Consciousness: a headache on a dimmer switch?

James Randerson is a Guardian science correspondent

There was a time when the study of human consciousness was out on the wacky fringes of science. It was the sort of thing you got into if you liked a heavy dose of philosophy, new age thinking and probably soft drugs with your science. As the US philosopher Dan Dennett once quipped: "With so many idiots working on the problem, no wonder consciousness is still a mystery."

The real reason why consciousness is still a mystery, though, is that understanding it is so head-hurtingly difficult. How do you measure someone's personal, subjective experience? Scientists tend to feel very uncomfortable when there is not anything they can see and count.

But the neuroscientist Baroness Susan Greenfield, who is director of the Royal Institution of Great Britain believes that times are changing. She will tell an audience at University College London on Friday night that brain scientists are starting to make progress. She has said:

The big idea is that consciousness is not all or none. You are not just conscious or unconscious. It's like a dimmer switch.
This way of looking at things throws up some difficult questions, because it means that any creature with a nervous system is conscious, to some extent.