The Science Behind How Sleep Makes You Smarter A good night's sleep is the foundation of physical health and mental energy.

I'm a science geek. I like to know why a particular approach to life or technique for success works. Otherwise, I tend to glaze over when faced with another "X Ways to Achieve Y Results" article. In the absence of research or evidence, I'm less likely to pay attention and less motivated to make a change in my life.

Maybe that's just me. But I'll assume you're also a "but how do we know that really matters?" person and lay it out for you -- on the subject of sleep.

Sleep is free, available to all, beyond good for us and largely ignored as the foundation of physical health and mental energy. It's the first thing that gets cut when life is busy and the last thing we add back in when a chunk of time comes our way. But if we were smart, it would be our main priority, and the rest of our lives would be built around it.

Why does sleep matter?

Sleep has a powerful effect on both mental and physical performance. This is true for exercise, sports, playing music, academics, business and most other pursuits. Knowing what happens when we sleep is the first step to understanding why it builds mental and physical health.

Related: How CEOs Optimize Their Sleep Schedule

The two main stages of sleep -- NREM (non-rapid eye movement) and REM (rapid eye movement) -- each have different effects on our ability to learn and create.

Professor Vincent Walsh from the University College of London has described the deep, slow wave sleep (NREM) that happens earlier in the night as being crucial for encoding information and facts that we encountered during the day. For example, a student practicing math questions during the day is really learning it while asleep. The brain does all kinds of sorting, organizing and storing while we sleep. And it takes time. If we cut back on our sleep, we learn a lot less.

The second half of the night (REM sleep) is when we encode procedural memories like how to perform a new physical skill or mental process. It is also when we do subconscious creative problem solving. Again, if we skimp on sleep time, we awaken with poor procedural memory and will likely have to repeat some steps again the next day. And that pressing problem we pondered before bed remains unresolved in the morning.

Simply, the first half of sleep is for mental recovery and learning, and the second half is for physical recovery and creativity.

Sleep soundly to learn better.

A school principal I know told me recently that many students show up to school with an array of energy drinks after pulling an all-nighter before an exam. Not only have they not used sleep to encode and solidify their learning, they start the day on sugar and caffeine. Adults do this too, of course. Skipping sleep to prepare for a case, presentation, meeting or interview means arriving with a poor memory of the crucial information you stayed up to memorize.

Related: Sleep: Why Successful Entrepreneurs Snooze More and Work Less

Here's what's going on when you sleep soundly:

Our brains are made up of approximately 100 billion neurons. When we sleep, we create new connections -- called synapses -- between those neurons. Neurons are building blocks, but the synapses are where the action is. They form the basis for our thoughts, memories, problem solving, decision-making, physical movement and other important aspects of what makes us human.

Scientists in China and the U.S. have recently used a microscope to witness new synapses being formed in the brain during deep and sustained sleep. In short, they watched the brain building memories. We've known for a while that good quality sleep is necessary to remember what we have experienced during the day, but not why. This study made visible the brain's work of replaying the day's activity like a movie and building new connections between neurons.

Sleep soundly to be more creative.

During sleep, our brains also grow new neurons -- which, as you know, start making thousands of connections to other neurons. In addition to encoding learning and building memory, the neurons and synapses also get busy solving difficult problems and coming up with new ways of performing a task.

Related: Why Entrepreneurs Should Never Feel Guilty for Sleeping (Infographic)

In a study at the University of California-San Diego, researchers found that REM sleep "directly enhances creative processing more than any other sleep or wake state." Yes, you heard that right -- even more than any wake state. One of the study's leaders explains: "We found that, for creative problems that you've already been working on, the passage of time is enough to find solutions. However, for new problems, only REM sleep enhances creativity." In REM sleep, the brain makes new and useful associations between unrelated ideas to creatively tackle problems that have just dropped in your lap.

Power up: Make sleep a priority.

We live in this crazy world where it's almost a badge of honor to get by on less sleep. People brag about it. To my mind, that's clear evidence of sleep deprivation. Anyone who tells you how great they perform on very little sleep is lacking the mental capacity to correctly assess their own learning and creativity -- because they're exhausted.

Don't let that be you. Hold the science in mind as you climb into bed for a sound sleep. And wake up the next day smarter and with some of your pressing problems resolved overnight.