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(CNN) Traveling to a different time zone can be very exciting. You are ready to explore and check items off your bucket list. Jet lag is probably the last thing you want to deal with. 
  
 A math model developed by a group of researchers at the University of Maryland explains why it takes you days to establish a new sleep-wake cycle when you travel east, but you may barely feel anything when going west. 
  
 Cross-time-zone travel causes disruptions in the brain's internal clock, known as the circadian rhythm. Cells in a brain region called suprachiasmatic nucleus maintain a healthy rhythm by oscillating in a synchronized manner. Known as a "pacemaker cell," these have a natural cycle slightly longer than 24 hours. 
  
 After rapid time zone shifts, these cells cannot instantly establish a rhythm appropriate to the new time zone, making it hard for people to immediately live by a new schedule. 
  
 The study , published Tuesday in the journal Chaos, uses math equations to look at how pacemaker cells in the brain resynchronize themselves to adapt to a new sleep cycle. 
  
 Michelle Girvan, co-author of the study and associate professor at the physics department of University of Maryland, said that the project is an extension of an undergraduate research program. She wanted the research to be relatable to everyday living while mathematically workable. 
  
 Modeling the brain clock with math 
  
 Think about how you set your watch forward to match the time in the destination when you head east. You would expect your brain clock to do the same for eastward trips, which basically makes you start the day earlier. But because most pacemaker cells in the internal clock have a natural cycle of 24.5 hours (longer than a day), it actually has a much easier time stretching the day than shrinking it. 
  
 The researchers worked out a math model to represent all the pacemaker cells in our brain clock and accounted for inputs such as lights and how sensitive a person is to sunlight, cloudiness, geographical latitude and seasonal factors, therefore creating new circadian rhythms over various trajectories. 
  
 The model shows that when your eastbound trip is long enough, the pacemaker cells adjust themselves to move the brain clock backward. This "wrong direction" is what makes it extra hard to recover from long-distance eastward travels. When you go east and cross nine time zones, instead of adjusting nine hours forward, the brain clock sets 15 hours backward. This is the kind of travel where jet lag is the toughest to overcome. 
  
 Even if your eastward trip is short and your internal clock manages to adjust itself forward, it still has a harder time doing so because of its 24.5-hour natural period. For instance, according to the model, it will take an average person about four days to recover from an eastward trip crossing three time zones, but only three days from a westward one. 
  
 The model also explains why different people suffer from jet lag of various severity. "Some people may have a natural circadian rhythm with a period of 24.5 hours, while others may have longer or shorter natural rhythms," said Girvan in a news release . "Our model suggests the difference between a person's natural period and 24 hours controls how they experience jet lag." 
  
 Girvan stressed that the mathematical model they used is a greatly simplified one. "We want to see people push this further in terms of the model parameters and biological data," said Girvan, "and make the model even more biologically realistic." 
  
 How to recover faster from jet lag 
  
 The dynamics among cells, the strength of external signals and a person's inherent sensitivity to natural stimuli all affect how soon the body clock readjusts itself, according to Girvan. So it is important to keep these things in mind when preparing for your next adventure. 
  
 Girvan suggested that you know your body well, and know what kind of travel is the most disruptive for you so you can start preparing beforehand. 
  
 Before your trip, try to artificially change external light sources corresponding to the ones in the new time zone. 
  
 Join the conversation See the latest news and share your comments with CNN Health on Facebook and Twitter. 
  
 When you arrive at your destination, resist the temptation of closing the curtains in your hotel room and diving right into bed when it is still bright outside. What you should do is to fully expose yourself to the local light-dark cycle. It might not be easy to do, but your recovery will be faster if you stay awake during daytime and sleep only when it gets dark. ||||| If you've ever found that recovery from jet lag took even longer than you expected it to, physicists have answers: A new mathematical model helps explain why flying east is tougher on jet-lag recovery. 
  
 The model takes into account how certain cells in the human brain respond to crossing time zones, according to the study, published today (July 12) in the journal Chaos. 
  
