Wakefulness is a daily recurring brain state in which an individual is conscious and engages in coherent cognitive and behavior responses to the external world such as communication, ambulation, nutritional ingestion and procreation. Being awake is the opposite of being asleep in which most external inputs to the brain are excluded from neural processing.
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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.[1] 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.[2]
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.[3] 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.[4] Orexin deficiency has been identified as responsible for narcolepsy.[5]
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 cognition and activation of cortical EEG.[6]
It has been suggested the fetus are not awake with wakeness occuring in the newborn due to the stress of being born and the associated activation of the locus coeruleus.[7]
As a state of awareness
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, are corresponding to the Asanas, the commonsensical understanding of Yoga exercises, but specifically refers to the corporeal conduct or seat of the wakefulness.
References
- ^ Vyazovskiy VV, Olcese U, Lazimy YM, Faraguna U, Esser SK, Williams JC, Cirelli C, Tononi G. (2009). Cortical firing and sleep homeostasis. Neuron. 24;63(6):865-78. doi:10.1016/j.neuron.2009.08.024 PMID 19778514
- ^ Benington JH, Heller HC. (1995). Restoration of brain energy metabolism as the function of sleep. Prog Neurobiol. 45(4):347-60. PMID 7624482
- ^ Takahashi K, Lin JS, Sakai K. (2006). Neuronal activity of histaminergic tuberomammillary neurons during wake-sleep states in the mouse. J Neurosci. 26(40):10292-8. PMID 17021184
- ^ Sakurai T. (2007). The neural circuit of orexin (hypocretin): maintaining sleep and wakefulness. Nat Rev Neurosci 8:171–181. PMID 17299454
- ^ Chemelli RM, Willie JT, Sinton CM, Elmquist JK, Scammell T, Lee C, Richardson JA, Williams SC, Xiong Y, Kisanuki Y, Fitch TE, Nakazato M, Hammer RE, Saper CB, Yanagisawa M. (1999). Narcolepsy in orexin knockout mice: molecular genetics of sleep regulation. Cell. 98(4):437-51. PMID 10481909
- ^ Anaclet C, Parmentier R, Ouk K, Guidon G, Buda C, Sastre J-P, Akaoka H, Sergeeva OA, Yanagisawa M, Ohtsu H, Franco P, Haas HL, Lin J-S. (2009). Orexin/Hypocretin and Histamine: Distinct Roles in the Control of Wakefulness Demonstrated Using Knock-Out Mouse Models. J. Neurosci. 29: 14423-14438. doi:10.1523/JNEUROSCI.2604-09.2009
- ^ Lagercrantz H. (2009). The birth of consciousness. Early Hum Dev. 85(10 Suppl):S57-8. PMID 19762170
See also
External links
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Look up wakefulness in Wiktionary, the free dictionary. |
- Sleep, dreams and wakefulness
- Wakefulness, Alertness, Sleep, and Dreams
- The Consequences of Excessive Wakefulness
- It's Wake-Up Time
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