For every stoner who has been overcome with profound insight and drawled, “Reality is a construct, maaan,” here is the astonishing affirmation. Reality – or, at least, our perception of it – is a “controlled hallucination”, according to the neuroscientist Anil Seth. Everything we see, hear and perceive around us, our whole beautiful world, is a big lie created by our deceptive brains, like a forever version of The Truman Show, to placate us into living our lives. Our minds invent for us a universe of colours, sounds, shapes and feelings through which we interact with our world and relate to each other, Seth argues. We even invent ourselves. Our reality, then, is an illusion, and understanding this involves tackling the thorny issue of consciousness: what it means to, well, be. Consciousness has long been the preserve of philosophers and priests, poets and artists; now neuroscientists are investigating the mysterious quality and trying to answer the hard question of how consciousness arises in the first place.