In this video we’ll consider a different state of consciousness that occurs during sleep. Our pattern of wakefulness and drowsiness varies throughout the course of the day and this is known as our circadian rhythm. This cycle is influenced by zeitgebers which help to set our internal clock. The most prominent of these is light, which actives the suprachiasmatic nucleus to inhibit the pineal gland from releasing melatonin, a hormone which makes us feel drowsy. Other zeitgebers include timing of meals, temperature, and social interaction.
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Video Transcript
Hi I’m Mike Corayer and this is Psych Exam Review. In the past few videos we’ve been talking about consciousness but we’ve mostly been focused on consciousness while you’re awake and we’ve been ignoring the fact that you’re going to spend about a third of your life in a different state of consciousness when you’re sleeping.
Now you might think that when you’re sleeping you’re unconscious but that’s not quite accurate because first you do have an experience of sleeping; you have dreams and it feels like something to be dreaming and you also still have some awareness of your external environment even when you’re asleep. So you toss and turn and move around while you’re sleeping but generally you don’t fall out of bed and that’s because you actually do have some bodily awareness of where your bed ends and so you manage to keep from moving too far in that direction.
You also can incorporate external information from the environment into your dreams. So this has been done in laboratory studies where people who are sleeping in a sleep lab are sprayed with a mist of water while they’re dreaming and then you wake them up and they report dreaming about water. They say you know “I was standing in front of a waterfall feeling the mist on on my face” or you have certain words spoken to people while they’re dreaming like “help, help, help!” and then you wake the person up and they report that they were dreaming about some emergency situation.
And you’ve probably experienced this yourself, probably not in the case that you’ve had somebody whispering help into your ear while you’re sleeping, but you’ve probably incorporated the sound of your alarm clock into a dream. So you’re dreaming and then suddenly there’s a dolphin that starts singing to you or something really bizarre and then you wake up and realize it was the sound of your alarm clock that you were incorporating into your dream. And this shows that you do have some awareness of your environment even while you’re sleeping.
Okay so in future videos we’ll look at sleep in more detail but before we do that I want to think about this transition between the sort of waking consciousness and our sleeping consciousness. And we sort of go back and forth between these states each day and this brings us to consider the circadian rhythm. So this comes from the Latin “circa” which means “about” and “dian” which means “day” and so this refers to this pattern that lasts about a day. It’s about a 24-hour cycle that gets repeated over and over again. It’s a pattern of how awake we feel, how alert we feel at different times of the day. So hopefully during the middle of the day you feel mostly wide awake and alert and at night you start feeling drowsy and tired and you are able to fall asleep. Now if you have an irregular schedule then you’ve probably experienced some mismatch between your circadian rhythm and sort of the timing of society and when you’re supposed to go to school and do things and when you’re supposed to be sleeping.
You might also experience this mismatch if you have traveled somewhere far away and you experience jet lag. So jet lag is again this mismatch between your body’s circadian rhythm and how alert and awake you feel at different times and, you know, what time it actually is in the place that you are. When it’s daytime and when it’s nighttime, but eventually you’ll adjust to this. If you stay in the place long enough your circadian rhythm will adjust itself to this new time. So how is it doing this?
This brings us to the factors that influence the circadian rhythm and these are called zeitgebers and this is German for “time givers”. So “zeit” means time and “geber” means “giver”. So we have “time givers”. These are zeitgebers; things that set your circadian rhythm. They set your internal clock so that you’ll feel awake at certain times and tired at other times and of course it makes sense that generally we feel more awake during the day and more tired at night.
This is because we’re not nocturnal animals and so one of the most important zeitgebers that we have is light. And it makes sense that we should be awake during the day; that’s when we can see the best. Of course, we don’t have particularly great night vision and so you don’t want to be trying to do your hunting and gathering. We think about our evolutionary past, you don’t want to be doing that at night when you can’t see very well and you’re quite vulnerable to predators that can see better than you in the dark. And so that’s a time when maybe you should hide away in your shelter and rest and recover and consolidate your memories and have all that happen when it’s dark outside and you can’t be particularly productive, and then during the day you can go out and do things because you can see better.
So this is why light plays such an important role in the circadian rhythm. Now of course today we have artificial light and this can you know sort of wreak havoc on this system but in order to figure out how light influences us, first we have to look at an area called the pineal gland. So you might remember I mentioned the pineal gland in a video on Descartes because he thought this was the seat of the soul. It’s a little gland near the center of your brain but it turns out pineal gland is actually related to this circadian rhythm. It’s not where your soul is located. And what the pineal gland does is it releases a hormone and this hormone is melatonin and what melatonin does is it makes you feel drowsy. It makes you feel tired and you might be aware of this because you can actually buy melatonin tablets that are sold as a sleep aid.
