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Descartes' Pineal Neuropsychology
36, 57–72 (1998) BR970954
BRAIN AND COGNITION ARTICLE NO.
Descartes’ Pineal Neuropsychology C. U. M. Smith Vision Sciences, Aston University, Birmingham B4 7ET, United Kingdom E-mail: [email protected] The year 1996 marked the quattrocentenary of Descartes’ birth. This paper reviews his pineal neuropsychology. It demonstrates that Descartes understood the true anatomical position of the pineal. His intraventricular pineal (or glande H) was a theoretical construct which allowed him to describe the operations of his manlike ‘‘earthen machine.’’ In the Treatise of Man he shows how all the behaviors of such machines could then be accounted for without the presence of self-consciousness. Infrahuman animals are ‘‘conscious automata.’’ In Passions of the Soul he adds, but only for humans, self-consciousness to the machine. In a modern formulation, only humans not only know but know that they know. 1998 Academic Press Bene vixit, bene qui latuit (he lives well who is well hidden) Descartes’Ovidian motto, (Letter to Mersenne, April 1643, in Adam & Tannery, Vol. i, p. 286) This little sprunt champion called the conarion, or Nux pinea, within which the soul is entirely cooped up. (Henry More, 1713, Preface to Divine Dialogues (2nd ed.), p. 12) . . . now that I come to ascend the stage of the world . . . I come forward in a mask. . . . (Early notebook, c. 1619)
Introduction
Rene´ Descartes was born just over 400 years ago on 31 March 1596 in the small village of La Haye near Tours. Although he is normally thought of as a mathematician and a philosopher, and with good reason, he in fact spent a good part of his later life investigating and puzzling over the human microcosm. The works in which he expounded his neuropsychology are principally L’Homme (1632; published 1662) usually translated into English as A Treatise of Man, and to a lesser extent the 1649 Les Passions de l’Ame An early version of this article was presented to the First Annual Meeting of the International Society for the History of the Neurosciences, Buffalo, NY, May 1966. 57 0278-2626/98 $25.00
Copyright 1998 by Academic Press All rights of reproduction in any form reserved.
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(The Passions of the Soul). He also left the manuscript of an anatomical manual Excerpta Anatomica (1631–1648). The Pineal
That Descartes singled out the pineal as primus inter pares among the brain’s structures is proverbial: ‘‘. . . although the soul is joined to the whole body there is a certain part where it exercises its functions more than all the others’ (Passions of the Soul, p. 31). His reason for according the pineal this preeminence seems philosophically weak. He writes in Passions of the Soul, p. 32) that the unitary nature of our introspection implies a corresponding unitary anatomical structure. It is worth noting that medieval theories of vision generally sought a unitary location where visual images from the two eyes could be combined to provide our phenomenological visual unity. The medievals normally took the chiasma for this location (see for example, Risner, 1572). It may be that Descartes, with his intense interest in physical and physiological optics, was influenced by this thought; he is known to have read Kepler’s Paralipomena when he was preparing the Treatise of Man (Marion, 1981). The problem of relating our unified sensory consciousness to its highly heterogeneous neuroanatomical correlative has not gone away. It is still very much with us today: it is known as the ‘‘binding problem’’ (see for instance, Crick, 1994). It is odd, however, to find an attempt at so simple-minded an identity in the work of a philosophical genius of Descartes’ rank. For Descartes’ fundamental and sustained premise was precisely the nonlocality of mind. However this may be, Descartes insists that there is only one unitary structure in the otherwise bilateral brain—and this is the pineal. Descartes and the Anatomy of the Pineal
The pineal has a long history in neuroanatomy, stretching back at least as far as Galen, and it was usually accorded a crucial role in controlling the flows of spirit in the ventricles (Hall, 1972, pp. 86–87). It is, however, worth noting that in de usu partium Galen recognized the external location of the pineal and consequently ridiculed the notion that it could control the tides of ventricular spirits: ‘‘The notion,’’ writes Galen, ‘‘that the pineal body is what regulates the passage of the pneuma is the opinion of those who are ignorant of the vermiform epiphysis and who give more than due credit to the gland. . . . Since this gland is . . . attached not to the inside but to the outside of the ventricle, how could it . . . have so great an affect [sic] on the canal? Why need I mention how ignorant and stupid these opinions are?’’ (translated by May, 1968, pp. 419–420). In Anatomical Procedures he explains, furthermore, how it should be dissected, remarking that when freed of its surrounding tissues it usually sinks back onto the roof of the brain (Singer, 1956). Descartes was no stranger to first-hand experience of dissection. Adrien
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Sheep brain: inferior aspect. From Descartes’ Excerpta Anatomica.
Baillet (1691), his earliest biographer, has a well-known story of visitors enquiring about his library and being shown into his dissecting room with the remark that ‘‘these are my books.’’ In the years 1629–1632, the years when he was composing his Treatise of Man, he is known to have been a frequent visitor to the butcher’s shops in Amsterdam. Baillet writes that in the late 1620s and 1630s, ‘‘his eagerness for knowledge of the subject made him visit, almost daily, a butcher’s shop to witness the slaughter; and that he caused to be brought thence to his dwelling whichever of the animal’s organs he desired to dissect at greater leisure’’ (trs. Cohen, 1972). Indeed (says Baillet) he exposed himself to the ridicule and malicious gossip of his Dutch neighbors. He writes to Mersenne in December 1632 that he ‘‘. . . is dissecting the heads of different animals in order to explain what memory, imagination, consist of’’ (Adam & Tannery, 1897–1913, Vol i, p. 263). And later on, in February 1639, in another letter to Mersenne he writes of how he has consulted not only Vesalius and the other writers on anatomy but has also been dissecting animals for over 11 years (Adam & Tannery, 1897– 1913, Vol. ii, p. 525). Figure 1 from the Excerpta Anatomica (Adam & Tannery, 1897–1913, Vol. xi, pp. 549–634) shows one of his dissections of the sheep brain.
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FIG. 2. Parasagittal section of sheep brain to show pineal (H).
