Wake up: The ‘Ascending reticular activating system’ (ARAS) and its role in consciousness & attention

The reticular formation is essential for governing some of the basic functions of higher organisms and is one of the phylogenetically oldest portions of the brain.

The ascending reticular activating system (ARAS), also known as the extrathalamic control modulatory system or simply the reticular activating system (RAS), is a set of connected nuclei in the brains of vertebrates that is responsible for regulating wakefulness and sleep-wake transitions. The ARAS is a part of the reticular formation and is mostly composed of various nuclei in the thalamus and a number of dopaminergic, noradrenergic, serotonergic, histaminergic, cholinergic, and glutamatergic brain nuclei.

The ascending reticular activating system is an important enabling factor for the state of consciousness.  The ARAS also helps mediate transitions from relaxed wakefulness to periods of high attention. There is increased regional blood flow (presumably indicating an increased measure of neuronal activity) in the midbrain reticular formation (MRF) and thalamic intralaminar nuclei during tasks requiring increased alertness and attention.

The reticular formation is divided into three columns: raphe nuclei (median), gigantocellular reticular nuclei (medial zone), and parvocellular reticular nuclei (lateral zone). The raphe nuclei are the place of synthesis of the neurotransmitter serotonin, which plays an important role in mood regulation. The gigantocellular nuclei are involved in motor coordination. The parvocellular nuclei regulate exhalation.


Further References

Datta, S.. (1995). Neuronal activity in the peribrachial area: Relationship to behavioral state control. Neuroscience and Biobehavioral Reviews, 19(1), 67–84.

Plain numerical DOI: 10.1016/0149-7634(94)00043-Z
DOI URL
directSciHub download

Edlow, B. L., Takahashi, E., Wu, O., Benner, T., Dai, G., Bu, L., … Folkerth, R. D.. (2012). Neuroanatomic connectivity of the human ascending arousal system critical to consciousness and its disorders. Journal of Neuropathology and Experimental Neurology, 71(6), 531–546.

Plain numerical DOI: 10.1097/NEN.0b013e3182588293
DOI URL
directSciHub download

Englot, D. J., D’Haese, P. F., Konrad, P. E., Jacobs, M. L., Gore, J. C., Abou-Khalil, B. W., & Morgan, V. L.. (2017). Functional connectivity disturbances of the ascending reticular activating system in temporal lobe epilepsy. Journal of Neurology, Neurosurgery and Psychiatry, 88(11), 925–932.

Plain numerical DOI: 10.1136/jnnp-2017-315732
DOI URL
directSciHub download

Jones, B. E.. (2011). Neurobiology of waking and sleeping. Handbook of Clinical Neurology (Vol. 98)

Plain numerical DOI: 10.1016/B978-0-444-52006-7.00009-5
DOI URL
directSciHub download

Kinomura, S., Larsson, J., Gulyás, B., & Roland, P. E.. (1996). Activation by attention of the human reticular formation and thalamic intralaminar nuclei. Science, 271(5248), 512–515.

Plain numerical DOI: 10.1126/science.271.5248.512
DOI URL
directSciHub download

Lin, J. S.. (2000). Brain structures and mechanisms involved in the control of cortical activation and wakefulness, with emphasis on the posterior hypothalamus and histaminergic neurons. Sleep Medicine Reviews

Plain numerical DOI: 10.1053/smrv.2000.0116
DOI URL
directSciHub download

McKinney, M.. (2005). Brain cholinergic vulnerability: Relevance to behavior and disease. Biochemical Pharmacology

Plain numerical DOI: 10.1016/j.bcp.2005.05.019
DOI URL
directSciHub download

Mesulam, M. M.. (2010). Attentional and confusional states. CONTINUUM Lifelong Learning in Neurology, 16(4), 128–139.

Plain numerical DOI: 10.1212/01.CON.0000368265.38415.35
DOI URL
directSciHub download

Newman, J.. (1995). Thalmic Contributions to Attention and Consciousness. Consciousness and Cognition

Plain numerical DOI: 10.1006/ccog.1995.1024
DOI URL
directSciHub download

Robbins, T. W.. (1997). Arousal systems and attentional processes. In Biological Psychology (Vol. 45, pp. 57–71)

Plain numerical DOI: 10.1016/S0301-0511(96)05222-2
DOI URL
directSciHub download

Siegel, J.. (2004). Brain mechanisms that control sleep and waking. Naturwissenschaften

Plain numerical DOI: 10.1007/s00114-004-0541-9
DOI URL
directSciHub download

Yeo, S. S., Chang, P. H., & Jang, S. H.. (2013). The Ascending Reticular Activating System from Pontine Reticular Formation to the Thalamus in the Human Brain. Frontiers in Human Neuroscience, 7

Plain numerical DOI: 10.3389/fnhum.2013.00416
DOI URL
directSciHub download

Young, G. B.. (2011). Impaired Consciousness and Herniation Syndromes. Neurologic Clinics

Plain numerical DOI: 10.1016/j.ncl.2011.07.008
DOI URL
directSciHub download

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