September 23, 2010 | David F. Coppedge

The Evolution of Speech, and v.v.

The brain just got more complex – that is, the part that helps us speak.  “Complex brain landscape controls speech,” reported PhysOrg, discussing findings by German researchers that show Broca’s region, implicated in speech disorders when damaged, appears to be “a much more complexly structured centre of language than was previously believed.”  Not just a sum of two parts, Broca’s region is now seen as a “a highly differentiated mosaic,” according to co-author of a study published in PLoS Biology.1 “It’s a complex world that’s dedicated to our faculty of speech.”
    The concluding paragraph described the impact of these findings on over a century of thought:

The discovery in question of several molecularly and cellularly different cortical areas in Broca’s language region and in neighbouring areas shows that our faculty of speech is actually embedded in a much more differentially developed brain landscape than we have believed for the past 150 years.  The findings are not just important for language research and the diagnosis and treatment of strokes.  They also alter the neurobiological basis for current discussions on the evolutionary development of language, speech training and language disorders.

The authors of the original paper did not describe how this complex region might have evolved.  They only mentioned one other paper that suggested where it might have evolved from: “Fadiga and coauthors have speculated that this capacity evolved from motor and premotor functions associated with action execution and understanding, such as those characterizing the mirror neuron system.”  But their next sentence fit more with intelligent design: “Others proposed that the role of this region is associated with complex, hierarchical or hypersequential processing.”
    Do monkeys show this level of complexity in their corresponding brains?  They noted that “the topography and the sulcal pattern of the ventral frontal cortex differ considerably between macaque and human brains,” but then tried to draw similarities: “If the abilities associated with Broca’s region have evolved from premotor functions, area 6r1 may be interpreted as some kind of ‘transitional’ area between the motor cortex and Broca’s region.”  That partial suggestion, however, needed more study: “Future cytoarchitectonic mapping studies would help to understand the extent of the inferior frontal lobe areas and its intersubject variability.”  Any actual evolutionary insight was going to take more work now that the complexity of this region of the brain has been revealed:

In conclusion, the novel parcellation of the ventro-lateral frontal cortex and Broca’s region provides a new anatomical basis both for the interpretation of functional imaging studies of language and motor tasks as well as for homologies between human and macaque brains.  It will, therefore, contribute to the understanding of the evolution of language.  The analysis of the receptor distribution sheds new light on the organizational principles of this region.  This direction is a further step from a rigid and exclusively cytoarchitectonic parcellation scheme as introduced by Brodmann 100 years ago towards a multimodal and functionally relevant model of Broca’s region and surrounding cortex.

Given that the complexity of their findings overturns a century of simplistic description, it would seem that a “multimodal and functionally relevant model” of the region raises even more difficult challenges to mutation and natural selection.

1.  Amuntz, Lenzen, Zilles et al, “Broca’s Region: Novel Organizational Principles and Multiple Receptor Mapping,” Public Library of Science: Biology, 8(9): e1000489; doi:10.1371/journal.pbio.1000489.

So these findings “alter the neurobiological basis for current discussions on the evolutionary development of language,” the press release said.  How do they alter them?  Let’s be specific.  Do they falsify, destroy, demolish, render irrelevant, capsize, ruin, annihilate, crush, nuke, extinguish, dismantle, ravage, suppress, repudiate, abolish, supersede, invalidate, abrogate, cancel, impair, mutilate, expunge, eradicate, dissolve, or obliterate them?  Use your Broca’s region, if you “understand” with mere neurons, and speak up.

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