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Voiceover: What is consciousness? Well that's not something we can easily answer in one video. In general, consciousness is usually defined as awareness of our selves and our environment. We can have different states of consciousness meaning different levels of awareness and they can occur naturally or be induced by external factors such as drugs or internal factors such us our own mental efforts. These states range from alertness to sleep and everything in between. Alertness is what most people think of when they think about being conscious. When you're alert, you are awake, aware of who you are, where you are, and what's going on in your environment. You can focus your attention, encode information and memory, engage in conversation, all the stuff you normally do when you're awake and aware of the world. That's alertness. We've all had the experience of daydreaming or being awake but not really aware of the world around you. Maybe you've had that experience in class or during this video. You may feel more relaxed but you're not as focused as you are during normal awareness. Daydreaming occurs naturally. Sometimes you'll find yourself daydreaming when you didn't mean to. Some people can induce a similar state through light meditation. Moving into the less conscious states of consciousness, we have drowsiness. That state when you're almost asleep but still semi aware of the world. You might feel this way just before falling asleep or maybe just as you're waking up. In all those drowsiness also comes naturally just like daydreaming, some people can induce this state of consciousness through deep meditation. Finally we have sleep, it's a little strange to call this a state of consciousness because it's really more of a state of unconsciousness. You're not aware of yourself or the world around you when you're asleep. Even though you might be aware of a dream world. One thing that's pretty cool is that even though you might not be aware of when you shift from one state of consciousness to another your brain knows. You have sets of neurons that fire rhythmically in your central nervous system leading to neural oscillations or just those rhythmic patterns of firing that we can measure. There's a machine called an electroencephalogram or EEG which measures those neural oscillations more commonly called brainwaves. There are four main types of brainwaves that we associate with different states of consciousness. Alpha, beta, delta, and theta. Each of these types of brainwaves oscillates at a different frequency and is associated with a particular state of consciousness. For example, beta waves which oscillate at about 12 to 30 hertz which is pretty fast. It means that it's going at about 12 to 30 cycles per second. Those are associated with normal waking consciousness and concentration. If you maintain this heightened alertness for too long though your beta levels get really high and you might experience increase stress, anxiety, and restlessness. Just sort of this constant awaken alertness. Alpha waves though are common during relaxed awake states such as daydreaming or light meditation. As you might expect an alpha waves have a lower frequency than beta waves. Alpha waves are about eight to 13 hertz. Although alpha waves disappear as you become drowsy they can reappear later when you're in deep sleep. When you do get drowsy or you're in deep meditation an EEG would show theta waves which are even slower than alpha waves. They're like four to seven hertz. You also see this pattern right after you first fall asleep, when you're sleeping very lightly. Sleep as a state of consciousness is surprisingly complex and involves multiple phases of it's own and different cycles of brainwaves including the delta waves, which we haven't talked about yet. The next video, is going to focus on the stages of sleep and what your brain does during those stages.