 These cells, called "neuronal oscillator cells," regulate people's circadian rhythm, or biological clock, by syncing up with one another and also linking up with external cues, said Michelle Girvan, an associate professor of physics at the University of Maryland and a co-author of the study. [10 Things You Didn't Know About the Brain] 
  
 But the cells don't quite operate on a perfect 24-hour schedule, Girvan told Live Science. Rather, their activity follows a cycle that lasts slightly longer than that, about 24.5 hours, she said. That means that it's easier for a person to extend the length of a day — for example, by flying west across time zones — than to shorten the day, by flying east, she said. 
  
 The researchers incorporated the activity of these cells into their model of jet lag, Girvan said. They found that jet-lag recovery doesn't quite fit into a neat pattern of the widely touted advice to give yourself "one day of recovery for every time zone crossed." 
  
 Rather, the amount of time it takes for a person to adjust to a new time zone depends on not only how many time zones are crossed but also the direction in which the person travels. 
  
 The researchers found that for westward travel, a person who crossed three time zones would fully adjust in a little less than four days. For six time zones, recovery would take about six days. For nine time zones, the recovery would take just less than eight days. 
  
 However, when a person travels eastward, the recovery times don't match up as neatly. When a person crosses three time zones going east, it takes a little more than four days to recover. For six time zones, the recovery time jumps to more than eight days. And for nine time zones, the recovery period is more than 12 days. 
  
 And when a person crosses 12 time zones, going either east or west, the recovery period is the same: around nine days. 
  
 Girvan noted that not everyone has a circadian rhythm of exactly 24.5 hours. Rather, it varies from person to person, she said. 
  
 The other factor to consider is external cues such as sunlight, Girvan added. How a person reacts to these external cues can also impact how quickly he or she will adjust to a new time zone, she said. 
  
 The researchers hope that their new model can be used in the future to figure out the best ways to beat jet lag, they wrote in their study. 
  
 But planning ahead can help you adjust. For example, if you will be traveling six time zones eastward, start by setting your clock ahead an hour or two several days before you leave, Girvan said. And when you arrive in a new time zone, make sure that the external cues you are exposed to match the new time zone, she said. That means that if it's daytime in the new time zone, expose yourself to sunlight. And if it's nighttime, avoid artificial lights, including those from smartphones and computers, to help your biological clock adjust, she said. 
  
 Originally published on Live Science. ||||| Cells in the brain's Suprachiasmatic Nucleus (SCN) are known to regulate circadian rhythms in mammals. We model synchronization of SCN cells using the forced Kuramoto model, which consists of a large population of coupled phase oscillators (modeling individual SCN cells) with heterogeneous intrinsic frequencies and external periodic forcing. Here, the periodic forcing models diurnally varying external inputs such as sunrise, sunset, and alarm clocks. We reduce the dimensionality of the system using the ansatz of Ott and Antonsen and then study the effect of a sudden change of clock phase to simulate cross-time-zone travel. We estimate model parameters from previous biological experiments. By examining the phase space dynamics of the model, we study the mechanism leading to the difference typically experienced in the severity of jet-lag resulting from eastward and westward travel. 
  
 Published by AIP Publishing. 
  
 Received Mon Mar 21 00:00:00 UTC 2016 Accepted Wed Jun 01 00:00:00 UTC 2016 Published online Tue Jul 12 00:00:00 UTC 2016 
  
 Lead Paragraph: Jet-lag due to cross-time-zone travel is thought to result from a disruption of the circadian clock within the human brain. After a rapid shift in time-zones, the brain's oscillatory pacemaker cells cannot instantly establish a rhythm appropriate to the new time-zone. We study the dynamics of how these coupled pacemakers cells adjust to the new time-zone. Experiments on suprachiasmatic nucleus (SCN) slice cultures from neonatal mice (similar results for humans are not available) show that when the pacemaker cells are uncoupled, they display dynamical periods that are near 24 h, but differ from cell to cell, with an average slightly longer than 24 h. In this paper, we model the dynamics of the circadian clock in response to travel, starting at the level of the individual coupled oscillators and then making use of a reduction of this microscopic model to a low dimensional macroscopic description. Our model helps to explain how eastward and westward travel can have different effects on the recovery of circadian rhythms. 
  
