Oliver Sacks fell over on a Norwegian mountain after an encounter with a bull. His main injury was to the muscles and nerves in one of his legs. A surgeon in a local hospital operated on his leg, saying, ‘We’ll just reconnect you’. According to the surgeon, the leg’s function had been perfectly restored, and Sacks’ notes were marked with the term ‘uneventful recovery’. However, when the plaster cast was taken off, Sacks couldn’t feel his leg. ‘There was absolutely no sensation whatever,’ he noted. ‘It was clear that I had a leg which looked anatomically perfect, and which had been expertly repaired, and healed without complication, but it looked and felt uncannily alien – a lifeless replica attached to my body.’

Most people experience this sort of alienation from time to time. You lie on an arm while asleep and wake to find it grotesquely numb, but, when you move it around, sensation returns. For Sacks, this didn’t happen. He could see the flesh of his leg, but he couldn’t feel it. His leg had disappeared subjectively. ‘I had lost something – that was clear. I seemed to have lost my leg – which was absurd, for there it was....safe and sound...a “fact”.’

When Sacks complained to his doctors that he couldn’t feel his leg, one didn’t believe him and the other said it wasn’t his business. A doctor himself, Sacks explains the fate of his leg in two ways. First, the femoral nerve, which was damaged in his encounter with the Norwegian bull, had become physically less efficient at conducting electrical impulses. This could be, and was, eventually picked up by the doctors – nerve conduction tests carried out after four years showed marked impairment of function in his left leg. But no medical tests or examinations could reveal the second problem. The nerve damage had resulted in a basic disturbance of Sacks’ entire sensory system, such that his brain no longer ‘knew’ what his leg was doing.

Sacks’ description of his leg as an alien object attached to his body exactly matched the perception of my hand that developed in the months following the accident. It’s shocking to experience part of one’s body as lifeless flesh when one ‘knows’ it isn’t.