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.

Horizon investigates a new era of Alzheimer's research, which is bringing hope to millions of sufferers across the world. New scanning and gene technology is allowing scientists to identify the disease at its earliest stages, often 15 years before symptoms appear and the brain cells are destroyed. A series of new drugs trials in Colombia, the USA and Europe are showing startling success in reducing beta amyloid, the protein which is a hallmark of the disease.

It is also becoming clear that changes in lifestyle can prevent the development of the disease. A new system inside the brain has been discovered which clears amyloid when we are in deep sleep, but allows it to accumulate if we don't sleep well.

The programme reveals that for sufferers in the early stages of the disease, brain connections, or synapses, can be strengthened and even replaced by absorbing enough of the right nutrients. A UK-wide trail helps sufferers in the early stages to concentrate on improving everyday tasks, and in the process not only make their lives easier, but helps to reactivate the planning and organisational parts of the brain.

In an aging world, where the biggest risk of developing Alzheimer's is old age, the scientific breakthroughs in Alzheimer's disease are bringing hope where once there was despair.