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Magnetoencephalography
Published in Andrei I. Holodny, Functional Neuroimaging, 2019
Timothy P.L. Roberts, Christopher Edgar, Erin Simon Schwartz
In many MEG clinics, EEG is collected simultaneously with MEG. EEG-compatible electrodes are placed on the scalp in either standard 10–20 montages or in higher- density 64- or 128-channel arrangements. Several manufactures make MEG-compatible EEG systems. Aside from the EEG sensors being compatible with MEG, MEG-compatible high-density EEG systems use thin adaptors to hold the electrodes, allowing placement of the MEG sensors as close to the head as possible. Picton et al. (20) provide EEG data collection and analysis guidelines. In most cases, the Picton et al. (20) guidelines apply also to MEG data collection and analysis procedures. If simultaneous EEG is not desired, it is still recommended that the electrooculogram (EOG) and electrocardiogram (ECG) be obtained for easy identification of eyeblink and heartbeat activity.
Nathaniel Kleitman (1895–1999)
Published in Andrew P. Wickens, Key Thinkers in Neuroscience, 2018
At the time of Aserinsky’s arrival, Kleitman had become interested in the possibility that blinking was an indicator of tiredness and sleep onset. Thus, he suggested to Aserinsky that this subject might be an interesting one to examine in infants. Although this would lead to months of tedious observation, it did show something more interesting: sleeping babies had roughly 20-minute periods each hour without eyelid movements. It was a simple observation but sufficient for Kleitman to suggest that Aserinsky enrol for a PhD despite having no suitable academic qualifications. Aserinsky recounts that the doctoral committee at Chicago was nonplussed at Kleitman’s act of faith, as it was essentially allowing him to jump from high school to a PhD degree! Nonetheless, Aserinsky became a PhD student and began to examine whether adults had the same 20-minute sleep episodes as those in infants. He also decided to measure eye lid movements using the electrooculogram (a machine that records the difference in electrical charge between the front and back of the eyes) and brain waves from the scalp with the electroencephalogram (EEG).
Minimal Recording Parameters and Extended Montage
Published in Ravi Gupta, S. R. Pandi Perumal, Ahmed S. BaHammam, Clinical Atlas of Polysomnography, 2018
Ravi Gupta, S. R. Pandi Perumal, Ahmed S. BaHammam
Some evidence suggests that a single EEG channel, that is, placement of central electrodes helps in optimal scoring of sleep stages, still the placement of three channels (along with three back-up channels) is considered gold standard.Electrooculogram (EOG): An EOG that records the movement of the eyeball is also recorded from both eyes. Having the data from both eyes not only prevents the data loss in case of fall-off of lead but also clearly delineates the eye-movement. For the reasons discussed in Chapter 3 (section on EOG), true eye movement is always in the opposite phase, that is, if one channel deflects towards the negative side, the other deflects towards the positive side (Figure 9.8). Since these channels are placed close to the frontal area, sometimes, delta waves may be spilled in these channels, giving the impression of eye movement (Figure 9.9). Eye movements, along with EEG, help in scoring wakefulness, quiet wakefulness, and REM sleep.Electromyogram (EMG):Muscle tone: An EMG is required to score the sleep stage as well as the abnormal movements during sleep. During wakefulness, muscles have a basal tone that reduces as well fall asleep . REM sleep is characterized by profound atonia, however, in patients with REM sleep behavior disorder, this atonia is not seen. Submentalis muscle has been chosen because it is a skeletal muscle, lies just beneath the skin, thus, provides good signals, and normally remains inactive during sleep, in contrast to other skeletal muscles that may get activated episodically during sleep. To prevent data loss, signals are recorded from sub-mentalis/mentalis muscles of both sides. Along with EEG, these signals help in recognizing REM sleep stage and REM sleep without atonia.Limb movements: To record the periodic limb movement during sleep (PLMS), signals are recorded from anterior tibialis muscles of both legs. To minimize data loss, signals are recorded from both legs separately (Figure 9.10). In addition, signals from both sides should not be combined as it may reduce the detectable numbers of limb movements. These signals, along with the EEG, help in scoring PLMS-associated arousals. In addition, these signals also help in scoring “alternate leg muscle activity” (ALMA), Hypnogogic foot tremors (HFT), and excessive fragmentary myoclonus (EFM).Respiratory Flow: Respiratory flow is an important signal to score apnea and hypopnea. It is measured using a thermistor and a pressure transducer (Figure 9.11). As discussed in Chapter 3, the thermistor is important for the diagnosis of apnea while a pressure transducer helps in recognizing hypopnea, Cheyne-Stokes breathing, and periodic breathing.
