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Ponto-Geniculo-Occipital PGO waves are biphasic field potentials identified in a range of mammalian species that are ubiquitous with sleep, but can also be identified in waking perception and eye movement. Their role in REM sleep and visual perception more broadly may constitute a promising avenue for further research, however what was once an active field of study has recently fallen into stasis.
With the reality that invasive recordings performed on animals cannot be replicated in humans; while animals themselves cannot convey experience to the extent required to elucidate how PGO waves factor into awareness and behavior, innovative solutions are required if significant research outcomes are to ever be realized. Advances in non-invasive imaging technologies and sophistication in imaging methods now offer substantial scope to renew the study of the electrophysiological substrates of waking and dreaming perception.
Among these, Magnetoencephalogram MEG stands out through its capacity to measure deep brain activations with high temporal resolution. With the current trend in sleep and dream research to produce translational findings of psychopathological and medical significance, in addition to the clear links that PGO wave generation sites share, pharmacologically, with receptors involved in expression of mental illness; there is a strong case to support scientific research into PGO waves and develop a functional understanding of their broader role in human perception.
Ponto-Geniculo-Occipital PGO waves are distinctive wave forms that are typically identified as propagating activity between three key brain regions, being the Pons, Lateral Geniculate Nucleus and Occipital Cortex. They have been confirmed and studied extensively in cats, rats and primates but never in humans, as the ethical implications for performing invasive recordings at three concurrent brain locations has not made such research justifiable or indeed practical.
Rare occasions where neurosurgical medical procedures have been performed around these key regions have indeed opened the prospective window for simultaneous invasive recording for scientific purposes, however to date this has only confirmed the Pontine elements of the phenomenon and as such, it can only be conservatively said that humans exhibit P waves Lim et al.
PGO waves were initially observed in in anesthetized cats McGaugh, , and have since been comprehensively studied in this species, to a lesser extent in rats Kaufman and Morrison, , and in non-human primates such as Macaques and Baboons Cohen and Feldman, ; Vuillon-Cacciuttolo and Seri, However, the network of brain regions that PGO waves propagate through does vary from species to species, with only the Pons and to some extent the Lateral Geniculate Body of the Visual Thalamus forming a common neurophysiological location across all mammalian species tested thus far.
The PGO wave profile strongly resembles that of a sub-threshold epileptiform burst Elazar and Hobson, , and like other epileptiform bursts they may propagate and spread throughout the brain, potentially via top-down activation by the Amygdala and the Prefrontal Cortex. However there are numerous indications that PGO waves function beyond sleep physiology alone, and may have additionally important implications for the systems that underpin waking perception and healthy psychological function Hobson, ; Hobson and Friston, While typically associated with REM sleep, PGO waves also correlate with saccadic eye movement in waking, albiet at lower electrophysiological amplitude, across all mammalian species tested Nelson et al.
PGO waves have been observed to occur several seconds after heightened activity within the feline pontine subregion known as the caudolateral peribrachial area C-PBL; Datta, , which receives inhibitory serotonergic projections from the Raphe Nuclei , which in turn is thought to partly mediate the specific pharmacological links between Serotonin 5-HT and PGO wave genesis.
This finding had initially complicated earlier models which had assumed psychoactive distortion of visual process would occur through modulation of a common receptor. However contemporary perspectives that allow macroscopic system behaviors to be considered without linear dependence on specific lower order variables now render this observation considerably less problematic to the broader role of PGO waves in human vision.
Given the anticipated role that 5-HT receptor subtypes play in the expression of psychopathological illness, such as body dysmorphic disorders and unipolar depression Celada et al. Indeed, PGO wave research may eventually provide an important link in explaining how the systems that allow internally generated imagery to unconsciously modulate and override retinal visual input synchronize in healthy perception, and subsequently break down in psychopathology. Thus a functional understanding into the genesis of unconscious perceptive systems, and the role of PGO waves within these systems, is likely to be of relevance in understanding important dynamical aspects of conscious experience.
