Different Levels Of Vigilance Research Articles

Muscle atonia index during multiple sleep latency test: A possible marker to differentiate narcolepsy from other hypersomnias

ObjectiveThe complexity and delay of the diagnosis of narcolepsy require several diagnostic tests and invasive procedures such as lumbar puncture. Our study aimed to determine the changes in muscle tone (atonia index, AI) at different levels of vigilance during the entire multiple sleep latency test (MSLT) and each nap in people with narcolepsy type 1 (NT1) and 2 (NT2) compared with other hypersomnias and its potential diagnostic value. MethodsTwenty-nine patients with NT1 (11 M 18F, mean age 34.9 years, SD 16.8) and sixteen with NT2 (10 M 6F, mean age 39 years, SD 11.8) and 20 controls with other hypersomnias (10 M, 10F mean age 45.1 years, SD 15.1) were recruited. AI was evaluated at different levels of vigilance (Wake and REM sleep) in each nap and throughout the MSLT of each group. The validity of AI in identifying patients with narcolepsy (NT1 and NT2) was analyzed using receiver operating characteristic (ROC) curves. ResultsAI during wakefulness (WAI) was significantly higher in the narcolepsy groups (NT1 and NT2 p < 0.001) compared to the hypersomniac group. AI during REM sleep (RAI) (p = 0.03) and WAI in nap with sudden onsets of REM sleep periods (SOREMP) (p = 0.001) were lower in NT1 than in NT2. The ROC curves showed high AUC values for WAI (NT1 0.88; Best Cut-off > 0.57, Sensitivity 79.3 % Specificity 90 %; NT2 0.89 Best Cut-off > 0.67 Sensitivity 87.5 % Specificity 95 %; NT1 and NT2 0.88 Best Cut-off > 0.57 Sensitivity 82.2 % Specificity 90 %) in discriminating subjects suffering from other hypersomnias. RAI and WAI in nap with SOREMP showed a poor AUC value (RAI AUC: 0.7 Best cutoff 0.7 Sensitivity 50 % Specificity 87.5 %; WAI in nap before SOREMP AUC: 0.66, Best cut-off < 0.82 sensitivity 61.9 % and specificity 67.35 %) differentiating NT1 and NT2. ConclusionsWAI may represent an encouraging electrophysiological marker of narcolepsy and suggests a vulnerable tendency to dissociative wake / sleep dysregulation lacking in other forms of hypersomnia. SignificanceAI during wakefulness may help distinguish between narcolepsy and other hypersomnias.

Contribution of obstructive sleep apnea to disrupted sleep in a large clinical cohort of patients with suspected obstructive sleep apnea.

The response of sleep depth to CPAP in patients with OSA is unpredictable. The odds-ratio-product (ORP) is a continuous index of sleep depth and wake propensity that distinguishes different sleep depths within sleep stages, and different levels of vigilance during stage wake. When expressed as fractions of time spent in different ORP deciles, nine distinctive patterns are found. Only three of these are associated with OSA. We sought to determine whether sleep depth improves on CPAP exclusively in patients with these three ORP patterns. ORP was measured during the diagnostic and therapeutic components of 576 split-night polysomnographic (PSG) studies. ORP architecture in the diagnostic section was classified into one of the nine possible ORP patterns and the changes in sleep architecture were determined on CPAP for each of these patterns. ORP architecture was similarly determined in the first half of 760 full-night diagnostic PSG studies and the changes in the second half were measured to control for differences in sleep architecture between the early and late portions of sleep time in the absence of CPAP. Frequency of the three ORP patterns increased progressively with the apnea-hypopnea index. Sleep depth improved significantly on CPAP only in the three ORP patterns associated with OSA. Changes in CPAP in the other six patterns, or in full diagnostic PSG studies, were insignificant or paradoxical. ORP architecture types can identify patients in whom OSA adversely affects sleep and whose sleep is expected to improve on CPAP therapy.

