What Is the Reticular Activating System?

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The reticular activating system (RAS) is a network within the brainstem that plays a role in regulating the alertness, or arousal, of the brain and thus plays an important role in regulating wakefulness and sleep-wake transitions.

The pathways included in this system start in the upper part of the brainstem and extend through the thalamus, and then on to the surface of the brain, called the cerebral cortex.

The areas deep within the brain that function as part of this system include: midbrain reticular formation, mesencephalic nucleus, thalamic intralaminar nucleus, dorsal hypothalamus and tegmentum.

If this system is damaged, it may result in deep sleep, lethargy, or coma. Dysfunction may also have a role in schizophrenianarcolepsy and other sleep disorders.

How the RAS Regulates Sleep

The reticular activating system helps your brain get geared up for a higher level of activity so you can get up in the morning. You can think of it as your brain's attention center: It processes outside stimuli and is responsible for awareness and consciousness. In order to get you up in the morning, it responds to various triggers, such as the sun and sounds and triggers your mind to become alert. Throughout the day, it keeps you alert and awake by helping your brain process what's going on around you.

Narcolepsy and the RAS

One sleep disorder associated with the reticular activating system is narcolepsy — a chronic brain disorder defined by poor control of sleep-wake cycles.

This disruption of sleep-wake cycles is in part due to a dysfunctional reticular activating system and people with narcolepsy have periods of extreme and uncontrollable daytime sleepiness and can fall asleep at any time. Narcolepsy can be very dangerous, as people with the disorder fall asleep without notice, which could include during activities such as driving, walking or other situations that could put them and others at risk.

How the RAS Can Become Damaged

The reticular activating system can become damaged in a few ways. One of those is when a person suffers from a traumatic brain injury (TBI), as a result of an accident or some other cause. Damage to the RAS from a TBI is usually not fixable, but the effects can be minimized through rehabilitation treatment focused on the sleep cycle, pain management, balance and filtering incoming stimuli.


Eastern Tennessee State University Faculty. (n.d.). A Lecture, Higher Brain Function: Activation of the BrainLine.org. (n.d.). Can a Brain Injury Damage the Reticular Activating System? Retrieved January 28, 2016

Brain and Levels of Consciousness. Retrieved January 23, 2016.

National Institute of Neurological Disorders and Stroke. (2015, January 5). Narcolepsy Fact Sheet. Retrieved January 28, 2016.

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