Summer vacation is in full swing, but that's no reason to let the brain veg. To keep that noggin in tip-top shape, we've put together a list of new and creative ways to increase brain function, like golfing, mowing the lawn, and munching on pumpkin seeds. Read on for more easy ways to hit genius status pronto.
1. Aerobic Exercise
Read books, study hard—and do jumping jacks? There’s a ton of research on the link between exercise and cognitive function Exercise and the brain: something to chew on. Van Praag, Henriette. Neuroplasticity and Behavior Unit, Laboratory of Neurosciences, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD. Trends in Neuroscience 2009; 32(5): 283-290. Wheel running attenuates microglia proliferation and increases expression of a proneurogenic phenotype in the hippocampus of aged mice. Kohman, R.A., Deyoung, E.K., Bhattacharya, T.K. Department of Psychology, University of Illinois, Beckman Institute, Urbana, IL. Brain, Behavior, and Immunity 2012;26(5):803-10.. And aerobic exercise seems like an especially great way to make it to MENSA—one study showed adults’ brain-processing speed improved after half an hour of moderate exercise. Do the brain a favor and get moving!
2. Listening to Music While Exercising
Pitbull, Lady Gaga, or old-school Madonna, pumping up the jams while working out can improve cognitive functions. In one study, cardiovascular rehabilitation patients who exercised to music performed better on a test of verbal fluency than those who worked out sans tunes Short-term effects of exercise and music on cognitive performance among participants in a cardiac rehabilitation program. Emery, C.F., Hsiao, E.T., Hill, S.M., et al. Department of Psychology, Ohio State University, Columbus. Heart & Lung: The Journal of Critical Care 2003;32(6):368-73.. Or maybe just waltz your way through a workout—other studies suggest listening to classical music can improve spatial processing and linguistic abilities Cortical responses to Mozart's sonata enhance spatial-reasoning ability. Suda, M., Morimoto, K., Obata, A., et al. Department of Social and Environmental Medicine, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka, Japan. Neurological Research 2008;30(9):885-8.. A way to work the brain and the muscles? Now that’s music to our ears.
3. Strength Training
Bulk up the brain and hit the weight room. Research suggests strength training not only builds strong muscles and bones—it can also increase brain functioning Spatial memory is improved by aerobic and resistance exercise through divergent molecular mechanisms. Cassilhas, R.C., Lee, K.S., Fernandes, J. et al. Psychobiology and Exercise Research Center, CEPE, Sao Paolo, Brazil. Neuroscience 2012 Jan 27;202:309-17.. That’s because lifting weights may increase levels of brain-derived neurotrophic factor (BDNF), which controls the growth of nerve cells.
Bust a brain-boosting move on the dance floor this weekend. Research suggests dancing involves mental challenges like coordination and planning, and may protect against cognitive decline Six months of dance intervention enhances postural, sensorimotr, and cognitive performance in elderly without affecting cardio-respiratory functions. Kattenstroth, J.C., Kalisch, T. Holt, S. Fronteirs in Aging Neuroscience 2013;5:5.. Duh—has anyone ever done the Macarena?
5. Golf A few rounds of golf may do more than just work out the arms Training-induced neural plasticity in golf novices. Bezzola, L., Merrilat, S., Gaser, C., et al. Institute of Psychology, Division Neuropsychology and International Normal Aging and Plasticity Imaging Center, University of Zurich, CH-8050 Zurich, Switzerland. Journal of Neuroscience 2011;31(35):12444-8.. One study found golfing causes structural changes in the parts of the brain associated with sensorimotor control. Get smart and hit the green.
A math test or spelling bee may be the last thing on anyone’s mind during savasana. But research suggests yoga can improve mood and concentration, enhance cognitive performance, and even prevent cognitive decline in older adults Long-term concentrative meditation and cognitive performance among older adults. Prakash, R., Rastogi, P., Dubey, I., et al. Ranchi Institute of Neuropsychiatry and Allied Sciences, Psychiatry, Ranchi, India. Neuropsychology, development, and cognition 2011. Epub ahead of print.. Namaste, Einstein.