Dynamics in the biparametric spaces of a three-species food chain model with vigilance

In nature, vigilance is a common anti-predator strategy prey individuals employ to protect themselves from a possible attack. It gives them sufficient time to take cover or flee. Yet this seemingly profitable strategy, which lowers the number of successful predatory attacks, has a significant impact on the prey's growth rate. Researchers attribute this to reduced foraging time. In this article, we study a three-species food chain model in which both the basal prey and middle predator show active vigilance against their respective predators. Apart from the positivity, boundedness, and local stability analysis of the equilibrium points of the model, we find the conditions for global stability and the occurrence of Hopf bifurcation around the coexisting equilibrium point. Bifurcation diagrams and their corresponding Lyapunov exponent diagrams (largest and second-largest) illustrate diverse dynamical scenarios ranging from stable coexistence to periodic to chaotic oscillations. The isospike diagrams and their associated largest Lyapunov exponent diagrams in the biparametric space of basal prey's and middle predator's vigilance reveal a broader picture of the effects of different levels of vigilance on the dynamics of the system. A great deal of attention has been paid to unwrapping the complex structural beauties like shrimp-shaped periodic structures inside the chaotic sea and multistability between several sets of attractors in the overlapping zones of periodic windows. We observe that multiple coexisting attractors possess fractal basin boundaries. We also explore the dynamics of the system in two other biparametric spaces. The density variation maps at the end show the effect of vigilance on the equilibrium density of all three species. Our results suggest that vigilance promotes regularity and coexistence, but too high levels of vigilance can cause species extinction. For better visualization of the system dynamics, we provide a few high-resolution animations of the phase portraits and the basins of attraction in the supplementary material.

Resisting Sleep Pressure: Impact on Resting State Functional Network Connectivity.

In today's 24/7 society, sleep restriction is a common phenomenon which leads to increased levels of sleep pressure in daily life. However, the magnitude and extent of impairment of brain functioning due to increased sleep pressure is still not completely understood. Resting state network (RSN) analyses have become increasingly popular because they allow us to investigate brain activity patterns in the absence of a specific task and to identify changes under different levels of vigilance (e.g. due to increased sleep pressure). RSNs are commonly derived from BOLD fMRI signals but studies progressively also employ cerebral blood flow (CBF) signals. To investigate the impact of sleep pressure on RSNs, we examined RSNs of participants under high (19h awake) and normal (10h awake) sleep pressure with three imaging modalities (arterial spin labeling, BOLD, pseudo BOLD) while providing confirmation of vigilance states in most conditions. We demonstrated that CBF and pseudo BOLD signals (measured with arterial spin labeling) are suited to derive independent component analysis based RSNs. The spatial map differences of these RSNs were rather small, suggesting a strong biological substrate underlying these networks. Interestingly, increased sleep pressure, namely longer time awake, specifically changed the functional network connectivity (FNC) between RSNs. In summary, all FNCs of the default mode network with any other network or component showed increasing effects as a function of increased 'time awake'. All other FNCs became more anti-correlated with increased 'time awake'. The sensorimotor networks were the only ones who showed a within network change of FNC, namely decreased connectivity as function of 'time awake'. These specific changes of FNC could reflect both compensatory mechanisms aiming to fight sleep as well as a first reduction of consciousness while becoming drowsy. We think that the specific changes observed in functional network connectivity could imply an impairment of information transfer between the affected RSNs.

Among-individual variation in vigilance at the nest in colonial Cliff Swallows

Enhanced vigilance against predation is often an advantage of living in groups, but most studies have not examined individual-specific variation in the propensity to be vigilant among the animals within a group. We studied vigilance at the nest in colonially nesting Cliff Swallows (Petrochelidon pyrrhonota) in southwestern Nebraska in 2011 and 2012, and asked whether differences among individuals were consistent over time, whether vigilance varied among different colonies, and whether there were positive or negative fitness consequences of different levels of vigilance. We found significant among-individual variation in extent of vigilance and some variation among different colony sites. Vigilance also varied with date and nesting stage, but other phenotypic characteristics of a bird had no effect on vigilance. Differences among individuals in vigilance were not strongly related to their reproductive success that season, but more vigilant individuals were more likely to attempt intrusions into their neighbors' nests. Vigilance at the nest may be partly directed at monitoring conspecifics' activities in neighboring nests. This study is among the few that have investigated individual variation in vigilance behavior, a possible index of personality for Cliff Swallows, and the first to measure variation in vigilance for a colonial bird while breeding.