Figure 1 is hardly of Vesalian standard. Descartes was no draftsman. We have also to recall the conditions of the time. He remarks to Mersenne, for instance, that he is not surprised that the pineal is difficult to see in human cadavers because of deterioration in the postmortem room (April, 1640: Adam & Tannery, 1897–1913, Vol. iii, p. 45). This is why he found animal material so much more rewarding. He was, he writes, accustomed to finding the pineal without difficulty in ‘‘freshly killed animals.’’ It is unfortunate that he includes no drawing of the superior aspect of the sheep brain in the Excerpta. For here we come to our first instructive puzzle. If he is accustomed to finding the pineal with ease, why do all his illustrations show it hanging down inside the ventricle? Figure 2 shows the very obvious position of the pineal in the sheep brain. The mystery is increased by looking at the authors he says (in his 1639 letter to Mersenne) that he has consulted. Not only Vesalius but also Caspar Bauhin give drawings of the pineal which show it resting on the superior surface of the brain and we have already seen that Galen was of the same opinion. Bitpol-Hesperies (1990) provides good evidence that Descartes had carefully studied Caspar Bauhin’s (1605/1621) Theatrum Anatomicum. Yet in the section of the Theatrum which discusses the pineal Bauhin quotes Vesalius as saying that the base of the pineal rests on the substance of the brain and that ‘‘the top regardeth upward’’ (in Crooke’s 1631 translation) and he goes on to say that ‘‘it neither adhereth to the inwarde sides of the
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ventricle, but lyeth upon the outside’’ (Crooke, 1631, p. 469) and thus cannot affect the flows of animal spirits within the ventricle. Descartes’ Diagrams
Nevertheless and in spite of all this Descartes gives his pineal an intraventricular position (see Fig. 3). Readers of the Treatise of Man are always struck by the contrast between its drawings and those of Vesalius and Bauhin. We are in a different world. A word of caution is, of course, necessary. We should remember that the Treatise was a posthumous publication. Descartes had died some 12 years before in Stockholm in the unusually cold Swedish winter of 1650. An apocryphal story has him voyaging to Stockholm accompanied by a trunk containing a life-sized mechanical doll (see Rosenfield, 1968). It would be nice to think that this story refracts through layers of rumor and prejudice the existence of the manuscript of the Treatise at the bottom of one of his boxes. Baillet relates that when he had arrived in Stockholm Queen Christina caused him to delve into his trunk and assemble his papers into treatises. According to Baillet these had been ‘‘bound up hand over head on his departure from Holland. They were all in pieces scattered up and down . . .’’ (Baillet, 1691, p. 247). And, of course, when his papers were returned from Stockholm the boat carrying them sank in the Seine and the papers were only recovered some days later. So the Treatise we have, and especially the figures, may very well not be exactly the ones Descartes would have published himself. In editing the first French edition (1664) Clerselier found only two drawings roughly drafted by Descartes himself (Hall, 1972, p. xxxv). He commissioned two eminent academics, La Forge and van Gutschoven, to construct sets of illustrations to fit the text. La Forge is quite candid about his own approach. In his own edition of the Treatise he writes (p. 326): ‘‘I am less committed to representing things according to Nature than to rendering them intelligible’’ and, in particular, that the pineal is drawn much larger than normal because of its central importance in the Cartesian neuropsychology (La Forge, 1664, p. 326). The illustrations in the Clerselier edition, except for that marked D (showing the action of antagonistic muscles on the eyeball), are drawn by either van Gutschoven (marked G) or La Forge (F). It is clear, then, that Descartes and/or his editors are not attempting the artistic realism of Vesalius but reverting back (and forward) to the diagram makers of earlier (and later) times. Medieval diagrams illustrating ventricular psychology are well known. Perhaps the most common is that published in Gregor Reisch’s widely read text The Pearl of Wisdom (1504). Many similarly fantastical figures were published in pre-Vesalian times. Vesalius, himself, had been forced to study the Pearl as a medical student in Louvain in the early 1500s. He has a characteristically caustic passage in the Fabrica (1543, Book VII, Chapter 1, p. 623) on the anatomical absurdities of the ventricular psychology.
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FIG. 3. Parasagittal view of human brain drawn by van Gutschoven (G) for L’Homme. H, gland H (pineal).
Schematic figures were, then, part of an old tradition, as was Descartes’ essentially ventricular neuropsychology. Descartes’ pipes and threads and valves can, perhaps, be seen as part of that tradition. Although it would take us too far from the theme of this article to consider in detail, it is also worth noting the Augustinian ghost lurking behind Descartes’ schematism. Descartes had been educated at the newly founded Jesuit college at La Fle`che. By all accounts he received one of the best classical educations then available and he was, of course, a star pupil. He cannot have been unfamiliar with the works of St. Augustine. Yet when Andreas Colvius, minister at nearby Dordrecht, pointed out that his cogito ergo sum seemed to be no more than a rewording of Augustine’s very similar arguments (de Trinitate, Book 10, para. 14 and elsewhere [see Mourant, 1979]), Descartes was surprised (or effected to be surprised) and replied that he had that day been to the town library to check the reference (Kenny, 1970, p. 83). Similarly it is possible to wonder how far conscious or unconscious memories of Augustine influenced his neuropsychology. Augustine’s fourth century neuropsychology drew on traditions reaching back to the Alexandrians of classical antiquity. Although Augustine’s neuropsychology was written to underpin his theology, especially his account of the soul, we can still find echoes of Erasistratus (see O’Daley, 1987). In De Genesi ad Litteram, for example, Augustine writes of how ‘‘the air which is contained in the nerves obeys the will and moves the members without itself being the will’’ (Et aer, qui neris
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infusus est, paret voluntati, ut membra moveat, non autem ipse voluntas est) (Book 7, 19, 25). Erasistratus, in the third century BC, had conceived that the tissues of the body, and the substance of the brain, consisted of tubes, subdivided again and again, and in the case of the brain and nervous system were filled with pneuma. This ancient theory, taken into Augustine’s neuropsychology, cannot but remind us of the spirit-filled nerve tubes, subdivided again and again below the level of visibility, which form the basis of Descartes’ conception of the brain. In this, as in much else, Descartes is a truly transitional figure, half in what we categorize as the modern world, half in the millennial traditions of the medievals. An ‘‘Earthen Machine’’
Nowhere in Augustine, however, is there mention of the pineal and nowhere is there the mechanistic metaphor. It is here that Descartes breaks entirely new ground. It is here, also, that it begins to come clear what Descartes is doing. He is not attempting to compete with Vesalius, Bauhin, and the other anatomists. He is well enough aware that his diagrams have little anatomical reality. They are theoretical constructs. Indeed, although in his letters he refers to his central gland as the pineal or conarium, it is never referred to as such in the pages of the Treatise. It is always ‘‘la petite glande, H.’’ Descartes is not striving for anatomical reality: he is trying to show how it could be, how it was not necessary to import a self-moving ‘‘soul’’ into the ‘‘earthen machine.’’ At the beginning of the Treatise Descartes is quite explicit: he proposes to treat human and animal bodies as if they were earthen machines. Insofar as this banished vital forces, eliminating the ‘‘animal’’ and ‘‘vegetable’’ souls of the scholastics, this was a liberating approach and we would have little to quibble with today. It had the virtue of concentrating the ‘‘hard’’ problem at the level of the rational soul. This could then be left to theologians to argue about. As Descartes says over and over again the earthen machines (Michael Foster intriguingly mistranslates as ‘‘earthly machines!’’ [Foster, 1970, p. 268]) he has described are (with the exception of the rational soul) indistinguishable from humans and other animals. Descartes’ larger project was identical to that of Galileo: to save the natural world from theology and the supernatural world from science. In parenthesis, this is not to say (as some of his followers and later expositors have said) that Descartes believed that infrahuman animals are insentient, that their squeals are no different than those of badly oiled machines or tires on a badly driven automobile. Leibniz, for instance, writes to Tschirnhaus in 1684 that the Dutch are ‘‘amusing themselves by ridiculing the Cartesians for imagining that a dog that is clubbed cries in the same way as a bagpipe which is pressed’’ (Wilson, 1989). Descartes, himself, is at worst equivocal. There is no doubt that Descartes modeled his ‘‘fantastical’’ neurophysiology on the water-powered automata which were so much the vogue in the
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French aristocratic circles of his youth. There is, for instance, every reason to suppose that he had visited and marveled at the automata devised by the Francini brothers at St. Germaine. It has even been speculated that he named his much loved and deeply mourned daughter Francine in their honor. These devices were driven by ‘‘external’’ forces. The Francinis built their ingenious mechanisms and then directed flows of water through them to generate appropriate movement. Hydrodynamics was, of course, not the only technological metaphor Descartes used. He was also the forerunner of a tradition which uses musical instruments to image the functioning of the brain. In his case it was the cathedral organ. He makes a comparison with the organ’s pipes and the hollow nerves of the brain. He likens external energies impinging on the body to the organist’s fingers. He goes on to say that the harmony of the organ in no way depends on the arrangement of the pipes and other parts or on their shapes but solely on ‘‘the air which comes from the bellows; the pipes that sound; the distribution of air to those pipes’’ (L’Homme, trs. Hall, 1972, pp. 71–72). Bene Vixit, Bene Qui Latuit
L’Homme was composed in 1632–1633 as the last section of Descartes’ overarching work on cosmology: Le Monde. He was readying the work for publication when he heard that Galileo’s Dialogue on the Two Great World Systems had been condemned in Rome (July 23, 1633), all copies to be burnt, its author to be confined to house arrest and forbidden to publish. Descartes writes to Mersenne in November 1633 expressing his horror, saying that he had nearly decided to burn all his papers, and ending ‘‘. . . I wouldn’t want to publish a discourse with a single word of which the Church disapproved; so I prefer to suppress rather than publish it in a mutilated form’’ (Adam & Tannery, 1897–1913, Vol. 1, p. 271). And, in the 1637 Discourse on Method, V, referring to his suppressed work, he says ‘‘certain considerations prevent me from publishing.’’ Discretion, as he remarked to Mersenne, is the better part of valor: Bene vixit, bene qui latuit! His ostensible reason for suppressing his work was that it, like Galileo’s Dialogue, supported the Copernican heresy. But he probably felt that the Treatise of Man might also have raised eyebrows in orthodox circles. The Treatise which has come down to us, saved when Descartes’ papers were submerged in the Seine after his death and published in 1662 (Latin) and 1664 (French), is perhaps a truncated version. It starts and ends abruptly. What it lacks at both ends are apologias linking it to the orthodox thought of the time. It starts almost in midsentence ‘‘. . . these men . . .’’ and then states ‘‘I assume their body to be but a statue, an earthen machine . . .’’ and it ends on the same note, saying that all the functions of the earthen machine, which he has shown to be indistinguishable from us humans, ‘‘follow naturally . . . from the disposition of the organs—no more and no less than do
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FIG. 4. Gland H hangs in the center of the ventricle. Van Gutschoven’s drawing for L’Homme.