7. A Good Night’s Sleep
Stay up all night studying or hit the hay? Slipping between the sheets might be the better option: For most people, a solid seven hours of sleep is important to maintain cognitive skills such as learning, concentration, and memory. One study even showed people who slept in on the weekends were sharper during the week Neurobehavioral Dynamics Following Chronic Sleep Restriction: Dose-Response Effects of One Night for Recovery. Banks, S., Van Dongen, H.P.A., Maislin, G., et al. Division of Sleep and Chronobiology, Department of Psychiatry, University of Pennsylvania School of Medicine, Philadelphia, PA. Sleep 2010;33(8):1013-1026.. Just don’t nod off during the meeting…
8. Power Naps
For those who didn’t quite catch enough zzzs last night, a power nap may be just the thing to help stay focused. It’s unclear how long the nap should last—in one study, young adults who napped for 90 minutes showed significant improvements in memory. But other research suggests even naps that last a few minutes can increase alertness The effects of napping on cognitive functioning. Lovato, N., Lack, L. School of Psychology, Flinders University, Adelaide, SA, Australia. Progress in Brain Research 2010;185:155-66.. On the other hand, some scientists say naps only improve memory if they involve dreaming.
9. Breaking a Routine
If the barista at the local coffee shop knows what “I’ll have the usual” means, it might be time to change that routine. Adding a twist to the day keeps the brain on its toes — try wearing a watch upside down or brushing your teeth with a nondominant hand.
10. Getting Organized
Leftover pizza crust and a pile of old receipts are more than just unsightly—they may also impede our ability to get stuff done. Clear the desk and the mind at the same time: An organized workspace may help improve memory and cognitive skills.
Stick it to those elementary school teachers and fill every margin to the brim. Research suggests doodling during a cognitive task helps improve memory because it keeps the brain stimulated. Just don’t draw funny pictures of the boss.
12. Letting the Mind Wander
Whether it’s “listening” to a pal talk about her BF or just strolling down the block, there are lots of times when the mind goes off in strange directions. But don’t hold back that brain—it turns out there are lots of cognitive benefits to letting the mind wander, like increased creativity and problem-solving ability Back to the future: autobiographical planning and the functionality of mind-wandering. Baird, B., Smallwood, J., Schooler, J.W. Department of Psychological and Brain Sciences, University of California, Santa Barbara, CA. Consciousness and Cognition 2011;20(4):1604-11..
Fresh breath, fewer cavities, and avoiding embarrassing situations with poppy seeds are all great reasons to floss. Here’s another: The plaque that accumulates between teeth can actually trigger an immune response that prevents arteries from getting nutrients to the brain. Pick up some mental—er, dental—floss on the way home today.
14. Lawn Mowing
The grass is always greener, and the brain may be sharper, after we mow the lawn. One study found lawn-mowing releases a chemical that relieves stress and might even boost memory in older adults. Unfortunately, the odor of taking out the trash probably doesn’t have the same effect.
15. Writing by Hand
Sans Serif and Cambria are awfully elegant, but writing words by hand can improve cognitive skills like learning and memory. Adults studying a new language may be more likely to remember words when they write them out instead of typing them. Stay sharp by writing out a to-do list or penning a heartfelt confession of love.
16. Sharpening the Senses
How exactly does that cold water feel traveling down the back of your throat? It’s important to challenge the brain in shape by keeping all the senses sharp. Try involving new senses in routine activities, like eating with the eyes closed and placing more emphasis on taste and smell (probably not the best exercise to try with hot soup).
Let’s get it on—our brainpower, that is. Research suggests sex can actually increase brain function. A tumble between the sheets raises levels of serotonin, which boosts creativity and logical decision-making, and the hormone oxytocin, related to problem-solving ability (skills that might help with figuring out where those undergarments ended up last night…) Rationality and Emotionality: Serotonin Transporter Genotype Influences Reasoning Bias. Stollstorf, M., Bean, S.E., Anderson, L.M., et al. Social Cognitive and Affective Neuroscience 2012. Epub ahead of print..
18. Positive Relationships
I get by—and smart!—with a little help from my friends. A study of elderly Americans suggests positive relationships can help protect against memory loss Effects of Social Integration on Preserving Memory Function in a Nationally Representative US Elderly Population. Ertel, K.A., Glymour, M., Berkman, L.F. Department of Society, Human Development, and Health, Harvard School of Public Health, Boston, MA. American Journal of Public Health 2008;98(7):1215-1220.. Spend some time with friends and fam today to avoid forgetting their names later in life.
