Tuesday, December 15, 2009

The parallel universes of Broca's area

Update on the function of Broca's area: we still don't know much.

It seems like everyone is studying Broca's area for any number of functions. The most recent is the Science paper that David commented on a while back. That paper argued that Broca's area supports sequential processing of lexical, grammatical, and phonological information. Like other claims about Broca's area, this paper has sparked a debate. For example, see the e-comment by Matt Goldrick et al.

But Broca's area is also a prime suspect in the hunt for mirror neurons, speech perception, syntactic movement, hierarchical structure processing, semantic integration, working memory, and cognitive control. What's interesting (or unfortunate) is that some of these debates go on without reference to others, like they are living in a parallel universe. E.g., you never hear the mirror neuron folks talking about cognitive control and vise versa.

New rule: when speculating about the function of Broca's area you have to at least mention the range of other ideas/data. Maybe this will promote cross-universe interaction.

New rule #2: don't use the term "Broca's area" without further specification. We all know that Broca's area is composed of at least two subregions that seem to do different things. Please specify.


Ellen Lau said...

that second one is the craziest one to me...after the number of high-profile papers arguing for functional parcellation of IFG I am always thrown for a loop when I see studies (usually also in high-profile journals) that simply state that there was differential activity 'in Broca's area'. kind of like a vision paper that says, oh yeah, we found an effect in the occipital lobe.

David Poeppel said...

Yes, to be able to make *any* claim about "Broca's area" or "Broca's region" without being anatomically more specific should be immediate grounds for rejection. To have papers in high-impact journals in 2009 that do not so a better job is just no longer acceptable, if we want to develop a genuine neurobiology of language, not just a 'weak, correlative neurolinguistics.'

To amplify, as well, the functional point: the brief response that Matt Goldrick published in Science raises the issue that the Sahin et al. intracranial data do not force the conclusion of a strict seriality in Broca's area, wherever that may be. As Matt et al. say, the

"full discreteness claim is not required by the Sahin et al. data and conflicts with an extensive body of research that has already demonstrated its inadequacy: reaction time and error data from neurologically intact monolingual speakers (1); aphasic language impairments (2, 3); and bilingual language processing (4). This body of evidence also indicates—consistent with Sahin et al.'s results—that a full interactivity claim is likewise incorrect"

So the lesson is, I guess, that we must force ourselves to operate at higher resolution, but anatomically and functionally.

David said...

As for rule #1: That's sort of what I was trying to accomplish in my paper in JoCN (published online this December) and my dissertation. My colleagues (Dr.Thompson-Schill and Dr. Trueswell) and I argue that many of the other notions about the role of Broca's Area can be captured under the rubric of cognitive control (at least syntactic movement, aspects of the hierarchical structure processing account, and working memory). Whether that's persuasive or not I leave to the reader's judgement.

Greg Hickok said...

Sounds like an interested paper David, I'll have to have a look. I certainly liked the earlier 1995 paper from the Penn crowd. So what portion of Broca's area do you think is critical for cognitive control operations?

David said...

Greg, I've (obviously) been influenced by Sharon Thompson-Schill's views on this question--and the results of my own study--but I think that the posterior extent of Broca's area is more related to cognitive control (more BA 44 than anything else). And I should say that Jared Novick started up this line of argument with a paper in Cognitive, Affective, and Behavioral Neuroscience a few years back. And that my dissertation does more of the arguing that cognitive control can subsume other frameworks than the JoCN paper.

Greg Hickok said...

Hmm. I think BA 44 supports articulatory processes and therefore phonological STM. For example, stimulation of the pars opercularus causes speech arrest. I don't see how cognitive control explains speech arrest. So either it is crowded in BA44 or we have some more thinking to do.

David said...

This might not be the forum for a full-on discussion of Broca's Area function, but Amunts has shown that 44 isn't one area--one "sub-area" seems more involved premotor processing and one seems more "frontal" (if that term can be used to describe "higher" cognitive functioning). I was speaking about the more superior, "frontal" part of 44.

I agree, though, that I don't know (now, at least) how cognitive control could account for speech arrest. I read an article in Scientific American a year or so ago that found that individuals who stutter have decreased Broca's Area (I don't think they got more specific than that) activity during production than non-stutterers, and that fact gave me an idea for wildly speculative hypothesis that stuttering might be partly to do with a cognitive control deficit related to the inability to adaptively change the activation of phoneme-to-articulation representations in working memory. If that (as far as I know) entirely unresearched idea has any merit to it, maybe it could be extended in some way to account for speech arrest from 44 stimulation (always assuming that the speech arrest comes from the non-premotor part of 44).