At present there is no holistically compelling model to justify how retinal sensory input is overridden, producing dreaming, creative experience and psychotic hallucination in human populations. What explanations do exist are largely confined to narrow disciplinary approaches, while these in turn remain relatively niche and often lack translational relevancy outside their specific fields. Thus a purely Psychodynamic account explains little more than a purely computational one—however much each coheres with its disciplinary techniques and traditions.
In order to fully understand and comprehend the complex issues surrounding false inferences in human sensory perception, an interdisciplinary approach is required, and this must thoroughly investigate the phenomenon in question, using both sound theoretical understanding and sophisticated imaging methods.
This is especially the case when attempting to develop a theoretical understanding of the relationship between PGO wave activity and macroscopic, observable behavior.
However, human subjects are ultimately required if the gap between theoretical and functional is ever to be closed, and experiments must be designed to falsify assertions made within the allowance of contemporary ethical constraints. As such, a detailed investigation into human PGO waves using non-invasive technologies such as Magnetoencephalogram MEG appear to be the best prospect for achieving such progress. PGO waves were first observed in the feline brain, during invasive electrophysiological investigations into sleep in that species.
The observed phenomenon was subsequently named after the three regions they most prominently appeared, being the Pons, the Geniculate Nucleus and the Occipital Cortex Jouvet and Michel, ; Mikiten et al. They can be observed as both single waves, occurring predominantly in NREM sleep and not time-locked to eye movement, and wave bursts, which occur primarily during REM and correlate strongly with saccadic movements see Figure 1. PGO wave bursts typically come in clusters of 3—5 and occur at approximately 30—60 spikes per minute both preceding and during REM sleep Bowe-Anders et al.
PGO Waves have also been recorded in a state of wakefulness, albeit at lower amplitude and frequency Brooks, ; Stern et al. Figure 1. Widespread distribution of PGO wave activity correlates with a triggering-neuron transitioning from tonic to high frequency activity. Image adapted from Datta and Hobson The neurons involved in generating and propagating PGO waves can be divided into two groups, being the Executive Neurons that trigger PGO wave onset and propagate similar electrophysiological activity to other brain regions; and Modulatory Neurons that respond to fluctuations in neuromodulators Datta, Neuromodulators are thought to facilitate some degree of involvement of forebrain and limbic structures in PGO wave generation and behavior, and while not directly being involved in their primary generation, have significant influence on how PGO waves are spread and maintained.
Executive Neurons are primarily located within the C-PBL of the Dorsolateral Pons Datta, , while Modulatory Neurons are located across disparate brain regions, including the Prefrontal Cortex, Amygdala, Suprachiasmatic Nucleus, as well as vestibular and auditory cell groups. As expected; lesions to the Peribrachial Area eliminate primary PGO wave generation, while a wide range of aminergic partial and full agonists, cholinergic agonists and reuptake inhibitors similarly affect PGO wave generation in a variety of ways, from delaying to prolonging onset, increasing or decreasing their amplitude and potentially even influencing how PGO waves and brain networks interact.
However the Geniculate Body in one hemisphere will typically produces a wave of considerably higher amplitude, a few milliseconds earlier than the other. When PGO waves appear in relation to a REM saccade, wave generation reliably correlates with the direction of eye movement, with Primary waves occurring in the ipsilateral 1 Geniculate body, and Secondary waves in the contralateral body to the saccade.
In rodents, PGO waves are generally referred to as pontine-waves or P waves , and do not appear to propagate in the same manner as in species with more developed visual systems. Nonetheless, the term PGO wave is still used, in broader reference to the interspecies phenomenon.