19. Pleasant Conversation
Oh, how do you do? A quick chat may do more than just pass the time—socializing can also improve cognitive functioning Mental exercising through simple socializing: social interaction promotes general cognitive functioning. Ybarra, O., Burnstein, E., Winkielman, P. Department of Psychology, Research Center for Group Dynamics, University of Michigan, Ann Arbor, MI. Personal and Social Psychology Bulletin 2008;34(2):248-59.. Even simple conversations may improve skills like memory and the brain’s ability to block out distractions. Take a few minutes to talk it out before the next big test or meeting.
Gosh, isn’t the brain funny?! A hearty laugh may be the key to solving a tough problem, since research suggests laughing encourages people to think more creatively Hedonic tone and activation level in the mood-creativity link: toward a dual pathway to creativity model. De Dreu, C.K., Baas, M., Nijstad, B.A. Department of Psychology, University of Amsterdam, Amsterdam, the Netherlands. Journal of Personality and Social Psychology 2008 May;94(5):739-56. Positive affect facilitates creative problem solving. Isen, A.M., Daubman, K.A., Nowicki, G.P. Journal of Personality and Social Psychology 1987;52(6):1122-31.. Panicking about what to say in a big presentation? Just picture everyone in their underwear.
21. Thinking About Ancestors
Brainpower’s a family affair. In one study, people who thought about their ancestors before a series of cognitive tests performed better than people who focused on something else. Researchers surmise thinking about family history increases people’s sense of control. These test results? I got ’em from my mama!
Who can think clearly with a mind full of worries? If the ability to sit still and silent for more than 10 seconds isn’t impressive enough, get this: Meditation helps improve memory, decision making, and attention span The Unique Brain Anatomy of Meditation Practicers: Alterations in Cortical Gyrification. Luders, E., Kurth, F., Mayer, E.A., et al. Laboratory of Neuro Imaging, Deparment of Neurology, UCLA School of Medicine Los Angeles, CA. Frontiers in Human Neuroscience 2012;6:34. Meditation training increases brain efficiency in an attention task. Kozasa, E.H., Sato, J.R., Lacerda, S.S., et al. Instituto do Cérebro, Instituto Israelita de Ensino e Pesquisa Albert Einstein, São Paulo, Brazil. Neuroimage 2012;59(1):745-9.. Plus the more you practice meditation, the better you get at making decisions. Start off with a few minutes of meditative belly breathing to improve concentration. Om-my.
23. Video Games
Guys who hang out in their basements playing Xbox games aren’t just supercool—they may also be smarter than the rest of us. Some researchers suggest playing video games improves a number of cognitive skills, from vision to multitasking to spatial cognition Neural bases of selective attention in action video game players. Bavelier, D., Achtman, R.L., Mani, M., et al. Rochester Center for Brain Imaging, Rochester, NY. Vision Research 2011. Epub ahead of print.. Tackle a game of Tetris for some mental exercise.
24. Watching TV
Turns out the tube may not be so terrible. One study found people who watched a half-hour TV show performed better on intelligence tests than people who listened to classical music, worked on crossword puzzles, or read books. Researchers suggest a small amount of TV might help people relax more than other activities. But make sure to keep viewing time to a minimum—a permanent butt-print on the couch is never a good sign.
25. Lying Down
Perfect posture’s important—but there’s no need to stand up nice and straight. Instead, make like a monkey and hang upside down: It’s possible that memory improves when the head hangs lower than the rest of the body. And one study found people solved anagrams faster when they were lying down than when they were standing Thinking on your back: solving anagrams faster when supine than when standing. Lipincki, D.M., Byrne, D.G. School of Psychology, The Australian National University, Canberra, ACT 0200, Australia. Brain Research. Cognitive Brain Research 2005;24(3):719-22.. Researchers think certain body postures might make us more insightful. Hwo eknw?
