A modern neurobiological concept of vigilance

EEG based cognitive task classification using multifractal detrended fluctuation analysis

Locating cognitive task states by measuring changes in electrocortical activity due to various attentional and sensory-motor changes, has been in research interest since last few decades. In this paper, different cognitive states while performing various attentional and visuo-motor coordination tasks, are classified using electroencephalogram (EEG) signal. A non-linear time-series method, multifractal detrended fluctuation analysis (MFDFA) , is applied on respective EEG signal for features. Using MFDFA based features a multinomial classification is achieved. Nine channel EEG signal was recorded for 38 young volunteers (age: 25 ± 5 years, 30 male and 8 female), during six consecutive tasks. First three tasks are related to increasing levels of selective focus vision; next three are reflex and response based computer tasks. Total of 90 features (ten features from each of nine channel) were extracted from Hurst and singularity exponents of MFDFA on EEG signals. After feature selection, a multinomial classifier of six classes using two methods: support vector machine (SVM) and decision tree classifier (DTC). An accuracy of 96.84% using SVM and 92.49% using DTC was achieved.

Social Context Influences Resting Physiology in Dogs

Domestication has affected the social life of dogs. They seem to be less dependent on their pack members than wolves, potentially causing dogs to be more alert towards their environment, especially when resting. Such a response has been found in dogs resting alone compared to wolves in the same situation. However, as this may be influenced by social context, we compared alertness (i.e., degree of activation along the sleep-wake continuum-measured via cardiac parameters) of pack-living and enclosure-kept dogs in two conditions: (1) alone, and (2) with pack members, and in two states of activation: (1) inactive wakefulness, and (2) resting. We found that when dogs were resting alone, alertness was higher than when resting in the pack; individual alertness was potentially influenced by social rank. However, alertness was similar in the two conditions during inactive wakefulness. Thus, depending on social context, familiar conspecifics may still provide support in dogs; i.e., domestication has probably only partly shifted the social orientation of dogs from conspecifics to humans. We suggest that cardiac responses of dogs may be more flexible than those of wolves because of their adaptation to the more variable presence of humans and conspecifics in their environment.

Does socio-ecology drive differences in alertness between wolves and dogs when resting?

Variation in resting behaviour across animals may be driven by adaptations towards their environment. Wolves and dogs seem promising models to examine this idea as they share a common ancestor, but occupy different socio-ecological niches. While wolves generally avoid humans, hunt, defend their territory, and raise offspring cooperatively, most dogs live in human-shaped environments. Hence, we hypothesized wolves to be more alert towards their environment than dogs, i.e. the degree of activation along the sleep-wake continuum (alertness) should be greater in wolves than in dogs. We estimated alertness via cardiac output. We tested similarly raised and kept pack-living wolves and dogs in two different behavioural conditions: (1) inactive wakefulness: animal is lying, head in an upward position with eyes opened, (2) resting: animal is lying, head in downward position with eyes mainly closed. In contrast to our expectations, we found that in both conditions wolves had a lower heart rate and higher heart rate variability than dogs, i.e. wolves might be less alert/more relaxed than dogs. Although our results are preliminary, we suggest that the higher alertness of dogs compared to wolves is potentially driven by differences in their socio-ecology (i.e. domestication) causing greater attention of dogs to human behaviour.