Rats appear to produce PGO waves following direct electrical stimulation of the Amygdala Deboer et al. PGO waves have been shown to function somewhat independently of the acoustic startle response, and may in this sense indicate endogenous activation of the retina independent of a behavioral response Kaufman, Localized injections of Carbachol to the rat brainstem have been successfully used to isolate PGO wave generation to the dorsal Nucleus Subcoeruleus of the Pons Datta et al.
This finding highlights a potentially important relationship between PGO wave generation and other cognitive functions, including sensorimotor function and memory consolidation. Further investigations into rats have revealed important links between the PGO waves and memory-related gene expression in both the Amygdala and Hippocampus Datta et al.
The influence of neuropharmacological compounds on PGO wave generation and behavior is complex and only partially understood, with the development of considerably more sophisticated theoretical models required to account for the often confounding experimental data. Existing models have combined observational findings with mathematical modeling, often involving Predictive Coding Hobson, Since there exists an experimental gulf between the quality of subjective experience produced from human subjects and the ethical constraints of administering psychomimetic compounds to non-animal cohorts; carefully designed research is required to translate the findings and theoretical implications of feline and rodent studies into a human context.
The difficulties in producing translational research from feline to humans is further compounded by the logistical barriers in accessing pharmacological compounds that may affect PGO waves in humans, as many are designated as controlled substances and are not legally accessible. Conservatively speaking, substances that globally deplete 5-HT in the feline brain are considerably likely to promote high amplitude, REM-like PGO waves, even while awake.
This can be effectively achieved through acute administration of vesicular monoamine transporter VMAT blockers such as Reserpine Brooks and Gershon, in addition to chronic administration of the tryptophan hydroxylase inhibitor Fenclonine Ruch-Monachon et al.
One example where the direct relationship between 5-HT receptor subtypes, internally generated perception and electrophysiological phenomenon has proven notably difficult to understand involves the well-known 5-HT2 A receptor agonist and recreational psychedelic, lysergic acid diethylamide LSD.
However, the hypothesis currently remains open regarding the precise mechanisms by which these substances induce their hallucinatory visual effects, with some anticipating a more complex mechanism involving NMDA antagonism Aghajanian and Marek, , while others anticipate a dopaminergic mechanism instead Marona-Lewicka et al.
As such, the role that 5-HT plays in promoting certain visual phenomenon in one context while suppressing it in another creates many problems.
It may be the case that the relationship between internally generated imagery, PGO waves and psychoactive 5-HT receptor agonists is considerably more complex than once thought, with further research and more innovative models needed to establish context for empirical findings that now span multiple academic disciplines. While PGO waves may ultimately facilitate information generated within the Default Mode Network to augment and override the information produced from the retina, there may be other mechanism by which this can occur, and indeed PGO waves may not present a mandatory precondition for this to happen.
Untangling the complex interactions between these two approaches electrophysiological and psychopharmacological may ultimately require human participants with an ability to subjectively report their experience.
In humans, PGO waves have been hypothesized to hold significance across important and diverse domains of cognition, such as learning Datta, , brain maturation and network organization Amzica and Steriade, Given the demonstrated importance REM sleep shares with these functions, this observation is not surprising, and thus the true importance and scientific relevance of human PGO waves is at best, only partially known.
Despite the potential value of further exploration and investigation into this area, experiments on human subjects have not matched those conducted on felines. This can broadly be seen as a twofold problem: the complexity and relative novelty of suitable non-invasive technology renders such research somewhat niche and unattractive, while logistical complexity and risk of performing invasive recordings on humans significantly limits the scope of the experimental paradigm, and very little can be safely confirmed other than the existence of the waves themselves.
Despite these difficulties, some progress has been made on both fronts, and as such; PGO wave research may soon undergo a significant resurgence. The patient was subsequently monitored over a 24 h period, 2 days post operatively, during which normal REM sleep stages were observed and recorded.