Effects of Habitat Degradation on Sleeping Site Choice and Use in Sahamalaza Sportive Lemurs (Lepilemur sahamalazensis)

Sleeping sites may be beneficial for animals in terms of thermoregulation, proximity to foraging sites, and protection from predators and infectious diseases. The abundance of adequate sleeping sites is thus essential for the survival of primates. We investigated microhabitats around sleeping sites, and the influence of habitat degradation on sleeping site choice and usage, in the nocturnal Sahamalaza sportive lemur, Lepilemur sahamalazensis. We used quarter point sampling (N = 315) to describe five forest fragments and 57 sleeping sites and continuous focal animal sampling (N = 45) to determine the diurnal activity budget, to determine whether individuals inhabiting different fragments or sleeping site types showed different levels of vigilance. Our results suggest that tall trees with large crowns, a high density of small trees, and dense canopy are particularly important for sleeping site choice. Microhabitat structure around sleeping sites did not differ between forest fragments or sleeping site types. Diameter at breast height, crown diameter, canopy cover, and bole height were similar for all sleeping trees, as were the number of lianas in trees with tree-tangle sleeping sites, and the volume of tree holes. Tree holes used as sleeping sites were most often found in dead trees of Bridelia pervilleana (50–62.5 %), whereas tree tangle sites were most often located in Sorindeia madagascariensis (20–62.5 %). Lemurs were active 5–14 % of the daytime, although they never left their sleeping sites or fed. Individuals occupying tree holes had higher levels of activity than those in tree tangles, and those in more degraded fragments were more active. Our results suggest that Sahamalaza sportive lemurs choose their sleeping sites according to specific habitat characteristics, and that factors associated with old and intact forest are likely to be crucial for their survival.

On the road to invariant recognition: Explaining tradeoff and morph properties of cells in inferotemporal cortex using multiple-scale task-sensitive attentive learning

Visual object recognition is an essential accomplishment of advanced brains. Object recognition needs to be tolerant, or invariant, with respect to changes in object position, size, and view. In monkeys and humans, a key area for recognition is the anterior inferotemporal cortex (ITa). Recent neurophysiological data show that ITa cells with high object selectivity often have low position tolerance. We propose a neural model whose cells learn to simulate this tradeoff, as well as ITa responses to image morphs, while explaining how invariant recognition properties may arise in stages due to processes across multiple cortical areas. These processes include the cortical magnification factor, multiple receptive field sizes, and top-down attentive matching and learning properties that may be tuned by task requirements to attend to either concrete or abstract visual features with different levels of vigilance. The model predicts that data from the tradeoff and image morph tasks emerge from different levels of vigilance in the animals performing them. This result illustrates how different vigilance requirements of a task may change the course of category learning, notably the critical features that are attended and incorporated into learned category prototypes. The model outlines a path for developing an animal model of how defective vigilance control can lead to symptoms of various mental disorders, such as autism and amnesia.

Level of vigilance influences licking frequency in rats

In rats, the basic licking rhythm is generated by the central pattern generator located in the brainstem. Nevertheless, the licking frequency can be regulated between about 7.5 and 4 Hz by changing the drinking conditions. If these conditions are kept constant, the licking frequency can be influenced only to a minor degree by factors such as deprivation level, type of solution, and phase of the session. The aim of our study was to compare the licking frequency of rats at different levels of vigilance. We investigated spontaneous licking of rats by an electrical lick sensor; parallel behavior monitoring was also performed. Animals kept in a stable environment and showing a lower level of vigilance licked at a rate of 5.96 Hz, fully vigilant rats licked significantly more rapidly at a frequency 6.57 Hz. The fastest rate of licking (6.49 Hz and 6.82 Hz, respectively) was encountered in alert rats under a mild stress caused by the presence of a second animal in the experimental box. The vigilance level is thus another factor affecting the licking rate of rats that should be taken into account in behavioral licking experiments.

