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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

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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
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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
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