Deep Brain Stimulation electrodes were surgically implanted under general anesthetic with recordings commencing 84 h after surgery. In this study, the target site was instead the Subthalamic Nucleus , and produced results considerably more in line with existing feline models. Clusters occurred in groups of approximately 3—13, with a density of 18—27 spikes per minute. Much like feline models, PGO wave clusters were observed to be closely related to REM Sleep and additionally demonstrated an observable fast oscillatory Subthalamic Beta activity in the 13—35 Hz range.
Importantly, this study also demonstrated a degree of homogeneity between feline and human PGO wave function, in finding that PGO wave singlets precede REM Sleep onset by 30—90 s in both species.
Figure 2. Human invasive recordings. A single-neuron study was most recently conducted, using depth-electrode EEG, in a cohort of 13 epilepsy patients Andrillon et al.
Potentials in the human Medial Temporal Lobe having a morphology similar to feline PGO waves were reliably observed time-locked to sleep REM, and added considerable support to the hypothesis that PGO waves propagate throughout the brain, and far beyond the three key regions from which they have traditionally been observed. While this study did not provide unequivocal evidence of the PGO wave phenomena in humans, it none the less gave support to the anticipated existence and purported complexity of these phenomena.
To date, there have been very few attempts to find non-invasive evidence for PGO waves in humans, however those that have proceeded have shown promise. The only non-invasive imaging technology that has both the temporal and spatial resolution to potentially isolate and measure deep brain activity with sufficient fidelity to produce the characteristic electrophysiological PGO wave shape, is at present the MEG.
However, many other non-invasive technologies, such as fMRI and positron emission tomography PET are capable of playing important roles in providing indirect evidence to support the existence of this phenomenon, for instance through recording of general brain activity time-locked to REM.
Such observations may contribute to understanding the nature and extent of the PGO wave generating network, their respective overlap with REM generation sites Miyauchi et al. Due to the widespread availability of such technologies, and their demonstrated capability for recording neuronal activation deep within the brain, the potential to explore the phenomenon of human PGO waves from a range of complementary non-invasive technologies appears promising.
Functional MRI in combination with polysomnographic recording has shown some promise in this regard. One study Miyauchi et al. Self-paced saccades in total darkness produced no specific changes, indicating that the observed activity related to phenomenal dream content, thus supporting the hypothesis that PGO waves may comprise the origins of such content. This observation was supported by an earlier study Wehrle et al.
In spite of this, it produced similar results, specifically; activations in the Ventroposterior Thalamus and V2 of the Occipital Cortex in 8 out of 11 subjects.
This study found notable activity during REM in the Ventroposterior Thalamus and V1 of the Occipital Cortex, with additional activity in a number of limbic regions and the Parahippocampal Gyrus. Importantly, like Miyauchi et al.
However like Wehrle et al. Since these technologies invariably rely on changes in hemodynamic activity, as a proxy for neural activity, their capacity to comprehensively demonstrate the existence of purely electrophysiological phenomenon such as PGO waves will remain limited, but nevertheless valuable to future research.
MEG has both the potential spatial and temporal resolution to advance the research conducted using hemodynamic measurements, with the additional advantage that it directly records electrophysiological activity. However due to the complexity of the imaging forming process and data analysis, and—until recently—the severe computational overheads required to process MEG data, very little has been done to fully capitalize on the MEG to scientifically investigate this phenomenon.
Importantly, it indicated high amplitude spiking activity in the same lateral hemisphere as the direction of the saccade, indicating a degree of homogeneity with feline models produced using invasive recordings Hobson and Friston, However the study was limited in that it only included three participants.
Source-space images were produced using Magnetic Field Tomography MFT 4 and subsequently overlayed on an fMRI topographical map constructed using Statistical Parametric Mapping to produce a spatially accurate representation of Pontine activity during saccades Ribary et al. This study was able to record electrophysiological phenomenon that bore a distinct resemblance to the characteristic PGO wave profile, something only possible using invasive depth electrode placement to date.
