Review of Oliver Sacks' new book, Hallucinations [300pp. Picador. £18.99,]

by Raymond Tallis for The Times Literary Supplement, Feb. 13, 2013

[....] the isolation hallucinations impose on those who suffer from them is compounded by a reluctance to speak of them. And yet they are extremely common, as Sacks points out in his opening chapter when he talks about the “silent multitudes” of visual images that may fill the gathering darkness when eyesight starts to fail. The Charles Bonnet syndrome – named after the polymath physician who first described it in the eighteenth century – is marked by extraordinarily complex and variable images. This is how Rosalie, a blind ninety-year-old woman in a nursing home, described what she “saw”: [....]

There is an intuitive explanation of why perceptual loss – as in blindness and in experimental sensory deprivation tanks – should be associated with hallucinations: that nature, the brain, the mind, abhors a vacuum. This, however, does not explain why, in Rosalie’s case, the symptoms began only many years after she had gone blind. Nor does it account for the richness of her hallucinations. The general propensity to hallucinate, however, is unsurprising, given the complexity of the processes – cerebral and mental – that underpin ordinary perception and the extent to which the world we experience around us is a construct that goes far beyond the raw material of sensation. It is not surprising that they can be induced in so many different ways. Sacks’s masterly catalogue raisonné of these coinages of the mind surveys the effect of drugs (prescribed and recreational), migraine (where there are transient alterations of the blood flow to parts of the brain), epilepsy (in which there are massive spontaneous neural discharges), delirium (associated with fevers and toxins of various sorts), sleep (normal and abnormal), disturbances of body image (following loss of a limb or a stroke), near-death experiences (after cardiac arrest), and direct stimulation of the brain (in waking subjects undergoing epilepsy surgery). In doing so, he draws on his previous writing, and in some respects this could be seen as the summa neurologica of this supreme observer of the phenomenology of neurological disease. [....]