Wakefulness is a daily recurring brain state and state of consciousness in which an individual is conscious and engages in coherent cognitive and behavior responses to the external world such as communication, ambulation, eating, and sex. Being awake is the opposite of the state of being asleep in which most external inputs to the brain are excluded from neural processing.
Effects upon the brain 
The longer the brain has been awake, the greater the spontaneous firing rates of cerebral cortex neurons with this increase being reversed by sleep. Another effect of wakefulness (which may or may not be related to this) is that it lowers the small stores of glycogen held in the astrocytes that can supply energy to the brain's neurons—one of the functions of sleep, it has been proposed, is to create the opportunity for them to be replenished.
Maintenance by the brain 
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 tuberomamillary nucleus and nearby adjacent posterior hypothalamus project to the entire brain and are the most wake-selective system so far identified in the brain. 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. Orexin deficiency has been identified as responsible for narcolepsy.
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.
As a state of awareness 
||This section only describes one highly specialized aspect of its associated subject. (July 2010)|
Wakefulness is described by the American physician and meditation teacher Jon Kabat-Zinn as a state of mindful awareness or mindfulness. By being fully awake in the present moment, Kabat-Zinn suggests that we can live more fully and with greater awareness and intent, which has the potential to give us an improved sense of peace, contentment and well-being. For lying down meditation practices (as opposed to sitting or walking meditation practices), Kabat-Zinn suggests that it may be helpful to begin by first splashing cold water on your face so that you are less likely to fall asleep. Instead, Kabat-Zinn describes the benefit of meditation as "falling awake". By being able to "fall awake", we learn to be more aware in the present moment no matter what else is happening.
Awakefulness has a special meaning within oriental schools of thought and associated esoteric teachings. These include the idea of antroposophy in which four modes of awareness are distinguished: wakefulness (conferring with dhyana), dream (conferring with dharani), sleep (conferring with pratyahara) and moment of death or absorption of spirit (conferring with samādhi). Each of these modes of awareness (citta) may be exercised (i.e. Yoga) in order to enhance wisdom (prajna) and enlightenment (buddhi). In Yoga these four modes of awareness, mental energies, are united with corresponding life forces (pranas.) The mental states of wakefulness, Dhyanas, correspond to the Asanas, which are the commonsensical understanding of Yoga exercises, but specifically refer to the corporeal conduct or the seat of wakefulness.
See also 
- Vyazovskiy, VV; Olcese, U; Lazimy, YM; Faraguna, U; Esser, SK; Williams, JC; Cirelli, C; Tononi, G (2009). "Cortical firing and sleep homeostasis". Neuron 63 (6): 865–78. doi:10.1016/j.neuron.2009.08.024. PMC 2819325. PMID 19778514.
- Benington, JH; Heller, HC (1995). "Restoration of brain energy metabolism as the function of sleep". Progress in neurobiology 45 (4): 347–60. doi:10.1016/0301-0082(94)00057-O. PMID 7624482.
- Takahashi, K; Lin, JS; Sakai, K (2006). "Neuronal activity of histaminergic tuberomammillary neurons during wake-sleep states in the mouse". Journal of Neuroscience 26 (40): 10292–8. doi:10.1523/JNEUROSCI.2341-06.2006. PMID 17021184.
- Sakurai, T (2007). "The neural circuit of orexin (hypocretin): maintaining sleep and wakefulness". Nature reviews. Neuroscience 8 (3): 171–81. doi:10.1038/nrn2092. PMID 17299454.
- Chemelli, RM; Willie, JT; Sinton, CM; Elmquist, JK; Scammell, T; Lee, C; Richardson, JA; Williams, SC; Xiong, Y (1999). "Narcolepsy in orexin knockout mice: molecular genetics of sleep regulation". Cell 98 (4): 437–51. doi:10.1016/S0092-8674(00)81973-X. PMID 10481909.
- Anaclet, C.; Parmentier, R.; Ouk, K.; Guidon, G.; Buda, C.; Sastre, J.-P.; Akaoka, H.; Sergeeva, O. A.; Yanagisawa, M. (2009). "Orexin/Hypocretin and Histamine: Distinct Roles in the Control of Wakefulness Demonstrated Using Knock-Out Mouse Models". Journal of Neuroscience 29 (46): 14423–14438. doi:10.1523/JNEUROSCI.2604-09.2009. PMC 2802289. PMID 19923277.
- Lagercrantz, H (2009). "The birth of consciousness". Early human development 85 (10 Suppl): S57–8. doi:10.1016/j.earlhumdev.2009.08.017. PMID 19762170.
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