The Main Sequence of Human Optokinetic Afternystagmus (OKAN)

2009 ◽  
Vol 101 (6) ◽  
pp. 2889-2897 ◽  
Author(s):  
Andre Kaminiarz ◽  
Kerstin Königs ◽  
Frank Bremmer
Keyword(s):  
Neural Networks ◽  
Eye Movements ◽  
Main Sequence ◽  
Critical Role ◽  
Saccade Target ◽  
Control Mechanisms ◽  
Visually Guided ◽  
Background Characteristics ◽  
Optokinetic Afternystagmus

Different types of fast eye movements, including saccades and fast phases of optokinetic nystagmus (OKN) and optokinetic afternystagmus (OKAN), are coded by only partially overlapping neural networks. This is a likely cause for the differences that have been reported for the dynamic parameters of fast eye movements. The dependence of two of these parameters—peak velocity and duration—on saccadic amplitude has been termed “main sequence.” The main sequence of OKAN fast phases has not yet been analyzed. These eye movements are unique in that they are generated by purely subcortical control mechanisms and that they occur in complete darkness. In this study, we recorded fast phases of OKAN and OKN as well as visually guided and spontaneous saccades under identical background conditions because background characteristics have been reported to influence the main sequence of saccades. Our data clearly show that fast phases of OKAN and OKN differ with respect to their main sequence. OKAN fast phases were characterized by their lower peak velocities and longer durations compared with those of OKN fast phases. Furthermore we found that the main sequence of spontaneous saccades depends heavily on background characteristics, with saccades in darkness being slower and lasting longer. On the contrary, the main sequence of visually guided saccades depended on background characteristics only very slightly. This implies that the existence of a visual saccade target largely cancels out the effect of background luminance. Our data underline the critical role of environmental conditions (light vs. darkness), behavioral tasks (e.g., spontaneous vs. visually guided), and the underlying neural networks for the exact spatiotemporal characteristics of fast eye movements.

Role of the Vermal Cerebellum in Visually Guided Eye Movements and Visual Motion Perception

2019 ◽  
Vol 5 (1) ◽  
pp. 247-268 ◽  
Author(s):  
Peter Thier ◽  
Akshay Markanday
Keyword(s):  
Eye Movements ◽  
Motion Perception ◽  
Visual Motion ◽  
Cerebellar Nuclei ◽  
Visually Guided ◽  
Past Performance ◽  
Visual Motion Perception ◽  
Oculomotor Vermis ◽  
Retinal Information

The cerebellar cortex is a crystal-like structure consisting of an almost endless repetition of a canonical microcircuit that applies the same computational principle to different inputs. The output of this transformation is broadcasted to extracerebellar structures by way of the deep cerebellar nuclei. Visually guided eye movements are accommodated by different parts of the cerebellum. This review primarily discusses the role of the oculomotor part of the vermal cerebellum [the oculomotor vermis (OMV)] in the control of visually guided saccades and smooth-pursuit eye movements. Both types of eye movements require the mapping of retinal information onto motor vectors, a transformation that is optimized by the OMV, considering information on past performance. Unlike the role of the OMV in the guidance of eye movements, the contribution of the adjoining vermal cortex to visual motion perception is nonmotor and involves a cerebellar influence on information processing in the cerebral cortex.

scholarly journals Transcranial Magnetic Stimulation Over the Human Medial Posterior Parietal Cortex Disrupts Depth Encoding During Reach Planning

2020 ◽  
Vol 31 (1) ◽  
pp. 267-280
Author(s):  
Rossella Breveglieri ◽  
Annalisa Bosco ◽  
Sara Borgomaneri ◽  
Alessia Tessari ◽  
Claudio Galletti ◽  
...  
Keyword(s):  
Transcranial Magnetic Stimulation ◽  
Parietal Cortex ◽  
Magnetic Stimulation ◽  
Posterior Parietal Cortex ◽  
Critical Role ◽  
The Body ◽  
Visually Guided ◽  
Visually Guided Reaching ◽  
Posterior Parietal

Abstract Accumulating evidence supports the view that the medial part of the posterior parietal cortex (mPPC) is involved in the planning of reaching, but while plenty of studies investigated reaching performed toward different directions, only a few studied different depths. Here, we investigated the causal role of mPPC (putatively, human area V6A–hV6A) in encoding depth and direction of reaching. Specifically, we applied single-pulse transcranial magnetic stimulation (TMS) over the left hV6A at different time points while 15 participants were planning immediate, visually guided reaching by using different eye-hand configurations. We found that TMS delivered over hV6A 200 ms after the Go signal affected the encoding of the depth of reaching by decreasing the accuracy of movements toward targets located farther with respect to the gazed position, but only when they were also far from the body. The effectiveness of both retinotopic (farther with respect to the gaze) and spatial position (far from the body) is in agreement with the presence in the monkey V6A of neurons employing either retinotopic, spatial, or mixed reference frames during reach plan. This work provides the first causal evidence of the critical role of hV6A in the planning of visually guided reaching movements in depth.

