THE VALLEY OF ASTONISHMENT

A tiny elfin woman journalist with a growly, gravelly voice reenacts a meeting she had with the editor of the newspaper she worked for. He asked why she didn’t have a notebook to record the names and addresses and phone numbers he’d given her for that day’s stories. ‘It’s all in here,’ says Sammy Costas (Kathryn Hunter), tapping her head. As if. Then she repeats his instructions word for word, wholly accurate in every detail. Gobsmacking.

He wants to march her off to a doctor. ‘I’m not ill,’ she insists and explains with matter-of-fact simplicity that she creates a narrative from the words, which becomes stored in vivid pictures in her brain, enabling her to have perfect recall. ‘It’s not a trick. It’s like breathing,’ she says. The remarkable Hunter makes you believe it.

Her condition is known as synaesthesia, which means she ‘sees’ sounds – an eight is a pregnant lady – just as a musician we meet later ‘hears’ colours, allowing him to create paintings out of the music of John Coltrane. And it’s the intriguing subject of the latest show, The Valley Of Astonishment, created by the visionary director Peter Brook, now in his 90th year, the third in his series, with collaborator Marie-Hélène Estienne, to unlock the secrets of the human brain.

Needless to say, Sammy’s editor considers her overqualified and fires her. She is signed up by a theatrical agent and becomes, quite literally, a freak show, able to remember even fragments of words, or a poem in a language she doesn’t speak. Crowds flock. But in a tremendously moving scene, Sammy reaches a state of near collapse, her brain choking from overload of images. ‘How do I forget?’ she cries, pitifully.

Sammy’s story is the most detailed of the case studies in the piece, which is really more of an illustrated lecture than a fully worked out drama, simply stage with three actors slipping in and out of white coats to play patients and neurologists. And yet it is extraordinarily absorbing in that minimalist, artfully artless fashion that is Brook’s trademark. As the musician listens to jazz, he dances around the stage with his brush and coloured filters ‘paint’ the space green and purple and red. A genial one-armed magician invites audience members to shuffle cards and performs the most amazing tricks ever, taking the idea of ‘sleight of hand’ to astonishing extremes.

Meanwhile, two musicians conjure marvellous moody music from pipes and strings, more evidence of the diff erent ways in which every individual’s brain is wired, some of which can be a blessing, some a curse, all part of the mystery and the miracle of the human brain. Quietly astonishing.

At the Young Vic, 66 The Cut, London SE1, until 12 July: 020-7922 2922, www.youngvic.org