Language Processing in Broca's Area

Language processing in Broca's area during word comprehension tasks is both surprisingly rich in content and complex in operation, according to the newest research. Although historically Broca's area has been associated with motor planning and execution for speech production, the new findings involve it in other types of linguistic processing: lexical (helping to identify forms, such as plurals or past tenses), and phonological (helping to identify pronunciations). Moreover, these three types of processing happen in rapid-fire sequence - three waves in succession that together span approximately one quarter of a second&#59 they register at approximately 200 milliseconds, 320 milliseconds, and 450 milliseconds after the stimulus on probes in Broca's area. Such tightly-clustered three-wave patterns of processing in response to linguistic stimuli have not appeared in probes outside of Broca's area. Such tightly-clustered three-wave patterns of processing in response to linguistic stimuli have not appeared in probes outside of Broca's area.

Making possible these findings is a new research technique, Intracranial Electrophysiology (ICE), which provides data of very high spatial and temporal resolution. The subjects in the studies are individuals who are undergoing brain surgery to identify and remove small areas that cause their seizure disorders. The patients are kept conscious so that the neuroscientists can identify and spare adjacent healthy regions necessary for language&#59 this is accomplished by giving the subjects language tasks to perform while the neuroscientists are recording and analyzing data from tiny probes in those healthy regions. Each highly sensitive probe reports data from neurons in its immediate vicinity.

Prior to ICE, non-invasive brain imaging using computer-aided tomography and functional magnetic resonance imaging technologies had already greatly expanded our knowledge of cerebral areas and activities involved in speech and language functioning. But these technologies are limited by their relatively low spatial and temporal resolution and often smaller lesions would go undetected, and rapidly occurring events be missed entirely or simply be registered together as an undifferentiated blur.

The new discovery of three-wave patterns in Broca's area contributes to basic science, in two distinct ways. First, we have newly identified the contents and operations of cerebral processing specifically in Broca's area during language comprehension tasks&#59 and second, the findings demonstrate the value of the new ICE research techniques, which establish a new awareness of Broca's area's involvements beyond motor planning and execution. The future application of ICE to other language areas in the brain should prove equally fruitful and possibly equally surprising. As future studies apply ICE research techniques to other areas, such as Wernicke's area (currently associated with comprehension) or the superior temporal gyrus (currently associated with lexical storage and retrieval), scientists should begin to piece together the involvements of each area individually as well as their patterns of collaboration and inhibition during speech and language activity.

For further reading: Ned T. Sahin, Steven Pinker, Sydney S. Cash, Donald Schomer, Eric Halgren. Sequential processing of lexical, grammatical, and phonological information within Broca's area. Science, 16 October 2009, vol. 326, no. 5951, pp. 445-49, doi: 10.1126/science.1174481

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