Monday, November 5, 2007

Anterior Temporal Lobe and Syntax

As promised, more from Richard Wise's visit to Talking Brains West...

When I asked Richard what he didn't like about our 2007 paper, his response was, our claim about the ATL involvement in syntax. I'm inclinded to agree. Here's the details.

I mentioned in a previous entry, as well as in our NRN paper, that because of the diffuse damage, semantic dementia (SD) cannot provide convincing evidence regarding what the anterior temporal lobe(s) (ATL) is(are) doing. However, it can provide fairly convincing evidence regarding what the ATL is not doing. If some function is spared despite extensive damage to the ATL bilaterally, we can conclude that the ATL is not critical for that function.

In the functional imaging literature, the ATL has emerged as a possible site involved in some form of syntactic computation because responses in this region tend to be sentence-selective. A big problem for this idea, however, is that resection of the ATL does not produce syntactic deficits or any substantial language deficits at all. This problem might be circumvented by proposing that syntactic functions are bilaterally organized in the ATL, explaining why unilateral resection doesn't impair function substantially.

Here's where SD comes in. It has been claimed that SD patients have relatively preserved syntactic ability. I never really understood how a patient could have severely impaired word comprehension with preserved syntactic ability (there's lots of syntactically relevant information in words), so I didn't view SD as strong evidence against a role for syntactic processing in the ATL. Consequently, we have claimed that the ATL may be a site for some kind of syntactic processing, despite claims emanating from the SD literature.

Back to Richard's visit: According to Dr. Wise, SD patients have no trouble with syntax, including a preserved ability to make grammaticality judgments. I believe him. While I wasn't terribly convinced by the published claim -- lots of published claims are wrong -- to hear it from a good clinician who has seen SD patients convinced me (clinical intuition is an extremely valuable research tool).

So does this mean we need to revise our views on the role of the ATL in syntactic processing. Yes, I think so. If SD patients have badly diseased ATLs bilaterally, and can still do reasonably good at the syntactic level, I think we need to rethink things. Part of this rethinking should involve (i) a clear specification of what SD patients can and cannot do syntactically (Grodzinsky, check it out for us will you?), (ii) understanding how word-level semantic deficits might impact sentence-level processing (it has to right?), and (iii) determining whether the ATL might still be involved in combinatorial semantic operations.

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