Remember the time There's no question that getting a good night's sleep helps you function better -- in most areas. But researchers from the University of Houston found that there's one instance where that may not hold true. They discovered that melatonin, the primary hormone responsible for sleep, may actually inhibit you from forming new memories. They conducted their experiment in zebrafish, whose circadian rhythms are similar to humans (meaning they're at rest during the night, and awake and active during the day). In both zebrafish and humans, levels of melatonin are naturally higher at night. So to test whether the hormone had any effect on the fishes' ability to learn, they treated the fish with supplemental melatonin during the day. The researchers found that the melatonin didn't necessarily affect overall learning but did negatively impact the fishes' ability to form new memories: They performed similarly to fish trained only at night -- when melatonin levels are naturally higher -- on tests designed to measure 24-hour memory. Their next step was to inhibit nighttime melatonin formation in the fish and then test their memory capacity. The difference was, as the lead investigator put it, like "night and day": The fish showed dramatic improvements in nighttime memory formation. The same thing happened when the researchers removed the pineal glands, which are the primary sources of melatonin, from some of the fish. Of course, it's important to keep in mind that melatonin is a natural substance present in all of our bodies -- and sleep is something we need in order to survive. The main take- home message here is not to expect too much of your memory once the sun goes down. If things like night classes and shift work are part of your daily life, try to do most of your studying or training for new job tasks during the day when the lessons are more likely to "stick." And if you find yourself in either of these situations, you may want to think twice about taking melatonin to help you sleep -- there's no use in putting yourself at an even greater disadvantage. In these cases, you may want to opt for another natural sleep aid, like valerian root, instead. Sources:
"Nighttime 'malfunction' of biological clock discovered," Medical News Today (www.medicalnewstoday.com), 11/16/07
"Melatonin suppresses nighttime memory formation in zebrafish," Science 2007; 318(5,853): 1,144-1,146 | 
