Saturday, 12 April 2014

Book review: Hallucinations by Oliver Sacks

Oliver Sacks’ book “The Man Who Mistook His Wife For A Hat” was one of the first books I read with a direct neuroscience focus, and since then I have always been interested in his work. One of the things I like most about his writing is that he covers a specific subject in depth that I would not normally have the chance to study in uni classes. 

His most recently published book, Hallucinations, is written in his distinctive style, with first-person narrative of different patients he has helped, as well as anecdotes from his personal life. His book focuses on the different types of hallucinations – visual, auditory, olfactory and tactile. Each chapter examines the different stimuli that can induce these (such as epilepsy, migraines or hallucinogenic drugs) and he explores this through cases of patients he has treated. 

It is important to note that hallucinations differ massively from conjured visual images; such as those you might see when you think back to a memory. A conjured image stays in your head, but a hallucination appears projected into the world around you and appears extremely real. This can be shown through use of fMRI imaging. A hallucination will activate your visual system in the occipital and inferotemporal cortex of your brain. However, a conjuring image will also activate the prefrontal cortex. This shows that there is a fundamental difference in the physiology behind hallucinations versus conjured images. 

Losing a sense is one of the most common causes for corresponding hallucinations. For example, total visual deprivation, or even just a monotony of vision can induce visual hallucinations. This can explain why sailors often see things on the horizon, or why prisoners confined to dark cells can experience vivid dreams or hallucinations. 
The same deprivation or monotony can be applied for auditory hallucinations. In patients Sacks’ has worked with, the commonest cause of musical hallucinations is hearing loss or deafness. However, with regard to auditory hallucinations, a thought-provoking idea is that those who hear voices experience these due to a failure to recognise the voice inside their head as their own. 
Another sense that loss of can induce hallucinations is our sense of proprioception (or the position of objects around us and our position in relation to them). A particularly poignant anecdote in the book is Sacks’ interaction with a patient who has lost this sense, and was unable to sleep as every time she got into bed and lay down she would hallucinate and feel as if she was standing up. 

Interestingly, abnormalities in different areas of the brain correspond to different types of hallucinations. The area of the visual pathway activated correlates with the form of hallucination. For example, an abnormality in the fusiform gyrus area of the brain results in hallucinations of faces that look sketched or cartoon-like. 

It is also important to realise that hallucinations do not always have pleasant characteristics. Sleep paralysis is a common phenomenon, and within this hallucinations are rife (referred to as hypnopompic or hypnagogic depending on the time they occur). However, as reported in Sacks' book, there are usually extremely frightening or disconcerting, with some patients reporting waking up to see a hooded cloaked figure (representing death) standing over them or a giant spider sitting on their chest.

A particularly interesting part of the book, in my opinion, was Sacks’ description of his own experimentation with hallucinogenic drugs. I was drawn in by this as not only was it refreshingly honest to hear a medical professional discuss illicit activities, but experimentation with drugs is also a topic rarely discussed in my uni lectures. One anecdote that stood out was his description of when he injected himself with morphine found in his parents’ drug cabinet at home. He then lay on his bed and became distracted by the sleeve of his dressing gown in the corner of his room; and hallucinated that in the patterned material of the sleeve he could see a medieval battle scene from a bird’s eye view. Eventually Sacks’ came out of his stupor and looked at his watch, surprised to find it only ten o’clock (as he had only injected the morphine at nine-thirty). However, he looked out a window and saw it was getting lighter instead of darker – and realised it was now ten o’clock in the morning. He had been hallucinating and staring at the dressing gown sleeve for over twelve hours! This showed the hallucinogenic power of a drug that is relatively commonplace (and used frequently in hospitals for its analgesic effects). 

I really enjoyed this book and highly recommend it – it contains complex neurological ideas that are set out in a simple way. The book provides an insight into an area of neuroscience that is usually regarded solely as a consequence of administering hallucinogenic drugs. Also, the use of different patient’s medical records makes the descriptions of different neurological conditions seem very real, even when some of their afflictions seem implausible.

Have you ever experienced a hallucination yourself? Feel free to comment and let me know!


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