the movements of a clock or other automation, from the arrangement of its counterweights and wheels.’’ The Centrality of the Pineal
At the center of Descartes’ earthen machine the pineal hangs in the cerebral ventricle. Animal spirits rising from the dark fire of the heart are purified by passing through the cold fabric of the brain and jet from the pineal into the ventricle (Fig. 4). Other spirits, with less of what we would call ‘‘kinetic energy,’’ flow from the ‘‘arteries which carpet the cavities of the brain’’ (Hall, 1972, p. 80). The spirits, says Descartes, never ‘‘stop for a moment in one place,’’ they are always moving like a wind and, as such, fill out the cerebral ventricle ‘‘as if it were a sail.’’ On death the ventricles consequently collapse: ‘‘very narrow and almost entirely closed.’’ In life, however, they are ballooning under pressure, the spirits streaming out from the pineal and escaping through the tubular nerves whose endings line the ventricular wall. Pineal Neuropsychology: Sensory Consciousness
Next, let us see how Descartes uses this mechanism to account for sensory consciousness and for reflex action. His account of sensory consciousness is most fully worked out for the visual sense. His diagram (Fig. 5) is famous. The rays coming from the arrow at A, B, and C are focused on the retina by the lens. Descartes was not the first to understand that an inverted image is thrown upon the retina. Famously, Kepler (1604) and before him Aranzi (1593) had discovered the true optics of the eye. Descartes had repeated
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FIG. 5. Visual perception in L’Homme. Explanation in text.
Kepler’s experiment of removing a piece of sclera from the back of the eye and covering the hole with a piece of transparent white paper (or an eggshell) and observing the inverted image (Optics, 116). But Descartes takes the theory further than Kepler. To understand it we have to appreciate that he believed nerves to be not only hollow spirit-filled tubes (in the Erasistratean tradition) but also to contain ‘‘tiny fibres’’ which, he writes, ‘‘compose the marrow of the nerve’’ (L’Homme, p. 141). He supposes that the rays affect (he says ‘‘pull’’) the fibers in nerves 1, 3, and 5 in the nerve endings lining the retina. This opens valves at ventricular ends 2, 4, and 6. We now recall that the ventricles are filled with pressurized animal spirits. These will escape through the opened valves. Now it is one of Descartes’ fundamental tenets that there is ‘‘no vacuum in nature.’’ In the Optics he makes a famous comparison with a wine vat at
FIG. 6. Descartes’ concept of tubular, thread-containing, nerve fibers. When the thread is pulled taut, the value opens and ‘‘spirits’’ enter as shown by the arrows.
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FIG. 7. Wine vat filled with grapes. Two perforations, A and B, are made in the bottom of the vat. Depressions on the surface show where the wine is escaping from the bottom. From Descartes’ Optics.
harvest time ‘‘full to the brim with half pressed grapes’’ but in the bottom of which are a few holes (Optics, 86); see Fig. 7. As soon as these holes are unblocked the wine flows out and indentations form on the surface of the wine directly above the newly opened holes. So it is, says Descartes, with the animal spirits in the cerebral ventricle. The spirits (says Descartes) ‘‘do not come indifferently from all points on the surface of (the pineal)’’ but those from point ‘a’ tend to enter tube 2, those from points ‘b’ and ‘c’ tend to enter tubes 4 and 6 and so on.’’ Hence a low-pressure outline of the retinal image will form on the pineal’s surface. Note that the artists who drew the figures for the Treatise (sometime after Descartes death) took care to reinvert the image. This was not necessarily Descartes’ intention. It is not only the shape which is ‘‘felt’’ by the pineal’s surface but also, says Descartes, other aspects of the visual image. Different colors, for instance, will (he says) affect the retinal threads and hence the ventricular valves differently, as will movement, size, distance, etc. And he generalizes to all the other senses: ‘‘sounds, odours. . . . pain, hunger, thirst, joy, sadness and other such passions.’’ Now it is these traces on the pineal’s surface which, according to Descartes of the Treatise, are ‘‘taken to be ideas, that is to say, to be the forms or images that the rational soul will consider directly when, being united with this machine, it will imagine or will sense any object.’’ He confirms this assessment in the Optics: ‘‘. . . we must not think that it is by means of this resemblance that the picture makes us aware of objects—as though we had another pair of eyes to see it, inside our brain: . . . rather, we must hold that the movements by which the image is formed act directly on our soul insofar as it is united to the body, and are ordained by nature to make it have such sensations’’ (Optics, p. 130).
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FIG. 8. Reflex movement of arm. The eye looks to point ‘‘B’’ on the arrow. Valves at positions ‘‘4’’ on the ventricular surface open so that the pineal moves to bring point ‘‘b’’ opposite nerve ending ‘‘8’’ so that spirits course down to ‘‘inflate’’ the biceps and hence move the arm. Further explanation in text. From Descartes’ L’Homme.
