Rethinking the Role of Broca’s Area—Or Did We?

Feb 22, 2015 by

brocas_area

A recent article “Brain’s iconic seat of speech goes silent when we actually talk”, published in Science Daily online on February 18, 2015, reviews the research of a team of scientists from New York University, the Helen Wills Neuroscience Institute at UC Berkeley, the Center for Aphasia and Related Disorders at the Veterans Affairs Northern California Health Care System, and Johns Hopkins School of Medicine (Flinker et al. 2015). According to the Science Daily article, this study “challenges the long-held assumption that ‘Broca’s area’ governs all aspects of speech production”. According to the study’s findings, “Broca’s area actually switches off when we talk out loud”. Flinker et al.’s article, published in PNAS, explains:

“Using direct cortical recordings of these dynamics during vocal repetition of written and spoken words, we found that Broca’s area mediates a cascade of activation from sensory representations of words in temporal cortex to their corresponding articulatory gestures in motor cortex, but it is surprisingly quiescent during articulation.”

Flinker et al.’s conclusion: “Broca’s area does not participate in production of individual words, but coordinates the transformation of information processing across large-scale cortical networks involved in spoken word production, prior to articulation”.

However, it is not clear whether the “long-held assumption” Flinker et al. supposedly challenge is really as widely held as this article implies. According to Flinker, “neuroscientists traditionally organized the brain’s language center into two main regions: one for perceiving speech and one for producing speech”. However, that traditional conception has long been abandoned by most linguists and neuroscientists alike. In his fascinating book The Boundaries of Babel, Andrea Moro writes:

“Nowadays we do not think that things are that simple. There is no single ‘language area,’ and it is likely that there is no single area specifically dedicated to any one function. The brain activates complex nets, and the ‘areas’ are merely zones of preferential activation, but they are not exclusively responsible for a certain function” (p. 127).

His own research has been dedicated to examining the role of the Broca’s area as the seat of Universal Grammar. In Moro’s experimental studies, subjects had to extrapolate grammatical patterns, some of which were UG-compatible rules of a real foreign language, such as placing the object before the verb in Japanese, while others were UG-incompatible rules of a “fake” language, such as forming yes/no questions by placing all words in a sentence in the reverse order. The subjects were then asked to judge the grammaticality of novel strings with respect to the “real” or “fake” language they had learned; at the same time, their brains were scanned by using the fMRI. Moro and colleagues found that “both real and pseudo-linguistic rules initially activated Broca’s area to a similar degree […] Most intriguingly, a specific subdivision in Broca’s area […] became more active over time as participants became adept with the real rules but less active over time during comparable presentations of their pseudo-linguistic counterparts” (Marcus et al. 2003: 651-652). Note, however, that Moro’s experiments did not involve speech production at all, thus showing that Broca’s area does something other than “govern[ing] all aspects of speech production”. Rather, it appears to be in charge of connecting the words together into phrases and sentences, and perhaps also other computational aspects of language, rather than production of individual words.

Flinker et al.’s findings, in conjunction with the work of Andrea Moro and his colleagues, seem to support another important conjecture, which goes as far back as Ferdinand de Saussure’s Course in General Linguistics: the distinction between language (langue) and speech (parole), or in Chomsky’s more recent terms, the distinction between competence and performance. Broca’s area, it seems, is responsible for language/competence, as evidenced from Moro’s experiments, and not for speech/performance, as have been shown by Flinker et al.

As noted in Marcus et al. (2003: 652), the interplay of Broca’s area with other parts of the brain may yet prove to be even more complex. For example, they cite Dronkers (2000) as showing that “not every lesion in Broca’s area leads to grammatical deficit”. Conversely, “other recent studies have shown that Broca’s area to be active in domains as diverse as music perception and motoric imitation” (cf. Maess et al. 2001 on music perception and Iacoboni et al. 1999 on motoric imitation).

Thus, as interesting as Flinker et al.’s study is, it is hardly as paradigm-shifting as the Science Daily article makes it sound.

 

Sources:

Dronkers, Nina F. (2000) The pursuit of brain–language relationships. Brain and Language, 71(1): 59-61.

Flinker, Adeen; Anna Korzeniewska; Avgusta Y. Shestyuk; Piotr J. Franaszczuk; Nina F. Dronkers; Robert T. Knight; Nathan E. Crone (2015) Redefining the role of Broca’s area in speech. Proceedings of the National Academy of Sciences.

Iacoboni, Marco; Roger P. Woods; Marcel Brass; Harold Bekkering; John C. Mazziotta; and Giacomo Rizzolatti (1999) Cortical mechanisms of human imitation. Science 286(5449): 2526-2528.

Maess, Burkhard; Stefan Koelsch; Thomas C. Gunter; and Angela D. Friederici (2001) Musical syntax is processed in Broca’s area: an MEG study. Nature Neuroscience 4(5): 540-545.

Marcus, Gary F.; Athena Vouloumanos; and Ivan A. Sag (2003) Does Broca’s play by the rules? Nature Neuroscience 6(7): 651-652.

Moro, Andrea (2008) The Boundaries of Babel. The Brain and the Enigma of Impossible Languages. Cambridge: The MIT Press.

Saussure, Ferdinand de (1959) Course in General Linguistics. New York: Philosophical Library.

 


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