14 December 2011

Crossed wires

Imagine not recognising your mother, or feeling missing limbs or tasting music. When brain wires get crossed, these things can happen. Even to you.


Imagine not recognising your mother, or feeling missing limbs or tasting music. When brain wires get crossed, these things can happen. Even to you.

After sustaining a head injury in a car accident David developed a strange affliction - while being neurologically intact otherwise, he was suddenly incapable of recognising his mother.

How could this happen? And what else could the wrong genes or a blow against the head do to your hold on reality? We take a look at five strange mental afflictions.

You are an impostor (Capgras syndrome)
Capgras syndrome leads people to believe that a close acquaintance or loved one has been replaced by an impostor, or a double. So, even though they can recognise that the person looks exactly like their loved one, they are convinced it is someone else.

That is why, after the accident, David says: “Doctor, this woman looks exactly like my mother, but she isn’t - she is an impostor.”

The story of David (not his real name) was recounted by Professor V. S. Ramachandran during his seminal lecture at the BBC’s 2003 Reith lecture series. Ramachandran is director of the Center for Brain and Cognition, and a professor with the psychology department and the neurosciences programme, at the University of California, US.

Ramachandran hypothesises that all the visual centres in David’s brain are intact, but that the final link in the chain of recognition may be broken. This final link is with the limbic system - the emotional centres - of the brain.

In other words, David recognises his mother, but because he feels no emotional response to her, he concludes that it cannot really be her.

Interestingly, David has no difficulty identifying his mother when speaking to her over the phone. According to Ramachandran, this could be due to the fact that the connection between the auditory system and the limbic system may not have been damaged by the accident.

Empty faces (Prosopagnosia)
Prosopagnosia, sometimes referred to as face blindness, is a disorder in which people struggle to identify faces even though there is nothing wrong with their eyes.

Whereas people with Capras syndrome identify a face but fail to make an emotional connection, people with prosopagnosia have difficulty identifying faces altogether - something which has been taken to suggest that the human brain may be wired for face recognition, and that damage to the brain’s face recognition centres may cause the condition.

Interestingly, when showed pictures of familiar and unfamiliar people, researchers have observed changes in the skin conductance of people with prosopagnosia. This suggests that, even though faces are not consciously recognised, they are being recognised on a subconscious level.

People with prosopagnosia use traits such as clothing, hair style, gait and the sound of someone’s voice, to make up for their difficulties with recognising faces. They are also said to have significant trouble following television shows.

The limb that is not there
According to figures quoted on Wikipedia, approximately 50 to 80 percent of amputees experience so-called phantom limbs. This means that they still experience the sensation of having a limb, even though the limb has been amputated.

Phantom limbs tend to feel shorter than normal limbs and can often provide great discomfort and pain.

Ramachandran relates a case in which a person’s phantom hand could be traced on his face. When a certain part of the man’s face was touched, he felt a sensation in his phantom thumb. Another part of the man’s face corresponded to his pinkie, and so on.

Ramachandran explains the occurrence as a kind of cross-wiring between the parts of the brain responsible for handling sensory input from the skin of the hand and the skin of the face. These areas are located on the Penfield homunculus, which is something like a small map of the body that is draped over an area of the brain.

Brain scans confirmed that when the patient’s face was touched, both the hand and the face areas lit up.

Interestingly, paralysed people and people born without limbs can also have phantom limbs.

Numbers have colours (Synaesthesia)
Imagine involuntarily associating numbers with colours, tasting music, or getting a physical sensation from hearing someone’s voice. This kind of sensory mingling is a reality for people with a condition called synaesthesia.

And, we are not just talking about metaphors or casual associations. For example, people with colour-language synaesthesia, the most common form of the condition, actually see numbers in different colours.

This has been proven by their ability to recognise a triangle of “2”s amidst a square of “5”s faster than people who do not have synaesthesia. According to Ramachandran, they can do this because they experience the ‘2’s as having a different colour.

One theory is that colour-language synaesthesia may be a result of the colour and numerical areas in a part of the brain known as the fusiform gyrus getting their wires crossed. Not surprisingly, these two areas are right next to each other.

Since synaesthesia runs in families, the thinking is that the root cause of this cross-wiring may well be genetic.

Laughing at your pain (pain asymbolia)
Imagine being pricked with a needle or cut with a knife, but instead of shouting or crying, you start laughing. This bizarre condition where pain induces laughter or giggling is called pain asymbolia.

According to Ramachandran, this condition, like those above, may also be explained by a communication error in the brain.

He explains his theory by first explaining how humour works. “The common denominator of all jokes and humour … is that you take a person along a garden path of expectation and at the very end you suddenly introduce an unexpected twist that entails a complete reinterpretation of all the previous facts,” he says.

The idea is that in people with pain asymbolia, the pain messages only travel far enough in the brain for the subject to know that he has been hurt, not far enough for him to actually experience the pain in a way that would elicit a normal response.

In a sense, part of the brain is saying, “this is going to hurt.” And then, when nothing happens, and it doesn’t start to hurt, the person starts laughing.

(Marcus Low, Health24, August 2007)


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