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Wakefulness is a daily recurring brain state and state of consciousness in which an individual is conscious and engages in coherent cognitive and behavioral responses to the external world.
Being awake is the opposite of being asleep, in which most external inputs to the brain are excluded from neural processing. [1] [2] [3] [4]
The longer the brain has been awake, the greater the synchronous firing rates of cerebral cortex neurons. After sustained periods of sleep, both the speed and synchronicity of the neurons firing are shown to decrease. [5]
Another effect of wakefulness is the reduction of glycogen held in the astrocytes, which supply energy to the neurons. Studies have shown that one of sleep's underlying functions is to replenish this glycogen energy source. [6]
Wakefulness is produced by a complex interaction between multiple neurotransmitter systems arising in the brainstem and ascending through the midbrain, hypothalamus, thalamus and basal forebrain. [7] The posterior hypothalamus plays a key role in the maintenance of the cortical activation that underlies wakefulness. Several systems originating in this part of the brain control the shift from wakefulness into sleep and sleep into wakefulness. Histamine neurons in the tuberomammillary nucleus and nearby adjacent posterior hypothalamus project to the entire brain and are the most wake-selective system so far identified in the brain. [8] Another key system is that provided by the orexins (also known as hypocretins) projecting neurons. These exist in areas adjacent to histamine neurons and like them project widely to most brain areas and associate with arousal. [9] Orexin deficiency has been identified as responsible for narcolepsy. [10]
Research suggests that orexin and histamine neurons play distinct, but complementary roles in controlling wakefulness with orexin being more involved with wakeful behavior and histamine with cognition and activation of cortical EEG. [11]
It has been suggested the fetus is not awake, with wakefulness occurring in the newborn due to the stress of being born and the associated activation of the locus coeruleus. [12]
The hypothalamus is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus is located below the thalamus and is part of the limbic system. In the terminology of neuroanatomy, it forms the ventral part of the diencephalon. All vertebrate brains contain a hypothalamus. In humans, it is the size of an almond.
Orexin, also known as hypocretin, is a neuropeptide that regulates arousal, wakefulness, and appetite. The most common form of narcolepsy, type 1, in which the individual experiences brief losses of muscle tone, is caused by a lack of orexin in the brain due to destruction of the cells that produce it. It exists in the forms of orexin-A and orexin-B.
Dopaminergic pathways in the human brain are involved in both physiological and behavioral processes including movement, cognition, executive functions, reward, motivation, and neuroendocrine control. Each pathway is a set of projection neurons, consisting of individual dopaminergic neurons.
The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain. The neurons of the reticular formation make up a complex set of networks in the core of the brainstem that extend from the upper part of the midbrain to the lower part of the medulla oblongata. The reticular formation includes ascending pathways to the cortex in the ascending reticular activating system (ARAS) and descending pathways to the spinal cord via the reticulospinal tracts.
The ventrolateral preoptic nucleus (VLPO), also known as the intermediate nucleus of the preoptic area (IPA), is a small cluster of neurons situated in the anterior hypothalamus, sitting just above and to the side of the optic chiasm in the brain of humans and other animals. The brain's sleep-promoting nuclei, together with the ascending arousal system which includes components in the brainstem, hypothalamus and basal forebrain, are the interconnected neural systems which control states of arousal, sleep, and transitions between these two states. The VLPO is active during sleep, particularly during non-rapid eye movement sleep, and releases inhibitory neurotransmitters, mainly GABA and galanin, which inhibit neurons of the ascending arousal system that are involved in wakefulness and arousal. The VLPO is in turn innervated by neurons from several components of the ascending arousal system. The VLPO is activated by the endogenous sleep-promoting substances adenosine and prostaglandin D2. The VLPO is inhibited during wakefulness by the arousal-inducing neurotransmitters norepinephrine and acetylcholine. The role of the VLPO in sleep and wakefulness, and its association with sleep disorders – particularly insomnia and narcolepsy – is a growing area of neuroscience research.
Cataplexy is a sudden and transient episode of muscle weakness accompanied by full conscious awareness, typically triggered by emotions such as laughing, crying, or terror. Cataplexy affects approximately 20% of people who have narcolepsy, and is caused by an autoimmune destruction of hypothalamic neurons that produce the neuropeptide hypocretin, which regulates arousal and has a role in stabilization of the transition between wake and sleep states. Cataplexy without narcolepsy is rare and the cause is unknown.
Slow-wave sleep (SWS), often referred to as deep sleep, consists of stage three of non-rapid eye movement sleep. It usually lasts between 70 and 90 minutes and takes place during the first hours of the night. Initially, SWS consisted of both Stage 3, which has 20–50 percent delta wave activity, and Stage 4, which has more than 50 percent delta wave activity.
