A Hole in the Head Page 4
Galen was the first to carry out systematic experiments on the effects of experimental lesions of the nervous system. Before him, no one had, as he put it, “ever taken the trouble to make a section themselves or put a ligature around parts in the living animal in order to learn which function is injured.” He usually used a pig in these experiments “to avoid seeing the unpleasant expression of the ape when it is vivisected.”25
Galen realized that the spinal cord was an extension of the brain. In his brilliant and systematic experiments on sectioning the cord he compared the effects of hemi-and total transection at different levels and noted that injuries interfered with sensory and motor function below the level of the section; that hemisection affected only one side; and that sagittal section did not produce paralysis. He accurately described the different roles of the spinal nerves in respiration. He even came very close to the Law of Spinal Roots: “The physicians do not even know that there is a special root at the origin of the nerves which are distributed to the entire hand and from which sensation arises; [nor do they know] that there is another root for the nerves moving the muscles.”26
Galen used piglets in his experiments on brain lesions. He found that anterior brain damage had less deleterious effects than posterior.27 He viewed sensation as a central process since he knew from his clinical observations and animal experiments that sensation could be impaired by brain injury even when the sense organs were intact. Since animals could survive lesions that penetrated to the ventricles, Galen thought the soul was not located there but rather in the cerebral substance.28 He ridiculed the view of the Alexandrian anatomist Erasistratus that intelligence was correlated with the number of cerebral convolutions, noting, “Even donkeys have a complex encephalon, whereas judging by their stupidity ought to be perfectly simple and uncomplicated.”29 This view continued to be cited in denigrating the role of the cerebral cortex well into the eighteenth century.30
One way to measure Galen’s achievements is to note how long it took for them to be superseded. His neuroanatomical discoveries were not surpassed until Vesalius in the seventeenth century, his studies of spinal transection not until Magendie in the eighteenth century, and his work on hemispheric function not until Gall in the nineteenth century.
Brain and Heart
The Hippocratic writers (4th C. BCE), particularly the author of On the Sacred Disease, had vigorously championed the hegemonic role of the brain in sensation, movement, and thought as did Plato (4th C. BCE). Indeed this view had been held earlier by several of the pre-Socratic philosopher physicians starting with Alcmaeon of Croton (6th C. BCE). Furthermore, in the second century BCE, the Alexandrian anatomists Herophilus and Erasistratus had explored the structure of the brain and its role in sensation, movement, and mentation in detail and probably in living humans.31
Yet, 400 years later in the Rome of Galen’s time, it was the common belief, even among leading physicians, that the heart rather than the brain was the central organ of sensation, movement, and mentation. This had been Aristotle’s view much earlier (4th C. BCE) and was a central tenet of the Stoic philosopher Chrysippus (280–207 BCE), whose views continued to be highly influential, if not dominant, in Galen’s time.32 Indeed Chrysippus’s importance is indicated by the large amount of space Galen devotes to refuting his views in On the Opinions of Hippocrates and Plato and other works.33
The Squealing Pig Demonstration
Before coming to Rome, Galen had conducted extensive experiments on the nerves that control breathing. In the course of one of these experiments, carried out on a strapped down pig as it struggled and squealed, Galen accidentally cut the recurrent laryngeal nerves which innervate the larynx and the pig stopped squealing but not struggling. Subsequently, he traced out the course of these nerves in detail in a variety of animals including long-necked birds. He accurately described how the nerves begin as a branch of the Vagus (his “6th”cranial nerve), extend down far past the larynx and then loop around the aorta on the left and the subclavian artery on the right before traveling upward to the larynx (figure 2.2). He also confirmed that their bilateral section in dogs, goats, bears, lions, cows, monkeys and other animals eliminated vocalization. Furthermore, he mentions two instances of loss of vocalization in human infants following accidental injury to the recurrent laryngeals in the course of surgery to remove goiters.34
In Rome, his powerful patron Boethus arranged for him to conduct a public demonstration that section of the recurrent laryngeal nerves would eliminate vocalization in the pig. Boethus hired the hall, obtained the requested pigs and widely advertised the event. Many distinguished politicians and scholars came, including Alexander Damascenus, an Aristotelian philosopher (see figure 2.3). Before beginning the surgery, Galen gave a brief summary of the demonstration and noted that “there is a hairlike pair [of nerves] in the muscles of the larynx on both left and right, which if ligated or cut render the animal speechless without damaging either its life or functional activity.” At that point Alexander Damascenus interrupted, objecting, “Even if we are shown that section of these nerves in animals renders them mute, it is not necessary to believe it true of human beings.” In any case, he said, he would not believe such a demonstration. His insistent view reflected both a general skepticism of the value of sensory information as opposed to logic and geometry in establishing proof and the Aristotelian (and Stoic) belief that thinking and therefore vocalizing were controlled by the heart and not the brain.
