Adults who had one half of their brain removed in childhood to treat seizures can still recognise faces and words at a reasonably high level, suggesting that the organ can reorganise itself after major childhood surgery.
It is typically understood that word recognition is generally processed in the left hemisphere of the brain and face recognition occurs in the right hemisphere.
at Carnegie Mellon University in Pittsburgh, Pennsylvania, and her colleagues wanted to find out how the loss of either brain hemisphere in childhood affects a person鈥檚 ability to recognise words and faces.
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The team tested 40 individuals who underwent surgery in childhood to remove their left or right brain hemisphere in order to stop epileptic seizures.
Of the participants, 16 still had their left cerebral hemisphere and 24 had their right hemisphere. Known as a hemispherectomy, the surgery is rare and used as a last resort to treat severe seizures that originate from one side of the brain. and causes no significant loss of language function or IQ.
To test the participants鈥� ability to recognise faces quickly, they were presented with grey faces that had their colour removed and any hair photoshopped out. These images appeared on the centre of a computer screen against a black background for 750 milliseconds each.
After a 150ms gap, the participants saw another face, this time for 150ms. They were then asked to report whether the two faces were the same.
Word recognition was tested in the same way, this time using pairs of similar four-letter words, such as tack and tank.
The 40 participants were also age and gender-matched with 58 people who had both brain hemispheres.
The team thought people with only their right hemisphere would perform better at face recognition, while those with just their left hemisphere were expected to score more highly at word recognition.
Instead, the people who had their left or right hemisphere removed scored an average accuracy of 86 per cent across both tasks, compared with 96 per cent accuracy in the control group.
In the second part of the experiment, the team tested whether the control group would still perform better than those with a single brain hemisphere if they were restricted to primarily using just one of their hemispheres.
The researchers repeated the experiments, this time placing the word or face stimuli on one side of the screen. Stimuli placed in the left visual field is primarily processed by the right hemisphere and vice versa.
The people with both brain hemispheres still performed better than the other participants at each task, with one exception.
When a word was placed on the left side of the screen, and would be expected to be primarily processed in the right hemisphere, the people with both hemispheres performed no better than those with a single hemisphere, regardless of whether the latter participants鈥� left or right hemisphere was intact.
Previous studies show that such high rates of accuracy in tasks like these
The latest study suggests that the childhood brain is very plastic, says at the University of Edinburgh in the UK. 鈥淚f only one hemisphere鈥檚 resources are available, then both behaviours will rely on that resource rather than splitting it between the two hemispheres,鈥� he says.
鈥淭he fact that above-chance and broadly comparable performance for face and word recognition can be achieved following childhood hemispherectomy attests to the remarkable adaptability of the juvenile brain,鈥� says at the University of Kent in the UK.
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