Figure 3. Non-invasive recordings of the mid-Pontine Nuclei during leftward saccades in humans, over three conditions. PGO wave like activity clearly evident in hemisphere ipsilateral to saccade direction.
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Ponto-Geniculo-Occipital PGO waves are biphasic field potentials identified in a range of mammalian species that are ubiquitous with sleep, but can also be identified in waking perception and eye movement. Their role in REM sleep and visual perception more broadly may constitute a promising avenue for further research, however what was once an active field of study has recently fallen into stasis. With the reality that invasive recordings performed on animals cannot be replicated in humans; while animals themselves cannot convey experience to the extent required to elucidate how PGO waves factor into awareness and behavior, innovative solutions are required if significant research outcomes are to ever be realized. Advances in non-invasive imaging technologies and sophistication in imaging methods now offer substantial scope to renew the study of the electrophysiological substrates of waking and dreaming perception. Among these, Magnetoencephalogram MEG stands out through its capacity to measure deep brain activations with high temporal resolution. With the current trend in sleep and dream research to produce translational findings of psychopathological and medical significance, in addition to the clear links that PGO wave generation sites share, pharmacologically, with receptors involved in expression of mental illness; there is a strong case to support scientific research into PGO waves and develop a functional understanding of their broader role in human perception. Ponto-Geniculo-Occipital PGO waves are distinctive wave forms that are typically identified as propagating activity between three key brain regions, being the Pons, Lateral Geniculate Nucleus and Occipital Cortex. They have been confirmed and studied extensively in cats, rats and primates but never in humans, as the ethical implications for performing invasive recordings at three concurrent brain locations has not made such research justifiable or indeed practical. Rare occasions where neurosurgical medical procedures have been performed around these key regions have indeed opened the prospective window for simultaneous invasive recording for scientific purposes, however to date this has only confirmed the Pontine elements of the phenomenon and as such, it can only be conservatively said that humans exhibit P waves Lim et al. PGO waves were initially observed in in anesthetized cats McGaugh, , and have since been comprehensively studied in this species, to a lesser extent in rats Kaufman and Morrison, , and in non-human primates such as Macaques and Baboons Cohen and Feldman, ; Vuillon-Cacciuttolo and Seri,
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Tungsten carbide chemical formula : WC is a chemical compound specifically, a carbide containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into shapes through a process called sintering for use in industrial machinery , cutting tools , abrasives , armor-piercing rounds , other tools and instruments, and jewelry. Tungsten carbide is approximately twice as stiff as steel , with a Young's modulus of approximately — GPa 77, to , ksi ,     and is double the density of steel —nearly midway between that of lead and gold. Historically referred to as Wolfram, Wolf Rahm , wolframite ore discovered by Peter Woulfe was then later carburized and cemented with a binder creating a composite now called "tungsten carbide".SEE VIDEO BY TOPIC: An introduction to cufflinks, buttons and studs
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David Staples: Cure for slippery winter sidewalks? Retractable spikes on boots
Sometimes called gravel crews. Scrutineers FIA-sanctioned technical officials who check the legality of WRC cars before, during and after each event. Gear selections are typically made by a steering wheel-mounted paddle rather than the traditional 'H' gate manual system typically found on production cars. Service There are usually three service periods during a WRC day — 15 minutes in the morning, 30 minutes at lunchtime and 45 minutes in the evening. Teams can perform repairs or modifications to cars during these periods, and select their tyre choice for the following loop of stages. Set-up The choice of tyres and suspension adjustments to give a WRC car maximum performance. Competitors must drive through the shakedown stage at least three times, with all passes timed. Stage Time The time recorded from the standing start of a stage to the flying finish.
Compare the most helpful customer reviews of the best rated products in our Sewing Snaps store. These products are shortlisted based on the overall star rating and the number of customer reviews received by each product in the store, and are refreshed regularly. Skip to main content Best Rated in Sewing Snaps. Best Rated by Department.
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