Food and Drink
26. Staying Hydrated
Water, water everywhere and... the mind gets sharper. Hydration is essential to keep the brain working properly, and research suggests being thirsty can distract us from the cognitive tasks we're trying to tackle. One study showed people who drank fruit and vegetable juice (yes, V8 in a Bloody Mary counts) were significantly less likely to develop Alzheimer’s than those who didn’t Fruit and Vegetable Juices and Alzheimer’s Disease: The Kame Project. Dai, Q., Borenstein, A.R., Wu, Y., et al. Department of Medicine, Division of General Internal Medicine and Public Health, Vanderbilt Center for Health Services Research, Vanderbilt-Ingram Cancer Center, Vanderbilt School of Medicine, VA. American Journal of Medicine 2006; 119(9):751-759.. For those looking to cut calories, eight glasses of water per day may work too.
Nope, it’s not the name of a frat—these fatty acids provide a ton of health benefits, like improving brain function Collaborative effects of diet and exercise on cognitive enhancement. Gomez-Pinilla, F. Department of Physiological Science, Department of Neurosurgery, University of California Los Angeles, Los Angeles, CA. Nutritional Health 2011;20(3-4):165-169.. Greatist superfood salmon’s a top source of omega-3s—or forgo the eau de fish and try walnuts and flaxseed oil instead.
People of the world, spice up your brain! Research suggests certain spices can help preserve memory Neuroprotection by Spice-Derived Nutraceuticals: You Are What You Eat! Kannapan, R., Gupta, S.C., Kim, J.H., et al. Cytokine Research Laboratory, Department of Experimental Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, TX. Molecular Neurobiology 2011;44(2):142-159.. A spoonful of cinnamon in a cup o’ joe can ward off Alzheimer’s disease, and a sprinkling of sage on pasta may prevent another WTF-is-that-guy’s-name situation. Cumin and cilantro are especially powerful memory-boosters—so chow down and make those trips to Mumbai and Cancun unforgettable.
29. Leafy Green Vegetables
Who knew Popeye was also a genius? Spinach and other leafy green vegetables are filled with vitamins and minerals that help fight dementia. Plus, the antioxidants in these lean greens offer powerful brain protection from conditions like strokes, Alzheimer’s, and Parkinson’s disease Effects of natural antioxidants in neurodegenerative disease. Albarracin, S.L., Stab, B., Casas, Z. Departamento de Nutrición y Bioquímica, Facultad de Ciencias, Pontificia Universidad Javeriana, Bogotá D.C., Colombia. Nutritional Neuroscience 2012;15(1):1-9..
30. Nuts and Seeds
Take a tip from squirrels and store up some brainpower: Nuts and seeds pack nutrients that seriously increase brain function. Zinc in pumpkin seeds may improve memory; the vitamin E in nuts can enhance cognitive skills Vesicular zinc promotes presynaptic and inhibits postsynaptic long-term potentiation of mossy fiber-CA3 synapse. Pan, E., Zhang, X.A., Huang, Z., et al. Department of Medicine (Neurology), Duke University Medical Center, Durham, NC. Neuron 2011;71(6):1116-26. Effects of fruits and vegetables on levels of vitamins E and C in the brain and their association with cognitive performance. Martin, A., Cherubini, A., Andres-Lacueva, C., et al. USDA-Neuroscience Laboratory, Jean Mayer USDA Human Nutrition, Research Center on Aging at Tufts University, Boston, MA. The Journal of Nutrition, Health, and Aging 2002;6(6):392-404..
Flintstone gummies or the kind that comes straight from fruits and veggies, vitamins may help prevent Alzheimer’s disease. Folic acid—found in bread, pasta, and some fortified cereals—and vitamin B12—found in animal products like fish, eggs, and milk—are especially powerful brain protectors, especially in the elderly Vitamin B12, cognition, and brain MRI measures: a cross-sectional examination. Tangney, C.C., Aggarwal, N.T., Li, H., et al. Department of Clinical Nutrition 425 TOB, Rush University Medical Center, 1700 West Van Buren St., Chicago, IL. Neurology 2011;77(13):1276-82. Cognitive function in an elderly population: interaction between vitamin B12 status, depression, and apolipoprotein E 4: the Horadland Homocysteine Study. Vogiatzoglou, A., smith, A.D., Nurk, E. OPTIMA, Department of Pharmacology, University of Oxford, Oxford, UK. Psychosomatic Medicine 2013 Jan;75(1):20-29..
