覚醒

覚醒は、意識が覚める生理的および心理的な状態であり、感覚器官が知覚の閾値に達することを含む。これは、脳内の上行網様体賦活系（ARAS）の活性化に関与し、覚醒状態、自律神経系、内分泌系を調整する。これにより、心拍数や血圧が上昇し、感覚の鋭敏さ、欲求、運動性、反応性の状態が生じる。

覚醒は、複数の神経系によって調節される。覚醒はARASによって調整され、これは脳幹から始まる五つの主要な神経伝達物質系の投射から構成され、皮質全体に延びる接続を形成する。ARAS内の活動は、ノルエピネフリン、アセチルコリン、ドパミン、セロトニン、ヒスタミンを放出するニューロンによって調節される。

これらのニューロンの活性化は、皮質の活動を増加させ、その結果として警戒状態をもたらす。

覚醒は、意識、注意、警戒、および情報処理を調節する上で重要である。これは、運動性、栄養の追求、闘争か逃走かの反応、性的活動（マスターズとジョンソンの人間の性的反応サイクルの覚醒段階）などの特定の行動を促進するために重要である。また、感情においても重要な役割を持ち、ジェームズ＝ランゲの情動理論などに含まれている。ハンス・アイゼンクによれば、基準覚醒レベルの違いは、人々を外向性または内向性に分ける要因となる。

ヤーキーズ・ドッドソンの法則によれば、パフォーマンスに対する最適な覚醒レベルが存在し、覚醒が少なすぎるまたは多すぎると、タスクのパフォーマンスに悪影響を及ぼす可能性がある。ヤーキーズ・ドッドソンの法則の一つの解釈は「イースターブルックの手がかり利用仮説」である。この仮説によれば、高ストレス条件下では、人々がより狭い範囲の手がかりに焦点を合わせ、関連情報を見落とす傾向があり、これが意思決定の効果を低下させることにつながる。

Wakefulness is regulated by the ascending reticular activating system, which is composed of five major neurotransmitter systems – the norepinephrine, acetylcholine, dopamine, serotonin and histamine, systems (each considered in the paragraphs below) – that originate in the brainstem and form connections which extend throughout the cerebral cortex.^[1]^[2]^[3] When stimulated, these systems produce cortical activity and alertness.^[1]^[2]

^ ^a ^b “Neurophysiological foundations of sleep, arousal, awareness and consciousness phenomena. Part 1”. Anaesthesiology Intensive Therapy 47 (2): 162–167. (2015). doi:10.5603/AIT.2015.0015. PMID 25940332. "The ascending reticular activating system (ARAS) is responsible for a sustained wakefulness state. It receives information from sensory receptors of various modalities, transmitted through spinoreticular pathways and cranial nerves (trigeminal nerve – polymodal pathways, olfactory nerve, optic nerve and vestibulocochlear nerve – monomodal pathways). These pathways reach the thalamus directly or indirectly via the medial column of reticular formation nuclei (magnocellular nuclei and reticular nuclei of pontine tegmentum). The reticular activating system begins in the dorsal part of the posterior midbrain and anterior pons, continues into the diencephalon, and then divides into two parts reaching the thalamus and hypothalamus, which then project into the cerebral cortex (Fig. 1). The thalamic projection is dominated by cholinergic neurons originating from the pedunculopontine tegmental nucleus of pons and midbrain (PPT) and laterodorsal tegmental nucleus of pons and midbrain (LDT) nuclei [17, 18]. The hypothalamic projection involves noradrenergic neurons of the locus coeruleus (LC) and serotoninergic neurons of the dorsal and median raphe nuclei (DR), which pass through the lateral hypothalamus and reach axons of the histaminergic tubero-mamillary nucleus (TMN), together forming a pathway extending into the forebrain, cortex and hippocampus. Cortical arousal also takes advantage of dopaminergic neurons of the substantia nigra (SN), ventral tegmenti area (VTA) and the periaqueductal grey area (PAG). Fewer cholinergic neurons of the pons and midbrain send projections to the forebrain along the ventral pathway, bypassing the thalamus [19, 20]."
^ ^a ^b “Chapter 12: Sleep and Arousal”. Molecular Neuropharmacology: A Foundation for Clinical Neuroscience (2nd ed.). New York: McGraw-Hill Medical. (2009). p. 295. ISBN 978-0071481274. "The ARAS is a complex structure consisting of several different circuits including the four monoaminergic pathways ... The norepinephrine pathway originates from the locus ceruleus (LC) and related brainstem nuclei; the serotonergic neurons originate from the raphe nuclei within the brainstem as well; the dopaminergic neurons originate in ventral tegmental area (VTA); and the histaminergic pathway originates from neurons in the tuberomammillary nucleus (TMN) of the posterior hypothalamus. As discussed in Chapter 6, these neurons project widely throughout the brain from restricted collections of cell bodies. Norepinephrine, serotonin, dopamine, and histamine have complex modulatory functions and, in general, promote wakefulness. The PT in the brain stem is also an important component of the ARAS. Activity of PT cholinergic neurons (REM-on cells) promotes REM sleep. During waking, REM-on cells are inhibited by a subset of ARAS norepinephrine and serotonin neurons called REM-off cells."
^ Brain arousal and information theory neural and genetic mechanisms. Cambridge, Mass.: Harvard University Press. (2006). ISBN 978-0674042100. オリジナルの9 February 2023時点におけるアーカイブ。 31 October 2015閲覧。

