Studies show that booze helps us fall asleep, but halfway through the night it may wake our brains up. (ISTOCKPHOTO) 
 
 “Alcohol makes you sleepy.” 
 
 We’ve all heard about it. Many of us have experienced it. A few of us even swear by it — enough to partake in a glass or two of wine before crawling into bed. 
 
 A nightcap. 
 
 In fact, a little booze has been experimentally (and anecdotally) demonstrated to help us fall asleep faster and increase slow-wave, or deep, sleep in the first half of the night. 
 
 But its effects on other aspects of sleep — notably, the second half of the night — leave little to be desired. 
 
 What causes alcohol’s strange and dichotomous effect on the sleeping brain? And the real question: Do you accept the nightcap or not? 
 
 Research on alcohol and sleep dates back to — well, almost to the dawn of sleep research. 
 
 Nathaniel Kleitman, in his book “Sleep and Wakefulness” (published in 1939, nearly 20 years before his discovery of REM sleep), first described the effects of alcohol before bed on sleep motility and body temperature in healthy nondrinkers. With the identification of the various sleep stages in the 1950s and 1960s, researchers could begin focusing their attention on alcohol and its effect on sleep disorders. 
 
 Perhaps the best replications of, er, college life, anyway, came with studies by Williams and Salamy in the early 1970s. Thirty to 60 minutes before bedtime — which yields the peak blood-alcohol concentration at lights-out — participants were assigned to consume anywhere one to six drinks. (A standard drink is 12 ounces of beer, five ounces of wine or 1.5 ounces of 80-proof distilled spirits.) 
 
 This yielded an interesting result: Despite falling asleep faster, the subjects who consumed more alcohol woke more frequently and experienced lighter sleep during the second half of the night. Williams and Salamy identified this as being a “rebound effect.” After alcohol had been metabolized and eliminated, sleep variables reversed themselves. 
 
 This manifests as disturbed sleep. 
 
 The idea is that the body initially adjusts for alcohol’s effects in order to maintain normal sleep during the first half of the night. During the second half of the night, however, the body stubbornly continues to adjust, ultimately overcompensating and resulting in sleep disruption. 
 
 But exactly what is adjusting, and what’s causing the rebound effect? 
 
 The short answer is: Nobody really knows the whole story — because nobody fully understands sleep yet. But, neurochemically, we have some theories. 
 
 When you take a swig of alcohol, it goes right into the bloodstream, and it’s in your brain within minutes. 
 
 Alcohol mimics gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the brain. When bound to a GABA receptor on a neuron, alcohol allows the influx of negative (or efflux of positive) ions, giving the cell a more negative charge. Thus, the neuron’s attempt to fire an action potential is thwarted. 
 
 Alcohol also inhibits the brain’s major excitatory neurotransmitter, glutamate, by blocking function at glutamate’s NMDA receptors. 
 
 Since glutamatergic and GABAergic neurons comprise 90 percent of all brain cells, this is a pretty big deal. Especially since alcohol also enhances GABA absorption back into the neuron, and even more especially since GABA is recycled into glutamate in a vicious cycle: After an evening of drinking, the theory is that GABA dominates the first half of the night, allowing us to fall asleep (and deeply!). But once GABA is metabolized, much of it becomes the excitatory glutamate. And it’s in glutamate-releasing brain regions (such as the reticular activating system which partially modulates sleep/wake and arousal) that the midnight disruptions kick in. 
 
 Should you partake in a college night of hard-partying and expect a good night’s sleep? No way. 
 
 But the real question: Is one drink before bed going to affect that much? 
 
 A typical person can metabolize something like a quarter of an ounce of alcohol each hour — which is quite slow, given the speed at which it’s absorbed. 
 
 So keep the drink small, and keep it early. An evening cap. 
 
 This was excerpted from the Gainesonbrains blog. ||||| Jordan Gaines Lewis 
 
 Scientific American 
 
 Post 
 
 The Guardian 
 
 and a Society for Neuroscience Early Career Policy Ambassador 
 
 Gaines, on Brains 
 
 website 
 
 is an award-winning science communicator whose work has been featured in, The Washington, TED, and NBC, among others. Jordan is associate editor of the. She's also working toward her Ph.D. in neuroscience at Penn State studying sleep in teens.is her corner of the Internet for mulling over the brain—minus the heavy scientific jargon that typically accompanies it. ||||| When Maria Papova, the creator of Brain Pickings, was distilling the things she'd learned from doing seven years of blogging interestingness at a recent talk—like why you should cultivate the ability to change your mind, build pockets of stillness into your life, and appreciate how long it takes to do anything worthwhile— the cultural curator was tough on a gentle point: to "be as religious and disciplined about your sleep as you are about your work." 
 
