Removing the superior colliculus silences eye movements normally evoked from stimulation of the parietal and occipital eye fields

After removal of the superior colliculus eye movements could no longer be electrically evoked from striate, prestriate of inferior parietal cortex. However, shifts of gaze induced by frontal eye-field stimulation were not disrupted by tectal surgery.     

Effects on eye movements of a GABA agonist and antagonist injected into monkey superior colliculus

Injection of muscimol, a GABA agonist, into the superior colliculus of awake monkeys produces saccades to visual targets in the movement field of colliculus cells near the injection site that have longer latency and shortened amplitude. Bicuculline, a GABA antagonist, leads to irrepressible saccades towards the movement field. These results are consistent with a tonic inhibition by the substantia nigra on the superior colliculus mediated by GABA which is reduced at the time of saccade initiation.     

Physiological and anatomical evidence for an inhibitory trigemino-oculomotor pathway in the cat

During blink down‐phase, the levator palpebrae superioris (levator) muscle is inactivated, allowing the orbicularis oculi muscle to act. For trigeminal reflex blinks, the excitatory connections from trigeminal sensory nuclei to the facial nucleus have been described, but the pathway whereby the levator is turned off have not. We examined this question by use of both physiological and anatomical approaches in the cat. Intracellular records from antidromically activated levator motoneurons revealed that periorbital electrical stimulation produced bilateral, long latency inhibitory postsynaptic potentials (IPSPs). Central electrical stimulation of the principal trigeminal nucleus produced shorter latency IPSPs. Intracellular staining revealed that these motoneurons reside in the caudal central subdivision and have 10 or more poorly branched dendrites, which extend bilaterally into the surrounding supraoculomotor area. Axons penetrated in this region could be activated from periorbital and central electrodes. Neurons labeled from tracer injections into the caudal oculomotor complex were distributed in a crescent‐shaped band that lined the ventral and rostral aspects of the pontine trigeminal sensory nucleus. Double‐label immunohistochemical procedures demonstrated that these cells were not tyrosine hydroxylase‐positive cells in the Kölliker‐Fuse area. Instead, supraorbital nerve afferents displayed a similar crescent‐shaped distribution, suggesting they drive these trigemino‐oculomotor neurons. Anterograde labeling of the trigemino‐oculomotor projection indicates that it terminates bilaterally, in and above the caudal central subdivision. These results characterize a trigemino‐oculomotor pathway that inhibits levator palpebrae motoneurons in response to blink‐producing periorbital stimuli. The bilateral distributions of trigemino‐oculomotor afferents, levator motoneurons, and their dendrites supply a morphological basis for conjugate lid movements. J. Comp. Neurol. 520:2218–2240, 2012. © 2012 Wiley Periodicals, Inc.     

Relation between visual input and motor outflow for eye movements in monkey frontal eye field

We recorded visual neurons with the Elgiloy microelectrode in the frontal eye field of the alert monkey. After determining their visual receptive field, saccadic eye movements were induced by applying electric pulses at the recording site through the same electrode. The saccades were generally induced so as to bring the gaze angle to a part within the receptive field.     

Connectivity of the tectal zones coding for upward and downward oblique eye movements in goldfish

Deep layers of the goldfish tectum code movements in a topographically ordered motor map. This work studies the relationship between tectal sites (coding eye movements with different vertical directions) and the distributions of boutons (left by their projections), within rostral mesencephalic structures and rhombencephalic reticular formations. These regions have been involved in the generation of the vertical and horizontal components of eye movement, respectively, as suggested by the Cartesian hypothesis of de-codification of tectal signal. With this aim, discrete injections of biotinylated dextran amine (BDA) and Fluoro-Ruby (FR) were made into functionally identified tectal sites, coding oblique eye movements with similar amplitude of the horizontal component but opposite upward and downward vertical directions, and the distribution of synaptic endings was determined. The main findings of the present work were as follows: 1) within the tectal descending tract, axons were organized according to the location of injected sites within the tectum; 2) BDA and FR boutons were distributed in separate clusters within the medial longitudinal fasciculus and oculomotor nuclei, as well as in the nearby mesencephalic reticular formation; and 3) the regions containing both types of bouton overlapped moderately within the mesencephalic reticular formation at the isthmus level. Overlapping was more extended at the different levels of the rhombencephalic reticular formation, although a shift in the distribution of both types of bouton was always observed. These results suggest that, within the vertical generator, the endings were separated to contact the different neuronal population that codes the upward and downward components of movements. In contrast, in the horizontal generator, tectal endings more likely converge on the same neuronal population to code the horizontal component of movements, irrespective of whether the oblique movements were directed upward or downward.     