Pineal Neuropsychology: Reflex Action
Let us turn to the motor outflow and reflex action. The pineal, as we have seen, is suspended very delicately in the cerebral ventricle. There are two cases. First, the gland may swing and sway at random in the swirling gas of the ventricle. Sometimes it will approach one wall of the ventricle, sometimes another. The jetting spirits are able to open the nearest neural tubes and flowing down them cause a muscle or group of muscles to move. This once again leaves a low-pressure image on the pineal surface which, of course, corresponds to an idea. ‘‘Note’’ says Descartes ‘‘that if we have an idea of moving a member, that idea—consisting of nothing but the way spirits flow from the gland—is the cause of the movement itself ’’ (Hall, 1972, p. 92). Second is the case of an ‘‘involuntary’’ movement. Descartes’ explanation makes use of a well-known figure (Fig. 8). He explains the neurophysiology which causes the arm to be moved from point C to point B on the arrow. He says that this is due to the pineal moving in such a way that the neural tubules for the arm are adjacent to point ‘‘b’’ on its surface. The ‘‘soul’’ (he continues) will ‘‘sense that the arm is turned toward object B provided the soul is already in this machine’’ (my italics). The earthen
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machine will move but not ‘‘know’’ that it has moved. This interpretation is supported by Descartes remarks on sleepwalking in a letter to the Marquess of Newcastle (1646) (Kenny, 1970, pp. 205–208) and in a reply to a set of objections from Arnauld: ‘‘When people take a fall,’’ he says, ‘‘and stick out their hands to protect their head, it is not reason that instructs them to do this; it is simply the sight of the impending fall reaches the brain and sends the animal spirits into the nerves in the manner necessary to produce this movement even without any mental volition, just as it would be produced in a machine, and since our own experience reliably informs us that this is so, why should we be so amazed that ‘light reflected from the body of a wolf on to the eyes of a sheep’ should be equally capable of arousing the movements of flight in a sheep’’ (Cottingham, Stoothoff, and Murdoch, Vol. ii, p. 161). Descartes goes on to generalize this mechanism by saying that ‘‘(a) each tubule on the internal surface of the brain corresponds to a member, and (b) that each point on the surface of the gland corresponds to a direction towards which those members can be turned: whence the movements of those members, and the ideas thereof, can be reciprocally caused the one by the other.’’ He shows how his mechanism can account for sense perception, for memory, for learning and reflex action, and for all the behaviors of the simulated human being. All derives, as we noted above, ‘‘from the disposition of the organs.’’ It is not necessary, he continues, ‘‘to conceive of any vegetative or sensitive soul’’ or of any other principle than those which occur ‘‘in inanimate bodies’’ (Hall, 1972, p. 113). Three hundred fifty years later we are still in the grip of this vision. THE RATIONAL SOUL IN THE TREATISE
Throughout the Treatise there is only infrequent reference to the ‘‘rational’’ soul, and then in a distinctively promissory way. Descartes writes, for instance, ‘‘of when there will be [a soul] in this machine it will sense different objects’’ (Adam & Tannery, 1897–1913, Vol. XI, p. 183) but that all the behavioral movements of real men are indistinguishable from his hydraulic simulacrum. He has made an immense effort to develop an entirely theoretical, mechanistic neurophysiology which has no need of any other principle. It is difficult to believe that so incisive a mind as that of Descartes could have believed in the detail of his model. It can only have been put forward as a possibility, as an argument to say that this is the ‘‘sort of thing’’ which could be happening. It was put forward as the first part of a larger argument. PASSIONS OF THE SOUL
If we turn to his next (and last) excursion into psychophysiology, Passions of the Soul, completed in the late 1640s, some 15 years after the Treatise, we find a crucially different pineal physiology. Here, instead of the mechanistic
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earthen machine, we find emphasis placed on what was missing in the Treatise, the rational soul. We saw in the Treatise (see Fig. 8) that the rational soul (if it is present) will sense the movement of an arm. This is entirely passive. But in Passions we read not only of how the image on the pineal ‘‘acts directly on the soul and makes it see . . .’’ but also of how the rational soul can move the pineal ‘‘in various different ways’’ and thus direct the spirits down appropriate nerve tubules to cause muscular movements (Sections 34–35). He sums up by saying that whereas perceptions and passions ‘‘are entirely dependent on the actions which produce them’’ (this is consistent with the account in the Treatise), the ‘‘will’’ is free and ‘‘. . . the activity of the soul consists entirely in the fact that by willing something it brings it about that the little gland to which it is closely joined moves in the manner required . . .’’ (Section 41). It is at this point, of course, that the Cartesian vision encounters its familiar difficulties. How can a by-definition ‘‘nonextended’’ soul cause movement in an ‘‘extended’’ pineal? Descartes never provides an answer. But even more dangerous is a query raised by Henry More in a letter dated July 23, 1649: ‘‘I ask: when the human mind stirs the animal spirits by thinking more attentively and for a longer time and, moreover, rouses the body itself, doesn’t it surely then increase the motion in the universe?’’ (Adam & Tannery, 1897–1913, Vol. v, p. 385). This reminds us of Sherrington’s dilemma: ‘‘Physics tells me that my arm cannot be bent without disturbing the sun. Physics tells me that unless my mind is energy it cannot disturb the sun. My mind then does not bend my arm. If it does, the theoretically impossible happens. Let me prefer to think the theoretically impossible does happen. Despite the theoretical I take it my mind does bend my arm, and that it disturbs the sun’’ (Sherrington, 1951, p. 258). Descartes, like Sherrington, believed that we live in a bounded universe containing a constant quantity of motion (in our terms mass/energy), yet the mind, res cogitans, has no physical dimensions. More received no satisfactory answer to his query. Soon after receiving his letter Descartes left for Stockholm and the court of Queen Christina and within 6 months had died from the pneumonia brought on by the freezing Swedish winter. Conclusion
Some have thought that the trial of Galileo caused Descartes to revise his neurophysiology. It depends on who we think was behind the mask. The neurophysiology of the Treatise seems fully consistent in its dreamy way (compare the ‘‘likely tale’’ of the Timaeus) with a materialistic dual-aspect identity theory of mind and body. The neuropsychology of the Passions, in allowing the rational soul an active and controlling role, supervenes upon this mechanistic vision. La Mettrie, in the next century, was not the only one to doubt Descartes’ intentions: ‘‘. . . (Descartes’) ‘real distinction’ be-
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tween mind and body,’’ he writes, ‘‘is a ruse which deceives only theologians’’ (La Mettrie, 1748). But this interpretation does not ultimately seem sustainable. La Mettrie, after all, had his own ax to grind. A reading of the whole of Descartes Oeuvre leaves little doubt that his intention was to support ecclesiastical authority. The Galilean contretemps must have seemed a catastrophe. In his withdrawal and reappraisal after 1633 we should rather see (I believe) prudence and a wish for a quiet life. Only at the insistence of Queen Christina in their early morning tutorials did he rummage in his trunk for Le Monde (Baillet, 1691). The complex, speculative, iatrohydraulics of his earthen machine can thus be seen as a ‘‘likely story’’ with which the nonspatial, immortal, ‘‘thinking substance’’ can (it is true rather shakily) be united. For Descartes, animals were conscious automata. They saw, heard, and ‘‘emoted’’ without ‘‘knowing’’ that they were so doing. Habitual commuters, long-distance lorry drivers, and, perhaps, patients with ‘‘blindsight’’ know that this is fully possible. It is thus, in spite of the common opinion, unCartesian to treat animals as unfeeling machines. The rational soul somehow grafted into the machine allows humans to go one step further: not only to know but also to ‘‘know that they know.’’ It also provides our introspective conviction of volitional freedom. Humans, in other words, differ from animals in being ‘‘self-conscious.’’ It was not, however, until Darwin that we began to have an inkling of how this phenomenon might be given a naturalistic explanation. References Adam, C., & Tannery, P. Eds. 1897–1913. Oeuvres de Descartes, Paris: L. Cerf. Aranzi, J. C. 1595. De humano foetu; anatomicarum observationum; etc. Carampellum; Venetis. Baillet, A. 1691. La vie de Monsieur Descartes. Paris: D. Horthemels. [Facsimile reprint, Geneva, 1970; trs. by S. R. London, 1693]. Bauhin, C. 1605/1621. Theatrum anatomicum. Frankfurt: Matthaei Bekeripp. Bitpol-Hesperies, A. 1990. Le principle de vie chez Descartes. Paris: Vrin. Cohen, I. B. 1972. in T. S. Hall, 1972. Treatise of Man, Cambridge, MA: Harvard Univ. Press. Pp. xiii–xiv. Crick, F. H. C. 1994. The astonishing hypothesis. London: Simon & Schuster. Crooke, H. 1631. Mikrosmographie: A description of the body of man. 2nd ed. London: T. and R. Cotes. Cottingham, J., Stoothoff, R., & Murdoch, D. 1984. The philosophical writings of Descartes. Cambridge, UK: Cambridge Univ. Press. Foster, M. 1970. Lectures on the history of physiology in the sixteenth, seventeenth and eighteenth centuries. New York: Dover. Hall, T. S. 1972. Treatise of man. Cambridge, MA: Harvard Univ. Press. Kenny, A. 1970. Descartes: Philosophical letters. Oxford: Clarendon.
