Monday, February 20, 2006

Unravelling the evolution of language?


There is now an online-only published paper in PNAS from the Max Planck Institute on the evolution of language. What is surprising is that the researchers have used functional MRI to infer the evolutionary lineage from their results. Basically, what Angela Friederici and her colleagues have done is to compare language processing that is "simple" to processing that is "complex". While simple processing activated left frontal operculum, a phylogenetically older region of the brain, more complex language processing also activated Broca's area, which is thought to be a more recent development specific to humans. in addition, the researchers also studied the white matter connectivity of the two brain regions by using MR tractography. Here, they found that the two regions showed different structural connectivity signatures, further supporting the functional segregation of these two areas.

This makes the researchers conclude:
"Here we report findings pointing toward an evolutionary trajectory with respect to the computation of sequences, from processing simple probabilities to computing hierarchical structures, with the latter recruiting Broca’s area, a cortical region that is phylogenetically younger than the frontal operculum, the brain region dealing with the processing of transitional probabilities"

I first found this through the Max Planck Society press release page. Just reflecting briefly on this, I think that despite the study is interesting itself in terms of functional segregation of language processes, I am not convinced about the argument about the phylogeny of the two regions. As we know from research on subcortical structures such as the "limbic system", we cannot divide between the phylogenetic "old" and limbic brain and the "newer" cortical brain. It is today considered total gibberis, because evolution of "higher" areas in the cortical surface has had a dynamic and synergetic co-evolution of cortical and subcortical areas. In similar vein, I suspect that the evolutionary trajectories of the frontal operculum and Broca's area share a lot, and that a clear-cut division between the two areas will prove hard to make.

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