Horizon uncovers the secret world of our dreams. In a series of cutting-edge experiments and personal stories, we go in search of the science behind this most enduring mystery and ask: where do dreams come from? Do they have meaning? And ultimately, why do we dream? What the film reveals is that much of what we thought we knew no longer stands true. Dreams are not simply wild imaginings but play a significant part in all our lives as they have an impact on our memories, the ability to learn, and our mental health. Most surprisingly, we find nightmares, too, are beneficial and may even explain the survival of our species.

We all agree lying is shameful. Yet we still deliberately deceive each other constantly. Are our brains wired for lying from a young age? The brains of pathological liars may provide insights. Will technology make it easier for us to be dishonest, or could it someday instantly reveal someone is lying? Perhaps we are deceitful because our limited senses prevent us from seeing the real truth. Scientists say our own memories deceive us, and have managed to implant false memories. Other scientists look for ultimate truth in the subatomic world … only to end up turning reality on its head.

Two and a half thousand years ago, the Greek philosopher Socrates worried that the wide use of writing would have a negative impact on people's minds. He said that writing would create forgetfulness, because people will not use their memories. They would trust the external written characters and not remember themselves. In a world with an ever-growing tech industry, Michael Stevens tries to find out what effect technology has on our brains. He finds Technology isn't just changing our lives, it's changing our brains. In his experiments he tests what just 10 days of gaming does to things like our spatial memory.