By Elli Leadbeater
The dementia patient's drawings get more bizarre with time
Although many people might not draw a duck very well, few would include four legs and eyebrows in their picture.
But those who suffer from a common type of dementia confuse concepts such as "bird" and "dog", and will produce the strangest drawings.
The area of the brain that stores meaning is damaged in these people.
Researchers from the University of Manchester may have finally solved a 150-year-old debate by pinpointing where that area actually is.
They think that a brain sector just underneath the ears, called the temporal pole, is responsible.
Professor Matthew Lambon Ralph, of Manchester University said: "At the heart of communication is me getting a meaning from me to you.
"If you don't understand that meaning, then the middle part of all communication falls away."
The researcher and his team had previously suspected the temporal pole was involved.
Their suspicions were based on images which had shown that people with semantic dementia, who can struggle with even simple concepts such as "car" and "fork", have lost tissue from that area.
But until now it was impossible to be sure, because these patients might also have other brain damage, too.
The temporal pole is found in a region of the brain near the ears
By artificially slowing down the temporal pole's activities in volunteers with normal brains, the researchers have been able to show that it does play a part in storing meanings.
The research team used a technique called transcranial magnetic stimulation, or TMS.
This involves placing a magnetic coil on the side of the head, just above the temporal pole. The magnetic pulses exhaust the part of the brain underneath, so that for about 10 minutes it is too tired to work properly.
"When we tire it out in normal subjects, we get some of the same effects that we see in the patients, although to a much milder degree," said Professor Lambon Ralph.
"The people don't make wild four-legged-duck errors, but if we ask them to name pictures or to understand concepts, they're about 10% slower than they were before.
"It really reinforces the idea that the temporal pole is where those concepts are encoded."
Researchers had previously thought that a different, nearby brain area, called Wernicke's area after a German neurologist, probably stored this information.
Although the team has not yet studied whether TMS would have similar effects if it was applied to Wernicke's area, it is confident that the temporal pole has the main role in storing meaning.
Semantic dementia is the second most common form of dementia in people under 65.
"For these patients, it's not like words have been deleted from the dictionary, so that you know about a duck one day and then the next day you don't," explained Professor Lambon Ralph.
"Instead, your information about ducks gradually gets fuzzy, and so you sort of vaguely know what a duck's like, but you don't know the details."
The symptoms are very obvious when the patients are asked to make drawings.
The patient who drew the strange duck had initially been asked to make a direct copy of a picture placed right in front of her. She made a good drawing.
But when asked to make the same copy either 10 or 60 seconds after seeing the picture, the patient started to confuse the concept of a duck with other animals.
Such patients can also no longer connect certain smells, or touch sensations, with particular objects. For example, if they smell a lemon, they no longer know what it is that produces that aroma.
The team is working with therapists to see if there is a form of speech training which could help the patients.