Master Your Sleep & Be More Alert When Awake | Huberman Lab Podcast #2 Flashcards
What is sleep?
sleep is this tremendously important period of life because it resets our ability to be focused, alert, and emotionally stable in the wakeful period, so we can’t really talk about wakefulness, focus, motivation, mood, wellbeing without thinking about sleep. What we do in the waking state determines when we fall asleep, how quickly we fall asleep, whether or not we stay asleep, and how we feel when we wake up the next day
What is sleephunger?
So what determines how well we sleep and the quality of our wakeful state? Turns out that’s governed by two forces, the first force is a chemical force, it’s called adenosine. Adenosine is a molecule in our nervous system and body that builds up the longer we are awake, so if you’ve just slept for 8, or 9, or 10 really deep, restful hours, adenosine is gonna be very low in your brain and body. If, however, you’ve been awake for 10, 15, or more hours, adenosine levels are going to be much higher. Adenosine creates a sort of sleep drive or a sleep hunger, and actually, hunger is the appropriate word here
because for most of what we’re gonna discuss today, we can think of it in an analogous way to nutrition. Your nutrition and how well you feel after you eat certain foods, your overall level of fitness and your cellular health and your heart health isn’t governed by any one food item that you might eat or not eat, it’s governed by a number of different factors, how often you eat, how much you eat, which items you eat, et cetera, and what works best for you.
Caffeine; devil or angel ?
So the reason caffeine wakes you up is because it blocks the sleepiness receptor, it blocks the sleepy signal, and this is why when that caffeine wears off, adenosine will bind to that receptor, sometimes with even greater, what we call affinity, and you feel the crash, you feel especially tired.
All of this has to do with the relationship between adenosine and these adenosine receptors, genetic variation, things that are very hard to find out except experimentally, meaning each of you needs to decide and figure out for yourselves whether or not you can tolerate caffeine and at what times of day you can tolerate caffeine in order to still fall asleep easily and get good sleep, so rather than demonize caffeine, or say that everyone can drink caffeine until late, you need to figure out what’s right for you.
That’s because adenosine is building up at levels higher and higher because you’ve been awake for those extra four hours. However, if you’ve ever pulled an all-nighter, you’ll notice something interesting, as morning rolls around, you’ll suddenly feel an increase in your energy and alertness again, even though adenosine has been building up for the entire night. Now, why is that? The reason that is is because there’s a second force which is governing when you sleep and when you’re awake, and that force is a so-called circadian force, circadian means about a day or about 24 hours, and inside all of us is a clock that exists in your brain and my brain, and the brain of every animal that we’re aware of, that determines when we want to be sleepy and when we want to be awake.
That block of sleep and when it falls within each 24-hour cycle is governed by a number of different things, but the most powerful thing that’s governing when you want to be asleep and when you want to be awake is light, and in particular, it’s governed by sunlight, and I can’t emphasize enough how important and how actionable this relationship is between light and when you want to sleep.
Caffeine; devil or angel ?
So the reason caffeine wakes you up is because it blocks the sleepiness receptor, it blocks the sleepy signal, and this is why when that caffeine wears off, adenosine will bind to that receptor, sometimes with even greater, what we call affinity, and you feel the crash, you feel especially tired.
All of this has to do with the relationship between adenosine and these adenosine receptors, genetic variation, things that are very hard to find out except experimentally, meaning each of you needs to decide and figure out for yourselves whether or not you can tolerate caffeine and at what times of day you can tolerate caffeine in order to still fall asleep easily and get good sleep, so rather than demonize caffeine, or say that everyone can drink caffeine until late, you need to figure out what’s right for you.
That’s because adenosine is building up at levels higher and higher because you’ve been awake for those extra four hours. However, if you’ve ever pulled an all-nighter, you’ll notice something interesting, as morning rolls around, you’ll suddenly feel an increase in your energy and alertness again, even though adenosine has been building up for the entire night. Now, why is that? The reason that is is because there’s a second force which is governing when you sleep and when you’re awake, and that force is a so-called circadian force, circadian means about a day or about 24 hours, and inside all of us is a clock that exists in your brain and my brain, and the brain of every animal that we’re aware of, that determines when we want to be sleepy and when we want to be awake.
That block of sleep and when it falls within each 24-hour cycle is governed by a number of different things, but the most powerful thing that’s governing when you want to be asleep and when you want to be awake is light, and in particular, it’s governed by sunlight, and I can’t emphasize enough how important and how actionable this relationship is between light and when you want to sleep.
Release your Hormones (At the right times)
we tend to wake up about the time that the sun is rising or so, and as we do that, adenosine levels tend to be low if we’ve been asleep for reasons that you now understand, and our system generates an internal signal that is in the form of a hormone. Now, I’ve talked a lot about neuromodulators and neurotransmitters, I haven’t talked a lot about hormones yet on this podcast. The definition of a hormone is it’s a substance, a chemical that’s released from one organ in your body that goes and acts on other organs elsewhere in your body, including your nervous system. When you wake up in the morning, you wake up because a particular hormone called cortisol is released from your adrenal glands, your adrenal glands sit right above your kidneys, and there’s a little pulse of cortisol.