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Kepler, J. 1604. Ad Vitellionem Paralipomena quibus Astronomiae pars optica Eraditur . . . : Francofurti. La Forge, L. 1664. L’homme de Rene´ Descartes et un traite´ de la formation du foetus du meˆme autheur. Paris: S. Jaques. La Mettrie, J. O. de. 1748. L’homme machine. Leyden. Marion, J.-L. 1981. Sur la the´ologie blanche de Descartes. Paris: Presses Univ. France. May, M. T. 1968. [trs. Galen] De usu partium: On the usefulness of the parts of the body. New York: Cornell Univ. Press. Mourant, J. A. 1979. The cogitos: Augustinian and Cartesian. Augustinian Studies, 10, 27– 42. O’Daley, G. 1987. Augustine’s philosophy of mind. London: Duckworth. Risner. 1572. Opticae thesaurus. Basel. Reisch, G. 1504. Margarita Philosophica. Basiliae. Rosenfield, L. G. 1968. From beast-machine to man-machine. New York. Octagon Books. Schiller, F. 1995. Pineal gland, perennial puzzle. Journal of the History of the Neurosciences, 4, 155–165. Sherrington, C. S. 1951. Man on his nature. Harmondsworth: Penguin. Singer, C. 1956. [trs. Galen] On anatomical procedures. London: Oxford Univ. Press. St. Augustine, De genesi ad litteram libri duodecim, Bibliotheque Augustinienne, Vol. 48, Paris: Descle´e de Brouwer, 1972. Vesalius, A. 1543. De humani corporis fabrica. Basiliae. [Facsimile reprint by Culture et Civilisation, Bruxelles, 1964] Wilson, C. 1989. Liebniz’s metaphysics. Manchester: Manchester Univ. Press.
BRAIN AND COGNITION ARTICLE NO.
Descartes’ Pineal Neuropsychology C. U. M. Smith Vision Sciences, Aston University, Birmingham B4 7ET, United Kingdom E-mail: [email protected] The year 1996 marked the quattrocentenary of Descartes’ birth. This paper reviews his pineal neuropsychology. It demonstrates that Descartes understood the true anatomical position of the pineal. His intraventricular pineal (or glande H) was a theoretical construct which allowed him to describe the operations of his manlike ‘‘earthen machine.’’ In the Treatise of Man he shows how all the behaviors of such machines could then be accounted for without the presence of self-consciousness. Infrahuman animals are ‘‘conscious automata.’’ In Passions of the Soul he adds, but only for humans, self-consciousness to the machine. In a modern formulation, only humans not only know but know that they know. 1998 Academic Press Bene vixit, bene qui latuit (he lives well who is well hidden) Descartes’Ovidian motto, (Letter to Mersenne, April 1643, in Adam & Tannery, Vol. i, p. 286) This little sprunt champion called the conarion, or Nux pinea, within which the soul is entirely cooped up. (Henry More, 1713, Preface to Divine Dialogues (2nd ed.), p. 12) . . . now that I come to ascend the stage of the world . . . I come forward in a mask. . . . (Early notebook, c. 1619)
Introduction
Rene´ Descartes was born just over 400 years ago on 31 March 1596 in the small village of La Haye near Tours. Although he is normally thought of as a mathematician and a philosopher, and with good reason, he in fact spent a good part of his later life investigating and puzzling over the human microcosm. The works in which he expounded his neuropsychology are principally L’Homme (1632; published 1662) usually translated into English as A Treatise of Man, and to a lesser extent the 1649 Les Passions de l’Ame An early version of this article was presented to the First Annual Meeting of the International Society for the History of the Neurosciences, Buffalo, NY, May 1966. 57 0278-2626/98 $25.00
Copyright 1998 by Academic Press All rights of reproduction in any form reserved.
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(The Passions of the Soul). He also left the manuscript of an anatomical manual Excerpta Anatomica (1631–1648). The Pineal
That Descartes singled out the pineal as primus inter pares among the brain’s structures is proverbial: ‘‘. . . although the soul is joined to the whole body there is a certain part where it exercises its functions more than all the others’ (Passions of the Soul, p. 31). His reason for according the pineal this preeminence seems philosophically weak. He writes in Passions of the Soul, p. 32) that the unitary nature of our introspection implies a corresponding unitary anatomical structure. It is worth noting that medieval theories of vision generally sought a unitary location where visual images from the two eyes could be combined to provide our phenomenological visual unity. The medievals normally took the chiasma for this location (see for example, Risner, 1572). It may be that Descartes, with his intense interest in physical and physiological optics, was influenced by this thought; he is known to have read Kepler’s Paralipomena when he was preparing the Treatise of Man (Marion, 1981). The problem of relating our unified sensory consciousness to its highly heterogeneous neuroanatomical correlative has not gone away. It is still very much with us today: it is known as the ‘‘binding problem’’ (see for instance, Crick, 1994). It is odd, however, to find an attempt at so simple-minded an identity in the work of a philosophical genius of Descartes’ rank. For Descartes’ fundamental and sustained premise was precisely the nonlocality of mind. However this may be, Descartes insists that there is only one unitary structure in the otherwise bilateral brain—and this is the pineal. Descartes and the Anatomy of the Pineal
The pineal has a long history in neuroanatomy, stretching back at least as far as Galen, and it was usually accorded a crucial role in controlling the flows of spirit in the ventricles (Hall, 1972, pp. 86–87). It is, however, worth noting that in de usu partium Galen recognized the external location of the pineal and consequently ridiculed the notion that it could control the tides of ventricular spirits: ‘‘The notion,’’ writes Galen, ‘‘that the pineal body is what regulates the passage of the pneuma is the opinion of those who are ignorant of the vermiform epiphysis and who give more than due credit to the gland. . . . Since this gland is . . . attached not to the inside but to the outside of the ventricle, how could it . . . have so great an affect [sic] on the canal? Why need I mention how ignorant and stupid these opinions are?’’ (translated by May, 1968, pp. 419–420). In Anatomical Procedures he explains, furthermore, how it should be dissected, remarking that when freed of its surrounding tissues it usually sinks back onto the roof of the brain (Singer, 1956). Descartes was no stranger to first-hand experience of dissection. Adrien
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Sheep brain: inferior aspect. From Descartes’ Excerpta Anatomica.
Baillet (1691), his earliest biographer, has a well-known story of visitors enquiring about his library and being shown into his dissecting room with the remark that ‘‘these are my books.’’ In the years 1629–1632, the years when he was composing his Treatise of Man, he is known to have been a frequent visitor to the butcher’s shops in Amsterdam. Baillet writes that in the late 1620s and 1630s, ‘‘his eagerness for knowledge of the subject made him visit, almost daily, a butcher’s shop to witness the slaughter; and that he caused to be brought thence to his dwelling whichever of the animal’s organs he desired to dissect at greater leisure’’ (trs. Cohen, 1972). Indeed (says Baillet) he exposed himself to the ridicule and malicious gossip of his Dutch neighbors. He writes to Mersenne in December 1632 that he ‘‘. . . is dissecting the heads of different animals in order to explain what memory, imagination, consist of’’ (Adam & Tannery, 1897–1913, Vol i, p. 263). And later on, in February 1639, in another letter to Mersenne he writes of how he has consulted not only Vesalius and the other writers on anatomy but has also been dissecting animals for over 11 years (Adam & Tannery, 1897– 1913, Vol. ii, p. 525). Figure 1 from the Excerpta Anatomica (Adam & Tannery, 1897–1913, Vol. xi, pp. 549–634) shows one of his dissections of the sheep brain.