Psychiatric symptoms of noradrenergic dysfunction: a pathophysiological view

What psychiatric symptoms are caused by central noradrenergic dysfunction? The hypothesis considered in this review is that noradrenergic dysfunction causes the abnormalities in arousal level observed in functional psychoses. In this review, the psychiatric symptoms of noradrenergic dysfunction were inferred pathophysiologically from the neuroscience literature. This inference was examined based on the literature on the biology of psychiatric disorders and psychotropics. Additionally, hypotheses were generated as to the cause of the noradrenergic dysfunction. The central noradrenaline system, like the peripheral system, mediates the alarm reaction during stress. Overactivity of the system increases the arousal level and amplifies the emotional reaction to stress, which could manifest as a cluster of symptoms, such as insomnia, anxiety, irritability, emotional instability and exaggerated fear or aggressiveness (hyperarousal symptoms). Underactivity of the system lowers the arousal level and attenuates the alarm reaction, which could result in hypersomnia and insensitivity to stress (hypoarousal symptoms). Clinical data support the hypothesis that, in functional psychoses, the noradrenergic dysfunction is in fact associated with the arousal symptoms described above. The anti-noradrenergic action of anxiolytics and antipsychotics can explain their sedative effects on the hyperarousal symptoms of these disorders. The results of animal experiments suggest that excessive stress can be a cause of long-term noradrenergic dysfunction.

Commentary from the Italian Association of Sleep Medicine on the AASM manual for the scoring of sleep and associated events: for debate and discussion

In 2007, the American Academy of Sleep Medicine (AASM) completed a new manual for the scoring of sleep and associated events. The AASM manual is divided into separate sections relative to the parameters reported for polysomnography. The present commentary, accomplished by a Task Force of the Italian Association of Sleep Medicine, focuses on sleep scoring data, arousal rules, movement and respiratory events. Comparisons with the previous Rechtschaffen and Kales system are detailed and a number of methodological weaknesses are pointed out. Major comments address the 30-s scoring epochs, the restrictive approach to arousals and EEG activating patterns, the incomplete quantification of motor events and the thresholds for the definition of hypopnea. Since the new AASM manual is an iterative process, proposals for discussion and re-examination of the agreed criteria with other national and international organizations are encouraged.

Definition of and mechanism for opioid-induced sedation

Although sedation is acknowledged to be one of the most common side effects of opioid analgesics, the mechanisms and characteristics of this phenomenon remain elusive, and research in this area is extremely limited. This report integrates research findings on the mechanism of action of opioids with research findings on the phenomenon of consciousness to develop a model of how opioids may act in the central nervous system to produce sedation. Based on this integration, a definition of opioid-induced sedation is proposed to encourage dialogue and research on this perplexing and clinically significant phenomenon.

Effects of methylenechloride-soluble fraction of Japanese angelica root extract, ligustilide and butylidenephthalide, on pentobarbital sleep in group-housed and socially isolated mice

We previously showed that the extract of Japanese angelica root (JAR-E) reversed the decrease in pentobarbital (PB) sleep induced by isolation stress and yohimbine and methoxamine, stimulants of central noradrenergic systems, in mice. Here, we tested the effects of several fractions from JAR-E and ligustilide and butylidenephthalide, phthalide components of JAR-E, on PB sleep in isolated mice to elucidate the mechanism of the action of JAR-E. Methanol-soluble (Met-S) and -insoluble (Met-IS) fractions were obtained from JAR-E. Methylenechloride-soluble (MC-S) and -insoluble fractions (MC-IS) were prepared from Met-S. MC-S (11.4-76 mg/kg, p.o.) reversed the isolation stress-induced decrease in PB sleep, but neither Met-IS (0.8-2.4 g/kg, p.o.) nor MC-IS (0.7-2 g/kg, p.o.) had the same effect. The i.p. administration of MC-S exhibited a similar activity to that observed after the p.o. administration of the same fraction. Ligustilide (5-20 mg/kg, i.p.) and butylidenephthalide (10-30 mg/kg, i.p.) reversed PB sleep decrease in isolated mice. Both components (20 mg/kg, i.p.) attenuated the suppressive effects of yohimbine (30 nmol, i.c.v.), methoxamine (200 nmol, i.c.v.) and a benzodiazepine inverse agonist FG7142 (10 mg/kg, i.p.) on PB sleep in group-housed mice. These results suggest the contribution of ligustilide and butylidenephthalide to the effect of JAR-E on PB sleep in isolated mice, and implicate central noradrenergic and/or GABA(A) systems in the effects of these components.

