How Broca's Area Computes Language

In the chapter INSIDE THE BRAIN I hint at the complexity of Broca's area - one of the main speech and language processing areas of the brain. Now some researchers from UC San Diego have listened in to Broca's area by asking epilepsy patients to do simple language tasks on a laptop while implanted with electrodes meant to find and destroy the sites of epileptic lesions. As they repeated words verbatim, or produced them in grammatical forms like their past tense or plural, the electrodes measured the time and place of electrical activity in Broca's. They found patterns of neuronal activity indicating lexical, grammatical and articulatory computations separated at 200, 320 and 450 milliseconds after the target word was presented. Although these different computations were done serially, the parts of Broca's area involved appeared to overlap. As principal investigator Eric Halgren says: "These results suggest that Broca's area actually consists of several overlapping parts, performing distinct computational steps in a tightly timed choreography, a dance that may simply have been undetectable due to the level of resolution of previous methods". Crucially, the article says, information about the identity of a printed word arrives in Broca's area very quickly after it is seen, and in parallel with its arrival in Wernicke's area. It had previously been thought that reception of words (reading and hearing) was the exclusive preserve of Wernicke's area, situated more posteriorly than Broca's, while Broca's area dealt exclusively with expression (speaking). This is clearly out of date. As one of the scientists involved, Ned Sahin, says: "Broca's area has several roles in both expressive and receptive language."