Role of the Oculomotor Vermis in Generating Pursuit and Saccades: Effects of Microstimulation

1998 ◽  
Vol 80 (4) ◽  
pp. 2046-2062 ◽  
Author(s):  
R. J. Krauzlis ◽  
F. A. Miles
Keyword(s):  
Eye Movements ◽  
Eye Movement ◽  
Transition Point ◽  
Contralateral Side ◽  
Movement Behavior ◽  
Visually Guided ◽  
Ipsilateral Side ◽  
Oculomotor Vermis ◽  
Eye Velocity

Krauzlis, R. J. and F. A. Miles. Role of the oculomotor vermis in generating pursuit and saccades: effects of microstimulation. J. Neurophysiol. 80: 2046–2062, 1998. We studied the eye movements evoked by applying small amounts of current (2–50 μA) within the oculomotor vermis of two monkeys. We first compared the eye movements evoked by microstimulation applied either during maintained pursuit or during fixation. Smooth, pursuitlike changes in eye velocity caused by the microstimulation were directed toward the ipsilateral side and occurred at short latencies (10–20 ms). The amplitudes of these pursuitlike changes were larger during visually guided pursuit toward the contralateral side than during either fixation or visually guided pursuit toward the ipsilateral side. At these same sites, microstimulation also often produced abrupt, saccadelike changes in eye velocity. In contrast to the smooth changes in eye velocity, these saccadelike effects were more prevalent during fixation and during pursuit toward the ipsilateral side. The amplitude and type of evoked eye movements could also be manipulated at single sites by changing the frequency of microstimulation. Increasing the frequency of microstimulation produced increases in the amplitude of pursuitlike changes, but only up to a certain point. Beyond this point, the value of which depended on the site and whether the monkey was fixating or pursuing, further increases in stimulation frequency produced saccadelike changes of increasing amplitude. To quantify these effects, we introduced a novel method for classifying eye movements as pursuitlike or saccadelike. The results of this analysis showed that the eye movements evoked by microstimulation exhibit a distinct transition point between pursuit and saccadelike effects and that the amplitude of eye movement that corresponds to this transition point depends on the eye movement behavior of the monkey. These results are consistent with accumulating evidence that the oculomotor vermis and its associated deep cerebellar nucleus, the caudal fastigial, are involved in the control of both pursuit and saccadic eye movements. We suggest that the oculomotor vermis might accomplish this role by altering the amplitude of a motor error signal that is common to both saccades and pursuit.

scholarly journals Expansion of Visual Space During Optokinetic Afternystagmus (OKAN)

2008 ◽  
Vol 99 (5) ◽  
pp. 2470-2478 ◽  
Author(s):  
André Kaminiarz ◽  
Bart Krekelberg ◽  
Frank Bremmer
Keyword(s):  
Eye Movements ◽  
Visual Space ◽  
Eye Position ◽  
Control Mechanisms ◽  
Position Information ◽  
Fast Phase ◽  
Optokinetic Afternystagmus ◽  
Perceptual Stability ◽  
Voluntary Eye Movements ◽  
The Brain

The mechanisms underlying visual perceptual stability are usually investigated using voluntary eye movements. In such studies, errors in perceptual stability during saccades and pursuit are commonly interpreted as mismatches between actual eye position and eye-position signals in the brain. The generality of this interpretation could in principle be tested by investigating spatial localization during reflexive eye movements whose kinematics are very similar to those of voluntary eye movements. Accordingly, in this study, we determined mislocalization of flashed visual targets during optokinetic afternystagmus (OKAN). These eye movements are quite unique in that they occur in complete darkness and are generated by subcortical control mechanisms. We found that during horizontal OKAN slow phases, subjects mislocalize targets away from the fovea in the horizontal direction. This corresponds to a perceived expansion of visual space and is unlike mislocalization found for any other voluntary or reflexive eye movement. Around the OKAN fast phases, we found a bias in the direction of the fast phase prior to its onset and opposite to the fast-phase direction thereafter. Such a biphasic modulation has also been reported in the temporal vicinity of saccades and during optokinetic nystagmus (OKN). A direct comparison, however, showed that the modulation during OKAN was much larger and occurred earlier relative to fast-phase onset than during OKN. A simple mismatch between the current eye position and the eye-position signal in the brain is unlikely to explain such disparate results across similar eye movements. Instead, these data support the view that mislocalization arises from errors in eye-centered position information.

