Hallucinations is an absorbing study of an exotic subject. Its author is perhaps best known for two books: Awakenings, a spellbinding account of treating post-encephalic patients with the ‘wonder drug’ L-DOPA; and The Man Who Mistook His Wife for a Hat, a hugely popular collection of outlandish neurological case studies. One of these, ‘The Dog Beneath the Skin’, described a ‘Stephen D’ who, under the influence of amphetamines, cocaine and PCP, woke up one morning to find he had acquired a tremendously heightened sense of smell. The Kafkaesque Stephen D was, the author later admitted, none other than Oliver S himself. Sacks is an authority on hallucinations – some of which were self-induced, as we discover in his latest book’s autobiographical passages. Not yet the distinguished neurologist and something of a late starter, he puffed his first joint in his thirties and, as an expat Englishman in 1960s California, made up for lost time by diligently working his way through the psychedelic pharmacopoeia: ‘“If you really want a far-out experience,” my friends on Muscle Beach told me, “Try Artane.” … So one Sunday morning, I counted out twenty pills, washed them down with a mouthful of water, and sat down to wait for the effect.’

Artane, the brand name for Trihexyphenidyl, is used in moderate doses in the treatment of Parkinson’s disease. Twenty pills was not a moderate dose and the author’s account of their effect is by turns unsettling and hilarious. Employed at the time as a resident in UCLA’s neurology department, Sacks subsequently