The remarkable ability for the brain to adapt to damage has been shown again in a new report into the language abilities of a 17-year-old Italian boy who had virtually his entire left brain hemisphere removed at the age of two and a half.
However, with the help of intensive rehab, beyond age five EB's language fluency improved remarkably over the ensuing two to three years until no language problems at all were reported at school or in the family home. EB had low IQ (78) at this time, but was described as "cooperative and talkative" and "well-oriented in time and place". He performed normally on many tasks including visuo-spatial skills and facial recognition.
Now a team led by Laura Danelli in Italy have documented the results of extensive language testing on EB at age 17, including functional brain scans of his language performance compared with healthy adult controls. Although EB's language appears almost normal in everyday life in terms of vocab and grammar, systematic testing revealed a more mixed picture. There were some subtle grammatical problems as well as poorer than normal scores on picture naming and reading loan words (English or French words incorporated into Italian).
The researchers said these results were consistent with past research suggesting that language function can be largely preserved after removal of the left hemisphere in childhood, but that "the lone right hemisphere cannot provide, by itself, a perfect mastery of each component of language and language-related functions."
Where this new study goes beyond past case reports is in the functional brain imaging of the patient, especially during reading tasks. The results showed that the functional organisation of language areas in EB's right hemisphere largely mirrored what's seen in the healthy left hemisphere of controls, as if following a "left-like linguistic neural blue print." The main differences from controls were extra dorsolateral prefrontal cortex activity in EB's brain during more challenging language production tasks - probably a sign of extra effort on his part - as well as reduced neural activity in inferior temporal and occipito-temporal regions during word and non-word reading.
This pattern of abnormal functioning in inferior temporal and occipito temporal regions fits with EB's specific reading deficits: they resemble surface dyslexia (a problem processing words as whole units, as opposed to reading them letter by letter), which has been linked by past research with abnormal function in these tempero-occipital brain regions. These parts of EB's brain appeared to function normally during non-verbal tasks, which suggests his right hemisphere had a specific problem allocating reading-specific functions to the inferior temporal and occipito temporal cortex.
"Our findings show that EB's right hemisphere may implement a number of basic linguistic skills by largely replicating a left-like neural blueprint," the researchers concluded. Caution is always required when interpreting single case studies, but this paper provides a dramatic example of the brain's huge capacity to adapt to profound injury and illness in early childhood.
Laura Danelli, Giuseppe Cossu, Manuela Berlingeri, Gabriella Bottini, Maurizio Sberna, and Eraldo Paulesu (2013). Is a lone right hemisphere enough? Neurolinguistic architecture in a case with a very early left hemispherectomy. Neurocase DOI: 10.1080/13554794.2011.654226
Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.