Frequency of the 22 kHz call of rats is modulated by the rhythm of the heart rate

The 22 kHz calls of rats are rhythmically frequency modulated. To test whether these modulations are correlated with the action of the heart, ECG was chronically registered in 16 male Wistar rats. In 11 rats loud acoustic stimuli provoked emission of the long calls or 22 kHz calls. In 10 self-vocalizing rats, we observed small frequency modulations (SFMs) in the constant frequency component of these calls. On the average, 7 ms after the R-peak of the ECG the call frequency is lowered by 151 Hz. The heart rate and the rate of the SFMs are highly correlated (r = 0.997). Further, we show that the SFMs are produced by a reduction of call amplitude. The comparison with the course of the blood pressure in rats suggests that this change in call amplitude is caused by the blood pressure change during the action of the heart. Measuring SFMs offers a noninvasive way to determine the heart rate in vocalizing rats.

Functional influence of the central noradrenergic system on the skin conductance activity in rats

Pharmacological studies on neuroleptics and amphetamine strongly suggest that some dysfunction of the central catecholamine system may play a key role in the pathogenesis of schizophrenia. Our previous studies have demonstrated that intraventricular administration of 6-hydroxydopamine, a selective neurotoxin of the catecholamine neuron, can reproduce schizophrenia-like abnormalities in the skin conductance activity. In the present experiments, effects of pharmacological modulation of the central noradrenergic activity were studied in rats. Stimulation of the central noradrenergic activity by yohimbine (0.6 mg/kg, i.m.) slowed down the habituation of the skin conductance response (SCR) and increase the spontaneous fluctuation of the skin conductance (SF), while inhibition of the activity by clonidine (0.06 mg/kg, i.m.) accelerated or obliterated the SCR and decreased the SF frequency. If the functional significance of the central noradrenergic system lies in vigilance control, the present results are consistent with classical theory in psychophysiology: the habituation rate of SCR and the frequency of SF are correlated well with each other and both indices reflect arousal level. The disorder of the system should produce not only these psychophysiological abnormalities but also psychological disturbances; i.e., overarousal and underarousal syndromes. Therefore, the dysfunction of the noradrenergic system might constitute an essential aspect of schizophrenic disorder.

Possible noradrenergic dysfunction in schizophrenia

In spite of extensive studies over the last 2 decades to find direct evidence in support of the dopamine hypothesis of schizophrenia, no undisputed experimental data has been obtained. In contrast, estimation of noradrenalin (another major catecholamine) and its metabolites in postmortem brain and in the cerebrospinal fluid appears to be producing consistent results. To understand the meaning of this change for the pathogenesis of the illness, we have carried out animal experiments in which reproducibility of schizophrenic signs and symptoms by noradrenergic dysfunction, and treatability of the disorder by modulation of noradrenergic activity were studied. First, psychophysiological signs in skin conductance responsiveness (nonhabituating or nonresponding change) and smooth pursuit eye movement (spiky or stepwise pursuit) could be reproduced by enhancing or suppressing central noradrenergic activity. Behavioral abnormalities resembling schizophrenic symptoms are known to be reproducible by over- or underactivity of the system (overarousal or underarousal syndrome). Secondly, the action of various drugs capable of modulating schizophrenic symptoms was analyzed in relation to noradrenergic activity. Haloperidol, in particular, had a potent suppressing effect on skin conductance activity (spontaneous fluctuation rate and habituation rate) when administered chronically, suggesting its inhibitory action on noradrenergic activity.

Measuring sleep (dys)function by polysomnography

A vigilance state is characterized by a particular activity state of the motorIautonomic and psychiclcognitive functional systems. S-W screening is possible through poly graphic monitoring of physiological variables and signals. Quantification of these signals introduces a set of parameters allowing the characterisation of the sleep (dys)function. There is no consensus regarding the choice or definition of these parameters. A particular cluster is presented and their informative value with respect to clinical practice and research is discussed.

