Study of man's brain who suffered damage reveals new insights
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Researchers at Carnegie Mellon and Princeton universities have gained unprecedented new insights into the brain of a man who has trouble recognizing everyday objects.
Led by Christina Konen at Princeton and Marlene Behrmann at CMU, the team recorded brain images of a man who had survived a severe car accident several years ago and suffered damage to the lower right half of his brain.
The man has trouble identifying objects and people's faces. In one case, he mistook a drawing of a harmonica for a cash register, thinking the air holes were cash register keys. In another case, the drawing of an octopus stumped him altogether.
One way the man compensates for his shortcomings in real life is to use other cues to help him guess what he is seeing, Ms. Behrmann said, "so if I show him a banana, he'll use its yellow color to make a guess as to what it is."
To eliminate that effect, the researchers used black and white line drawings to test his recognition ability while he underwent brain imaging.
The new study, published last week in the journal Neuron, produced two surprising results, the researchers said.
First, even though his injury was on the lower right part of the brain, the corresponding area on the left half of his brain also was dysfunctional.
That may mean that the brain's right temporal lobe, which sits above the right ear, is the critical area for recognizing objects, and if it is damaged, it cannot send a strong enough signal to activate the same area in the left temporal lobe, Ms. Konen said.
It also may mean that functions like visual recognition rely on a whole network of brain areas, said Ms. Behrmann. Many brain scientists have believed that damage in a single area is responsible for any behavior changes that result, she said, but "in this case, it turns out that [the right temporal] lesion has pretty remote effects in the other hemisphere. So now we need to think of small parts of the brain being part of a much more widespread network whose parallel activity gives rise to behavior."
The second unusual finding was that the patient's brain worked hard to compensate for the damage by recruiting a more primitive part of the visual system to attempt to recognize objects.
Even though his recognition ability is still poor, the adaptation of his brain seems to have given him some ability to identify objects and faces, the scientists said.
Patients like this man are extremely rare, so scientists are often eager to study their brains to see how they differ from those of typical people.
Discovering that damage to one part of his brain might have had remote effects on another part of the brain fits with some of Ms. Behrmann's other work showing that brain networks are vital for several behaviors.
She has found that people born with an inability to recognize faces often have poor connections between several key brain areas. She has also discovered that adults with autism have inadequate links between different sections of the brain.
First Published July 19, 2011 12:00 am
