Oliver Sacks

HALLUCINATIONS

In his first chapter Sacks describes Charles Bonnet syndrome, which is the occurrence of visual hallucinations in people whose sight is partially or completely lost. These visions can be extraordinarily vivid and complex; they may be completely integrated into any remainder of the real world that the patient can still see, so that it may be difficult for him or her to detect their unreality. Occasionally the visions are frightening but often they are neutral or even entertaining; Sacks comments that it is as if the eyes were bringing up the show as an apology for not being able to do their job properly. What is difficult to explain is why only some (a minority) of those who lose their sight have these experiences.

Auditory hallucinations, often of music or voices, can also be caused by loss of a normal sense, in this case hearing. But auditory hallucinations differ from visual ones in important ways. Vision is generated by the interaction of many brain areas and this leads to very complex and continually changing permutations. Musical hallucinations in contrast, are 'performed' by the brain and are rather like listening to a recording.

Epilepsy was known in ancient times as the sacred disease, because it was thought to be due to intervention by a god, and even today there is sometimes a connection between epilepsy and religiosity. Some epileptic patients are obsessed with religion and the instant before the onset of certain kinds of epilepsy may give rise to a moment of timeless ecstasy in which the meaning of life appears to be revealed. Dostoievsky recorded this experience and made use of it in his fiction.

Drugs of various kinds have been used to induce altered states of consciousness since the earliest times of which we know, and this is, of course, true of modern societies. Sack has himself experimented with a variety of drugs and he gives a detailed account of what he has learnt from doing so. At one point he was in danger of becoming seriously psychotic as a result of his experiences, but was able to rescue himself by writing a detailed description of what was happening to him. After this he became disillusioned with the spurious illumination offered by drugs.

Sacks describes a wide range of hallucinatory states in this book. In addiction to those I have already mentioned he talks about migraine, Parkinson's disease, phantom limbs, and hallucination associated with sleep (though he has relatively little to say about dreams, which are hallucinations but differ in many ways from those discussed here).

Reading this book cannot but raise questions in one's mind about the reliability our perceptions in general. What do hallucinations imply for reports of UFOs, ghosts, angels, or religious visions? Descriptions of thest things are indistinguishable from those of the hallucinations that Sacks describes. And what about the afore-mntioned mystical ecstasy that can accompany an epileptic seizure? Like William James before him, Sacks is ambivalent about this.

To speak of a biological basis and biological precursor of religious emotion—and even, as ecstatic seizures suggest, a very specific neural basis, in the temporal lobes and their connections—is only to speak of natural causes. It says nothing of the meaning, the 'function' of such emotions, or of the narratives and beliefs we may construct on their basis,

Thus the primal, animal, sense of 'the other' which may have evolved for the detection of threat can take on a lofty, even transcendent function in human beings, as a biological basis for religious passion and conviction, where the 'other', the 'presence', becomes the person of God.

15 January 2013