Macula-predominant retinopathy associated with biallelic variants in RDH12
Published in Ophthalmic Genetics, 2020
Rola Ba-Abbad, Gavin Arno, Anthony G. Robson, Konstantinos Bouras, Michalis Georgiou, Genevieve Wright, Andrew R. Webster, Michel Michaelides
An eight-year-old asymptomatic boy was referred with bilateral macular changes noted during routine ocular screening. The child was otherwise fit and well and the family history was non-contributory. Visual acuity at the time of referral was 6/9 bilaterally. At the age of 10 years, the VA was 6/36 in both eyes without a significant refractive error. He was able to identify only 2 of the 17 Ishihara color vision plates with the right eye, and 4 of 17 with the left. Clinical examination showed clear ocular media, and both fundi had outer retinal changes in the perifoveal region, but the foveal reflex appeared intact. The optic discs and retinal vasculature had a normal appearance. Fundus AF showed unusual cloverleaf-shaped hypoautofluorescent areas with a border of increased AF, and relative preservation of the fovea (Figure 1B). OCT identified attenuation of the ellipsoid zone (EZ) nasal to the fovea, with a sharp decline of the outer nuclear layer thickness, and preservation of the foveal EZ with a prominent band representing the external limiting membrane. The outer retinal bands temporal to the fovea appeared severely attenuated, with preservation of inner retinal lamination. There was no ERG evidence of generalized (peripheral) retinal dysfunction but PERG P50 reduction indicated macular dysfunction bilaterally (Supplementary Figure S1). A normal electrooculogram (EOG) excluded generalized RPE dysfunction.
Investigating the role of BEST1 and PRPH2 variants in the molecular aetiology of adult-onset vitelliform macular dystrophies
Published in Ophthalmic Genetics, 2020
Cemal Çavdarli, Büşranur Çavdarlı, Mehmet Numan Alp
The age of onset for AVMD is variable and patients may remain asymptomatic throughout their lifetime. Despite a relatively benign prognosis, patients mainly complain of metamorphopsia and decreased vision (4,5). The yellow to gray vitelliform lesions of AVMD, which can be observed by funduscopy, can gradually increase and/or decrease over time. In the majority of cases, these lesions have a dome-shaped hyperreflective heterogeneous appearance and subretinal accumulation on macular optical coherence tomography (OCT) scans. They affect both neuro-retinal and RPE cells, and have a hyper-autofluorescence on fundus autofluorescence (FAF) images. Despite the variability of the electrophysiological electroretinogram and/or electrooculogram (EOG) results, these are generally reported as normal in clinical AVMD practice (6).
A pilot study on salivary cortisol secretion and auditory P300 event-related potential in patients with physical disability-related stress
Published in International Journal of Neuroscience, 2020
Vorasith Siripornpanich, Sunisa Rachiwong, Amornpan Ajjimaporn
Participants were asked to avoid any substances which could influence cognitive performance, such as CNS-acting drugs, caffeine, and alcohol beverage, the day prior to the ERP recording. In addition, they were advised to wash their hair without using hair spray or oil. Standard electroencephalogram (EEG) protocols were followed. Ag/AgCl disk electrodes were fixed with electrode gel. The impedance was kept below 5 kΩ at all sites. All electrodes were referenced to the average value calculated from both earlobe electrodes (A1 + A2/2). ERP was recorded using Stim2 Neuroscan Software (Neurosoft, Inc.). The P300 component was elicited with a simple discrimination task known as the auditory ‘oddball’ paradigm. In order to reject artifacts from the eye, the electrooculogram (EOG) recorded from four electrodes placed at both orbits was used to discriminate eye blink and eye movement artifacts from EEG signal. During data analysis, the EEG data were cut into 1000 ms length epoch, from −200 ms pre-stimulus to 800 ms post-stimulus. The artifact rejection was set at +80 microvolts. The bandpass filter was set from 0.3 to 30 Hz. Then, all epochs were averaged in the time domain.