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FIG. 2. Parasagittal section of sheep brain to show pineal (H).
Figure 1 is hardly of Vesalian standard. Descartes was no draftsman. We have also to recall the conditions of the time. He remarks to Mersenne, for instance, that he is not surprised that the pineal is difficult to see in human cadavers because of deterioration in the postmortem room (April, 1640: Adam & Tannery, 1897–1913, Vol. iii, p. 45). This is why he found animal material so much more rewarding. He was, he writes, accustomed to finding the pineal without difficulty in ‘‘freshly killed animals.’’ It is unfortunate that he includes no drawing of the superior aspect of the sheep brain in the Excerpta. For here we come to our first instructive puzzle. If he is accustomed to finding the pineal with ease, why do all his illustrations show it hanging down inside the ventricle? Figure 2 shows the very obvious position of the pineal in the sheep brain. The mystery is increased by looking at the authors he says (in his 1639 letter to Mersenne) that he has consulted. Not only Vesalius but also Caspar Bauhin give drawings of the pineal which show it resting on the superior surface of the brain and we have already seen that Galen was of the same opinion. Bitpol-Hesperies (1990) provides good evidence that Descartes had carefully studied Caspar Bauhin’s (1605/1621) Theatrum Anatomicum. Yet in the section of the Theatrum which discusses the pineal Bauhin quotes Vesalius as saying that the base of the pineal rests on the substance of the brain and that ‘‘the top regardeth upward’’ (in Crooke’s 1631 translation) and he goes on to say that ‘‘it neither adhereth to the inwarde sides of the
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ventricle, but lyeth upon the outside’’ (Crooke, 1631, p. 469) and thus cannot affect the flows of animal spirits within the ventricle. Descartes’ Diagrams
Nevertheless and in spite of all this Descartes gives his pineal an intraventricular position (see Fig. 3). Readers of the Treatise of Man are always struck by the contrast between its drawings and those of Vesalius and Bauhin. We are in a different world. A word of caution is, of course, necessary. We should remember that the Treatise was a posthumous publication. Descartes had died some 12 years before in Stockholm in the unusually cold Swedish winter of 1650. An apocryphal story has him voyaging to Stockholm accompanied by a trunk containing a life-sized mechanical doll (see Rosenfield, 1968). It would be nice to think that this story refracts through layers of rumor and prejudice the existence of the manuscript of the Treatise at the bottom of one of his boxes. Baillet relates that when he had arrived in Stockholm Queen Christina caused him to delve into his trunk and assemble his papers into treatises. According to Baillet these had been ‘‘bound up hand over head on his departure from Holland. They were all in pieces scattered up and down . . .’’ (Baillet, 1691, p. 247). And, of course, when his papers were returned from Stockholm the boat carrying them sank in the Seine and the papers were only recovered some days later. So the Treatise we have, and especially the figures, may very well not be exactly the ones Descartes would have published himself. In editing the first French edition (1664) Clerselier found only two drawings roughly drafted by Descartes himself (Hall, 1972, p. xxxv). He commissioned two eminent academics, La Forge and van Gutschoven, to construct sets of illustrations to fit the text. La Forge is quite candid about his own approach. In his own edition of the Treatise he writes (p. 326): ‘‘I am less committed to representing things according to Nature than to rendering them intelligible’’ and, in particular, that the pineal is drawn much larger than normal because of its central importance in the Cartesian neuropsychology (La Forge, 1664, p. 326). The illustrations in the Clerselier edition, except for that marked D (showing the action of antagonistic muscles on the eyeball), are drawn by either van Gutschoven (marked G) or La Forge (F). It is clear, then, that Descartes and/or his editors are not attempting the artistic realism of Vesalius but reverting back (and forward) to the diagram makers of earlier (and later) times. Medieval diagrams illustrating ventricular psychology are well known. Perhaps the most common is that published in Gregor Reisch’s widely read text The Pearl of Wisdom (1504). Many similarly fantastical figures were published in pre-Vesalian times. Vesalius, himself, had been forced to study the Pearl as a medical student in Louvain in the early 1500s. He has a characteristically caustic passage in the Fabrica (1543, Book VII, Chapter 1, p. 623) on the anatomical absurdities of the ventricular psychology.
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FIG. 3. Parasagittal view of human brain drawn by van Gutschoven (G) for L’Homme. H, gland H (pineal).
Schematic figures were, then, part of an old tradition, as was Descartes’ essentially ventricular neuropsychology. Descartes’ pipes and threads and valves can, perhaps, be seen as part of that tradition. Although it would take us too far from the theme of this article to consider in detail, it is also worth noting the Augustinian ghost lurking behind Descartes’ schematism. Descartes had been educated at the newly founded Jesuit college at La Fle`che. By all accounts he received one of the best classical educations then available and he was, of course, a star pupil. He cannot have been unfamiliar with the works of St. Augustine. Yet when Andreas Colvius, minister at nearby Dordrecht, pointed out that his cogito ergo sum seemed to be no more than a rewording of Augustine’s very similar arguments (de Trinitate, Book 10, para. 14 and elsewhere [see Mourant, 1979]), Descartes was surprised (or effected to be surprised) and replied that he had that day been to the town library to check the reference (Kenny, 1970, p. 83). Similarly it is possible to wonder how far conscious or unconscious memories of Augustine influenced his neuropsychology. Augustine’s fourth century neuropsychology drew on traditions reaching back to the Alexandrians of classical antiquity. Although Augustine’s neuropsychology was written to underpin his theology, especially his account of the soul, we can still find echoes of Erasistratus (see O’Daley, 1987). In De Genesi ad Litteram, for example, Augustine writes of how ‘‘the air which is contained in the nerves obeys the will and moves the members without itself being the will’’ (Et aer, qui neris
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infusus est, paret voluntati, ut membra moveat, non autem ipse voluntas est) (Book 7, 19, 25). Erasistratus, in the third century BC, had conceived that the tissues of the body, and the substance of the brain, consisted of tubes, subdivided again and again, and in the case of the brain and nervous system were filled with pneuma. This ancient theory, taken into Augustine’s neuropsychology, cannot but remind us of the spirit-filled nerve tubes, subdivided again and again below the level of visibility, which form the basis of Descartes’ conception of the brain. In this, as in much else, Descartes is a truly transitional figure, half in what we categorize as the modern world, half in the millennial traditions of the medievals. An ‘‘Earthen Machine’’
Nowhere in Augustine, however, is there mention of the pineal and nowhere is there the mechanistic metaphor. It is here that Descartes breaks entirely new ground. It is here, also, that it begins to come clear what Descartes is doing. He is not attempting to compete with Vesalius, Bauhin, and the other anatomists. He is well enough aware that his diagrams have little anatomical reality. They are theoretical constructs. Indeed, although in his letters he refers to his central gland as the pineal or conarium, it is never referred to as such in the pages of the Treatise. It is always ‘‘la petite glande, H.’’ Descartes is not striving for anatomical reality: he is trying to show how it could be, how it was not necessary to import a self-moving ‘‘soul’’ into the ‘‘earthen machine.’’ At the beginning of the Treatise Descartes is quite explicit: he proposes to treat human and animal bodies as if they were earthen machines. Insofar as this banished vital forces, eliminating the ‘‘animal’’ and ‘‘vegetable’’ souls of the scholastics, this was a liberating approach and we would have little to quibble with today. It had the virtue of concentrating the ‘‘hard’’ problem at the level of the rational soul. This could then be left to theologians to argue about. As Descartes says over and over again the earthen machines (Michael Foster intriguingly mistranslates as ‘‘earthly machines!’’ [Foster, 1970, p. 268]) he has described are (with the exception of the rational soul) indistinguishable from humans and other animals. Descartes’ larger project was identical to that of Galileo: to save the natural world from theology and the supernatural world from science. In parenthesis, this is not to say (as some of his followers and later expositors have said) that Descartes believed that infrahuman animals are insentient, that their squeals are no different than those of badly oiled machines or tires on a badly driven automobile. Leibniz, for instance, writes to Tschirnhaus in 1684 that the Dutch are ‘‘amusing themselves by ridiculing the Cartesians for imagining that a dog that is clubbed cries in the same way as a bagpipe which is pressed’’ (Wilson, 1989). Descartes, himself, is at worst equivocal. There is no doubt that Descartes modeled his ‘‘fantastical’’ neurophysiology on the water-powered automata which were so much the vogue in the
