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Feb 09

What Modern Technology Tells Us About Two Famous 19th-Century Brains

Maria Konnikova has posted a fascinating account of how recent brain scans of two preserved brains (one from 1861) has expanded our understanding of Broca’s aphasia. Along the way, she tells the story of the origins of what is today called cognitive neuroscience.

In 2007, a team of researchers led by Nina Dronkers, at the University of California, Davis, decided to reexamine the brains that [Broca] had carefully preserved.

To examine the extent of both the cortical and subcortical lesions of each brain, Dronkers’s team used high resolution volumetric MRI. What they saw was damage that went far further than Broca had suspected. In both cases, the lesions extended to the superior longitudinal fasciculus, a network of fibers that connects posterior and anterior language regions and had gone unobserved by Broca (he had made the decision to preserve the brain intact rather that slice it open).

Modern brain-imaging techniques (not just MRI) have revealed that the brain is a more complex organ than had been known. I discussed some of this in an earlier post. In addition, we know that brain plasticity makes it possible for different areas of the brain to take up, to some extent anyway, functions that are performed poorly (or not at all) when areas typically responsible for those functions are damaged by disease or accident. I have written a little about plasticity in this post and I touch on it briefly at the end of this post.

The important point here is that modern neuroscience has learned that early pioneers, like Broca, were perhaps overzealous in their attempts to pinpoint specific areas of the brain as controlling behavioral or cognitive outcomes. It is probably more accurate to say that complex functions, such as language or emotional regulation, involve several areas of the brain.

Our modern understanding does nothing to discredit the work of early researchers, who made brilliant discoveries without having access to any of the technology so commonly used today. Konnikova pays tribute in this way:

Still, the extent of Broca’s contribution to psychology and neuroscience can’t be underestimated. His work set the stage for much of what we now term cognitive neuroscience and neuropsychology. Two major principles that now govern how we think about the brain—the localization and lateralization of function and the notion that an impairment in one area of cognition (i.e., language) as a result of brain damage does not necessarily signify a general impairment in intellect—are in large part a result of Broca’s pioneering work. … Without Broca, our understanding of language would not have likely evolved as quickly as it did—or have had as great an impact on the study of other cognitive processes.

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