 Why? Because every sleeping moment affects every waking moment: as we've covered before, sleep allows you to consolidate your memories (good for knowing things!), let your body relax (good for not feeling anxious all day!) and maybe even clean your brain (good for preventing dementia!). 
 
 Yet not all sleep is experienced equally: it's not just about the quantity of sleep you get, but the quality of the sleep. For instance, if you've had a hard workout during the daytime, you'll be more restful by the nighttime. But there's another factor that affects our sleep: what we put into our bodies. Namely, drinks. 
 
 We have a fun word for the practice of a late night beverage: a nightcap, which, WiseGeek tells us, comes from back in the 1700s when people would don a soft, silly hat to warm themselves and rest better. From our own firsthand research as undergraduates, we can say that an alcoholic nightcap is something analogous: alcohol sedates you and makes your blood vessels dilate, making you feel warmer. 
 
 There's even something slyly sophisticated and sexy about the pre-bed drink, summoning images of Jane Austen and Charles Dickens characters "retiring" to mahogony-lined libraries and sitting before fires checking their iPhones discussing the last matters of the day. Even the New York Times is hip to this, saying that if you should nightcap, you should "stick with the classics: top-shelf whiskey, good brandy (usually Cognac), a burnished, potent, amber liqueur." 
 
 That warm coolness is cool if you want to employ an army of orphans or arrange games of whist, but not so much if you want to do your best work the next day. Because, as scientist Jordan Gaines Lewis says, a nightcap will disrupt your sleep—hampering the recuperation we spoke of above. 
 
 While alcohol has been shown to help you fall asleep faster, it makes you have lighter sleep in the second half of the night. You can thank that counterintuitive trend to the "rebound effect": as in your body adjusts to alcohol over the first half of your sleep, allowing you to sleep normally for the first part of the night—but then actually overcompensates in the second half, messing up your sleep. 
 
 Since we don't have a perfect picture of what happens during sleep, the reasons why, at a neuronal level, alcohol disturbs our sleep aren't quiet clear. If you feel like getting technical, head to Gaines's blog; for our purposes, we can borrow her insight that alcohol mimics one of our most important neurotransmitters—the chemicals that transmit signals from neurons to cells across synapses. 
 
 Gaines's take: 
 
 After an evening of drinking, the theory is that GABA dominates the first half of the night, allowing us to fall asleep (and deeply!). But once GABA is metabolized, much of it becomes the excitatory glutamate. And it's in glutamate-releasing brain regions like the reticular activating system (which partially modulates sleep/wake and arousal) where the midnight disruptions kick in. 
 
 In other words, your brain tries to make up for the weirdness that alcohol brings into your system—and that overcompensation prevents the full benefits of a full night's sleep. So avoid the nightcap, unless, as Gaines says, you make it an early evening one. 
 
 Hat tip: "Alcohol, Sleep, and Why You Might Re-Think that Nightcap."
– A nightcap might help you drift off—but don't expect a good night's sleep for your trouble. In the 1970s, researchers gave subjects each between one and six drinks a half-hour to an hour before bedtime. Those who had more booze fell asleep quicker, but during the second half of the night, they experienced what researchers called a "rebound effect": They woke more often and didn't sleep as deeply, the Washington Post explains in an excerpt from the blog Gaines, on Brains. Why? Experts theorize that at first, the body compensates for the alcohol; as the night goes on, however, the brain "overcompensates," writes Jordan Gaines, worsening our sleep. The metabolization process wakes us up as gamma-aminobutyric acid, an inhibitory neurotransmitter, is turned into glutamate, an excitatory neurotransmitter which affects our sleep. Binge drinking is sure to prevent a good night's sleep. As for a small nightcap, Gaines recommends that if you have it, have it early, so the body has time to process it and your sleep is undisturbed. That will improve your waking life: As Fast Company has put it, "Hate productivity? Enjoy that nightcap." In related news, hangovers cost the US economy $160 billion annually.