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Tuesday, January 27, 2009

Man who mistook his wife for a hat (1/2)

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Man who mistook his wife for a hat” is a book of medical maladies by Oliver Sacks. It is book of so rare yet so bewildering deceases that it questions our own understanding of ourselves and the world. What we see is not what is there but what our brain makes us see, and brain can be a funny thing, so it can make you see what others don’t see, and vice-versa, because world as we know it doesn’t really exist except in our perception of it. We might as well be living in a Matrix and there is no way we can find out. As I wrote in my review on librarything:
[The book is a] fascinating collection of amazing and unimaginable mental illness (neuropsychological) revoking horror, sadness and wonder at the same time. You cannot imagine what could go wrong with you as much as you try.

If tales of wonder amazes you, go ahead and bewilder yourself. If not, you are advised to skip this post. For best effect, imagine yourself in the place of patient.

Prosopagnosia is visual memory loss when one can lose ability to recognize objects, particularly faces. Patient can see alright but cannot differentiate, much like we can identify among human faces but not among cow faces. Patients can understand features, voice, movement and other discernible characteristics of object but cannot identify it because of loss of body image in the memory. Subsequently, he can not see visual dreams and can only identify things by mental definition and association. Author cites example where patient cannot see rose as a rose but a convoluted fragrant red object with green linear base and learns to call it rose. In extreme cases, they can even forget their own faces or their family members’. Title of the book comes from this disorder.

Retrograde Amnesia (Korsakov’s Syndrome) is special type of amnesia where memory suddenly freezes at some point in past. So up to that point everything is clear in mind but nothing remains in memory after that moment. Every day is next day after day of freezing, irrespective of number of decades passed between them. Current memory is very short term (few minutes), even though there is no general loss of intelligence or mental capabilities. Patient lives with no past or future but only present. Sometime retrograde amnesia moves backward in time with date of frozen memory shifting back. Sometimes there may be feeling of familiarity with things done few minutes earlier but there is no mental time frame to link to immediate past. Author mentions that even hypnosis fails to recover traces of past memories for these patients since they forget what hypnotist is saying in time it takes to hypnotize. In extreme case, retrograde amnesia travels back to birth and whole life is erased from memory leading to loss of self.

In one case complete loss of visual cortex in brain of patients eliminates whole idea of seeing. There is no concept of image in memory and patient is not even aware that he is blind because he doesn’t even know what seeing means. Such a thing is simply unimaginable for us and can only crudely be understood by noting that we are not bothered by lack of sonar capabilities in ourselves unlike bats because that concept is meaningless to us.

Our senses help our body interact with outside world. We are commonly aware of five external senses (exteroception): gustation/taste, olfaction/smell, vision/sight, audition/hearing, and tactation/touch (which include thermoception/thermal and nociception/pain). There are two more internal senses (interoception), which are internal information in brain about bodily balance/equilibrioception and relative positions of parts of body/proprioception. Equilibrioception helps us walk straight in dark or rise up when lying down because body knows what is right side and what is proper balance. Proprioception helps us touch our nose from finger without looking because our brain has a schema or diagram of current and ideal position of body parts.

Loss of equilibrioception leads to loss of sense of balance in a person. Without actively visually monitoring himself, person cannot walk straight. He is not even aware that he is tilted nor does he find his vision and world tilted because he has completely lost the concept of balance and upside. Patients need to use external level, not unlike used by plumbers, with a weight hanging from his eye glasses.

Loss of proprioception leads to loss of possession of body and loss of map of body to brain. It’s like brain is blind and deaf because nervous system doesn’t carry senses about body parts movement back to brain. This affects body posture because additional senses such as vision or touch have to substitute for loss of proprioception. Symptoms of this simple loss of information are drastic. Brain losses ability to control voice since lips and jaws don’t automatically adjust to tone, and one has to use ears to listen to self and then control vocal modulation. Face doesn’t display expression commensurate with emotions one is feeling. Unless actively monitored visually, body part don’t maintain their position so that jaws may be hanging down and one cannot open door without guiding hand to position of handle visually. In one extreme case, a patient couldn’t associate his own leg with himself and kept falling out of bed in attempt t throw off an “odd, cold, hairy, severed human leg”. You may recall mild degree of these symptoms with alcohol consumption, and that’s why tests for alcohol level might include walking straight on a line and trying to touch your nose from behind.

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