Part of the human brain, the basal forebrain structures are located in the forebrain to the front of and below the striatum. They include the ventral basal ganglia, nucleus basalis, diagonal band of Broca, substantia innominata, and the medial septal nucleus. These structures are important in the production of acetylcholine, which is then distributed widely throughout the brain. The basal forebrain is considered to be the major cholinergic output of the central nervous system (CNS) centred on the output of the nucleus basalis. The presence of non-cholinergic neurons projecting to the cortex have been found to act with the cholinergic neurons to dynamically modulate activity in the cortex.
The dorsal raphe nucleus is one of the raphe nuclei. It is situated in the brainstem at the midline. It has rostral and caudal subdivisions:
The dorsomedial hypothalamic nucleus is a nucleus of the hypothalamus. It is involved in feeding, drinking, body-weight regulation and circadian activity. More specifically, it is a necessary component for the expression of numerous behavioral and physiological circadian rhythms. The dorsomedial hypothalamic nucleus receives information from neurons and humors involved in feeding regulation, body weight and energy consumption, and then passes this information on to brain regions involved in sleep and wakefulness regulation, body temperature and corticosteroid secretion.
The lateral hypothalamus (LH), also called the lateral hypothalamic area (LHA), contains the primary orexinergic nucleus within the hypothalamus that widely projects throughout the nervous system; this system of neurons mediates an array of cognitive and physical processes, such as promoting feeding behavior and arousal, reducing pain perception, and regulating body temperature, digestive functions, and blood pressure, among many others. Clinically significant disorders that involve dysfunctions of the orexinergic projection system include narcolepsy, motility disorders or functional gastrointestinal disorders involving visceral hypersensitivity, and eating disorders.
The tuberomammillary nucleus (TMN) is a histaminergic nucleus located within the posterior third of the hypothalamus. It is part of the tuber cinereum. It largely consists of histaminergic neurons. It is involved with the control of arousal, learning, memory, sleep and energy balance.
Orexin-A, also known as hypocretin-1, is a naturally occurring neuropeptide and orexin isoform. The orexinergic nucleus in the lateral hypothalamus is the primary orexin projection system in the brain.
Narcolepsy is a chronic neurological disorder that involves a decreased ability to regulate sleep–wake cycles. Symptoms often include periods of excessive daytime sleepiness and brief involuntary sleep episodes. Narcolepsy paired with cataplexy is evidenced to be an autoimmune disorder. These experiences of cataplexy can be brought on by strong emotions. Less commonly, there may be vivid hallucinations or an inability to move while falling asleep or waking up. People with narcolepsy tend to sleep about the same number of hours per day as people without, but the quality of sleep tends to be lessened.
SB-334867 is an orexin antagonist. It was the first non-peptide antagonist developed that is selective for the orexin receptor subtype OX1, with around 50x selectivity for OX1 over OX2 receptors. It has been shown to produce sedative and anorectic effects in animals, and has been useful in characterising the orexinergic regulation of brain systems involved with appetite and sleep, as well as other physiological processes. The hydrochloride salt of SB-334867 has been demonstrated to be hydrolytically unstable, both in solution and as the solid. Orexin antagonists have multiple potential clinical applications including the treatment of drug addiction, insomnia, obesity and diabetes.
Sleep onset is the transition from wakefulness into sleep. Sleep onset usually transmits into non-rapid eye movement sleep but under certain circumstances it is possible to transit from wakefulness directly into rapid eye movement sleep.
Suvorexant, sold under the brand name Belsomra, is an orexin antagonist medication which is used in the treatment of insomnia. It is indicated specifically for the treatment of insomnia characterized by difficulties with sleep onset and/or maintenance in adults. Suvorexant helps with falling asleep faster, sleeping longer, being awake less in the middle of the night, and having better quality of sleep. Its effectiveness is modest, and is similar to that of other orexin antagonists, but is lower than that of benzodiazepines and Z-drugs. Suvorexant is taken by mouth.
The neuroscience of sleep is the study of the neuroscientific and physiological basis of the nature of sleep and its functions. Traditionally, sleep has been studied as part of psychology and medicine. The study of sleep from a neuroscience perspective grew to prominence with advances in technology and the proliferation of neuroscience research from the second half of the twentieth century.
Thomas S. Kilduff is an American neuroscientist and the director of SRI International's Center for Neuroscience. He specializes in neurobiology related to sleep and wakefulness, and was involved in the discovery of hypocretin, a neuropeptide system that is highly involved in wakefulness regulation.
The parafacial zone (PZ) is a brain structure located in the brainstem within the medulla oblongata believed to be heavily responsible for non-rapid eye movement (non-REM) sleep regulation, specifically for inducing slow-wave sleep.
The dictionary definition of wakefulness at Wiktionary