 Acknowledgments: This work was supported by the Army Research Office under Grant No. W911NF-12-1-0101, and by the National Science Foundation under Grant No. PHY-1461089. ||||| Jet lag is terrible no matter where you're going. But regular travellers will know that your body clock seems to take way longer to recover when you're flying east, rather than heading west. 
  
 Now physicists have finally been able to explain why this could be happening, using a mathematical model to show that our brain cells respond differently depending on which direction we're travelling. 
  
 Jet lag occurs when the brain cells that regulate our circadian rhythm, called neuronal oscillator cells, can't adjust to our new time zone fast enough, messing up our metabolism, sleep pattern, and pretty much everything else on the first few days of our vacation. 
  
 Up until now, the general advice has been to give yourself one day of recovery for every time zone crossed. But the new research, led by physicists from the University of Maryland, suggests that might not be enough if you're flying east. 
  
 That's because our neuronal oscillator cells - the pacemakers for the rest of our brain - don't follow a perfect 24-hour schedule. 
  
 Studies have shown that without any external cues, their activity follows a slightly longer cycle - around 24.5 hours. And that means it's easier for someone to extend the length of their day - for example, by flying westward across time zones - than shorten their day by flying east. 
  
 To figure this out, the physicists took this 24.5-hour rhythm and applied it to a mathematical model that calculates how long it takes someone to recover from jet lag - and they showed that it's not just the amount of time zones crossed that impacts recovery time, but also the direction someone's travelling. 
  
 Their model showed that someone who crosses three time zones heading westward can adjust fully in a little less than four days. And for six time zones, recovery takes around six days - much as you'd expect based on the "one day per time zone crossed" principle. 
  
 But when people are travelling east, the model predicts that it'll take more than four days to recover from a flight that crosses three time zones, and a whopping eight days to recover from crossing six time zones (which is why it feels so hellish to fly from New York to Paris). 
  
 The model also explains why some people can cope with jet lag so much better than others - they likely have slight variations in their natural brain cell cycle. 
  
 "Some people may have a natural circadian rhythm with a period of 24.5 hours, while others may have longer or shorter natural rhythms," said lead researcher Michelle Girvan, from the University of Maryland. "Our model suggests that the difference between a person's natural period and 24 hours controls how they experience jet lag." 
  
 The research has been published in the journal Chaos, but it's important to note that none of this has been tested experimentally as yet - the researchers made their predictions by factoring in everything they know about how the human brain adjusts to new time zones, and let maths do the rest. 
  
 Further research is now needed to back up these predictions, but the researchers' ultimate goal is to help people better manage their expectations when they travel, and will "serve as a guide for developing more in-depth qualitative approaches, as well as strategies to combat circadian rhythm disruptions due to rapid cross-time-zone travel, shift work, or blindness," said Girvan. |||||
Output:
A flight from Paris to New York is easier on the brain than one from New York to Paris, according to a new study that finds jet lag is based not only on distance traveled, but also the direction of travel. In the journal Chaos, researchers from the University of Maryland present a mathematical model that considers the brain's "neuronal oscillator cells," which regulate a person's biological clock, or circadian rhythm. Though everyone's clock is different, it tends to operate on a schedule slightly longer than 24 hours, study author Michelle Girvan explains, per Live Science. That means the brain responds better to a longer day achieved by flying west across time zones than a shorter one achieved by flying east. Researchers say a person flying west across three time zones can recover in less than four days, while a person flying east would need a little more than four days. The divide becomes more apparent across more time zones. A person flying west across nine time zones would need a little less than eight days to recover, compared to more than 12 days for those flying east—though the recovery for crossing 12 time zones is about nine days either way. The mathematical model—which considers external cues like sunlight and geographical latitude, per CNN—was based on a circadian rhythm of 24.5 hours, and some people "may have longer or shorter natural rhythms," Girvan says. But overall, the study shows that the general rule of giving yourself one day of recovery for every time zone crossed is off base. Girvan says researchers hope the model will "serve as a guide for developing more in-depth qualitative approaches, as well as strategies to combat circadian rhythm disruptions due to rapid cross-time-zone travel, shift work, or blindness," per Science Alert. (This trick might stop jet lag before it starts.)