Artifact detection and signal reconstruction in the pupillogram

Just as the EEG reflects different wake and sleep stages, changes in pupil dynamics reflecting different levels of vigilance are also to be found. The literature contains numerous reports on experimental set-ups for the recording of the pupillogram. Interesting methods of signal processing are to be found in [7] and [5]. Currently, such recordings are being used to check the success of sleep therapy. A problem that still needs solving is the optimal handling of artifacts caused by blinking. The present article proposes a procedure for artifact detection by back-propagation networks, and subsequent reconstruction of the signal by an AR model. Estimation of the signal is first demonstrated by a test signal, and then by a corrupted pupillogram.

Synchronized activities of coupled oscillators in the cerebral cortex and thalamus at different levels of vigilance.

The cerebral cortex and thalamus constitute a unified oscillatory machine displaying different spontaneous rhythms that are dependent on the behavioral state of vigilance. In vivo multi-site recordings from a variety of neocortical areas and related thalamic nuclei in cat, including dual simultaneous intracellular recordings, demonstrate that corticofugal volleys are effective in synchronizing fast (20-50 Hz) and low-frequency (< 15 Hz) oscillations in thalamocortical networks, characterizing activated and de-afferented states. (i) Fast spontaneous oscillations depend on the depolarization of thalamic and cortical cells and appear in a sustained manner during waking and REM sleep. Corticothalamic neurons, discharging high-frequency (400 Hz) spike-bursts at 30-40 Hz, are good candidates to synchronize fast oscillations in reentrant thalamocortical loops. Weakly synchronized, fast spontaneous oscillations may be reset and become robustly coherent after relevant sensory stimuli in waking or internal signals during the dreaming state. (ii) During quiescent sleep, the long-range synchronization of brain electrical activity results from synchronous hyperpolarizations in forebrain neurons. The corticothalamic inputs during the depolarizing component of the slow oscillation (< 1 Hz) are effective in grouping the thalamic-generated sleep rhythms (spindles at 7-14 Hz and delta at 1-4 Hz) into complex wave-sequences. These inputs also control the shape of spindles, and favor the long-range synchronization and nearly simultaneous appearance of spindles. (iii) The cortical control of thalamic activity is also demonstrated in spike-wave-seizures developing from sleep patterns. More than half of thalamocortical neurons are silent during spike-wave seizures, being tonically hyperpolarized, and display IPSPs (closely related to the paroxysmal depolarizing shifts of cortical cells) that are determined by the pattern of activities in thalamic reticular cells. All these data congruently show the power of cortical control upon thalamic oscillators.

24-h variation of vigilance in the cockroach Blaberus giganteus.

Our objective was to investigate whether sleep-like states occur in the cockroach, Blaberus giganteus by applying the methods formerly used for another cockroach species, Leucophaea maderae and the scorpions, Heterometrus and Pandinus. The behaviour of isolated animals (n = 10) kept under LD 12:12 h was recorded by time-lapse video for three consecutive 24-h periods. Nine behavioural states were scored for 1-min real-time epochs. Rest was subdivided into 4 sub-states on the basis of body posture and the position of the antennae. The cockroaches showed a nocturnal behaviour exhibiting a bout of locomotion at dark onset which lasted several hours, and a preference for rest in the light period. Immobility with both the body and the antennae touching the substrate (state 1) was the predominating state in the light period. In order to establish whether the sub-states of rest represented different levels of vigilance the arousal threshold was measured by determining the latency of a behavioural response to a vibration stimulus. The levels of arousal differed significantly in four behavioural states in the light period but not in the dark period. In state 1 the animals exhibited the lowest arousal whereas in the activity states arousal was the highest. The state with the highest arousal threshold occurred in the beginning of the light period. Thereafter, arousal progressively increased and remained relatively high during the dark period. The effect of 6-h deprivation of rest by the gentle shaking of the cages whenever the animals were immobile, resulted in a reduced latency to state 1, a small increase of state 1 and a more prominent initial increase of activity during recovery. In conclusion, this study provides evidence for the existence of a 24-h variation of vigilance in the cockroach. It further indicates that a 'rest deficit' gives rise to a compensatory response. The data support the notion that sleep-like states are present in these insects.

