differ must be viewed with caution if the data have been obtained under different tracking conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Discharge characteristics of medial rectus and abducens motoneurons in the goldfish

1991 ◽  
Vol 66 (6) ◽  
pp. 2125-2140 ◽  
Author(s):  
A. M. Pastor ◽  
B. Torres ◽  
J. M. Delgado-Garcia ◽  
R. Baker
Keyword(s):  
Eye Movements ◽  
Firing Rate ◽  
Eye Movement ◽  
Vestibular Stimulation ◽  
Medial Rectus ◽  
Eye Position ◽  
Sensory Stimuli ◽  
Time Constants ◽  
Recruitment Threshold ◽  
Eye Blink

1. The discharge of antidromically identified medial rectus and abducens motoneurons was recorded in restrained unanesthesized goldfish during spontaneous eye movements and in response to vestibular and optokinetic stimulation. 2. All medial rectus and abducens motoneurons exhibited a similar discharge pattern. A burst of spikes accompanied spontaneous saccades and fast phases during vestibular and optokinetic nystagmus in the ON-direction. Firing rate decreased for the same eye movements in the OFF-direction. All units showed a steady firing rate proportional to eye position beyond their recruitment threshold. 3. Motoneuronal position (ks) and velocity (rs) sensitivity for spontaneous eye movements were calculated from the slope of the rate-position and rate-velocity linear regression lines, respectively. The averaged ks and rs values of medial rectus motoneurons were higher than those of abducens motoneurons. The differences in motoneuronal sensitivity coupled with structural variations in the lateral versus the medial rectus muscle suggest that symmetric nasal and temporal eye movements are preserved by different motor unit composition. Although the abducens nucleus consists of distinct rostral and caudal subgroups, mean ks and rs values were not significantly different between the two populations. 4. Every abducens and medial rectus motoneuron fired an intense burst of spikes during its corresponding temporal or nasal activation phase of the "eye blink." This eye movement consisted of a sequential, rather than a synergic, contraction of both vertical and horizontal extraocular muscles. The eye blink could act neither as a protective reflex nor as a goal-directed eye movement because it could not be evoked in response to sensory stimuli. We propose a role for the blink in recentering eye position. 5. Motoneuronal firing rate after ON-directed saccades decreased exponentially before reaching the sustained discharge proportional to the new eye position. Time constants of the exponential decay ranged from 50 to 300 ms. Longer time constants after the saccade were associated with backward drifts of eye position and shorter time constants with onward drifts. These postsaccadic slide signals are suggested to encode the transition of eye position to the new steady level. 6. Motoneurons modulated sinusoidally in response to sinusoidal head rotation in the dark, but for a part of the cycle they went into cutoff, dependent on their eye position recruitment threshold. Eye position (kv) and velocity (rv) sensitivity during vestibular stimulation were measured at frequencies between 1/16 and 2 Hz. Motoneuronal time constants (tau v = rv/kv) decreased on the average by 25% with the frequency of vestibular stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Precerebellar Hindbrain Neurons Encoding Eye Velocity During Vestibular and Optokinetic Behavior in the Goldfish

2006 ◽  
Vol 96 (3) ◽  
pp. 1370-1382 ◽  
Author(s):  
James C. Beck ◽  
Paul Rothnie ◽  
Hans Straka ◽  
Susan L. Wearne ◽  
Robert Baker
Keyword(s):  
Firing Rate ◽  
Eye Movement ◽  
Time Course ◽  
Mossy Fiber ◽  
Vestibular Stimulation ◽  
Neuronal Firing ◽  
Velocity Storage ◽  
Head Velocity ◽  
Motor Error ◽  
Eye Velocity

Elucidating the causal role of head and eye movement signaling during cerebellar-dependent oculomotor behavior and plasticity is contingent on knowledge of precerebellar structure and function. To address this question, single-unit extracellular recordings were made from hindbrain Area II neurons that provide a major mossy fiber projection to the goldfish vestibulolateral cerebellum. During spontaneous behavior, Area II neurons exhibited minimal eye position and saccadic sensitivity. Sinusoidal visual and vestibular stimulation over a broad frequency range (0.1–4.0 Hz) demonstrated that firing rate mirrored the amplitude and phase of eye or head velocity, respectively. Table frequencies >1.0 Hz resulted in decreased firing rate relative to eye velocity gain, while phase was unchanged. During visual steps, neuronal discharge paralleled eye velocity latency (∼90 ms) and matched both the build-up and the time course of the decay (∼19 s) in eye velocity storage. Latency of neuronal discharge to table steps (40 ms) was significantly longer than for eye movement (17 ms), but firing rate rose faster than eye velocity to steady-state levels. The velocity sensitivity of Area II neurons was shown to equal (±10%) the sum of eye- and head-velocity firing rates as has been observed in cerebellar Purkinje cells. These results demonstrate that Area II neuronal firing closely emulates oculomotor performance. Conjoint signaling of head and eye velocity together with the termination pattern of each Area II neuron in the vestibulolateral lobe presents a unique eye-velocity brain stem-cerebellar pathway, eliminating the conceptual requirement of motor error signaling.