There’s also a pulse of some, and when I say a pulse, I just mean the release of a little bit, there’s also a pulse of epinephrine, which is adrenaline, from your adrenals and also in your brain, and you feel awake. Now, that pulse of cortisol and adrenaline and epinephrine might come from your alarm clock, it might come from you naturally waking up, but it tends to alert your whole system in your body that it’s time to increase your heart rate, it’s time to start tensing your muscles, it’s time to start moving about.
but there’s this normal, healthy rising tide of cortisol that happens early in the day, and I say healthy because it wakes you up, it makes you feel alert, and it makes you feel able to move and wanting to move and to go about your day for work, for exercise, for school, for social relations, et cetera. So when you wake up in the morning is when that cortisol pulse takes off,
and something else important happens, a timer is set in your body and in your nervous system that dictates when a different hormone called melatonin, which makes you sleepy, will be secreted from a particular brain region, so let’s talk about that.
So there’s two mechanisms here, a wakefulness signal and a sleepiness signal, and the wakefulness signal triggers the onset of the timer
for the sleepiness signal.
Pineal Melatonin warning
Now, that sleepiness signal that we call melatonin that’s released from the pineal comes only from the pineal. Okay, so the rhythm of cortisol and melatonin is what we call endogenous, it’s happening in us all the time without any external input, in fact, if we were in complete darkness, living in a cave with no artificial lights whatsoever, or we were in complete brightness where we never experienced any darkness, these rhythms of cortisol and melatonin would continue you would have a bump in cortisol, or a pulse in cortisol, that would drop off with time, and then melatonin would come up about 12 to 14 hours later, but these endogenous systems of our body, which are both hormonal and neural, were set so that external things could govern when they happen.
Strange vision is Good vision
what happens is you wake up, and what happens when you wake up? You open your eyes. When your open your eyes, light comes into your eyes. Now, the way this system works is that you have a particular set of neurons in your eye, they’re called retinal ganglion cells.
Well, it turns out that these neurons in our eye that set the circadian clock and then allow our circadian clock to set all the clocks of all the cells and organs and tissues of our body responds best to a particular quality of light and amount of light, and those are the qualities of light and amount of light that come from sunlight, so these neurons, what they’re really looking for, although they don’t have a mind of their own, is the sun at what we call low solar angle, the eye and the nervous system don’t know anything about sunrises or sunsets, it only knows the quality of light that comes in when the sun is low in the sky, the system evolved so that when the sun is low in the sky, there’s a particular contrast between yellows and blues that triggers the activation of these cells
so many people find that they need to use sunlight simulators in the form of particular lights that were designed to simulate sunlight, however, and I’m not out to attack the companies that produce those, there’s another solution to that, you can simply go outside for longer, even if there’s a lot of dense cloud cover, you’re probably getting anywhere from 10,000 to 50,000 lux, L-U-X, which is just a measure of light energy, and that should be sufficient to set the circadian clock
Blue light is great! (in the morning)
A lot of people will say, “Oh, I should be “wearing blue blockers throughout the day.” No, that’s the exact wrong thing, if you’re going to use blue blockers, we can talk about that, that should be reserved for late in the evening because light suppresses melatonin. I’ve been asked many times before about this pineal gland and there are a lot of ancient practices
that map to some of the things that I’m saying, and people will always say, “Oh, I heard that sunlight “is great for the pineal.” Well, perhaps, but we have to careful about that phrase, sunlight inhibits the pineal, it prevents it from releasing melatonin, darkness allows the pineal to release melatonin, so the pineal is not the gland or the organ of sunlight, it is the gland of darkness, in fact, melatonin can be thought of as a sleepiness signal that’s correlated with darkness, so get up each morning, try and get outside, I know that can be challenging for people, but anywhere from 2 to 10 minutes of sunlight exposure is going to work well for most people, and you wanna do this on a regular basis and you don’t have to do it exactly at sunrise,
The importance of sunlight
So viewing light early in the day, ideally sunlight, is key for establishing healthy sleep-wake rhythms and for allowing you to fall asleep easily at night. Now, it’s not gonna make sure that all that happens every single time, but it is the foundation of proper sleep and what we call circadian health, it governs metabolism and so many other things that are supposed to exist on a regular 24-hour cycle.
Using exercise & food to set your clock
Some of you, many of you, might be asking, “What else can help set this rhythm?” Well, it turns out that light is what we call the primary zeitgeber, the time giver, but other things can help establish this rhythm of cortisol followed by melatonin 12 to 16 hours later as well. The other things besides light are timing of food intake, timing of exercise, as well as various drugs or chemicals that one might ingest, not illegal drugs, although those will impact circadian mechanisms as well, but the reason we focus so heavily on light is that light is the main way that this central clock, the suprachiasmatic nucleus, was supposed to be set, and we know that because it’s the only direct input to the clock.