Skin conductance response after 6-hydroxydopamine lesion of central noradrenaline system in cats

Absence of skin conductance response (SCR) is a psychophysiological sign frequently observed among schizophrenic patients. This alteration of electrodermal activity can be reproduced in cats and rats by intraventricular administration of 6-hydroxydopamine (6-OHDA), a neurotoxin selectively destroying catecholamine neurons. The finding appears to be quite consistent with the catecholamine hypothesis of schizophrenia. To determine which catecholamine system--the dopamine (DA) or the noradrenaline (NA)--is responsible for the induction of this abnormality, the same dose of 6-OHDA was microinjected to either the ventral tegmental area (VTA, n = 3), through which most DA fibers ascend, or to the ascending noradrenergic bundle (ANB, n = 3), through which most NA fibers ascend. Four cats remained intact as a control for later brain catecholamine estimation. The skin conductance of all pretreatment intact cats (n = 10) showed not only spontaneous fluctuations but also SCRs to auditory stimuli (5 kHz, 100 dB, 1 sec) which habituated with repetition. In contrast, ANB-lesioned cats showed a complete abolition of auditory SCRs, few spontaneous fluctuations, and a low basal skin conductance level. These abnormalities were statistically significant. On the other hand, no change was found in the skin conductance activity of the VTA-lesioned cats. Catecholamine estimation after the experiment confirmed selective destruction of the appropriate system corresponding to each type of lesion. These findings are discussed in the context of the DA or NA theory of schizophrenia, and involvement of the NA system in the pathogenesis of this illness is suggested.

Increased firing of locus coeruleus neurons associated with preparatory set in rats

The activity of locus coeruleus (LC) neurons was studied during the performance of a reaction-time task with warning. Seventeen cells were tentatively identified as LC neurons using two criteria: (1) Relative location from the mesencephalic trigeminal (Me5) neurons, which have large-amplitude bursting discharges synchronized with masticatory movements. (2) The presence of an antidromic response to the stimulation of the dorsal pathway. Of these 17 cells, 16 neurons showed intense and consistent firing during the period between the warning stimulus and the response. Neither the stimuli nor the lever pressing movements alone were accompanied by such a change, suggesting that increased firing occurs in association with preparatory set. The one remaining neuron of the 17 cells showed no change with the task performance. It is supposed that only the 16 homogeneous neurons belong to the LC.

Sleep and memory relationships in intact old and amnestic young rats

Age-related changes in sleep are observed in many species, including rats and humans. Old rats often exhibit less total and paradoxical sleep, shorter sleep bouts and more random sleep-wake periods across 24 hours, than young rats. This paper evaluates recent evidence that deterioration of selected sleep parameters, usually involving levels of paradoxical sleep or durations of sleep bouts, may be related to deterioration of memory in old rats. Similar findings are reviewed with respect to young animals with different forms of experimentally-induced amnesia. Furthermore, a drug that enhances memory in rats and old humans, glucose, also enhances paradoxical sleep in old rats. These data suggest the utility of sleep measures as neurobiological markers of memory dysfunction in old rats.

Comparison of the central and peripheral effects of cetirizine and terfenadine

The peripheral and central effects of 10 mg cetirizine 2 HCl and 60 mg terfenadine have been compared with placebo in 9 healthy male volunteers. The peripheral effect, in terms of cutaneous reactivity to 1 microgram histamine i.d., was measured by planimetry of the wheal and erythemas. Central effects were assessed with a self-evaluation visual scale and from the results of electroencephalographic spectrum analysis. Peripheral inhibition of histamine reactivity was more intense and quicker for cetirizine than for terfenadine. On the self-evaluation scale, no significant difference between terfenadine, cetirizine and placebo was noted. The quantified EEG did not show any variation in spectral parameters at any time after cetirizine. By contrast, at 6 h terfenadine had increased slow waves and had inhibited the alpha band. Thus, 10 mg cetirizine 2 HCl had less effect on the central nervous system than terfenadine 60 mg, whilst its peripheral action appeared more quickly and was more intense.

