There is a new paper in the journal Trends in Cognitive Sciences that, once again, examines the role of Broca's area and language processing.
The battle for Broca’s region, by Yosef Grodzinsky and Andrea Santi, summarizes four positions about the role of Broca's area and concludes -- who would have thunk it? -- that the 'syntactic movement account' is the best account to date.
Grodzinsky and Santi distinguish between four positions: an "action perception" model (advocated, for example, by Arbib and Rizzolatti), a "working memory" model (Caplan), a "syntactic complexity" model (Goodglass, Friederici), and a "syntactic movement" model (supported by the authors). I think one can quibble about the attributions, but by and large this is more or less of a fair characterization of various positions. The former two are of the "general" variety; the latter two are language specific. The authors examine these positions in light of data from deficit-lesion correlation and neuroimaging evidence, basically from fMRI. They argue, reasonably, that a single model account is likely to underspecified. That being said, they conclude that the recent evidence is most consistent with a "syntactic movement" model Broca's area.
I have rather mixed feelings about this brief review/perspective piece. On the one hand, it is perfectly reasonable for Yosef to work hard on supporting the view that he is fought hard for for a long time. Indeed, attempting to identify a particular kind of computation that's executed in a chunk of brain tissue seems like a sensible goal. On the other hand, I do think it's really time to go further now, and I wish that these authors might lead the way on a more biologically sophisticated perspective.
The fact that their view is too simple is something they state repeatedly. "Importantly, Broca’s region might well be multi-functional." And: "Indeed, Broca’s region might be multifunctional." And so on. Well, yes, then let's actually entertain that...
The fact that we have to make careful distinctions between areas 44, 45, 47, and the frontal operculum is now well established. Yosef has supported important progress in this area, and Friederici and her colleagues as well as Amunts and her colleagues have provided impressive evidence for functionally relevant subdivisions. Moreover, even for a single piece of tissue a la Brodmann, the probability is very a very high that more than one operation is executed. Obviously ... Look, take Brodmann area 17 (primary visual cortex, striate cortex). Beyond subdivisions into ocular dominance columns, orientation pinwheels, and -- obviously -- six differentiated layers of cortical tissue, there are further functionally critical subdivisions into cytochrome oxidase blobs, etc. We are perfectly comfortable attributing multiple functions to local pieces of tissue in the visual system. Yet we persist in trying to find surprisingly monolithic interpretations of the chunk of brain as extensive as Broca's region. Now admittedly we don't have the necessary cell biological analysis of this part of the brain; nevertheless, isn't it time we come up with some more nuanced hypotheses about what gets calculated in these various different parts of the frontal lobe?
Inquiring minds want to know. I'm pretty frustrated with the state-of-the-art in this area of research. Please, somebody, figure this piece of brain out!
Y GRODZINSKY, A SANTI (2008). The battle for Broca’s region Trends in Cognitive Sciences DOI: 10.1016/j.tics.2008.09.001