Sunday, 19 July 2009

Speaking without Broca's area

Psychology is moving away from a view of the brain that ties functions to specific brain areas. Instead, researchers recognise that the brain is made up of dynamic, flexible networks, in which diverse regions are recruited according to task demands. Complementing this account is a growing recognition of the brain's ability to adapt to damage, even in adulthood - a characteristic known as plasticity. These views are captured in a new clinical case study that documents the recovery of language performance in a man known as "FV". He'd had a tumour removed from a relatively large section of his brain, including "Broca's area" - considered since the nineteenth century to be a vital neural centre for speech production.

Broca's area is named after the nineteenth century French surgeon Paul Broca for his work with a patient who, following localised damage to the rear part of his left frontal lobe, lost the ability to produce speech, with the exception of the syllable 'tan', hence his nickname 'Tan tan'. The man's comprehension, meanwhile, remained intact, leading to the popular conclusion that Broca's area is important for speech production, but not comprehension.

Monique Plaza and colleagues thoroughly tested FV's language skills before, during and after his tumour was surgically removed. Importantly, additional to standard neuropsychological tests, the researchers used a narrative task that required FV to tell the story played out in a children's picture book - a test the researchers said was sensitive to deficits not detected by standard measures.

The researchers found that FV's tumour and its subsequent removal did not lead to the severe language deficits that would be expected based on a traditional localisation approach to brain function. Because his tumour had grown slowly, the researchers said other areas of FV's brain, adjacent to Broca's area, had been able to take over language functions, including the premotor cortex and the head of the caudate nucleus. FV showed some expected deficits after surgery, but quickly regained most of his speech production abilities.

However, the narrative task did expose some intriguing, subtle deficits that FV's brain obviously hadn't been able to shop out to adjacent brain areas. These included an inability to represent speech within speech - that is, FV didn't seem to be able to talk about other people's speech.

The researchers said: "The present case confirms the relevance of connectionist approaches [to language] based on studies of slow-growth tumours, which demonstrate that compensatory mechanisms start before surgery, in reaction to tumour infiltration, and consolidate during and after surgical procedures."
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ResearchBlogging.orgPlaza, M., Gatignol, P., Leroy, M., & Duffau, H. (2009). Speaking without Broca's area after tumor resection. Neurocase, 15 (4), 294-310 DOI: 10.1080/13554790902729473

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

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