"Crossed wires" in the brain

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

Capgras syndrome
Capgras syndrome leads people to believe that a close acquaintance has been replaced by a double. Even though they recognise that the person looks exactly like their loved one, they are convinced it is someone else. This is what happened to David: after the car accident, he became sure that the woman who resembled his mother was in fact an impostor.

This may occur because, while all the visual centres in the brain are intact, the final link in the chain of recognition is broken. This final link is with the limbic system ? the emotional centres ? of the brain. David recognised his mother, but because he felt no emotional response to her, he concluded that it could not really be her.

Interestingly, David had no difficulty identifying his mother when speaking to her over the phone.  This could be because the connection between the auditory system and the limbic system was not damaged in the accident.

Prosopagnosia, sometimes referred to as “face blindness”, is a disorder in which people struggle to identify faces, although 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.  Damage to the brain’s face-recognition centres may cause this condition.

In one experiment, people with prosopagnosia were shown pictures of people. It was observed that the subjects’ skin conductance changed, according to whether the people in the photos were familiar or unfamiliar. This suggests that the faces were somehow being recognised on a subconscious level.

To identify people, people with prosopagnosia pay attention to traits such as clothing, hair style, gait and voice.
Phantom limbs

Many amputees have “phantom limbs”: they still experience the sensation of having a limb, even though it is missing. This is often associated with great discomfort and pain. Phantom limbs also tend to feel shorter than normal limbs.

In one case, 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 little finger, and so on. This can be explained as a kind of “cross-wiring” between the parts of the brain that handle sensory input from the skin of the hand and the skin of the face. Brain scans confirmed that when the patient’s face was touched, both hand and face areas lit up.
Paralysed people and those born without limbs can also experience phantom limbs.

Some people involuntarily associate numbers with colours, or can “taste” music. This is not merely a metaphorical or casual association:  sensory mingling is a reality for people with a condition called synaesthesia.

For example, people with colour-language synaesthesia, the most common form of the condition, actually see numbers in different colours.

One possible explanation is that colour-language synaesthesia is a result of “cross-wiring” between the colour and numerical areas in a part of the brain called the fusiform gyrus. Not surprisingly, these two areas are right next to each other.
Since synaesthesia runs in families, this condition may be genetic.

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 is called pain asymbolia.

This condition may also be explained by a communication error in the brain. One theory is that, in people with pain asymbolia, the pain messages travel far enough in the brain for subjects to know they have been hurt, but not far enough for them to 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.” When nothing happens, and it doesn’t hurt, this surprising “twist” triggers laughter.

Source: Professor V. S. Ramachandran, Reith Lecture Series, BBC, 2003.
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