So melatonin makes me feel drowsy and it’s released by the pineal gland. So what does this have to do with light? Well, we have light that stimulates your eyes, it doesn’t just get sent to the occipital lobe for visual processing, it also stimulates another area of your brain called the suprachiasmatic nucleus.
Now this might sound like a bit of a mouthful suprachiasmatic nucleus but this “suprachiasmatic” just refers to fact this is just over the optic chiasm. Remember that point where these nerves crossed from your eyes, that’s the optic chiasm and just above that in the hypothalamus we have the suprachiasmatic nucleus and what the suprachiasmatic nucleus does is it inhibits the pineal gland. So it stops the release of melatonin.
So when light is present you stop releasing melatonin and so you don’t feel as drowsy. When it’s dark then the pineal gland is more active; it’s releasing more melatonin and you start feeling more drowsy. So this explains why when you’re sitting in a dark room it’s easier to fall asleep then you know out in the middle of the sunshine.
Now of course you can override this if you’re tired enough. You can fall asleep in a very bright environment so it’s not deterministic it’s not not the case that light definitely causes you to be awake or causes you to be asleep. You can be feeling alert in the dark and you can be feeling drowsy in light but generally this is how light influences your level of alertness.
Now I mentioned before that we have this problem that we are surrounded by artificial light. In our evolutionary past when you know these systems were developing over the course of millions of years we didn’t have light at night, you know? Maybe we have some fire but it’s not particularly bright and so it made sense that we’d be able to sleep then but now we have we can have light at any time of day and you probably spend a lot of time at night staring at your computer screen which is shining light directly into your eyes and stimulating your suprachiasmatic nucleus.
And it’s worth noting that we’re especially sensitive to blue light and again this makes sense if we think about the fact that the way that our atmosphere filters light makes the sky blue and so we would be sensitive to that right in daylight. We have this blue light that’s hitting our eyes. Of course the light isn’t actually blue if you remember that video on color vision it’s, you know, the wavelengths of light that we perceive as blue.
But in any case, it makes sense that we would be more sensitive to those because that’s, you know, the sky is blue and we’d be looking at it during day. And so one way that you can use this information is if you spend a lot of time at night looking at your computer screen, the best thing to do is to try to reduce that but the second best thing you can do if you have to be looking at your screen is to reduce the amount of blue light that’s being emitted.
And so there’s actually apps that you can install, one is f.lux that I’ve used before, and what this will do is reduce the blue light being emitted by your screen. So it does influence the colors a little bit but the idea is that you will have less stimulation of the suprachiasmatic nucleus and it will not keep you awake quite as much. You can also get this on your phone and another thing you can do is some people actually wear glasses or goggles that block blue light. So they start wearing these at night, so if you have trouble falling asleep at night and you want to try to adjust your circadian rhythm you might look into something like this.
Ok, but light is not the only zeitgeber that we have. There’s other things that influence our circadian rhythm. So what are these other things? Well one of them is timing of meals. So this plays a role in sort of setting how drowsy we feel or how awake we feel and so generally it’s a good idea to have your meals time to happen at about the same time every day because this helps you to set this consistent clock in the same way that is you know it’s ideal to wake up and go to sleep around the same time every day. This helps you get this circadian rhythm into a regular pattern.
And another thing that influences your circadian rhythm is temperature and again this makes sense temperature fluctuates throughout the day and this is going to play a role in in our body temperature fluctuating throughout the day and that’s going to influence our circadian rhythm.
And lastly, we have social interaction and you probably know that social interaction makes you feel more awake and alert right? This is why if you’re sitting in a boring lecture and there’s no chance of social interaction, you know, the teacher is just kind of droning on and not gonna ask you any questions or interact with you in any way and you’re not interacting with anybody else around you, it’s quite easy to feel drowsy trying to feel more tired in this situation. Whereas if the teacher is talking directly to you and asking you a question or you’re responding, you’re gonna feel more awake and alert.
Or maybe you’ve even had the experience, I know I have, where you’re sitting in a class that’s kind of boring and you’re not interacting with the teacher and then suddenly the teacher asks you a question and you snap awake. You’re like suddenly wide awake and part of this because social interaction helps you feel awake and alert.
And you’ve probably also experienced this if you’ve ever been to a slumber party because it turns out that’s where you end up staying up until like 5:00 in the morning because it turns out it’s really hard to slumber when you’re having this social interaction, where you’re sitting around talking with your friends you feel more awake and alert. And so you end up staying up much later than you would if you were alone.
Okay, so these are the zeitgebers that influence our circadian rhythm. I hope you found this helpful, if so, please like the video and subscribe to the channel for more. Thanks for watching!
