The Reticular Activating System functions like a filter or a security guard scanning a series of video screens to make sure there isn't something that needs to be attended to. It plays a big role in the sensory information you perceive on a regular basis and makes sure your brain doesn't have to attend to more than it can handle. Think of it this way, in any given moment we are bombarded with sensory stimuli, from the hum of the fluorescent lights, the tapping of someone's keys as they furiously type away, the color of people's clothes, the room decor, the temperature of the room, the pressure of the chair your sitting in, etc... The RAS helps us filter through what's important (e.g., the professor talking about today's lecture) vs. what gets processed in the background or safely ignored by out conscious mind (i.e., all the other sensory stuff).