Site of interaction between saccade signals and vestibular signals induced by head rotation in the alert cat: functional properties and afferent organization of burster-driving neurons

1995 ◽  
Vol 74 (1) ◽  
pp. 273-287 ◽  
Author(s):  
T. Kitama ◽  
Y. Ohki ◽  
H. Shimazu ◽  
M. Tanaka ◽  
K. Yoshida
Keyword(s):  
Eye Movements ◽  
Superior Colliculus ◽  
Firing Rate ◽  
Regression Line ◽  
Head Rotation ◽  
Eye Position ◽  
Alert Cat ◽  
The Mean ◽  
Horizontal Head ◽  
Stimulation Of

1. Extracellular spikes of burster-driving neurons (BDNs) were recorded within and immediately below the prepositus hypoglossi nucleus in the alert cat. BDNs were characterized by short-latency activation after stimulation of the contralateral vestibular nerve (latency: 1.4-2.7 ms) and the ipsilateral superior colliculus (latency: 1.7-3.5 ms). Convergence of vestibular and collicular inputs was found in all of 85 BDNs tested. Firing of BDNs increased during contralateral horizontal head rotation and decreased during ipsilateral rotation. A burst of spikes was induced in association with contralateral saccades and quick phases of nystagmus. 2. BDNs showed irregular tonic discharges during fixation. There was no significant correlation between the firing rate during fixation and horizontal or vertical eye position in most BDNs. During horizontal sinusoidal head rotation, the change in firing rate was approximately proportional to and in phase with contralateral head velocity. The phase lag of the response relative to head angular velocity was 13.8 +/- 20.1 degrees (mean +/- SD) at 0.5 Hz and 7.2 +/- 13.5 degrees at 0.2 Hz on the average. The gain was 0.88 +/- 0.25 (spikes/s)/(degrees/s) at 0.5 Hz and 1.19 +/- 0.49 (spikes/s)/(degrees/s) at 0.2 Hz. 3. Quantitative analysis of burst activity associated with saccades or quick phases indicated that the ON direction of BDNs was contralateral horizontal. The number of spikes in the burst was linearly related to the amplitude of the contralateral component of rapid eye movements. The slope of regression line was, on the average, 1.14 +/- 0.48 spikes/deg. There was no significant difference between the mean slopes for saccades and quick phases. The number of spikes depended on the difference between initial and final horizontal eye positions and not on the absolute eye position in the orbit. The mean burst firing rate was proportional to the mean velocity of the contralateral component of rapid eye movements. The slope of the regression line was 0.82 +/- 0.34 (spikes/s)/(degrees/s). Significant correlation was also found between intraburst instantaneous firing rate and instantaneous component eye velocity. 4. Objects presented in the contralateral visual field elicited a brief burst of spikes in BDNs independent of any eye movement. Contralateral saccades to the target were preceded by an early response to the visual stimulus and subsequent response associated with eye movement. 5. Excitation of BDNs produced by stimulation of the ipsilateral superior colliculus was facilitated by contralateral horizontal head rotation. Therefore saccadic signals from the superior colliculus to BDNs may be augmented by vestibular signals during head rotation.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Dynamics of abducens nucleus neurons in the awake mouse

2012 ◽  
Vol 108 (9) ◽  
pp. 2509-2523 ◽  
Author(s):  
John S. Stahl ◽  
Zachary C. Thumser
Keyword(s):  
Eye Movement ◽  
Viscoelastic Model ◽  
Stimulus Frequency ◽  
Eye Position ◽  
Ocular Motor ◽  
Abducens Nucleus ◽  
Firing Rates ◽  
Eye Size ◽  
Linear Relationships ◽  
Area Centralis

The mechanics of the eyeball and orbital tissues (the “ocular motor plant”) are a fundamental determinant of ocular motor signal processing. The mouse is used increasingly in ocular motor physiology, but little is known about its plant mechanics. One way to characterize the mechanics is to determine relationships between extraocular motoneuron firing and eye movement. We recorded abducens nucleus neurons in mice executing compensatory eye movements during 0.1- to 1.6-Hz oscillation in the light. We analyzed firing rates to extract eye position and eye velocity sensitivities, from which we determined time constants of a viscoelastic model of the plant. The majority of abducens neurons were already active with the eye in its central rest position, with only 6% recruited at more abducted positions. Firing rates exhibited largely linear relationships to eye movement, although there was a nonlinearity consisting of increasing modulation in proportion to eye movement as eye amplitudes became small (due to reduced stimulus amplitude or reduced alertness). Eye position and velocity sensitivities changed with stimulus frequency as expected for an ocular motor plant dominated by cascaded viscoelasticities. Transfer function poles lay at approximately 0.1 and 0.9 s. Compared with previously studied animal species, the mouse plant is stiffer than the rabbit but laxer than cat and rhesus. Differences between mouse and rabbit can be explained by scaling for eye size (allometry). Differences between the mouse and cat or rhesus can be explained by differing ocular motor repertoires of animals with and without a fovea or area centralis.

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