32. Complex Carbs
Energizer batteries aren’t the only thing that keeps that bunny going. Complex carbohydrates boost alertness by offering energy that lasts all day. And they’re a better option than sugary energy drinks, which usually end up making people feel drowsier. Go for whole-wheat bread, brown rice, and oatmeal instead of nodding off before lunchtime.
Hey, guess what?! Coffee boosts brainpower! And energy! ’Cause it’s great! And I just had some! But seriously, studies suggest the caffeine in an eight-ounce cup of coffee can improve attention and short-term memory Caffeine and cognition in functional magnetic resonance imaging. Koppelstaetter, F., Poeppel, T.D., Siedentopf, C.M., et al. Department of Radiology, Medical University of Innsbruck, Innsbruck, Austria. Journal of Alzheimer’s Disease 2010;Suppl 1:S71-84..
How do you like them brain-boosters? Research suggests quercetin, a chemical in apples, offers powerful neuroprotection, meaning it arms brain cells against damage from free radicals that can cause cognitive decline Polychlorinated Biphenyls-Induced Oxidative Stress on Rat Hippocampus: A Neuroprotective Role of Quercetin. Selvakumar, K., Bavithra, S., Krishnamoorthy, G., et al. Department of Endocrinology, Dr. ALM Post Graduate Institute of Basic Medical Sciences, University of Madras, Chennai 600113, India. Scientific World Journal 2012. Epub.. Most of the quercetin’s in the apple skin, so keep the peel for extra brainpower. And, for those who aren’t fans of red, delicious fruit, quercetin also comes in citrus fruits, onions, parsley, sage, tea, and red wine.
We know how unappealing a double fudge brownie sounds right now, but here’s a convincing reason to eat one: A recent study found the flavonols in dark chocolate (also found in red wine, green tea, and blueberries) offer a short-term boost in cognitive skills The effect of flavanol-rich cocoa on the fMRI response to a cognitive task in healthy young people. Francis, S.T., Head, K., Morris, P.G., et al. Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, UK. Journal of Cardiovascular Pharmacology 2006;47 Suppl 2:S215-20.. And other researchers recommend dipping into a chocolate fountain of youth, since the polyphenols in cocoa may prevent some cognitive impairments associated with aging Effects of long-term administration of a cocoa polyphenolic extract (Acticoa powder) on cognitive performances in aged rats. Bisson, J.F., Nejdi, A., Rozan, P., et al. ETAP-Applied Ethology, 13 rue du Bois de la Champelle, Vandoeuvre-lès-Nancy 54500, France. The British Journal of Nutrition 2008;100(1):94-101..
36. Grape Juice
Those cute kids in Welch’s commercials got a head start in protecting their brains from cognitive decline. The polyphenols in grape leaves that produce wine and grape juice help brain cells communicate, so they may improve memory and learning skills Phenolic content of grapevine leaves (Vitis labrusca var. Bordo) and its neuroprotective effect against peroxide damage. Dani, C., Oliboni, L.S., Agostini, F., et al. Laboratório de Estresse Oxidativo e Antioxidantes, Instituto de Biotecnologia, Universidade de Caxias do Sul, Caxias do Sul, RS, Brazil. Toxicology In Vitro 2010;24(1):148-53..
37. Chewing Gum
Not to burst your bubble, but a stick of Bazooka may be the key to making it through a busy day. Studies have found chewing gum improves mood and alertness—plus it’s the way to go after indulging in some Greatist superfoods Effects of chewing gum and time-on-task on alertness and attention. Allen, A.P., Smith, A.P. School of Psychology, Cardiff University, Cardiff, UK. Nutritional Neuroscience 2012 Jul;15(4):176-85. Effects of chewing gum on cognitive function, mood and physiology in stressed and non-stressed volunteers. Smith, A. Centre for Occupational and Health Psychology, School of Psychology, Cardiff University, 63 Park Place, Cardiff, CF10 3AS, UK. Nutritional Neuroscience 2010;13(1):7-16. Effects of chewing gum on mood, learning, memory and performance of an intelligence test. Smith, A. Centre for Occupational and Health Psychology, School of Psychology, Cardiff University, Cardiff, UK. firstname.lastname@example.org. Nutritional Neuroscience 2009;12(2):81-8..
