Ever wonder what's happening inside your head? From dreaming to anxiety disorders, discover how your brain works with this illuminating series. The first episode looks at how memory works and examines the way in which the brain stores, processes, and retrains memories. It also looks at the ways in which memory can fail and discusses how memories can warp over time. It talks to neuroscientists and a memory champion who explains her techniques.

In January, 2015, American rock climbers Tommy Caldwell and Kevin Jorgeson captivated the world with their effort to climb the Dawn Wall, a seemingly impossible 3,000 foot rock face in Yosemite National Park, California. The pair lived on the sheer vertical cliff for weeks, igniting a frenzy of global media attention. But for Tommy Caldwell, the Dawn Wall was much more than just a climb. It was the culmination of a lifetime defined by overcoming obstacles. At the age of 22, the climbing prodigy was taken hostage by rebels in Kyrgyzstan. Shortly after, he lost his index finger in an accident, but resolved to come back stronger.
When his marriage fell apart, he escaped the pain by fixating on the extraordinary goal of free climbing the Dawn Wall. Blurring the line between dedication and obsession, Caldwell and his partner Jorgeson spend six years meticulously plotting and practicing their route.

Ottoman Sultan Mehmed II wages an epic campaign to take the Byzantine capital of Constantinople. Twenty-three armies have tried to take the legendary city and all have failed. Out of the carnage, one ruler will emerge victorious and shapes the course of history for centuries. For one empire to rise, another must fall.
The Ottomans, former Anatolian warlords and nomads who've built a burgeoning empire are the biggest threat to the Romans' 1100-year reign. The death of Ottoman Sultan Murad II in 1451 unleashes a chain of events that will soon bring the Ottomans and Romans to the brink of war. After claiming the Ottoman throne, Mehmed II sends an unmistakable signal to Byzantine emperor Constantine XI.

At 11 o'clock on New Year's Eve of the Cosmic Calendar, Homo erectus stood up for the first time, freeing its hands and earning the species its name. They began to move around, to explore, daring to risk everything to get to unknown places. Our Neanderthal relatives lived much as we did and did many of the things we consider to be 'human.' More restless than their cousins the Neanderthals and Denisovans, our Homo sapiens ancestors crossed seas and unforgiving landscapes, changing the land, ocean and atmosphere, leading to mass extinction. The scientific community gave our age a new name, 'Anthropocene.'
Since the first civilizations we've wondered if there's something about human nature that contains the seeds of our destruction. Syukuro Manabe was born in rural Japan and took an intense interest in Earth's average global temperature. In the 1960's, he would assemble the evidence he needed to predict the increase of Earth's temperature due to greenhouse gases until it becomes an uninhabitable and toxic environment, leading to our extinction. 'This doesn't have to be,' says Neil deGrasse Tyson, 'it's not too late. There's another hallway, another future we can still have; we'll find a way.'

Hanging in the Barnes Foundation in Philadelphia, Seurat’s Les Poseuses is probably his least-known painting. It is also a picture brimming with codes and hidden meanings. It shows three nudes in the artist’s studio, but included in the background is Seurat’s famous masterpiece, A Sunday Afternoon on the Island of La Grande Jatte. Why is it there? What is it trying to say? Why two pictures at once? Waldemar Januszczak investigates.

A child lies on the rug of a tenement dreaming of interstellar adventures. At the dawn of the space age, a young Carl Sagan’s career is forged in the clash of his mentors, two scientific titans. Sagan goes on realize his childhood dreams, to carry their research forward and communicate its significance to the whole world.