Brain command centre for speech shuts down when we talk loud

23 Feb 2015

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The part of the brain identified as the command centre for human speech actually shuts down when people speak loudly, reveals a study.

The area named after 19th century French physician Pierre Paul Broca had been recognised for over 150 years as the command centre for human speech, including vocalisation.

The long-held assumption is now being challenged by scientists at the University of California Berkeley and Johns Hopkins University in Maryland with new evidence that Broca's area actually switched off when people talk loudly.

Study lead author Adden Flinker said Broca's area shut down during the actual delivery of speech, though, it might remain active during conversation as part of planning future words and full sentences.

According to neurologists, the brain's language centre was organised into two main regions - one for perceiving speech and one for producing speech.

According to Flinker, the finding helped research move towards a view that Broca's area was not a centre for speech production but rather a critical area for integrating and coordinating information across other brain regions.

There are major implications for the diagnoses and treatments of stroke, epilepsy and brain injuries that result in language impairments from the finding, according to Flinker.

Flinker and fellow researchers found that Broca's area, located in the frontal cortex above and behind the left eye - engaged with the brain's temporal cortex, which organises sensory input, and later the motor cortex, as people processed language and planned which sounds and movements of the mouth to use, and in what order, PTI reported. The study found, however, that it disengaged when one actually started to utter word sequences.

In the study, electrical signals emitted from the brains of seven hospitalised epilepsy patients as they repeated spoken and written words aloud were tracked.

The brain activity was followed using event-related causality technology - from the auditory cortex, where the patients processed the words they heard, to Broca's area, where they prepared to articulate the words to repeat, to the motor cortex, where they finally spoke the words out loud.

The findings can be read in the Proceedings of the National Academy of Sciences.

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