The Role of Broca’s Area in Language Processing

Language is a complex an multifaceted brain function underlain by distributed circuit of interconnected brain areas (Moritz-Gasser & Duffau, 2009). Up until the 1970s the research on the organisation of language production and comprehension has been predominantly based on the analysis of behavioural deficits in patients with brain lesions. Using this technique the classical neurological model of language processing was developed by Broca (1861) and Wernicke (1874), later extended by Lichtheim (1885). It implicated two brain regions involved in language production and comprehension - Broca’s area in the inferior frontal gyrus (IFG) and Wernicke’s area in the posterior superior temporal gyrus (pSTG), respectively. It suggested that Broca’s area stores motor representations of words while Wernicke’s area contains the information about what the words sound like as well as what their meanings are.

While the early neurological model of language broke away from the ideas of phrenology and offered a new framework for neuropsychological research, it had numerous shortcomings. It was not able to account for the fact that people with Broca’s aphasia (also known as non-fluent, expressive or agrammatic aphasia) had a variety of ostensibly diverse impairments or that some people with focal Broca’s area damage did not show agrammatic aphasia (Bookheimer, 2002).

Only with the advance of neuroimaging techniques it has been established that this is due to functional specification. Specific regions in the inferior frontal gyrus are responsible for specific language skills: speech articulation, comprehension of complex syntactic structures, sentence production, object naming ect. (Bookheimer, 2002). Notably, not all of these functions are affecte...

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...del considers LIFG to have a role in unification of semantic, syntactic and phonological processing (Hagoort, 2005)

Mapping the language functions onto the cortical regions has been a complicated task considering the use of different terminologies by different reports – some of them define cortical regions in terms of Broadmann areas (i.e BA44/45) other use anatomical nomenclature based on the gyri (e.g. pars opercularis/triangularis of the IFG) Different terminologies cause confusion as the regions do not necessarily occupy the same space.

The overlapping functions of different IFG areas suggest that it might be best to move away from the paradigm of modular representation of language in the brain and focus on uncovering the network of interconnected modules between different parts of the brain that are responsible for specific aspects of language production.