Cerebellar projections to the macaque midbrain tegmentum: Possible near response connections

2021 ◽  
Vol 38 ◽  
Author(s):  
Martin O. Bohlen ◽  
Paul D. Gamlin ◽  
Susan Warren ◽  
Paul J. May
Keyword(s):  
Macaca Fascicularis ◽  
Mesencephalic Reticular Formation ◽  
Ciliary Muscle ◽  
Medial Rectus ◽  
Oculomotor Nucleus ◽  
Central Mesencephalic Reticular Formation ◽  
Midbrain Tegmentum ◽  
Premotor Neurons ◽  
Levator Palpebrae ◽  
Anterograde Tracer

Abstract Since most gaze shifts are to targets that lie at a different distance from the viewer than the current target, gaze changes commonly require a change in the angle between the eyes. As part of this response, lens curvature must also be adjusted with respect to target distance by the ciliary muscle. It has been suggested that projections by the cerebellar fastigial and posterior interposed nuclei to the supraoculomotor area (SOA), which lies immediately dorsal to the oculomotor nucleus and contains near response neurons, support this behavior. However, the SOA also contains motoneurons that supply multiply innervated muscle fibers (MIFs) and the dendrites of levator palpebrae superioris motoneurons. To better determine the targets of the fastigial nucleus in the SOA, we placed an anterograde tracer into this cerebellar nucleus in Macaca fascicularis monkeys and a retrograde tracer into their contralateral medial rectus, superior rectus, and levator palpebrae muscles. We only observed close associations between anterogradely labeled boutons and the dendrites of medial rectus MIF and levator palpebrae motoneurons. However, relatively few of these associations were present, suggesting these are not the main cerebellar targets. In contrast, labeled boutons in SOA, and in the adjacent central mesencephalic reticular formation (cMRF), densely innervated a subpopulation of neurons. Based on their location, these cells may represent premotor near response neurons that supply medial rectus and preganglionic Edinger–Westphal motoneurons. We also identified lens accommodation-related cerebellar afferent neurons via retrograde trans-synaptic transport of the N2c rabies virus from the ciliary muscle. They were found bilaterally in the fastigial and posterior interposed nuclei, in a distribution which mirrored that of neurons retrogradely labeled from the SOA and cMRF. Our results suggest these cerebellar neurons coordinate elements of the near response during symmetric vergence and disjunctive saccades by targeting cMRF and SOA premotor neurons.

scholarly journals Central mesencephalic reticular formation control of the near response: lens accommodation circuits

2019 ◽  
Vol 121 (5) ◽  
pp. 1692-1703 ◽  
Author(s):  
Paul J. May ◽  
Isabelle Billig ◽  
Paul D. Gamlin ◽  
Julie Quinet
Keyword(s):  
Rabies Virus ◽  
Reticular Formation ◽  
Formation Control ◽  
Present Report ◽  
Mesencephalic Reticular Formation ◽  
Time Frame ◽  
Medial Rectus ◽  
Depth Of Field ◽  
Central Mesencephalic Reticular Formation ◽  
Premotor Neurons

To view a nearby target, the three components of the near response are brought into play: 1) the eyes are converged through contraction of the medial rectus muscles to direct both foveae at the target, 2) the ciliary muscle contracts to allow the lens to thicken, increasing its refractive power to focus the near target on the retina, and 3) the pupil constricts to increase depth of field. In this study, we utilized retrograde transsynaptic transport of the N2c strain of rabies virus injected into the ciliary body of one eye of macaque monkeys to identify premotor neurons that control lens accommodation. We previously used this approach to label a premotor population located in the supraoculomotor area. In the present report, we describe a set of neurons located bilaterally in the central mesencephalic reticular formation that are labeled in the same time frame as the supraoculomotor area population, indicating their premotor character. The labeled premotor neurons are mostly multipolar cells, with long, very sparsely branched dendrites. They form a band that stretches across the core of the midbrain reticular formation. This population appears to be continuous with the premotor near-response neurons located in the supraoculomotor area at the level of the caudal central subdivision of the oculomotor nucleus. The central mesencephalic reticular formation has previously been associated with horizontal saccadic eye movements, so these premotor cells might be involved in controlling lens accommodation during disjunctive saccades. Alternatively, they may represent a population that controls vergence velocity. NEW & NOTEWORTHY This report uses transsynaptic transport of rabies virus to provide new evidence that the central mesencephalic reticular formation (cMRF) contains premotor neurons controlling lens accommodation. When combined with other recent reports that the cMRF also contains premotor neurons supplying medial rectus motoneurons, these results indicate that this portion of the reticular formation plays an important role in directing the near response and disjunctive saccades when viewers look between targets located at different distances.