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French aristocratic circles of his youth. There is, for instance, every reason to suppose that he had visited and marveled at the automata devised by the Francini brothers at St. Germaine. It has even been speculated that he named his much loved and deeply mourned daughter Francine in their honor. These devices were driven by ‘‘external’’ forces. The Francinis built their ingenious mechanisms and then directed flows of water through them to generate appropriate movement. Hydrodynamics was, of course, not the only technological metaphor Descartes used. He was also the forerunner of a tradition which uses musical instruments to image the functioning of the brain. In his case it was the cathedral organ. He makes a comparison with the organ’s pipes and the hollow nerves of the brain. He likens external energies impinging on the body to the organist’s fingers. He goes on to say that the harmony of the organ in no way depends on the arrangement of the pipes and other parts or on their shapes but solely on ‘‘the air which comes from the bellows; the pipes that sound; the distribution of air to those pipes’’ (L’Homme, trs. Hall, 1972, pp. 71–72). Bene Vixit, Bene Qui Latuit
L’Homme was composed in 1632–1633 as the last section of Descartes’ overarching work on cosmology: Le Monde. He was readying the work for publication when he heard that Galileo’s Dialogue on the Two Great World Systems had been condemned in Rome (July 23, 1633), all copies to be burnt, its author to be confined to house arrest and forbidden to publish. Descartes writes to Mersenne in November 1633 expressing his horror, saying that he had nearly decided to burn all his papers, and ending ‘‘. . . I wouldn’t want to publish a discourse with a single word of which the Church disapproved; so I prefer to suppress rather than publish it in a mutilated form’’ (Adam & Tannery, 1897–1913, Vol. 1, p. 271). And, in the 1637 Discourse on Method, V, referring to his suppressed work, he says ‘‘certain considerations prevent me from publishing.’’ Discretion, as he remarked to Mersenne, is the better part of valor: Bene vixit, bene qui latuit! His ostensible reason for suppressing his work was that it, like Galileo’s Dialogue, supported the Copernican heresy. But he probably felt that the Treatise of Man might also have raised eyebrows in orthodox circles. The Treatise which has come down to us, saved when Descartes’ papers were submerged in the Seine after his death and published in 1662 (Latin) and 1664 (French), is perhaps a truncated version. It starts and ends abruptly. What it lacks at both ends are apologias linking it to the orthodox thought of the time. It starts almost in midsentence ‘‘. . . these men . . .’’ and then states ‘‘I assume their body to be but a statue, an earthen machine . . .’’ and it ends on the same note, saying that all the functions of the earthen machine, which he has shown to be indistinguishable from us humans, ‘‘follow naturally . . . from the disposition of the organs—no more and no less than do
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FIG. 4. Gland H hangs in the center of the ventricle. Van Gutschoven’s drawing for L’Homme.
the movements of a clock or other automation, from the arrangement of its counterweights and wheels.’’ The Centrality of the Pineal
At the center of Descartes’ earthen machine the pineal hangs in the cerebral ventricle. Animal spirits rising from the dark fire of the heart are purified by passing through the cold fabric of the brain and jet from the pineal into the ventricle (Fig. 4). Other spirits, with less of what we would call ‘‘kinetic energy,’’ flow from the ‘‘arteries which carpet the cavities of the brain’’ (Hall, 1972, p. 80). The spirits, says Descartes, never ‘‘stop for a moment in one place,’’ they are always moving like a wind and, as such, fill out the cerebral ventricle ‘‘as if it were a sail.’’ On death the ventricles consequently collapse: ‘‘very narrow and almost entirely closed.’’ In life, however, they are ballooning under pressure, the spirits streaming out from the pineal and escaping through the tubular nerves whose endings line the ventricular wall. Pineal Neuropsychology: Sensory Consciousness
Next, let us see how Descartes uses this mechanism to account for sensory consciousness and for reflex action. His account of sensory consciousness is most fully worked out for the visual sense. His diagram (Fig. 5) is famous. The rays coming from the arrow at A, B, and C are focused on the retina by the lens. Descartes was not the first to understand that an inverted image is thrown upon the retina. Famously, Kepler (1604) and before him Aranzi (1593) had discovered the true optics of the eye. Descartes had repeated
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FIG. 5. Visual perception in L’Homme. Explanation in text.
Kepler’s experiment of removing a piece of sclera from the back of the eye and covering the hole with a piece of transparent white paper (or an eggshell) and observing the inverted image (Optics, 116). But Descartes takes the theory further than Kepler. To understand it we have to appreciate that he believed nerves to be not only hollow spirit-filled tubes (in the Erasistratean tradition) but also to contain ‘‘tiny fibres’’ which, he writes, ‘‘compose the marrow of the nerve’’ (L’Homme, p. 141). He supposes that the rays affect (he says ‘‘pull’’) the fibers in nerves 1, 3, and 5 in the nerve endings lining the retina. This opens valves at ventricular ends 2, 4, and 6. We now recall that the ventricles are filled with pressurized animal spirits. These will escape through the opened valves. Now it is one of Descartes’ fundamental tenets that there is ‘‘no vacuum in nature.’’ In the Optics he makes a famous comparison with a wine vat at
FIG. 6. Descartes’ concept of tubular, thread-containing, nerve fibers. When the thread is pulled taut, the value opens and ‘‘spirits’’ enter as shown by the arrows.
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FIG. 7. Wine vat filled with grapes. Two perforations, A and B, are made in the bottom of the vat. Depressions on the surface show where the wine is escaping from the bottom. From Descartes’ Optics.
harvest time ‘‘full to the brim with half pressed grapes’’ but in the bottom of which are a few holes (Optics, 86); see Fig. 7. As soon as these holes are unblocked the wine flows out and indentations form on the surface of the wine directly above the newly opened holes. So it is, says Descartes, with the animal spirits in the cerebral ventricle. The spirits (says Descartes) ‘‘do not come indifferently from all points on the surface of (the pineal)’’ but those from point ‘a’ tend to enter tube 2, those from points ‘b’ and ‘c’ tend to enter tubes 4 and 6 and so on.’’ Hence a low-pressure outline of the retinal image will form on the pineal’s surface. Note that the artists who drew the figures for the Treatise (sometime after Descartes death) took care to reinvert the image. This was not necessarily Descartes’ intention. It is not only the shape which is ‘‘felt’’ by the pineal’s surface but also, says Descartes, other aspects of the visual image. Different colors, for instance, will (he says) affect the retinal threads and hence the ventricular valves differently, as will movement, size, distance, etc. And he generalizes to all the other senses: ‘‘sounds, odours. . . . pain, hunger, thirst, joy, sadness and other such passions.’’ Now it is these traces on the pineal’s surface which, according to Descartes of the Treatise, are ‘‘taken to be ideas, that is to say, to be the forms or images that the rational soul will consider directly when, being united with this machine, it will imagine or will sense any object.’’ He confirms this assessment in the Optics: ‘‘. . . we must not think that it is by means of this resemblance that the picture makes us aware of objects—as though we had another pair of eyes to see it, inside our brain: . . . rather, we must hold that the movements by which the image is formed act directly on our soul insofar as it is united to the body, and are ordained by nature to make it have such sensations’’ (Optics, p. 130).
