Form follows function. This axiom claims some of its scientific origins from the writings of Jean-Baptist-Lamarck (remember him? the wrong version of Darwin), among others. And what it means, in health at least, is that the form of organs have evolved to best carry out their function (this is more Darwinian than Lamarckian). But the brain was this giant glob of folded goo. What kind of function did that serve? Given there were no obvious unique MACROscopic features to it, the prevailing thought before the mid nineteenth century was that all cognitive functions were distributed evenly throughout the grey goo. And then scientists like Marc Dax and Paul Broca and Karl Wernicke surfaced with their own theories…
Neuroscientists like Dax, Broca, Wernicke, Gerstmann and Lictheim proffered a revolutionary theory:
Specific functions of the brain were carried out by specific regions of the brain. You can imagine how dumb this must have sounded. It would be as if I told you that the small hairs over your hand are to keep you warm, the hairs over your ankles are to protect you from the brush, and the hairs over your neck–when they rise up–are to warn you of danger. And that’s basically how the theory of phrenology sounded to many physicians at the time. Phrenology, as Franz Joseph Gall envisioned it, was the practice of reading skull bumps in order to determine which mental organs (respectfulness, secrecy) were most and least proficient in an individual: the larger the bump, the larger the organ, the more proficient that skill. To some extent, maybe there was a bit of science to support it; but in reality, it’s a load of BS.
In this week’s BrainWaves installment, cognitive neuroscientist Dr. Anjan Chatterjee (who also has a Wikipedia page) joins me to discuss how revolutionary this idea was, and how the knowledge of language localization can guide you when you are clinically evaluating a patient. The first 8-9 minutes are entirely dedicated to the historical context of functional specialization in the early-mid 1800s and what it took before the idea really gained international acceptance. But if this history really isn’t your jam, I would skip over it.
Dr. Chatterjee had previously walked us through a simple model of lesion localization when there is a language disturbance, and you can find that episode in our Quanta series. I highly recommend you check that out if you’re looking for brief, high yield neurology background. But moving on in our current show (and fast-forward to 8:30 to get to this part), Dr. Chatterjee speaks to how disturbances in specific areas responsible for linguistics result in disconnection syndromes. In particular, he references alexia without agraphia, which is a condition characterized by the ability to write but the inability to read–even what it was that was just written! We have included several of the more interesting of these clinical states here, but this list is by no means comprehensive.
Then there is the question of how you can distinguish someone with the inability to produce verbal language (aka, speak) and the inability to produce language in any form. What I mean here is that a patient who cannot speak may still be able to communicate, just not in the form of sound. They can still write. And this is what we, in the business, refer to as aphemia.
The remainder of the show features a more detailed discussion on the difference between lesion localization and functional organization of the brain. More specifically that having a brain lesion (e.g., stroke) does not necessarily mean that the area you have lesioned was actually responsible for carrying out the function that is now impaired.
Yeah, that just happened. And even more, it kind of means that people we idolize–people like Broca and Wernicke and Lichtheim–they didn’t get it perfectly right. The fact of the matter is that the brain isn’t made up of discrete units that are responsible for a function. You don’t have a neuron dedicated to solving algebra, or a synapse that tells you it has been ten minutes and you should check on Trump’s most recent Tweet. (And that’s not perfectly true either, there may be nerve cells in your brain whose sole function is to recognize places.) Rather, the brain represents a network of distributed function. Lesioning a specific node in a network can cause the network to fail–for example, your car may not be able to drive because the ignition is broken. But does that mean the ignition is responsible for moving the car? No. The ignition is necessary, but not sufficient. A lot like Broca’s area is necessary but not sufficient for producing spoken language, and Wernicke’s area is necessary but not sufficient for permitting language comprehension. These areas are part of a larger whole. A lot like this episode is part of a larger series of really, really, really incredibly fantastic neuromedicohistorical content for your eyes and ears. Until next time…
BrainWaves podcasts and online content are intended for medical education only and should not be used to guide medical decision making in routine clinical practice.
- Pearce JM. Broca’s aphasiacs. Eur Neurol. 2009;61:183-9.
- Ajax ET, Schenkenberg T and Kosteljanetz M. Alexia without agraphia and the inferior splenium. Neurology. 1977;27:685-8.
- Schiff HB, Alexander MP, Naeser MA and Galaburda AM. Aphemia. Clinical-anatomic correlations. Archives of neurology. 1983;40:720-7.