On-going EEG in depression: A topographic spectral analytical pilot study

Spontaneous EEG activities recorded with 19 electrodes (10–20 system) on the scalp were quantified by spectral analytical methods (power and coherence spectra) to reveal changes of power and coherence during different conditions (eyes closed/relaxed, eyes opened/relaxed, flicker stimulation, reading, listening to a story). Control subjects and depressive patients were compared. Power as well as coherence changes were found in all frequency bands. Changes in the organization of the EEG were found in different areas of both hemispheres. The EEG organization was different in control subjects and depressive patients, indicating different levels of vigilance and/or different cognitive strategies in verbal tasks in the two groups.

Vigilanz - ihre Bestimmung im EEG

The definition of vigilance was based primarily on criteria of overt behaviour and concomitant electrographic patterns of functional states as well as on psychometrically tested performance. It turned out that the combination of well defined electroencephalographic activity patterns is an utile and reliable measure for the classification of different vigilance levels, even when there is no experimental testing of performance possible or the observation of behaviour misleading. We know today defined mixtures of characteristic regional EEG activities for the estimation on different levels of vigilance between supervigilance and subvigilance. There are however also deviations from regularly observed combinations of signs with dissociations between behaviour, performance and EEG-activity patterns. For the theory of vigilance one can use the analyses of topological and chronological organization of EEG-activities as starting point. Not only characteristic frequency mixtures are correlated with given vigilance levels; moreover the diffusion of regional activities interfering with all other regional activities builds up the socalled "vigilance profile". This profile varies with time slowly or quickly. The regular topological process distribution of activities is commonly the expression of a dominating mental process interfering with other submental processes. The chronological variations of vigilance profiles show their dynamism with transitions from fixed, strictly bound interest or "concentration" on selected objects to freely fluctuating interest, rapidly jumping from object to the other.

Computer simulated discharges of thalamic ventrobasal neurones during sleep and wakefulness.

A theoretical model is described which in response to combinations of poissonian pulse trains with different mean frequencies on three independent incoming lines, generated output signals simulating spontaneous discharges of thalamic ventrobasal (VB) neurones during sleep and wakefulness. Some dynamic neuronal properties as refractoriness, facilitation, short term memory were simulated and characteristics of response to single pulses on different lines properly selected to reproduce those exhibited by VB neurones upon artificial stimulation of thalamic afferent systems. The data obtained from the model are briefly discussed in relation to possible contributions of specific and nonspecific afferent systems in producing spontaneous VB discharges characteristic of different levels of vigilance.

Epileptic electroencephalographic activity induced by cobalt foci in the dorsal hippocampus and-or thalamus.

The paper analyses the EEG pattern, distribution over the brain and incidence of epileptic episodes of spike and waves or spikes (ESWC/S) induced in rats (with chronic electrodes in the cortex and hippocampus bilaterally and in the mesencephalic reticular formation) by implanting cobalt-gelatine into the dorsal hippocampus and/or thalamus unilaterally.A quantitative analysis of the incidence of ESWC/S-s at different levels of vigilance proves that the ESWC/S-s are related mainly to relaxed wakefulness and somnolence. No relationship between the parameters of the ESWC/S and the localization of the cobalt focus in the hippocampus and/or thalamus could be found.