38. Chicken and Eggs
Which came first, the chicken or the egg? In this case, it doesn’t matter—both foods are great sources of choline, which can help improve cognitive performance, especially memory The relation of dietary choline to cognitive performance and white-matter hyperintensity in the Framingham Offspring Cohort. Poly, C., Massaro, J.M., Sesahdri, S. Department of Neurology, Boston University School of Medicine, MA. The American Journal of Clinical Nutrition 2011;94(6):1584-91.. Other good sources of choline include legumes, liver, fish, and milk.
39. Fatty Foods
Don’t put the brain in skinny jeans—research suggests fatty foods improve long-term memory. A hormone released during the digestion of some fats strengthens the part of the brain responsible for long-term memory formation. (But gorging on a carton of Heath Bar Crunch will probably just create some bad memories.)
Give me some sugar. A little bit of glucose (25 grams) can boost alertness and improve memory Acute ingestion of different macronutrients differentially enhances aspects of memory and attention in healthy young adults. Jones, E.K., Sunram-Lea, S.I., Wesnes, K.A. Department of Psychology, Fylde College, University of Lancaster, Lancaster LA1 4YF, UK. Biological Psychology 2012;89(2):477-86.. But don’t down a whole bag of M&M’s—excess sugar consumption can have some adverse health effects.
Bessie’s got brainpower. A recent study suggests milk is good for more than just strong bones. According to one study, people who drink a glass of milk daily perform better on tests of memory and other cognitive functions.
A Sudoku puzzle might be challenging, but after the 100th puzzle, the brain craves something new. Trying new activities stimulates the release of dopamine, which increases motivation and the growth of new neurons. So take an unfamiliar route home or read a book about a new topic, and feel the brain grow!
43. Navigating Cities
How did the man inside the GPS get so smart? Probably from spending time navigating cities. In one study, London taxi drivers showed structural changes in the part of the brain associated with spatial memory Acquiring “the Knowledge” of London's Layout Drives Structural Brain Changes. Woolett, K., Maguire, E.A. Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, 12 Queen Square, London WC1N 3BG, UK. Current Biology 2011;21(24-2):2109-2114.. Copy Columbus and practice creating a mental map of the neighborhood.
44. Playing an Instrument
Play that funky music, smart guy. The parts of the brain responsible for motor control, hearing, and visuospatial skills may be more developed in musicians than in non-musicians Gray matter differences between musicians and nonmusicians. Gaser, C., Schlaug, G. Department of Psychiatry, University of Jena, Jena, Germany. Annals of the New York Academy of Sciences 2003;999(514-7).. Practice scales on a keyboard, chords on a guitar, or do what you want and just bang on the drum all day.
45. Speaking Out Loud
Better recite this tip to whomever’s sitting next to you. There’s evidence that we remember ideas better when we speak them out loud The production effect: delineation of a phenomenon. MacLeod, C.M., Gopie, N., Hourihan, K.L. Department of Psychology, University of Waterloo, Waterloo, Ontario, Canada. Journal of Experimental Psychology. Learning, Memory, and Cognition 2010;36(3):671-85.. No guarantees it won’t look strange when you talk to yourself on the street.
46. Learning a Second Language
Cerebre, cerveau, or just plain brain. Being bilingual may protect the body against Alzheimer’s—even when people learn a new language as adults. Studies show Alzheimer’s symptoms develop more slowly in bilingual speakers than in those who speak just one language Lifelong Bilingualism Maintains White Matter Integrity in Older Adults. Luk, G., Bialystok, E., Craik, F.I.M., et al. Rotman Research Institute at Baycrest, Toronto, Ontario M6A 2E1, Canada. Journal of Neuroscience 2011;31(46):16808-16813.. Start learning, pronto.
47. Positive Thinking
It’s possible to get smarter, savvier, and more creative—after reading this list! Research suggests people learn more when they believe intelligence isn’t fixed Why do beliefs about intelligence influence learning success? A social cognitive neuroscience model. Mangels, J.A., Butterfield, B., Lamb, J., et al. Psychology Department, Columbia University, Taub Institute, Columbia Presbyterian Medical Center, Columbia University. Social Cognitive and Affective Neuroscience 2006;1(2). The bottom line: Believe in the brain!
This article originally published February 2012. Updated November 2017.