Figure 2.2
The U-shaped course of the recurrent laryngeal nerves (after Singer, 1957). The laryngeal nerves are branches of the vagus nerve that start far below the larynx and then loop under the subclavian artery on the right and under the aorta on the left before moving upward to innervate the larynx.
Figure 2.3
Galen demonstrating the effect of cutting the recurrent laryngeal nerves in a pig. Labeled in the audience are Barbarus, former consul and uncle of the co-emperor Lucius Verus; Severus, another former consul, who introduced Galen to Marcus Aurelius; Boethus, who sponsored the demonstration; Paulus, a leading lawyer; Hadrian, a Sophist who held the imperial chair of rhetoric; Demetrius, another Sophist; and Alexander of Damascus. The latter, an Aristotelian and public professor of philosophy in Athens, heckled Galen, thereby causing a postponement of the demonstration. From the bottom panel of the title page of the 1541 Junta edition of Galen’s Works, courtesy of Yale University, Harvey Cushing/ John Hay Whitney Medical Library.
Galen later recorded his response to Alexander’s interruption:
When I heard this, I left them and went off, saying only that I was mistaken in not realizing that I was coming to meet boorish skeptics; otherwise I should not have come. . . . On my departure, the others condemned Alexander. . . . When this was made known to all the intellectuals living in Rome . . . they all roundly reproached him and demanded that the dissections be performed in their presence when they assembled all others distinguished in medicine and philosophy. The meeting lasted several days, in which I showed them [the nerves controlling breathing] and how damage to the nerves activating the muscles of the larynx results in a loss of voice. My detractors were all put to confusion when I showed them this and Boethus begged me to give him my lecture notes on it. He even sent trained shorthand writers to whom I dictated all my demonstrations and arguments.35
From this shorthand came the treatise On the Voice, now lost but probably the basis of the section in On the Usefulness of Parts of the Body on the recurrent laryngeals, since that section is very much in the form of a public lecture.36
Reasons for the Recurrent Course
Galen’s adoption of Aristotle’s biological teleology was consistent and relentless. Like Aristotle, he believed everything in the body was designed in the best possible way for the best possible reason, and that the perfection of this design demonstrated the existence and genius of the Creator. (Although believing in a supreme being, Galen had so little interest in Christianity that he did not even disti
nguish it from Judaism.37)
What then was the teleological reason for the tortuous route traveled by the laryngeal nerves down from the brain into the trunk and then around the aorta and subclavian arteries and back up to the laryngeal muscles? Before considering Galen’s answer, we must summarize his notions of muscular action. Galen thought that when a motor nerve enters the origin of the muscle it breaks up into small fibers, and that the ligaments do so as well. At the point of insertion these muscle and ligament fibers unite to form the tendon, which is then much stronger than if it had been made by the nerves alone. It is this tendon that contracts, while the body of the muscle is mere “flesh” that protects the fibers.38 Since in muscle action the pulling is done by the tendon (made up in part by the nerve), the nerve must enter the muscle in the direction of pull. This provided a rationale for the recurrent pathway of the laryngeals; they had to enter the larynx muscles from the bottom. Galen compares the passing of the nerves around the aorta and subclavian to a rope passed through a pulley.39 Apparently, pulley action was not well known to his audience, so he explains it in reference to the “glossocomion,” a gadget for reducing fractures of the femur and tibia, which was “a common device familiar to most physicians” and which involved pulley action (see figure 2.4).40
