Penfield's homunculus and the like

"I am a little world made cunningly." A meditation on connections of people and the world.

Mar 09, 2023

Read time: about 6 minutes. This week: A brief post on captivating illustrations of brains, little men, and body parts. Next week: Maybe a guest post! But, then, maybe a brief catch-up of previous topics.

The Boulangerie offers glimpses of what’s in a warm place rising or already in the bakery oven. This past week, Penfield’s homunculus (topic for today’s post, too). I only announce when something happens in the Boulangerie with my Mastodon loudspeaker: @mrdelong@mastodon.online.

Share this one with someone who has gone to a doctor, please. If you got this from a friend, how about getting your own copy? A subscription is free, and it’s only another email delivered on Thursday morning.

The motor homunculus. Penfield, Wilder, and Theodore Rasmussen. *The Cerebral Cortex of Man: A Clinical Study of Localization of Function*. Lane Medical Lectures; 1947. New York: Macmillan and Co, 1957. Rights: Fair use.

In 1937, Wilder Penfield and Edwin Boldrey published their first “homunculus” that they claimed showed “the order and comparative extent” of body parts as they relate to the brain’s “sensorimotor strip.” In effect, the more brain real estate devoted to a part of the body, the bigger that part was depicted in the image of the “little man” — homunculus translated from its Latin root. It was a bold and revolutionary move to try rendering such scientific observations into a map. It was also humorous, though some felt the illustration was sordidly grotesque.

The distortions on the homunculus represent their correspondence to differently sized regions of the brain. Note the large lips, tongue, and hands. This figure renders Penfield and Boldrey’s 1937 homunculus illustration. Credit: “Mpj29.” *Front of Sensory Homunculus*. December 11, 2016. Digital photograph. Own work. https://commons.wikimedia.org/wiki/File:Front_of_Sensory_Homunculus.gif. Rights: CC-BY 4.0

I first ran across the homunculus when I was looking into scholarship on the hand and gesture, and I saw Penfield’s and Theodore Rasmussen’s 1950 rendering of the homunculus overlaid on two cerebral hemispheres, the parts of the body stretched along the outline of a cross section of the brain. (The “motor homunculus” of that version is the illustration leading this post.) The size of the hand, fingers, and thumb in this illustration and in its counterpart of the “sensory homunculus” (not shown here) particularly struck me. The hand is enormous relative to any other body part, though the parts of the face come close.

The homunculus had real power. Of the 1950 drawings, G. D. Schott wrote,

These drawings are so memorable and have been reproduced so often that it is difficult to appreciate that here, even more than with the first homunculus [in 1937], a new concept in representation and imagery had been created. Moreover, for the first time the homunculus can be considered as some form of “map” of human cortical representation, being more or less precisely in relation to actual brain areas identified at surgery.

Penfield published other homuncili as well, though the 1950 version probably most clearly relates body part and brain region. But the clarity in the illustration is a bit illusory, as other neurosurgeons and researchers pointed out. Of course, part of the problem has to do with the limits of the medium; a journal page rendering is two-dimensional, and the brain is three-dimensions. Where would the cross-section be located along the missing dimension in the illustration? And other objections had to do with the widely recognized “plasticity” of the brain and natural variations, both of which were probably complicated by the fact that Penfield and his collaborators gathered their data from surgeries on people who had brain abnormalities or disease — not exactly a pristine set of normal subjects.1 Penfield and Jasper were aware of the criticism of reading too much into the correctness of the renderings and qualified their various homunculi in a book from 1954, saying that “the exact position of the part must not be considered topologically accurate. They are aids to memory, no more.”

Correspondences and analogies

We like connection, and the homunculus connects the useful and familiar parts of our bodies with the mysterious and hidden organ in our heads. The renderings also apply a familiar — though also deceptively simple — scale to the importance or weight that the brain assigns to the various parts of the body that carries it: “bigger” can be interpreted as “more important.” Perhaps the brain’s assignments are right in some contexts, and so the homunculus makes correspondences of body and brain (body and “soul”?) visible and “real” to our senses.

I had coffee with a friend as I was wrestling with this essay, and I explained that my interest in Penfield’s homunculus was not constrained to an interest in the use of the hand or for that matter the ways that our senses and actions converge in the brain. Rather, I’m intrigued by what seems a universal human desire to tie our experience into a larger landscape beyond ourselves. Penfield’s homunculus builds a perspective of how the physical organ of the brain is connected to the body, but beyond that the image of the “little man” also opens the organ to a sensory world and links the “motor” activities of the body to a world it acts within.

The homunculus runs around in the world with its big hands and lips, feeling, eating, and maybe kissing the world around him.

A homunculus rendered in an alchemical manuscript. Uncredited. Image from Monster Wiki. “Homunculus.” Accessed March 8, 2023. https://monster.fandom.com/wiki/Homunculus.

Penfield and his collaborators may have felt the desire to bind human experience into a larger world. They chose the label “homunculus,” which as Schott notes, “can scarcely have escaped Penfield’s notice that both the term and the concept of the ‘homunuclus’ are old, dating at least since medieval times; they are also strange…. A special use for the term seems implied.” The homunculus was part of alchemical lore and was supposed to have special magical powers, not necessarily entirely benign. Schott reminds us that in Penfield’s use of the idea the “little man” has the function “to provide an explanation or interpretation of the outside world … responsive to one’s pain, or to visual images, or other experiences.”

The homunculus is a captivating but scientifically inaccurate and probably misleading fancy, and I think it’s captivating because the illustration taps our desire for connection. How do our sensory and active lives have a connection and a place in the larger scheme of things?

New York Academy of Medicine. *Books, Health and History.* “Zodiac Figure, 1522,” May 15, 2018. https://nyamcenterforhistory.org/2018/06/04/facendo-il-libro-the-making-of-the-book-and-a-digital-collection-and-exhibit/zodiac-figure_1522-watermarked/.

Long ago, physicians leveraged other kinds of connections of human bodies with the universe. If you got sick, your doctor might just consult a horoscope while considering your case. The assumption, of course, was that the heavens influenced health. Know where we get the term “influenza”? It’s a lingering remnant of the belief in a connection between human well-being and the cosmos. Rebecca Whiteley eloquently describes the principle underlying the connection:

Knowledge of the stars and planets could, for instance, tell you about a person’s health, and the inherent links between celestial and corporeal bodies meant that the planets could also be used to effect healing. The human body was, in this system, the center of all things, as Michel Foucault describes it, “the possible half of a universal atlas” and “the great fulcrum of proportions—the centre upon which relations are concentrated and from which they are once again reflected.”

Aside: Bond Girl Bride and her horse

BGB had a riding accident about a week ago. While traversing a little creek, “Pumpkin Jack,” her faithful steed, decided it was time to go a little crazy. BGB was ejected, and unfortunately trampled in the mud. I was in the Duke archives looking at old Ford Motor Company things, and I got her call. “Meet me at Urgent Care.” I knew what was up. She got through with no broken bones but nasty, nasty bruising and a colorful hematoma in the shape of a horseshoe. General knocking of the body, too.

“Off the leg for a month,” the doc said. “At least.”

Well, we both knew that would be a pain more significant than the bruising and probably unlikely anyway.

So, I’m occupied. And I’m very thankful that BGB is on the mend.

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