scholarly journals Neural control of rapid binocular eye movements: Saccade-vergence burst neurons

2020 ◽  
Vol 117 (46) ◽  
pp. 29123-29132 ◽  
Author(s):  
Julie Quinet ◽  
Kevin Schultz ◽  
Paul J. May ◽  
Paul D. Gamlin
Keyword(s):  
Eye Movements ◽  
Neural Control ◽  
Three Dimensional ◽  
Mesencephalic Reticular Formation ◽  
Burst Neurons ◽  
Central Mesencephalic Reticular Formation ◽  
3D Space ◽  
Modeling Studies ◽  
Premotor Neurons ◽  
Highly Correlated

During normal viewing, we direct our eyes between objects in three-dimensional (3D) space many times a minute. To accurately fixate these objects, which are usually located in different directions and at different distances, we must generate eye movements with appropriate versional and vergence components. These combined saccade-vergence eye movements result in disjunctive saccades with a vergence component that is much faster than that generated during smooth, symmetric vergence eye movements. The neural control of disjunctive saccades is still poorly understood. Recent anatomical studies suggested that the central mesencephalic reticular formation (cMRF), located lateral to the oculomotor nucleus, contains premotor neurons potentially involved in the neural control of these eye movements. We have therefore investigated the role of the cMRF in the control of disjunctive saccades in trained rhesus monkeys. Here, we describe a unique population of cMRF neurons that, during disjunctive saccades, display a burst of spikes that are highly correlated with vergence velocity. Importantly, these neurons show no increase in activity for either conjugate saccades or symmetric vergence. These neurons are termed saccade-vergence burst neurons (SVBNs) to maintain consistency with modeling studies that proposed that such a class of neuron exists to generate the enhanced vergence velocities observed during disjunctive saccades. Our results demonstrate the existence and characteristics of SVBNs whose activity is correlated solely with the vergence component of disjunctive saccades and, based on modeling studies, are critically involved in the generation of the disjunctive saccades required to view objects in our 3D world.

Neural control of vergence eye movements: convergence and divergence neurons in midbrain

1984 ◽  
Vol 51 (5) ◽  
pp. 1091-1108 ◽  
Author(s):  
L. E. Mays
Keyword(s):  
Eye Movements ◽  
Firing Rate ◽  
Neural Control ◽  
Cell Activity ◽  
Mesencephalic Reticular Formation ◽  
Medial Rectus ◽  
Oculomotor Nucleus ◽  
Position Signal ◽  
Binocular Single Vision ◽  
Convergence And Divergence

Animals with binocular single vision use disjunctive (vergence) eye movements to align the two eyes on a visual target. Several lines of evidence suggest that conjugate and vergence eye movement commands are generated independently and combined at the medial rectus motoneurons. If this were true, then a pure vergence eye-position signal should exist. This signal would be proportional to the horizontal angle between the eyes (vergence angle), without regard to the direction of conjugate gaze. The purpose of this experiment was to identify and study neurons that carry a pure vergence signal. Extracellular unit recordings were made from midbrain and pontine sites in monkeys trained to track visual targets moving in the horizontal, vertical, and depth (or target vergence) planes. The most commonly encountered neuron that had a vergence signal was the convergence cell. These units had a firing rate that was linearly proportional to the convergence angle; their activity was unaffected by changes in conjugate gaze. Changes in convergence cell activity preceded the change in vergence angle slightly. Convergence cell activity increased for increased convergence regardless of whether the change was in response to purely accommodative or disparity cues. Divergence cells were found far less frequently. These cells were similar to convergence cells except that they decreased their firing rate for increases in convergence. The activity of divergence cells was unaffected by changes in the direction of conjugate gaze. Both convergence and divergence cells were found, intermixed, in the mesencephalic reticular formation must outside the oculomotor nucleus. Most cells with a vergence signal were found within 1-2 mm of the nucleus. These results support the view that conjugate and vergence signals are generated independently and are combined at the extraocular motoneurons. Convergence cells seem ideally suited to provide the vergence signal required by the nearby medial rectus motoneurons.

