Let’ do some sleep math. You lost two hours of sleep every night last week because of a big project due on Friday. On Saturday and Sunday, you slept in, getting four extra hours. On Monday morning, you were feeling so bright-eyed, and you only had one cup of coffee, instead of your usual two. But dons’ be cheated by your energy: You’re still carrying around a heavy load of sleepiness, or what experts call “sleep debt” - in this case something like six hours, almost a full night’s sleep.

Sleep debt is the difference between the amount of sleep you should be getting and the amount you actually get. It’s a deficit（缺乏）that grows every time we skim some extra minutes off our nightly sleep. “People accumulate（积累）sleep debt gradually without being noticed,” says William C. Decent, founder of the Stanford University Sleep Research Center. Studies show that such short-term lack of sleep leads to a foggy brain, worsened vision, and trouble remembering. Long-term effects include obesity（肥胖）and heart disease.A survey by the National Sleep Foundation reports that we’re losing one hour of sleep each night---more than two full weeks of sleep every year.

The good news is that, like all debts, with some work, sleep debt can be repaid. Adding an extra hour or two of sleep a night is the way to catch up on sleep debt. For the long-term lack of sleep, take it easy for a few months to get back into a natural sleep pattern. Go to bed when you are tired, and allow your body to wake you in the morning (no alarm clock allowed). You may find yourself catatonic（有紧张感的）in the beginning of the recovery cycle: expect to have ten hours shut-eye per night. As the days pass, however, the amount of sleeping time will gradually decrease.

So earn back that lost sleep---and follow the orders of your inner sleep needs, and you’ll feel better. “When you put away sleep debt, you become a superman,” says Stanford’s Dement, talking about the improved mental and physical abilities that come with being well rested.

When we’re solving a complicated problem, we often gather a group to brainstorm. We’re looking to get the best ideas as quickly as possible. I love seeing it happen — except for one tiny wrinkle. Group brainstorming usually backfires.

Extensive evidence shows that when we generate ideas together, we’re unlikely to maximize collective intelligence. As the humourist John Smith said, “If you had to identify, in one word, the reason why the human race has not achieved, and never will achieve, its full potential, that word would be: ‘meetings’.” But the problem isn’t meetings themselves — it’s how we run them.

Think about the brainstorming sessions you’ve attended. You’ve probably seen people bite their tongues due to ego threat (“I don’t want to look stupid.”), noise (“We can’t all talk at once.”), and conformity pressure (“Let’s all jump on the boss’s ship!”). Goodbye diversity of thought, hello group-think.

To unearth the hidden potential in teams, instead of brainstorming, we’re better off shifting to a process called “brainwriting”. The initial steps are solo. You start by asking everyone to generate ideas separately. Next, you pool them and share them among the group. To preserve independent judgment, each member evaluates them on their own. Only then does the team come together to select and refine the most promising options. By developing and assessing ideas individually before choosing them, teams can surface and advance possibilities that might not get attention otherwise.

Research by organizational behaviour scholar Anita Woolley and her colleagues helps to explain why this method works. They find that a key to collective intelligence is full and fair participation. In brainstorming meetings, it’s too easy for participation to become lopsided in favour of the biggest egos, the loudest voices, and the most powerful people. The brainwriting process makes sure that all ideas are brought to the table and all voices are brought into the conversation. The goal isn’t to be the smartest person in the room — it’s to make the room smarter.

Collective intelligence begins with individual creativity. But it doesn’t end there. Individuals produce a greater volume and variety of novel ideas when they work alone. That means that they come up with more brilliant ideas than groups — but also more terrible ideas than groups. It takes collective judgment to find the signal in the noise and bring the best ideas to fruition.