[ARAS-1] “Neurophysiological foundations of sleep, arousal, awareness and consciousness phenomena. Part 1”. Anaesthesiology Intensive Therapy 47 (2): 162–167. (2015). doi:10.5603/AIT.2015.0015. PMID 25940332. "The ascending reticular activating system (ARAS) is responsible for a sustained wakefulness state. It receives information from sensory receptors of various modalities, transmitted through spinoreticular pathways and cranial nerves (trigeminal nerve – polymodal pathways, olfactory nerve, optic nerve and vestibulocochlear nerve – monomodal pathways). These pathways reach the thalamus directly or indirectly via the medial column of reticular formation nuclei (magnocellular nuclei and reticular nuclei of pontine tegmentum). The reticular activating system begins in the dorsal part of the posterior midbrain and anterior pons, continues into the diencephalon, and then divides into two parts reaching the thalamus and hypothalamus, which then project into the cerebral cortex (Fig. 1). The thalamic projection is dominated by cholinergic neurons originating from the pedunculopontine tegmental nucleus of pons and midbrain (PPT) and laterodorsal tegmental nucleus of pons and midbrain (LDT) nuclei [17, 18]. The hypothalamic projection involves noradrenergic neurons of the locus coeruleus (LC) and serotoninergic neurons of the dorsal and median raphe nuclei (DR), which pass through the lateral hypothalamus and reach axons of the histaminergic tubero-mamillary nucleus (TMN), together forming a pathway extending into the forebrain, cortex and hippocampus. Cortical arousal also takes advantage of dopaminergic neurons of the substantia nigra (SN), ventral tegmenti area (VTA) and the periaqueductal grey area (PAG). Fewer cholinergic neurons of the pons and midbrain send projections to the forebrain along the ventral pathway, bypassing the thalamus [19, 20]."

[NHM_-_ascending_reticular_activating_system-2] “Chapter 12: Sleep and Arousal”. Molecular Neuropharmacology: A Foundation for Clinical Neuroscience (2nd ed.). New York: McGraw-Hill Medical. (2009). p. 295. ISBN 978-0071481274. "The ARAS is a complex structure consisting of several different circuits including the four monoaminergic pathways ... The norepinephrine pathway originates from the locus ceruleus (LC) and related brainstem nuclei; the serotonergic neurons originate from the raphe nuclei within the brainstem as well; the dopaminergic neurons originate in ventral tegmental area (VTA); and the histaminergic pathway originates from neurons in the tuberomammillary nucleus (TMN) of the posterior hypothalamus. As discussed in Chapter 6, these neurons project widely throughout the brain from restricted collections of cell bodies. Norepinephrine, serotonin, dopamine, and histamine have complex modulatory functions and, in general, promote wakefulness. The PT in the brain stem is also an important component of the ARAS. Activity of PT cholinergic neurons (REM-on cells) promotes REM sleep. During waking, REM-on cells are inhibited by a subset of ARAS norepinephrine and serotonin neurons called REM-off cells."

[Pfaff-3] Brain arousal and information theory neural and genetic mechanisms. Cambridge, Mass.: Harvard University Press. (2006). ISBN 978-0674042100. オリジナルの9 February 2023時点におけるアーカイブ。 31 October 2015閲覧。

[1]

[2]

[3]