How Testosterone Allowed Norman Geschwind to Bridge an Intellectual Century

The Center for the History of Medicine at the Francis A. Countway Library in Boston is magnificent! But very cold. I guess I brought the wrong clothes, being spoiled by Philly summers (or what shall I call it?).

I have been here for three weeks now, and will stay for one more. I am slowly making way through Norman Geschwind’s papers. Geschwind and his colleagues’ theory from the early 1980s is quite (in)famous among science critics.

Frankly, Geschwind and his colleagues almost designed a Grand Unified Theory of humanity there. The level of testosterone in prenatal life, so they suggested, affects the asymmetrical maturation of a human brain, and by extension one’s immune system, sexual orientation, language abilities, handedness and much more.

And what am I learning from the archival sources?

First of all, Norman Geschwind was (or seems to have been) a very generous and humble individual. For a white man in the mid-to-late 20th-century, he was also notably supportive towards women researchers. And notwithstanding the close association he made between left-handedness and various physical, psychological, and psychiatric abnormalities, Geschwind explicitly asked his colleagues not to pathologize left-handedness per se.

Secondly, Geschwind firmly believed that neurology started with Pierre-Paul Broca. Geschwind’s historical consciousness is remarkable. But he tended to project 20th-century ideas backwards into the 19th century. This way, he overinterpreted the importance of Broca’s work in his time. Geschwind is not the only one who did that. Who knew that physicians and scientists debated after Broca’s seminal publication whether Franz Joseph Gall or Broca located the speech center correctly? Only the historians of science, I shall say, not the scientists themselves.

Thirdly, Geschwind relied heavily on brain organization theory to build his framework. One of the most intriguing letters that I found in the archives was written to Geschwind by his female junior colleague Jerre Levy. Levy, politely but directly, called Geschwind off. She cited several studies as evidence for why the brain organization theory is wrong, and she cautioned Geschwind to further build on it. Apparently, Geschwind didn’t agree. He brushed off her critique in his reply and continued building his theory of cerebral asymmetry and associated characteristics on the brain organization theory.

Fourth, and this blew my mind, Geschwind was a propagator of the idea of brain plasticity despite his insistence on the prenatal wiring of human brains.

We need some background in the history of brain plasticity research in order to understand why this is so surprising. The very simplified version is this (and a longer one is here): In the late 19th and early 20th centuries, the mind/brain sciences staged a big trans-Atlantic controversy between localizationists and “diffusionists.” The former believed that each cognitive ability and motor action has a fixed neural correlate. The diffusionists advocated for a distributed origin of cognition and behavior. They proposed that no one singular area in the brain can ever be the correlate of a complex brain function.

Broca and his followers seemed to win the argument in favor of localizationism. With the rise of psychoanalysis (and, as Geschwind suggested, the growing hatred of Germans and their anatomical knowledge in the world), the debate lost its momentum. But the localizationist idea lingered as an underlying framework in the mind/brain sciences.

This was due to the research of Ramón y Cajal, Sherrington, Hebb, Konorski, Kandel, etc. These gentlemen argued that synaptic plasticity is as good as it gets. Apart from minor reconnections between neurons, so the theory in the early and mid-20th century, adult brains are static. But then, in the 60s, 70s, 80s, and 90s, people like Altman, Kaplan, Nottebohm, Gould, Prochiantz, and their coworkers discovered and rediscovered adult neurogenesis. Their battles against Rakić and others were eventually successful and the field embraced the idea of a malleable brain towards the turn of the millennium.

Geschwind seems to be right in the middle of it. His claims are quite contradictory, actually. He believed that modern neurology started with Broca. He began almost every talk with a reference to him. Localizationism seemed to be Geschwind’s daily bread. And yet, he organized and attended panels and conferences together with people like Altman, Kaplan, and Nottebohm! (And Rakić, believe it or not.)

Geschwind firmly believed in localizationism and in “wiredness,” but his entire research from the later 1970s on pertained to the malleability of brains under the influence of testosteronein pre- and post-natal life.

I can’t seem to get these two things together. Geschwind adhered to localizationism and he praised plasticity, which is pretty close to the concept of the old diffusionism and the related idea of equipotentiality. Out of loyalty or ideological habit, Geschwind held on to the localizationist ideas of the 19th century, and in need of an explanation for behavioral changes in “handled” animals, he embraced a theory of plasticity that was a late-20th-century novelty.

Now here is my attempt for an explanation: Geschwind used hormones to build a bridge between the old theory of localizationism and the new theory of plasticity. This might have seemed logical because hormones are at the same time “biological,” i.e., they agree with a concept of “wiredness,” and they can induce change in plastic brains.

Maybe the fact that this large-scale change in the adult brain was caused by a chemical agent that is probably governed by genes at least as much as by environmental influences made the new idea of a malleable brain less scary.

This is just a hypothesis for how Geschwind could have been able to live with a combination of a late-19th-century theory of static brains and a late 20th-century framework of plastic brains. But isn’t it funny that the concept with which Geschwind “married” localizationism and plasticity, namely hormones, were all the rage right in between the first utterings of localizationism in the 19th century and plasticity 100 years later? In the end, maybe his combination of the two theories is not so contradictory after all, but a nice bridge between two seemingly opposing thought styles.

But isn’t it sad that Geschwind’s allegedly progressive behavioral neurology rested on the back of what he called “the male hormone”? My Grand Unified Theory of human brains, character, abilities, and actions would certainly be a sex-neutral one.


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