Now if the heart were the source of the nerves, as some think who know nothing of what is to be seen in dissection, it would readily move the [laryngeal] muscles by sending nerves directly into them. . . . Actually . . . every nerve obviously takes origin from the brain or spinal cord . . . [but the laryngeal] muscles could receive nerves from the brain only if they followed a reversed route. . . . [He then digresses to attack several rivals who fail to recognize the wisdom of nature]. Hence I find it necessary to tell now about the devices Nature has employed in order to give the muscles in question their share of nerves and motion. In order that my discourse may be clear you must first understand this reversed motion which is made use of in many devices both by engineers and surgeons.41
Figure 2.4
Glossocomion for reducing fractures. When the wheel is turned, traction is applied to the leg (Galen, 1968).
A long discussion of pulley action in the glossocomion is then followed by a detailed and accurate account of the course of the vagus nerve and its branches, particularly the recurrent laryngeals and how they loop abound the subclavian and aorta. Galen explains that they do not use the clavicle as a pulley, although it is encountered first, because that would make the nerves too “exposed close under the skin and easily harmed by every mischance.” Rather the nerves continue down and then use the large horizontal blood vessels as a “pulley or turning post.” This account is interrupted several times by exhortations to the audience to pay attention, praise of the Creator, and insults to rival anatomists as in the following passage.
I want you now to pay me closer attention than you would if you were being initiated into the mysteries of Eleusis or Samothrace or some other sacred site . . . You should consider that this mystery is in no way inferior to those and no less able to show forth the wisdom, foresight and power of the Creator of animals, and in particular you should realize that I was the very first to discover this mystery which I now practice. Certainly, no other anatomist has known about any of these nerves or about the things of which I have spoken earlier in the construction of the larynx and this is the reason why they have erred so greatly in determining actions and have not told a tenth of the utilities of the parts. Accordingly, . . . fix your mind now on holier things . . . and follow closely my discourse as it explains the wonderful mysteries of Nature.42
Fame of the Squealing Pig Experiment
Galen’s experiment on eliminating vocalization by cutting the recurrent laryngeals has been heralded by one twentieth-century student of Galen as “establishing for all time that the brain is the organ of thought and one of the most important additions to anatomy and physiology . . . as great as the discovery of the circulation of the blood.”43 This and similar claims are somewhat exaggerated and uninformed. As noted above, that the brain was the organ of thought was clearly set out in many pre-Galenic writings and particularly in the Hippocratic treatise On the Sacred Disease and in Plato’s Timaeus. Even Galen, in his lengthy arguments against the Stoic Chrysippus, concentrates on experiments involving direct damage to the brain.44 It is true, however, that this was the first experimental and publicly repeatable evidence that the brain controlled behavior. Previous evidence for the importance of the brain had been either exclusively clinical or based on indirect inferences from anatomy.
Galen’s demonstration on the squealing pig became one of the most famous single physiological demonstrations of all time. It inspired Leonardo da Vinci to produce a beautiful drawing of the recurrent laryngeal nerves.45 Vesalius gives it a prominent place (without mentioning Galen) in the last chapter of his great On the Fabric of the Human Body and included it in his public lectures in Padua.46 Finally, Renaissance editions of Galen included in their frontispiece an illustration of Galen cutting the recurrent nerve in a huge pig (figure 2.3).
The Persistence of Galenism
At about the time of Galen’s death, classical science and medicine die. People prefer to believe rather than to discuss, critical faculty gives way to dogma, interest in this world declines in favor of the world to come, and worldly remedies are replaced by prayer and exorcism.
