Sequential Processing in Broca’s Area

Single-sentence Summary of the Paper:    Three linguistically distinct processes, often associated with widely separated parts of the brain, were discovered to be separated in time (indeed sequential) but co-located within a small region of the brain the size of a single fMRI voxel, within the well-known if poorly understood Broca’s area, and the processes were identical for producing nouns versus verbs.     See below for more info.

Alternate Single-sentence Summary:    We recorded neuronal activity during language production from electrodes within Broca’s area — a region assigned many roles in language over many decades — and discovered that computations of lexical information, grammar, and articulation all happened within overlapping patches of cortex, but were segregated sequentially in time.

Abstract of the Paper: Words, grammar, and phonology are linguistically distinct, yet their neural substrates are difficult to distinguish in macroscopic brain regions. We investigated whether they can be separated in time and space at the circuit level using intracranial electrophysiology (ICE), namely by recording local field potentials from populations of neurons using electrodes implanted in language-related brain regions while people read words verbatim or grammatically inflected them (present/past or singular/plural). Neighboring probes within Broca’s area revealed distinct neuronal activity for lexical (~200 milliseconds), grammatical (~320 milliseconds), and phonological (~450 milliseconds) processing, identically for nouns and verbs, in a region activated in the same patients and task in functional magnetic resonance imaging. This suggests that a linguistic processing sequence predicted on computational grounds is implemented in the brain in fine-grained spatiotemporally patterned activity.     download:     [PDF with supplement]  •  [PDF]

Citation: Ned T. Sahin, Steven Pinker, Sydney S. Cash, Donald Schomer, and Eric Halgren, “Sequential Processing of Lexical, Grammatical, and Phonological Information Within Broca’s Area.” Science 326(5951): 445-449 (Oct 16, 2009).
[DOI: 10.1126/science.1174481]

         (click image – Page 1 of journal, with Editor’s highlights for the issue.)

The Speaking Brain

Peter Hagoort & Willem J. M. Levelt

(This was a “Perspectives” piece written about this paper in the same issue of the journal – abstract is reprinted here; links to the whole piece are below.)

How does intention to speak become the action of speaking? It involves the generation of a preverbal message that is tailored to the requirements of a particular language, and through a series of steps, the message is transformed into a linear sequence of speech sounds (1, 2). These steps include retrieving different kinds of information from memory (semantic, syntactic, and phonological), and combining them into larger structures, a process called unification. Despite general agreement about the steps that connect intention to articulation, there is no consensus about their temporal profile or the role of feedback from later steps (3, 4). In addition, since the discovery by the French physician Pierre Paul Broca (in 1865) of the role of the left inferior frontal cortex in speaking, relatively little progress has been made in understanding the neural infrastructure that supports speech production (5). One reason is that the characteristics of natural language are uniquely human, and thus the neurobiology of language lacks an adequate animal model. But on page 445 of this issue, Sahin et al. (6) demonstrate, by recording neuronal activity in the human brain, that different kinds of linguistic information are indeed sequentially processed within Broca’s area.    [Science www]  •  [PDF]  •  [Max Planck]

Several popular-press articles were written about the paper, putting it in a broad context. (Please click for press page.)

Thanks for visiting!
~ned