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Brain damage and perception

 

Can brain damage make you think your mother is an impostor? Can damage to certain brain areas make you blind to faces or motion? And what can brain science tell us about creativity?

 

Explore four of the most intriguing conditions caused by brain damage – all of which alter the amazing way the world is perceived.

 

Capgras syndrome (‘my mother is an impostor’)

Face blindness (prosopagnosia)

Motion blindness

Creativity and brain damage

 


Capgras syndrome

 

 

‘Doctor, this woman looks exactly like my mother, but she is an impostor’.

 

These were the words of an alert, intelligent, emotionally healthy man after he came out of a coma following a head injury.

 

Ramachandran and colleagues argue that Capgras syndrome is caused by a disruption of the nerve pathways between the vision centres of the brain and the emotion centre.

 

 

How do you normally see?

Light comes into your eyes, excites cells in your retina and these send messages to your brain. Through an astounding process your brain perceives the item in front of you, identifies it and decides whether you should eat it, run away from it, or mate with it.

 

For faces, this process of identification happens in your fusiform gyrus in your temporal lobe. The message is then relayed to your amygdala – the gateway to the emotional centre of your brain.

How do you see faces?

 

If Ramachandran is correct, and the nerve pathways between the vision centres of the brain and the emotion centre have been damaged, then the man with Capgras syndrome sees his mother but feels no emotion towards her, therefore concludes she must be an impostor.

 

Amazingly, when his mother telephoned him, he recognised her voice straight away and knew it was truly her. The connections between his auditory centres and the emotion centre of his brain had not been damaged so by voice alone, always knew it was his ‘real’ mother.

 

Many reports of Capgras syndrome still describe it as a delusional state of psychological cause. This seems extremely out-dated since frequently it appears after a head injury in otherwise healthy people. In addition, the delusion is not preserved when the impostor’s voice is heard on the phone.

 

Finally, one would have to argue, that any ‘psychological’ disorder has a physical basis (though not necessarily a physical cause).

 

Whether one day we will unravel its astounding complexities to explain how the brain functions is an entirely different question.

 

 

Face blindness (prosopagnosia)

 

Humans are spectacularly good at recognising faces.

 

This is an astounding feat, given that most humans have the same collection of eyes, nose, eyebrows, ears and mouth, arranged in an almost identical manner on similar shaped faces.

 

Brain-scanning studies show we have an area of the brain that responds hugely when we see a face. This area is called the fusiform gyrus in the temporal lobes on the side of your brain.

 

When this part of the brain is damaged on both sides, for example by a stroke, people can no longer recognise faces, a condition known as prosopagnosia.

 

This is not due to generalised visual problems; reading books, seeing motion and enjoying colour pose no difficulties to someone with prosopagnosia.

 

Equally there is no difficulty identifying other categories of objects such as fruit or cars, and there is no general reduction in cognitive capacities.

 

It seems that we have evolved a specific part of the brain to do the evolutionary vital task of recognising faces – and damage to this area specifically disrupts that process.

 

For more on face blindness, click here

 

 

Motion blindness

 

 

‘I see the world in snapshots like the frames of a movie, but most of the frames are missing’.

 

In 1983 Josef Zihl in Munich treated a women who had suffered a stroke that damaged the middle temporal area (area MT or V5) in both sides of her brain. This area is just above the ear.

 

She was terrified to cross the street. She saw a car in the distance then in the next ‘frame’ the car was nearly on top of her.

 

Pouring a cup of tea was traumatic; she saw the cup empty, but in the next ‘frame’ it was over-flowing.

 

However her visual perception was intact in other ways. She could tell the colour and make of the car, its number plate and how far away it was. What she was unable to do was seeing anything moving in the world.

 

This woman had the extremely rare condition of akinetopsia. Since then, scientists have discovered that even temporary inactivation of this part of the brain (by transcranial magnetic stimulation) can cause temporary motion blindness ( Beckers and Zeki, 1995).

 

 

Creativity and brain damage

 

 

An intriguing study led by Dr Mark Lythgoe investigates whether certain types of brain damage could be related to creativity.

 

In 2001, 51-year old Tommy McHugh had a brain haemorrhage that changed his life. Formerly a builder with a criminal record, Tommy developed an artistic compulsion. He now writes poetry, draws, paints and makes sculptures throughout the day and night.

 

Dr Mark Lythgoe, a neurophysiologist at University College London said: "It may be that the brain damage Tommy has sustained has caused dis-inhibition of brain pathways, allowing Tommy's creativity to surface.

 

It seems a floodgate has been opened.”

 

He added “We are still a long way from understanding the brain bases of the artistic drive, but we hope that by studying rare and intriguing cases like Tommy's, we might get a glimpse of what could be going on"

 

For more about Tommy visit Dr Mark Lythgoe’s website

 

And finally …

 

Charles Bonnet syndrome

 

Seeing fairies, goblins and invisible people.