Re-establishing Broca’s initial findings

The importance of the left inferior pre-frontal cortex (LIPC) for speech production was first popularized by Paul Broca, providing a cornerstone of behavioral neurology and laying the foundation for future research examining brain-behavior relationships. Although Broca’s findings were rigorously challenged, comprehensive contradictory evidence was not published until 130 years later. This evidence suggested that damage to left anterior insula was actually the best predictor of motor speech impairment. Using high-resolution structural magnetic resonance imaging (MRI) in patients with chronic stroke, we reveal that LIPC involvement more accurately predicts acquired motor speech impairment than insula damage. Perfusion-weighted MRI provides complementary evidence, highlighting how damage to left inferior pre-frontal gyrus often includes insula involvement, and vice versa. Our findings suggest that Broca’s initial conclusions associating acquired motor speech impairment with LIPC damage remain valid nearly 150 years after his initial report on this issue.

► Apraxia of speech is most reliably associated with Broca’s area damage.
► Left pars opercularis damage was the strongest predictor of apraxia of speech.
► Perfusion deficits in the left pars opercularis predicted apraxia of speech.
► Broca’s area damage is a better predictor of apraxia of speech than insula damage.