The big idea: what if dreaming is the whole point of sleep?

Rather than being an optional extra, dreams might be vital to our functioning

Exposed, the undulating surface of the brain is shimmering and opalescent, punctuated with arteries and veins. Give any part of it the tiniest jolt of electricity with a pen-like probe and it will activate the neurons in that spot. Neurosurgeons use this technique during some types of brain surgery to locate the source of seizures, or to avoid damaging vital tissue.

While the procedure is happening, the patient is awake, but feels nothing, since the brain doesn’t have so-called nociceptors, or pain sensors. Because the thin, outermost layer is responsible for consciousness, language, perception, memory and thought, moving the probe from spot to spot can reveal quite a lot. It can trigger smells, memories of childhood – even nightmares. Use the probe to touch a particular part of the brain: nightmare on. Remove the probe: nightmare off. In this way, I’ve witnessed first-hand how dreams are truly part of the neural architecture. They’re very much built into our bodies.