scholarly journals A central mesencephalic reticular formation projection to the Edinger–Westphal nuclei

2015 ◽  
Vol 221 (8) ◽  
pp. 4073-4089 ◽  
Author(s):  
Paul J. May ◽  
Susan Warren ◽  
Martin O. Bohlen ◽  
Miriam Barnerssoi ◽  
Anja K. E. Horn
Keyword(s):  
Reticular Formation ◽  
Mesencephalic Reticular Formation ◽  
Central Mesencephalic Reticular Formation

Saccadic Dyskinesia, Other Involuntary Eye Movements, and Gaze Deviations

2008 ◽  
Author(s):  
Agnes Wong
Keyword(s):  
Multiple Sclerosis ◽  
Eye Movements ◽  
Normal Subjects ◽  
Mesencephalic Reticular Formation ◽  
Frontal Eye Field ◽  
Square Wave ◽  
Central Mesencephalic Reticular Formation ◽  
Cerebellar Diseases ◽  
Eye Field ◽  
Small Saccade

■ A small saccade of 0.5–3° that takes the eye away from fixation, followed by a saccade that returns the eye back to fixation after about 200 msec (i.e., presence of intersaccadic interval during which visual feedback occurs) ■ So named because of its appearance in eye movement tracings ■ Normal subjects often have square wave jerks (SWJ), but the rate is only 4–6 per minute. ■ Pathologic SWJ occurs at a rate of >15 per minute. ■ Cerebellar diseases Square wave jerks result from damage of projections from the frontal eye field, rostral pole of the superior colliculus, and the central mesencephalic reticular formation to the omnipause cells in the pons. If symptomatic, SWJ may be treated with methylphenidate, diazepam, phenobarbital, or amphetamines. ■ Burst of saccades with defective steps of innervation (i.e., stepless saccades) ■ Conjugate or monocular Saccadic pulses are associated with multiple sclerosis. Saccadic pulses result from damage of omnipause cells or the neural integrator.

Response Properties of Saccade-Related Burst Neurons in the Central Mesencephalic Reticular Formation

1997 ◽  
Vol 78 (4) ◽  
pp. 2164-2175 ◽  
Author(s):  
Ari Handel ◽  
Paul W. Glimcher
Keyword(s):  
Reticular Formation ◽  
Light Emitting Diode ◽  
Low Frequency ◽  
Mesencephalic Reticular Formation ◽  
Restricted Range ◽  
Response Properties ◽  
Burst Neurons ◽  
Central Mesencephalic Reticular Formation ◽  
Saccadic Target ◽  
Behaving Monkeys

Handel, Ari and Paul W. Glimcher. Response properties of saccade-related burst neurons in the central mesencephalic reticular formation. J. Neurophysiol. 78: 2164–2175, 1997. We studied the activity of saccade-related burst neurons in the central mesencephalic reticular formation (cMRF) in awake behaving monkeys. In experiment 1, we examined the activity of single neurons while monkeys performed an average of 225 delayed saccade trials that evoked gaze shifts having horizontal and vertical amplitudes between 2 and 20°. All neurons studied generated high-frequency bursts of activity during some of these saccades. For each neuron, the duration and frequency of these bursts of activity reached maximal values when the monkey made movements within a restricted range of horizontal and vertical amplitudes. The onset of the movement followed the onset of the burst by the longest intervals for movements within a restricted range of horizontal and vertical amplitudes. The range of movements for which this interval was longest varied from neuron to neuron. Across the population, these ranges included nearly all contraversive saccades with horizontal and vertical amplitudes between 2 and 20°. In experiment 2, we used the following task to examine the low-frequency prelude of activity that cMRF neurons generate before bursting: the monkey was required to fixate a light-emitting diode (LED) while two eccentric visual stimuli were presented. After a delay, the color of the fixation LED was changed, identifying one of the two eccentric stimuli as the saccadic target. After a final unpredictable delay, the fixation LED was extinguished and the monkey was reinforced for redirecting gaze to the identified saccadic target. Some cMRF neurons fired at a low frequency during the interval after the fixation LED changed color but before it was extinguished. For many neurons, the firing rate during this interval was related to the metrics of the movement the monkey made at the end of the trial and, to a lesser degree, to the location of the eccentric stimulus to which a movement was not directed.

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