Simultaneous unitary neuronal activity in both superior colliculi and its relation to eye movements in the cat

The analysis of simultaneous unitary neuronal activity related to eye movement and recorded in both superior colliculi has shown a mirror-functioning image. Increase of the frequency discharge in a collicular unit, was associated with a decrease of the frequency discharge in the contralateral superior colliculus unit. This unitary neuronal reciprocal behaviour was observed each time a horizontal or oblique eye movement was produced. It is possible that this reciprocal functioning between neurones in both superior colliculi could exert an important influence on oculomotor brainstem structures. These results give a better idea of the role played by both superior colliculi in the control of conjugate eye movements.     

Catecholamine inputs to expiratory laryngeal motoneurons in rats

Many respiration‐related interneurons and motoneurons receive a catecholaminergic input, but the extent and distribution of this input to recurrent laryngeal motoneurons that innervate intrinsic muscles of the larynx are not clear. In the present study, we examined the catecholaminergic input to expiratory laryngeal motoneurons in the caudal nucleus ambiguus by combining intracellular labeling of single identified motoneurons, with immunohistochemistry to reveal tyrosine hydroxylase immunoreactive (catecholaminergic) terminal varicosities. Close appositions were found between the two structures, with 18 ± 5 close appositions per motoneuron (n = 7). Close appositions were more frequently observed on distal rather than proximal dendrites. Axosomatic appositions were not seen. In order to determine the source of this input, microinjections of cholera toxin B subunit (1%, 20 nl) were made into the caudal nucleus ambiguus. Retrogradely labeled neurons, located in the ipsilateral nucleus tractus solitarius and the area postrema, were tyrosine hydroxylase‐positive. Our results not only demonstrate details of the extent and distribution of potential catecholamine inputs to the expiratory laryngeal motoneuron, but further indicate that the inputs, at least in part, originate from the dorsomedial medulla, providing a potential anatomical basis for previously reported catecholaminergic effects on the laryngeal adductor reflex. J. Comp. Neurol. 523:381–390, 2015. © 2014 Wiley Periodicals, Inc.     

Cerebellar vermis involvement in monkey saccadic eye movements: Microstimulation

The cerebellar vermis (lobules V to VII) was focally stimulated (maximum current = 300 microA) through microelectrodes in alert monkeys trained to fixate on visual targets located at different positions in the eye movement field. Microstimulation of this area evoked saccades whose direction and amplitude were dependent on the spatial locus of the vermal point stimulated and on the position of the eye at the time of stimulation. Stimulation evoked saccades on most (70%) of the electrode penetrations. By alternatively stimulating and recording through the electrode as it advanced through the depth of the vermis, it was possible to map the threshold for evoking saccades along a penetration as well as to ascertain the type of tissue (white matter or Purkinje cell layer) situated at the stimulation points. On penetrations where saccades were evoked, there was generally one (90%) and sometimes two (10%) low-threshold region(s). These low-threshold regions were located in fiber tracks and not in the Purkinje or other cellular layers of the cerebellar cortex. The direction and size of the evoked saccades were dependent on position of the eye in the orbit. At a few sites, even the presence or the absence of an evoked saccade depended on the initial eye position. Postsaccadic drifts after termination of evoked saccades were also a common feature (50% of the tracks) associated with vermal microstimulation. The presence or absence as well as the direction of the postsaccadic drift were also dependent on initial eye position. These observations suggest that the vermal stimulations evoked saccades by the antidromic activation of mossy fiber afferent inputs that emanate from the brain stem saccadic burst generator. Furthermore, stimulation in this manner would actually bypass the cerebellar circuitry and produce saccades without the usual modifying influence of the cerebellum.     