The influence of contextual faces on bilingual language control

2019 ◽  
Vol 72 (9) ◽  
pp. 2313-2327 ◽  
Author(s):  
Cong Liu ◽  
Kalinka Timmer ◽  
Lu Jiao ◽  
Yuan Yuan ◽  
Ruiming Wang
Keyword(s):  
Cultural Identity ◽  
Switch Cost ◽  
Dominance Effect ◽  
Critical Role ◽  
Control Mechanisms ◽  
Language Dominance ◽  
The Face ◽  
Language Control ◽  
Global Language

How do faces with social-cultural identity affect bilingual language control? We approach this question by looking at the switch cost patterns and reversed language dominance effect, which are suggested to reflect bilingual language control mechanisms, in the absence (i.e., baseline context) or presence of faces with socio-cultural identity (Asian or Caucasian). In separate blocks, the face matched (i.e., congruent context) or mismatched (i.e., incongruent context) the language to be spoken. In addition, cue preparation time was manipulated to be long (Experiment 1) or short (Experiment 2). In both experiments, a unique asymmetric switch cost with larger costs for L2 was observed in the congruent context as compared with the baseline and incongruent contexts. Furthermore, the reversed language dominance effect was not modulated across contexts. These results suggest a critical role of contextual faces in modulating local but not global language control. Thus, bilingual language control changes flexibly within an environment that includes faces with socio-cultural identity.

scholarly journals Role of astrocytes and altered regulation of spinal glutamatergic neurotransmission in stress-induced visceral hyperalgesia in rats

2011 ◽  
Vol 301 (3) ◽  
pp. G580-G589 ◽  
Author(s):  
Sylvie Bradesi ◽  
Viktoriya Golovatscka ◽  
Helena S. Ennes ◽  
James A. McRoberts ◽  
Iordanes Karagiannidis ◽  
...  
Keyword(s):  
Chronic Stress ◽  
Critical Role ◽  
Nociceptive Response ◽  
Control Mechanisms ◽  
Glutamatergic Neurotransmission ◽  
Visceral Hyperalgesia ◽  
Excitatory Neurotransmitter ◽  
Pharmacological Inhibition ◽  
Male Wistar Rats

Glutamate (Glu) is the primary excitatory neurotransmitter in the central nervous system and plays a critical role in the neuroplasticity of nociceptive networks. We aimed to examine the role of spinal astroglia in the modulation of glutamatergic neurotransmission in a model of chronic psychological stress-induced visceral hyperalgesia in male Wistar rats. We assessed the effect of chronic stress on different glial Glu control mechanisms in the spinal cord including N-methyl-d-aspartate receptors (NMDARs), glial Glu transporters (GLT1 and GLAST), the Glu conversion enzyme glutamine synthetase (GS), and glial fibrillary acidic protein (GFAP). We also tested the effect of pharmacological inhibition of NMDAR activation, of extracellular Glu reuptake, and of astrocyte function on visceral nociceptive response in naive and stressed rats. We observed stress-induced decreased expression of spinal GLT1, GFAP, and GS, whereas GLAST expression was upregulated. Although visceral hyperalgesia was blocked by pharmacological inhibition of spinal NMDARs, we observed no stress effects on NMDAR subunit expression or phosphorylation. The glial modulating agent propentofylline blocked stress-induced visceral hyperalgesia, and blockade of GLT1 function in control rats resulted in enhanced visceral nociceptive response. These findings provide evidence for stress-induced modulation of glia-controlled spinal Glu-ergic neurotransmission and its involvement in chronic stress-induced visceral hyperalgesia. The findings reported in this study demonstrate a unique pattern of stress-induced changes in spinal Glu signaling and metabolism associated with enhanced responses to visceral distension.

The Hippocampus Promotes Effective Saccadic Information Gathering in Humans

2019 ◽  
Vol 31 (2) ◽  
pp. 186-201 ◽  
Author(s):  
Heather D. Lucas ◽  
Melissa C. Duff ◽  
Neal J. Cohen
Keyword(s):  
Eye Movements ◽  
Critical Role ◽  
Study Phase ◽  
Memory Encoding ◽  
Information Theoretic ◽  
Memory Processing ◽  
Subsequent Performance ◽  
Spatial Reconstruction ◽  
The Moment

It is well established that the hippocampus is critical for memory. Recent evidence suggests that one function of hippocampal memory processing is to optimize how people actively explore the world. Here we demonstrate that the link between the hippocampus and exploration extends even to the moment-to-moment use of eye movements during visuospatial memory encoding. In Experiment 1, we examined relationships between study-phase eye movements in healthy individuals and subsequent performance on a spatial reconstruction test. In addition to quantitative measures of viewing behaviors (e.g., how many fixations or saccades were deployed during study), we used the information–theoretic measure of entropy to assess the amount of randomness or disorganization in participants' scanning behaviors. We found that the use of scanpaths during study that were lower in entropy (e.g., more organized, less random) predicted more accurate spatial reconstruction both within and between participants. Scanpath entropy was a better predictor of reconstruction accuracy than were the quantitative measures of viewing. In Experiment 2, we found that individuals with hippocampal amnesia tended to engage in viewing patterns that were higher in entropy (less organized) relative to healthy comparisons. These findings reveal a critical role of the hippocampus in guiding eye movement exploration to optimize visuospatial relational memory.

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