Reticular Activating System: Definition & Function

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  • 0:01 Definition
  • 0:49 Function
  • 2:45 What Always Gets Through
  • 3:53 Cherry Picking & Goal…
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Lesson Transcript
Instructor: Sharon Linde

Sharon has a Masters of Science in Mathematics

The reticular activating system is an impressive-sounding name for a fairly small piece of the brain. This lesson describes the structure and function of this piece of the brain, which is important in attention, goal-achievement, and keeping you alive.


To understand what the reticular activating system does, we first have to know what it is! The reticular activating system, or RAS, is a piece of the brain that starts close to the top of the spinal column and extends upwards around two inches. It has a diameter slightly larger than a pencil. All of your senses (except smell, which goes to our brain's emotional center) are wired directly to this bundle of neurons that's about the size of your little finger.

Often, the RAS is compared to a filter or a nightclub bouncer that works for your brain. It makes sure your brain doesn't have to deal with more information than it can handle. Thus, the reticular activating system plays a big role in the sensory information you perceive daily.


While it may be a fairly small part of your brain, the RAS has a very important role: it's the gatekeeper of information that is let into the conscious mind. This little bit of brain matter is responsible for filtering the massive amounts of information your sensory organs are constantly throwing at it and selecting the ones that are most important for your conscious mind to pay attention to. Why do we need this little gatekeeper? Well, your senses are constantly feeding so much information to your brain that you can't possibly pay attention to all of it. The RAS never gets a break!

Try to see just how much information you pick up every minute. Take ten seconds and listen to every sound around you that you can'll be surprised at what you miss on a regular basis, but this is because your RAS decides what is important and what can be safely ignored. This doesn't just happen with sounds. Our skin is roughly 20 square feet that abounds with around a million nerve cells detecting pressure, pain, temperature, and location. And a human eye captures more than 300 megapixels of visual information every second!

Despite all of this sensory information, it's estimated that the conscious mind can only handle slightly more than 100 pieces of information every second. There's a tremendous amount of paring down that needs to happen between your senses and your conscious mind. Your RAS is the way evolution has decided to handle this excessive information problem. It is uniquely suited to distinguish between relevant and irrelevant pieces of information. For example, it distinguishes between the honk of a car right next to you and one far down the street, or it tells a husband, 'Unless you want a fight, you better pay attention to what your wife just said!'

Not only does it do all of that, the RAS also plays an important role in motivation and goal setting. Not bad for something tiny nestled close to your brain stem!

What Always Gets Through

There are certain types of information that always seem to get through the gates of the RAS: for example, the sound of your name being called, anything that threatens your safety or that of your loved ones, or an indication from your partner concerning sex. Our brains are literally wired to bring these things to the very top of our consciousness because they're considered highly important.

There is still a lot of information that doesn't fall under those highly important categories, though, so who sets the rest of the agenda for this attention bouncer? We do, of course! Sometimes this is conscious, but other times it's not. What we are interested in at the moment, as well as our deeper belief systems, have a lot of control over what information is let through.

Imagine you've misplaced your keys. While you search, your mind is looking for a familiar grouping of shape and color. Unbeknownst to you, your roommate has moved the peanut butter from the kitchen and stashed it in the shoe closet. As you search, even if you see the peanut butter, you won't necessarily notice it's been moved until later, when you specifically want to make a sandwich. Until then, that information was not as important as searching for your keys.

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