Evidence for Broca's Aphasia

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Chapter 8 endnote 25, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:

...Broca had scant evidence for his claims, and other scientists had plenty of evidence that he was wrong. They pointed out, for example, that other patients with nonfluent aphasia had a perfectly healthy Broca’s area. [...] This matches other evidence available at the time.

Armand Trousseau, another French physician practicing at the time, documented over 130 cases that failed to confirm the link (compared to Broca's 32 patients).[1]

But it should be noted that Broca’s instructor, the French neurologist Jean-Baptiste Bouillaud (who was taught by Franz Gall of phrenology fame), collected evidence from over 100 patients who had both frontal lobe damage and speech fluency problems (similar to Broca's patients). So Broca set out to test Bouillaud's hypothesis himself.

There is now ample evidence to show clearly that the function of "Broca's area" is not specific to language, and that people with damage to Broca's area often show no evidence of nonfluent aphasia (also called Broca's aphasia).[2][3]

Presumably, this is an example of degeneracy at work. A wonderful, modern day demonstration of this degeneracy in the brain basis of language comes from neuroscientist Cathy Price; I watched her give an address a few years ago at the annual Human Brain Mapping meeting. She described an experiment that performed brain scanning on three groups of people while they performed a language task: patients with brain lesions within the intrinsic brain network that supports the understanding of language, patients with lesions elsewhere, and a healthy control group. One might guess that she saw three different patterns of brain activity, one per group, but that’s not at all what happened. Instead she saw four different patterns of activity for normal performance, and all four showed up in patients and in healthy subjects. This is degeneracy in action.


Notes on the Notes

  1. Harrington, Anne. 1991. "Beyond Phrenology: Localization theory in the modern era." In The Enchanted Loom: Chapters in the History of Neuroscience, edited by Pietro Corsi, 207-215. New York: Oxford University Press.
  2. Novick, Trueswell, and Thompson-Schill. 2005. "Cognitive control and parsing: Reexamining the role of Broca’s area in sentence comprehension." Cognitive, Affective, & Behavioral Neuroscience 5 (3): 263-281.
  3. Novick, Jared M., John C. Trueswell, and Sharon L. Thompson‐Schill. 2010. "Broca’s area and language processing: Evidence for the cognitive control connection." Language and Linguistics Compass 4 (10): 906-924.