Rhythm and blues. Neurochemical, neuropharmacological and neuropsychological implications of a hypothesis of circadian rhythm dysfunction in the affective disorders

Current views on the organisation and functions of the circadian rhythm system are outlined. Evidence is presented supportive of the notion that the pathophysiology of the affective disorders involves a disruption of circadian rhythms and that the primary locus of action of agents effective in the affective disorders is on the circadian rhythm system. Potential disruptions of this system are enumerated. Such a hypothesis, it is argued, might potentially unite the disparate neurochemical and neuroendocrinological findings emerging in both depression and mania. There are in addition neuropsychological and nosological implications of such a framework, which may help bridge the divide between molecular and behavioural approaches to research on the affective disorders which are outlined.

CNS-related (side-)effects of beta-blockers with special reference to mechanisms of action

beta-Adrenoreceptor antagonists are liable to produce behavioural side-effects such as drowsiness, fatigue, lethargy, sleep disorders, nightmares, depressive moods, and hallucinations. These undesirable actions indicate that beta-blockers affect not only peripheral autonomic activity but also some central nervous mechanisms. In experimental animals beta-blockers have been found to reduce spontaneous motor activity, to counteract isolation-, lesion-, stimulation- and amphetamine-induced hyperactivity, and to produce slow-wave and paradoxical sleep disturbances. Furthermore, central effects such as tranquilizing influences are used for the treatment of conditions such as anxiety. Several different mechanisms of action could be responsible for these CNS effects: Centrally mediated specific actions on centrally located beta-adrenergic receptors, known to exist downstream from, and at the terminals of, 'vigilance-enhancing' central noradrenergic pathways. Centrally mediated specific actions on centrally located receptors of the non-adrenergic type; an affinity of some beta-blockers towards 5-HT-receptors is well documented. Centrally mediated non-specific actions on centrally located neurones, owing to the membrane-stabilizing effects of beta-blockers. Peripherally mediated actions whereby beta-blockers induce changes in the autonomic activity in the periphery, which are relayed to the CNS to induce changes in activity of a variety of central systems. It can be assumed that with any one of the beta-blockers all these mechanisms come into play, yet with varying degrees depending on characteristics of the drugs such as lipophilicity and hydrophilicity, the ratio of antagonist versus (partial) agonist properties, affinity to 'alien' receptor sites, strength of membrane-stabilizing activity, stereospecific affinity, and potency.

Habituation failure of skin conductance response after intraventricular administration of 6-hydroxydopamine in cats

The effects of intraventricular administration of 6-hydroxydopamine on electrodermal activity were studied in cats. The treatment slowed down or eliminated habituation of the skin conductance response to repeated auditory stimuli. However, the impairment of habituation was not accompanied by an increase in the rate of spontaneous skin conductance fluctuation.

Anaesthesia: the role of adrenergic mechanisms

The beta-blocker propranolol administered intraperitoneally to rats prior to the barbiturate anaesthetic thiopentone caused a dose-dependent increase in anaesthesia duration. Sotalol, which only poorly crosses the blood-brain barrier, had no such effect, implying a central site of action. The selective beta 1-blockers, metoprolol and atenolol, did not alter thiopentone anaesthesia duration; implying that the effect of propranolol was mediated by a beta 2-receptor. The selective alpha 1-blocker prazocin increased thiopentone anaesthesia duration, while the alpha 1-agonist ST 587 decreased it. Since the alpha 1-agonist methoxamine, which only poorly crosses the blood-brain barrier, was ineffective, a central site of action is indicated. The alpha 2-agonist clonidine markedly increased thiopentone-anaesthesia duration, while the alpha 2-blocker yohimbine, shortened the duration. These effects were shown to be noradrenergic since they were blocked by prior depletion of brain noradrenaline using 6-hydroxydopamine. A model is proposed in which drug-induced alterations in the firing of locus coeruleus cells, or drug-induced changes in the postsynaptic effect of released noradrenaline, may be responsible for modulation of cortical arousal, wakefulness and the processing of sensory stimuli; thus affecting the duration of barbiturate anaesthesia.