Essentials: Time Perception, Memory & Focus

**Andrew Huberman** (0:00)
Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health and performance.
I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today, we are talking about time perception. Our perception of time is perhaps the most important factor in how we gauge our life. And the reason for that is that our perception of time is directly linked to the neurochemical states that control mood, stress, happiness, excitement. And of course, it frames the way in which we evaluate our past. It frames our present, whether or not we think we are on track or off track, and it frames our sense of the future. So let's talk about time perception. And the most fundamental aspect of time perception is something called entrainment. Entrainment is the way in which your internal processes, your biology and your psychology, are linked to some external thing. And the most basic form of entrainment that we are all a slave to all year round for our entire life are so-called circennial rhythms. We have neurons, nerve cells in our eye, in our brain and in our body that are marking off the passage of time throughout the year. Literally a calendar system in your brain and body. And the way this works is beautifully simple. Light seen by your eyes inhibits, meaning it reduces the amount of a hormone released in your brain called melatonin. Melatonin has two major functions. One function is to make you sleepy at night. And the other is to regulate some of the other hormones of the body, in particular testosterone and estrogen. Throughout the year, depending on where you live, day length varies. And as a consequence, the amount of light from the sun that is available to you varies. So when days are long, the amount of melatonin in your brain and body that's released tends to be less. When days are very short, the amount of melatonin that's released and the duration that that melatonin exists in your brain and body tends to be much longer. So melatonin correlates with day length. And if we are viewing more light, we have less melatonin, we view less light, we have more melatonin.
You see different amounts of light each day, but we have a process in our brain and body that averages the amount of light that you're seeing, both from artificial sources and from sunlight, and measures that off. And it's so exquisitely precise that for a given, say, eight-hour day in the spring, because spring in the Northern Hemisphere or elsewhere, you know, days are getting longer, that means that the amount of melatonin is getting progressively less and less, and that signal is conveyed to all the systems of your brain and body. And this is why most people, not all, but most people feel like they have more energy in the spring. Conversely, when you have an eight-hour day in the winter, the amount of melatonin that corresponds to that eight-hour day is getting progressively greater and greater, because why? Days are getting shorter, so melatonin is increasing from day to day to day. Every cell and system of your body pays attention to this, and as a consequence, most people, not all, but most people feel they have a little less or sometimes a lot less energy and a slightly lower mood in the winter months. Now, there are exceptions to this, of course, but the melatonin signal is the way in which your internal state, your mood, your sense of energy, even your appetite is entrained, is matched to some external event. In this case, the event is the rotation of the earth around the sun. There are other forms of entrainment, meaning the matching of your brain and body to things that are happening in your external environment. Across the calendar year, the amount of testosterone and estrogen that human beings make varies, such that in longer days, they tend to make more testosterone and estrogen than in shorter days. The next level of time or bin of time, as we say, that we are all entrained or matched to is the so-called circadian time cycle, which is 24-hour rhythm. This is perhaps the most powerful rhythm that we all contain and that none of us can escape from.
We all have this circadian clock that resides over the roof of our mouth, the cells in that circadian clock fire, meaning they release chemicals into our brain and body on a very regular rhythm. Not surprisingly, there are periods of every 24-hour cycle when we are very active and we tend to be alert and others when we are asleep. We have the circadian clock, it oscillates, it goes up and down once every 24 hours and then repeats. Every cell of our body has a 24-hour oscillation in the expression of various genes. They are entrained, as we say, to the outside light-dark cycle because morning sunlight, evening sunlight, and the lack of light in the middle of the night make sure that the changes, these oscillations that are occurring within the cells of our brain and body are matched to the outside light-dark cycle. And I cannot emphasize enough how important it is that your circadian entrainment be precise. Why? Because disruptions in circadian entrainment cause huge health problems. They increase cancer risk. They increase obesity. They increase mental health issues. They decrease wound healing. They decrease physical and mental performance. They disrupt hormones. You want your cells to be linked to the circadian cycle that's outside you and the circadian cycle outside you mainly consists of when there's sunlight and when there is not. And that's why the simple protocols to fall out of this whole discussion about circadian entrainment are the following. View 10 to 30 minutes of bright light, ideally sunlight within an hour of waking, assuming that you're waking early in the day, especially you wake up early in the day, get outside, see sunlight. Do that again in the afternoon or around evening, 10 to 30 minutes, depending on how bright it is outside. Basically, you want as much bright light, ideally from sunlight, coming in through your eyes throughout the day. And then in the evening, you want as little bright light coming in through your eyes. There are other ways to so-called entrain your circadian clock. One of the best ways to do that is to engage in physical activity at fairly regular times of day. You don't have to do it every day, but if you're going to exercise, try and exercise at a fairly consistent time of day. What happens when this circadian clock starts getting disrupted? I mean, this is, after all, an episode about time perception. It's not an episode about circadian rhythms and entrainment. Well, there's a classic study by Ashoff done in 1985 that's now been repeated many times where they had people go into environments where they didn't have clocks and they didn't have windows and they didn't have watches. And they were sometimes even in constant dark or constant light. And they evaluated how well people perceive the passage of time on shorter time scales. And what they found was really interesting. What they found is that people underestimate how long they were in these isolated environments. So after 42 days or so, they'd ask people, how long do you think you've been in here? And people would say 28 days or 36 days. They generally underestimated how long they had been in this very odd environment with no clocks or watches or exposure to sunlight or regular rhythms of artificial light. In addition, they found that their perception of shorter time intervals was also really disrupted. So if they asked them to measure off two minutes, normally people are pretty good at measuring off two minutes. People come within five to 15 seconds at most. Well, when people's circadian clocks or circadian entrainment, I should say, was disrupted, their perception of time measurement on shorter time scales of minutes or even seconds was greatly disrupted. And as we'll see in a couple of minutes, that actually causes great problems for how you contend with work, how you contend with challenges of different kinds. You want your circadian entrainment to be pretty locked in or pretty entrained to the outside light dark cycle so that your perception of time on shorter time intervals can be precise because the ability to perceive time accurately for the given task or given thing that you're involved in turns out to be one of the most fundamental ways that predicts how well or poorly you perform that thing or task. We've known for a long time that there are things that we can do to improve our sleep and that includes things that we can take. Things like magnesium threonate, theanine, chamomile extract and glycine along with lesser known things like saffron and valerian root. These are all clinically supported ingredients that can help you fall asleep, stay asleep and wake up feeling more refreshed. I'm excited to share that our long time sponsor AG1 just created a new product called AGZ, a nightly drink designed to help you get better sleep and have you wake up feeling super refreshed. Over the past few years, I've worked with the team at AG1 to help create this new AGZ formula. It has the best sleep supporting compounds in exactly the right ratios in one easy to drink mix. This removes all the complexity of trying to forge the vast landscape of supplements focused on sleep and figuring out the right dosages and which ones to take for you. AGZ is, to my knowledge, the most comprehensive sleep supplement on the market. I take it 30 to 60 minutes before sleep. It's delicious, by the way. And it dramatically increases both the quality and the depth of my sleep. I know that both from my subjective experience of my sleep and because I track my sleep. I'm excited for everyone to try this new AGZ formulation and to enjoy the benefits of better sleep. AGZ is available in chocolate, chocolate mint and mixed berry flavors. And as I mentioned before, they're all extremely delicious. My favorite of the three has to be, I think chocolate mint, but I really like them all. If you'd like to try AGZ, go to drinkagz.com/huberman to get a special offer. Again, that's drinkagz.com/huberman.