Serotonin inputs to inspiratory laryngeal motoneurons in the rat

Serotonergic neurons are distributed widely throughout the central nervous system and exert a tonic influence on a range of activities in relation to the sleep-wake cycle. Previous morphologic and functional studies have indicated a role for serotonin in control of laryngeal motoneurons. In the present study, we used a combination of intracellular recording, dye-filling, and immunocytochemistry in rats to demonstrate close appositions between serotonin immunoreactive boutons and posterior cricoarytenoid (PCA) and cricothyroid (CT) motoneurons, both of which are located in the nucleus ambiguus and exhibit phasic inspiratory activity. PCA motoneurons received 29 +/- 5 close appositions/neuron (mean +/- SD, n = 6), with the close appositions distributed more frequently on the distal dendrites, less frequently on the proximal dendrites, and sparsely on the axons and somata. CT motoneurons received 56 +/- 15 (n = 6), with close appositions found on both the somata and dendrites, especially proximal dendrites. Close appositions on the axons were only seen on one CT motoneuron. These results demonstrate a significant serotonin input to inspiratory laryngeal motoneurons, which is more prominent on CT compared with PCA motoneurons, and may reflect the different functional role of the muscles that they innervate during the sleep-wake cycle.     

Inferior parietal lobule neurones related to eye and hand reach movements in rhesus monkey

Analysis was made on neuronal responses of the inferior parietal lobule to visual, jump, or 'reach' behavioral paradigm in 2 awake, trained rhesus monkeys. Preconditioning and antidromic electrical stimulation of medial and oral pulvinar LP nuclei and the arcuate gyrus aided the study. The results reveal two reach cell categories: one with no definable visual sensitivity (NVHRN) and one with visual receptive field responsiveness (VHRN). The VHRN reach cell firing is characterized by an early component. As the latter was observed only when the monkey reached loci inside but not outside of the cell-receptive field, it was equated with the cell visual receptive field response. This component could be voided by preconditioning stimulation of medial pulvinar or LP, the latencies of the VHRN responses becoming longer and comparable to NVHRN. If the consequences of reaching were nulled in any of a few different ways, such as preventing the monkey from reaching, disenabling the panel key, or denying the reward, a reach cell biphasic firing response showed no change in the first burst, but the second burst was absent, suggesting the latter's relation to satiation. If a jump cell's visual responses enhanced by the 'jump' paradigm were negated by preconditioning stimulation, the saccadic eye movement that otherwise followed the enhanced signals was replaced by another saccade, different in direction and amplitude, as if of other frames of reference. It seems, therefore, that the inferior parietal lobe system subserves in two types of reach behaviour: one with and one without visual guidance, playing perhaps a role in selecting strategies such as the dynamic option to do away with the visual guidance, if circumstances demand.     

Saccadic eye movements after extremely short reaction times in the monkey

Monkeys were trained to change their direction of gaze from one point (fixation point) to another (target). If the fixation point was extinguished at the same time when the new target occurred the saccadic reaction times (SRT) were in the order of 200 ms. If the fixation point disappeared 150-250 ms before the new target occurred (gap with no visible stimulus) monkeys made regular saccades after shorter reaction times of about 140 ms. In addition animals in the gap situation made saccades that had reaction times of no more than 70-80 ms measured from the onset of the new target (Express-Saccades). The reaction times of the E-saccades have standard deviations of only +/- 3 ms. E-saccades occurred with a frequency of up to 80% for gaps of 200-240 ms. If the gap was shorter than 180 ms increasingly more regular saccades were made with reaction times of 140-160 ms. With gap duration decreasing from 140 ms to zero all saccades were regular with SRTs increasing linearly to more than 200 ms. In one animal almost all E-saccades fell short and were corrected after less than 250 ms depending on the size of the error: large errors were corrected faster than small ones.     

