Watch these recommended TED-Ed Lessons:

Are there universal expressions of emotion?
The 40 or so muscles in the human face can be activated in different combinations to create thousands of expressions. But do these expressions look the same and communicate the same meaning around the world regardless of culture? Is one person’s smile another’s grimace? Sophie Zadeh investigates.

The importance of a breakdown
Having a nervous breakdown could seem like the ultimate calamity. Far from it. The School of Life explains how, handled correctly, it can be a unique opportunity to learn - and to get properly well.

What is depression?
Depression is the leading cause of disability in the world; in the United States, close to ten percent of adults struggle with the disease. But because it’s a mental illness, it can be a lot harder to understand than, say, high cholesterol. Helen M. Farrell examines the symptoms and treatments of depression, and gives some tips for how you might help a friend who is suffering.

A brief history of melancholy
If you are a living, breathing human being, chances are you have felt sad at least a few times in your life. But what exactly is melancholy, and what (if anything) should we do about it? Courtney Stephens details our still-evolving understanding of sadness -- and even makes a case for its usefulness.

What causes insomnia?
What keeps you up at night? Pondering deep questions? Excitement about a big trip? Stress about unfinished work? What if the very thing keeping you awake was stress about losing sleep? This seemingly unsolvable loop is at the heart of insomnia, the world’s most common sleep disorder. So what is insomnia? And is there any way to break the cycle? Dan Kwartler details the science of insomnia.

Why do we cry? The three types of tears
Whether we cry during a sad movie, while chopping onions, or completely involuntarily, our eyes are constantly producing tears. Alex Gendler tracks a particularly watery day in the life of Iris (the iris) as she cycles through basal, reflex and emotional tears.

How to stay calm under pressure
Your favorite athlete closes in for a win; the crowd holds its breath, and at the crucial moment ... she misses the shot. That competitor just experienced the phenomenon known as “choking,” where despite months, even years, of practice, a person fails right when it matters most. Why does this happen, and what can we do to avoid it? Noa Kageyama and Pen-Pen Chen explain why we choke under pressure.

How stress affects your brain
Stress isn’t always a bad thing; it can be handy for a burst of extra energy and focus, like when you’re playing a competitive sport or have to speak in public. But when it’s continuous, it actually begins to change your brain. Madhumita Murgia shows how chronic stress can affect brain size, its structure, and how it functions, right down to the level of your genes.

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