The power of sunset
The main thing is that bright light early in the day, the other thing is sunset, when the sun is also at low solar angle, low, close to the horizon, by viewing sunlight at that time of day in the evening, or afternoon, depending on what time of year it is and where you are in the world, these melanopsin cells, these neurons in your eye, signal the central circadian clock that it’s the end of the day. viewing light early in the day is key, viewing light later in the day when the sun is setting, or around that time, can help protect these mechanisms, your brain and body, against the negative effects of light later in the day. so the best thing to do is just to get outside for a few minutes, anywhere from 2 to 10 minutes, also in the afternoon. Having those two signals arriving to your central clock that your body, your internal world, knows when it’s morning and knows when it’s evening, is tremendously powerful.
Light during the day
So the simple way to think about this is you want as much light as is safely possible early in the day, morning and throughout the day, including blue light, so take those blue blockers off during the day unless you have a real issue with screen light sensitivity, and you want as little light coming into your eyes, artificial or sunlight, after, say, 8:00 p.m., and certainly, you do not want to get bright light exposure to your eyes between 11:00 p.m. and 4:00 a.m. so the simple way to think about this is if you’re having trouble waking up early and feeling alert early in the day, you’re going to wanna try and get bright light exposure even before waking up because it will advance your clock, it’s sort of like turning the clock forward, whereas if you are having trouble waking up early, you definitely don’t want to get too much light exposure or any light exposure to your eyes late in the evening and in the middle of the night because it’s just gonna delay your clock more and more,
How about naps?
A brief note about naps, naps, provided that they’re less than one ultradian cycle, provided they’re 20 minutes or 30 minutes or even an hour, can be very beneficial for a lot of people, you don’t have to take them, but many people naturally feel a dip in energy and focus late in the afternoon, in fact, if we were gonna look at wakefulness, what we would find is that you get that morning light exposure, hopefully, your cortisol goes up, people will start feeling awake, and then around two, or three, or four in the afternoon, there’s a spike in everything from alertness to ability to learn, some metabolic factors drop, and then it just naturally comes back up, and then it tapers off as the night goes on. So for some of you, naps are great, I love taking naps, some people, they wake up from naps feeling really groggy, that’s probably because they’re not sleeping as well as they should at night or as long as they should at night, and so they’re dropping into REM sleep or deeper forms of sleep in the day time, and then they wake up and they feel kind of disoriented, other people feel great after a nap, so that’s another case where, just like with caffeine,
so sort of have to evaluate for yourself.
What are other options beside napping?
it’s a thing that they call yoga nidra, yoga nidra actually means yoga sleep, and it’s a sort of meditation that you listen to, there are number of scripts, I’ve talked about this on podcasts before but I’m going to post a link to the two that I like most, that allows you to consciously bring your entire body and mind into a state of deep relaxation, and sometimes you fall asleep and sometimes you don’t, this is done for 10 to 30 or even 60 minutes at a time. The other thing that works really well is meditation, so I’m talking about naps, but I’m also talking about yoga nidra, which is sort of a form of meditation, and then more standard forms of meditation, all three of those do something powerful which is that they bring our mind into a state of less so-called sympathetic nervous system activation, go back and listen to episode one if that doesn’t make any sense, which is what governs your alertness, and instead, it activates cells and circuits in your body that promote the parasympathetic nervous system, or the calming system.
If we wanna stay up late on New Year’s or we wanna push an all-nighter, some people can do that more easily than others, but we’re all capable of doing that,
but it’s very hard to make ourselves fall asleep, and so there’s a sort of asymmetry to the way our autonomic nervous system, which governs this alertness-calmness thing, the sympathetic and parasympathetic nervous system, there’s an asymmetry there
where we are more easily able to engage wakefulness and drive wakefulness, we can force ourselves to stay awake, than we are able to force ourselves to fall asleep, and one of the things that I say over and over again, and I’m gonna continue to say over and over again, is it’s very hard to control the mind with the mind, when you have trouble falling asleep, you need to look to some mechanism that involves the body, and all the things I described, meditation, hypnosis, yoga nidra, all involve exhale-emphasized breathing, certain ways of lying down and controlling the body, we’re gonna get into breathing in real depth at another time, but all of those involve using the body to control the mind rather than trying to, you know, wrestle your mind into a certain pattern of relaxation,
how can you use the body to control the mind
I’m not going into details right now but you can see the yoga nidra script or the reveriehealth.com, or Headspace would be a great place to adopt a meditation practice, any of those are really teaching you to use your body to control your mind, and to allow you to explore the mind-body relationship in a way that gives you more control over your mind and the mind-body relationship, okay? So we talked about light, we talked about activity and timing of light, we talked about the usefulness of naps, and these things that I’m calling non-sleep deep rest, which include meditation, yoga nidra, and hypnosis,
non-sleep deep rest, or what I, hereafter, we will refer to as NSDR,