The worldview of medieval Christendom found Galen’s teleology congenial to its own and by a smothering of critical facility froze Galen and all biology into a sterile system for over 1,500 years. Galen was not to blame. Rather than develop his discoveries and methods, the medieval world chose to accept as fixed and unchangeable fact his views in every branch of medicine.
POSTSCRIPT
Since this article was published in 1998 there have been dozens of new translations, symposia, and scholarly articles on Galen. Indeed, Nutton estimates that “since 1945 a new fragment of Galen and often a whole work has been announced or published every two years.”47 Even his life span has been increased, his previous age apparently based on mistranslations from Arabic.48 Perhaps the most interesting new work on Galen from a neuroscience perspective is Rocca’s Galen on the Brain, published in 2003.49 Although Galen dissected the brains of a great variety of animals including monkeys, his detailed brain anatomy and his model for the human brain was based primarily on the ox brain. Rocca himself followed Galen’s descriptions of his brain dissections with actual ox brains and shows how amazingly accurate Galen was, particularly given that Galen’s brains were not fixed. He shows how Galen’s detailed account of the complex ventricular system was important because of the crucial role it played in his physiological theory. Although Galen placed thought, memory, and the control of movement in the solid portions of the brain and not in the ventricles, his emphasis on the importance of the ventricles contributed to the ventricular (or “cellular”) localization of psychological functions by Nemius of Emesa (ca. 400) that dominated medieval thought and was influential into the nineteenth century.50
The debate between brain and heart as the seat of intellect continued into the Renaissance. One resolution was to combine the two views. For example, the Arab Aristotelian and physician Ibn Sina (980–1037, known in the west as Avicenna) located sensation, cognition, and movement in the brain, which in turn he believed was controlled by the heart.51 Similarly, according to the thirteenth-century Hebrew encyclopedist Rabbi Gershon ben Schlomoh d’Arles, the brain and heart share functions so “when one . . . is missing, the other alone continues its activities . . . by virtue of their partnership.”52 As Scheherazade tells it on the 439th night, when the Caliph’s savant asks the brilliant slave girl Tawaddud, “where is the seat of understanding,” she answers, “Allah casteth it in the heart whence its illustrious beams ascend to the brain and there become fixed.”53 Eventually, the “debate” became more of a metaphorical one, as Portia’s song in The Merchant of Venice asks,
Tell me where is fancies bred,
Or in the heart or in the head.
And, metaphorically the heart usually wins, as in Longfellow’s poem “The Building of the Ship”:
It is the heart and not the brain
That to the highest doth attain,
And he who followeth Love’s behest
Far excelleth all the rest.
NOTES
This chapter is an article that appeared in The Neuroscientist (4: 216–221 [1998], “Galen and the Squealing Pig”), with a new introduction and postscript. The very first version of this paper was in an early draft of my 1961 doctoral dissertation on the frontal cortex in monkeys.
1. Sigerist, 1951, 1961; Sarton, 1959; Keele, 1957. The Yellow Emperor’s Classic is now believed to be a compendium of different early Chinese medical writings. See the new introduction by Lo in Lu and Needham (1980).
2. Lloyd, 1975; Longrigg, 1993; Gross, 1998a. All of the writings of the pre-Socratic philosophers are lost. All we know about them comes from later classical writers. These “fragments” or putative quotes were collected by the ancient so-called doxographers and were assembled by H. Diels in the nineteenth century and translated into English by Freeman (1954).
3. Hippocrates, 1950. Although Hippocrates was a historical figure, it is unclear which of the Hippocratic corpus he wrote, which were written by his followers, which were just found in the library of his medical school on the Aegean island of Cos, or even which were assembled later (Smith, 1979; Lloyd, 1978). On the Sacred Disease is usually judged as by, or representative of, Hippocrates and his close followers.