Thyrotropin-releasing hormone inputs are preferentially directed towards respiratory motoneurons in rat nucleus ambiguus

In the present study, we assessed the extent of the thyrotropin-releasing hormone (TRH) input to motoneurons in the ambigual, facial, and hypoglossal nuclei of the rat using a combination of intracellular recording, dye filling, and immunohistochemistry. Twelve motoneurons in the rostral nucleus ambiguus were labelled by intracellular injection in vivo of Neurobiotin (Vector). Seven out of 12 ambigual motoneurons displayed rhythmic fluctuations of their membrane potential in phase with phrenic nerve discharge, whereas the other five had no modulations of any kind. Seven facial motoneurons and seven hypoglossal motoneurons were also filled with Neurobiotin. All three motor nuclei contained TRH-immunoreactive varicosities, with the largest numbers found in the nucleus ambiguus. Close appositions were seen between TRH-immunoreactive boutons and every labelled motoneuron. Respiratory- related motoneurons in the nucleus ambiguus received the largest number of TRH appositions with 74 ± 38 appositions/neuron (mean ± S. D.; n = 7). In contrast, nonrespiratory ambigual motoneurons received significantly fewer TRH appositions (11 ± 5; n = 5; P < 0. 05; Mann-Whitney U test). Facial motoneurons received about the same number of TRH appositions as nonrespiratory ambigual motoneurons, with 13 ± 4 (n = 7). Hypoglossal motoneurons received the fewest appositions from TRH-containing boutons, with 8 ± 2 (n = 7). There were no differences in the TRH inputs to respiratory and nonrespiratory motoneurons in the facial and hypoglossal nuclei. These results demonstrate that, among motoneurons in the medulla, respiratory motoneurons in the rostral nucleus ambiguus are preferentially innervated by the TRH-immunoreactive boutons. © 1995 Wiley-Liss Inc.     

Pretectal projections to the oculomotor complex of the monkey and their role in eye movements

The nucleus of the optic tract (NOT) is associated with the generation of optokinetic nystagmus (OKN), whereas the olivary pretectal nucleus (ol), which lies embedded in the primate NOT, is believed to be essential for the pupillary light reflex. In this anatomical study of the pretectum, projections from NOT and ol to structures around the oculomotor nucleus were traced in the monkey, to determine which cell groups they innervated. 1. ³[H]-leucine injections were placed into NOT and ol, and labelled terminals were observed just outside the classical oculomotor nucleus (nIII), in the ‘C-group’ and midline cell clusters, both of which contain small motoneurons of the extraocular eye muscles. In addition, there were strong projections to the lateral visceral cell column of the Edinger-Westphal complex (lvc), but not to the Edinger-Westphal nucleus (EW) itself. All of these projections were mainly contralateral. 2. NOT efferents terminated over the ipsilateral medial accessory nucleus of Bechterew (nB), but not over the adjacent nucleus Darkschewitsch. 3. Injections of a retrograde tracer into the oculomotor complex showed that the pretectal afferents described above originated mainly from the dorsomedial part of NOT and from ol. 4. The use of a transsynaptic retrograde tracer, tetanus toxin fragment (BII_b), established the monosynaptic nature of the connection between dorsomedial NOT (contralaterally) and ol (bilaterally), to the small extraocular motoneurons outside classical nIII. The ‘C-group’ motoneurons may play a role in vergence, and lvc in pupillary constriction and depth of focus. Our results imply that NOT and ol participate in the control of some aspects of the near-response, which may be important in the generation of some components of OKN in primates. © 1996 Wiley-Liss, Inc.     

Single-neuron evidence for a contribution of the dorsal pontine nuclei to both types of target-directed eye movements, saccades and smooth-pursuit

