We're all familiar with false popular memes that spread faster than they can be stomped out: You only use 10% of your brain. Al Gore said he invented the internet. Perhaps it doesn't surprise you that some memes in popular culture can't be killed. But does the same thing happen in science?
Most of you have probably heard of Broca's aphasia and Wernicke's aphasia. Every textbook and every college course on language and the brain describes the connection between damage to these areas, and the speech deficits named after them.
Also, both are probably wrong. Both areas were mistakenly associated with their aphasias because they are near or surrounded by other areas which, when damaged, cause the aphasias. Yet our schools continue teaching the traditional, erroneous story; including a lecture in 9.14 at MIT given in 2005. Both the Wikipedia entry on Wernicke's aphasia and the Wikipedia entry on Broca's aphasia are still in error; the Wikipedia entry on Wernicke's area has got it straight.
Is it because this information is considered unimportant? Hardly; it's probably the only functional association you will find in every course and every book on the brain.
Is it because the information is too new to have penetrated the field? No; see the dates on the references below.
In spite of this failure in education, are the experts thoroughly familiar with this information? Possibly not; this 2006 paper on Broca's area by a renowned expert does not mention it. (In its defense, it references many other studies in which damage to Broca's area is associated with language deficits.)
So:
- Am I wrong, and the evidence still implicates Broca's area and Wernicke's area in their aphasias above other areas?
- If I'm right, why can't the new understanding displace the old understanding?
- Is this a general failure in the way we do science? Can you think of other examples where an important discovery can't penetrate its field?
References
Bogen JE, Bogen GM (1976). Wernicke's region—Where is it? Ann. N. Y. Acad. Sci. 280: 834–43.
Dronkers, N. F., Shapiro, J. K., Redfern, B., & Knight, R. T. (1992). The role of Broca’s area in Broca’s aphasia.
Journal of Clinical and Experimental Neuropsychology, 14, 52–53.
Dronkers NF., Redfern B B., Knight R T. (2000). The neural architecture of language disorders. in Bizzi, Emilio; Gazzaniga, Michael S.. The New cognitive neurosciences (2nd ed.). Cambridge, Mass: MIT Press. pp. 949–58.
Dronkers et al. (2004). Lesion analysis of the brain areas involved in language comprehension. Cognition 92: 145-177.
Mohr, J. P. (1976). Broca’s area and Broca’s aphasia. In H. Whitaker, Studies in neurolinguistics, New York: Academic Press.
I asked a neuroscientist about this who in turn asked a friend who studies language disorders of the brain at Cambridge. Here is what he had to say:
"This fellow sounds like he must be an undergrad, or a non-psychologist. No-one believes that the area traditionally defined as Broca's area is the only frontal area involved in language processing or even in Broca's aphasia, and even less for Wernicke's. Those anatomical labels are only used as heuristics; it's much more accurate (and common) when writing on the subject to use anatomical names like 'left inferior frontal gyrus pars triangularis / pars orbitalis / pars opercularis'. I think the general understanding is that you rarely get straightforward, unambiguous cases of patients who definitely only show sypmtoms of one specific type of aphasia anyway. More to the point, it's not the case that all researchers have the same point of view on these things, and it's certainly not unusual to see papers that claim to have a new, different explanation for something. They're ten-a-penny. From a systems neuroscience perspective it's much more meaningful to think about things in terms of disconnection syndromes and hodological principles - i.e. the effects of certain types and locations of damage on the properties of the system/network as whole, rather than be strictly localizationist about the causes of aphasias."
Thank you for that cogent ad-homimen argument!
Which is why I never said that anyone believed that. It is common for damage to a number of different, often nearby, structures, to cause similar symptoms. It's common for it to be difficult to distinguish symptoms caused by different underlying damage.
I... (read more)