The primate dorsolateral pontine nucleus (DLPN) is a key link in a cerebro-cerebellar pathway for smooth pursuit eye movements, a pathway assumed to be anatomically segregated from tegmental circuits subserving saccades. However, the existence of afferents from several cerebrocortical and subcortical centres for saccades suggests that the DLPN and neighbouring parts of the dorsal pontine nuclei (DPN) might contribute to saccades as well. In order to test this hypothesis, we recorded from the DPN of two monkeys trained to perform smooth pursuit eye movements as well as visually and memory-guided saccades. Out of 281 neurons isolated from the DPN, 138 were responsive in oculomotor tasks. Forty-five were exclusively activated in saccade paradigms, 68 exclusively by smooth pursuit and 25 neurons showed responses in both. Pursuit-related responses reflected sensitivity to eye position, velocity or combinations of velocity and position with minor contributions of acceleration in many cases. When tested in the memory-guided saccades paradigm, 65 out of 70 neurons activated in saccade paradigms showed significant saccade-related bursts and 20 significant activity in the memory period. Our finding of saccade-related activity in the DPN in conjunction with the existence of strong anatomical input from saccade-related cerebrocortical areas suggests that the DPN serves as a precerebellar relay for both pursuit and saccade-related information originating from cerebral cortex, in addition to the classical tecto-tegmental circuitry for saccades.     

Electrooculogram and submandibular montage to distinguish different eye,eyelid, and tongue movements in electroencephalographic studies

Objective

We propose an electrooculogram and submandibular montage that helps to discriminate eye/eyelid/tongue movements and to differentiate them from epileptiform activity or slowing on electroencephalography (EEG).

Projections from the functional subdivisions of the frontal eye field to the superior colliculus in the monkey

The frontal eye field (FEF) can be divided into the lateral subdivision representing the central visual field (VF), and the medial subdivision representing the peripheral VF. In this report, we examined neurally projected parts within the superior colliculus (SC) from those electrophysiologically identified subdivisions in the FEF using the horseradish peroxidase anterograde transport method. We found that the lateral subdivision projected into the anterolateral portion of the SC, whereas the medial one into the posteromedial portion, indicating that there is a correlation in the VF representation between the source and the target of this corticotectal system.     

Frontal eye field projection to the paramedian pontine reticular formation traced with wheat germ agglutinin in the monkey

Injections of the retrograde tracer [125I]wheat germ agglutinin have been placed in different areas of the paramedian pontine reticular formation (PPRF), a well known premotor center for gaze control. Experiments in 5 monkeys revealed 3 major sources of input: (1) bilateral projections from the so-called frontal eye field (FEF), which is situated in the frontal cortex around the arcuate sulcus; (2) the intermediate and deep layers of mainly the contralateral superior colliculus; and (3) ipsilateral projections from brainstem structures such as the accessory oculomotor nuclei (nucleus interstitialis of Cajal, nucleus of Darkschewitsch, and nucleus of the posterior commissure), the mesencephalic reticular formation, the vestibular nuclei, the nucleus prepositus hypoglossi, and the cerebellar fastigial nucleus. The results are compared with previous anatomical investigations and confirm the electrophysiologically demonstrated FEF-PPRF-abducens disynaptic pathway.     

Relationship between exploratory eye movements and brain morphology in schizophrenia spectrum patients

The exploratory eye movements of schizophrenia patients and their relatives have been shown to differ from those of patients without schizophrenia and healthy controls. However the mechanism of exploratory eye movement disturbances in schizophrenia patients remains elusive. We investigated the relationship between the exploratory eye movements and brain morphology in 39 schizophrenia spectrum patients. Voxel–based morphometric analysis on three–dimensional magnetic resonance imaging was conducted by means of statistical parametric mapping 99. The decrease in the responsive search score, which is the total number of sections on which the eyes fixed in response to questioning in a comparison task, was significantly correlated with the decreased gray matter in the right frontal eye field (rFEF) including the right supplementary eye field (rSEF), right parietal eye field (rPEF), and right inferior frontal region. These results suggest that disturbance in exploratory eye movement in schizophrenia spectrum patients may be related to neural network dysfunction in FEF, SEF and PEF, which are the eye movement related areas, and in the inferior frontal region that may be related to information organization.     

An anterograde HRP study of the retinocollicular pathways in normal hamsters and hamsters with one eye enucleated at birth

The present anterograde HRP study indicated that the uncrossed retinal projection to the superior colliculus in both normal hamsters and hamsters with one eye enucleated at birth was more extensive than previously reported. In addition, a small retinal projection to the contralateral inferior colliculus was also observed in all animals studied.