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FIG. 8. Reflex movement of arm. The eye looks to point ‘‘B’’ on the arrow. Valves at positions ‘‘4’’ on the ventricular surface open so that the pineal moves to bring point ‘‘b’’ opposite nerve ending ‘‘8’’ so that spirits course down to ‘‘inflate’’ the biceps and hence move the arm. Further explanation in text. From Descartes’ L’Homme.
Pineal Neuropsychology: Reflex Action
Let us turn to the motor outflow and reflex action. The pineal, as we have seen, is suspended very delicately in the cerebral ventricle. There are two cases. First, the gland may swing and sway at random in the swirling gas of the ventricle. Sometimes it will approach one wall of the ventricle, sometimes another. The jetting spirits are able to open the nearest neural tubes and flowing down them cause a muscle or group of muscles to move. This once again leaves a low-pressure image on the pineal surface which, of course, corresponds to an idea. ‘‘Note’’ says Descartes ‘‘that if we have an idea of moving a member, that idea—consisting of nothing but the way spirits flow from the gland—is the cause of the movement itself ’’ (Hall, 1972, p. 92). Second is the case of an ‘‘involuntary’’ movement. Descartes’ explanation makes use of a well-known figure (Fig. 8). He explains the neurophysiology which causes the arm to be moved from point C to point B on the arrow. He says that this is due to the pineal moving in such a way that the neural tubules for the arm are adjacent to point ‘‘b’’ on its surface. The ‘‘soul’’ (he continues) will ‘‘sense that the arm is turned toward object B provided the soul is already in this machine’’ (my italics). The earthen
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machine will move but not ‘‘know’’ that it has moved. This interpretation is supported by Descartes remarks on sleepwalking in a letter to the Marquess of Newcastle (1646) (Kenny, 1970, pp. 205–208) and in a reply to a set of objections from Arnauld: ‘‘When people take a fall,’’ he says, ‘‘and stick out their hands to protect their head, it is not reason that instructs them to do this; it is simply the sight of the impending fall reaches the brain and sends the animal spirits into the nerves in the manner necessary to produce this movement even without any mental volition, just as it would be produced in a machine, and since our own experience reliably informs us that this is so, why should we be so amazed that ‘light reflected from the body of a wolf on to the eyes of a sheep’ should be equally capable of arousing the movements of flight in a sheep’’ (Cottingham, Stoothoff, and Murdoch, Vol. ii, p. 161). Descartes goes on to generalize this mechanism by saying that ‘‘(a) each tubule on the internal surface of the brain corresponds to a member, and (b) that each point on the surface of the gland corresponds to a direction towards which those members can be turned: whence the movements of those members, and the ideas thereof, can be reciprocally caused the one by the other.’’ He shows how his mechanism can account for sense perception, for memory, for learning and reflex action, and for all the behaviors of the simulated human being. All derives, as we noted above, ‘‘from the disposition of the organs.’’ It is not necessary, he continues, ‘‘to conceive of any vegetative or sensitive soul’’ or of any other principle than those which occur ‘‘in inanimate bodies’’ (Hall, 1972, p. 113). Three hundred fifty years later we are still in the grip of this vision. THE RATIONAL SOUL IN THE TREATISE
Throughout the Treatise there is only infrequent reference to the ‘‘rational’’ soul, and then in a distinctively promissory way. Descartes writes, for instance, ‘‘of when there will be [a soul] in this machine it will sense different objects’’ (Adam & Tannery, 1897–1913, Vol. XI, p. 183) but that all the behavioral movements of real men are indistinguishable from his hydraulic simulacrum. He has made an immense effort to develop an entirely theoretical, mechanistic neurophysiology which has no need of any other principle. It is difficult to believe that so incisive a mind as that of Descartes could have believed in the detail of his model. It can only have been put forward as a possibility, as an argument to say that this is the ‘‘sort of thing’’ which could be happening. It was put forward as the first part of a larger argument. PASSIONS OF THE SOUL
If we turn to his next (and last) excursion into psychophysiology, Passions of the Soul, completed in the late 1640s, some 15 years after the Treatise, we find a crucially different pineal physiology. Here, instead of the mechanistic
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earthen machine, we find emphasis placed on what was missing in the Treatise, the rational soul. We saw in the Treatise (see Fig. 8) that the rational soul (if it is present) will sense the movement of an arm. This is entirely passive. But in Passions we read not only of how the image on the pineal ‘‘acts directly on the soul and makes it see . . .’’ but also of how the rational soul can move the pineal ‘‘in various different ways’’ and thus direct the spirits down appropriate nerve tubules to cause muscular movements (Sections 34–35). He sums up by saying that whereas perceptions and passions ‘‘are entirely dependent on the actions which produce them’’ (this is consistent with the account in the Treatise), the ‘‘will’’ is free and ‘‘. . . the activity of the soul consists entirely in the fact that by willing something it brings it about that the little gland to which it is closely joined moves in the manner required . . .’’ (Section 41). It is at this point, of course, that the Cartesian vision encounters its familiar difficulties. How can a by-definition ‘‘nonextended’’ soul cause movement in an ‘‘extended’’ pineal? Descartes never provides an answer. But even more dangerous is a query raised by Henry More in a letter dated July 23, 1649: ‘‘I ask: when the human mind stirs the animal spirits by thinking more attentively and for a longer time and, moreover, rouses the body itself, doesn’t it surely then increase the motion in the universe?’’ (Adam & Tannery, 1897–1913, Vol. v, p. 385). This reminds us of Sherrington’s dilemma: ‘‘Physics tells me that my arm cannot be bent without disturbing the sun. Physics tells me that unless my mind is energy it cannot disturb the sun. My mind then does not bend my arm. If it does, the theoretically impossible happens. Let me prefer to think the theoretically impossible does happen. Despite the theoretical I take it my mind does bend my arm, and that it disturbs the sun’’ (Sherrington, 1951, p. 258). Descartes, like Sherrington, believed that we live in a bounded universe containing a constant quantity of motion (in our terms mass/energy), yet the mind, res cogitans, has no physical dimensions. More received no satisfactory answer to his query. Soon after receiving his letter Descartes left for Stockholm and the court of Queen Christina and within 6 months had died from the pneumonia brought on by the freezing Swedish winter. Conclusion
Some have thought that the trial of Galileo caused Descartes to revise his neurophysiology. It depends on who we think was behind the mask. The neurophysiology of the Treatise seems fully consistent in its dreamy way (compare the ‘‘likely tale’’ of the Timaeus) with a materialistic dual-aspect identity theory of mind and body. The neuropsychology of the Passions, in allowing the rational soul an active and controlling role, supervenes upon this mechanistic vision. La Mettrie, in the next century, was not the only one to doubt Descartes’ intentions: ‘‘. . . (Descartes’) ‘real distinction’ be-
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tween mind and body,’’ he writes, ‘‘is a ruse which deceives only theologians’’ (La Mettrie, 1748). But this interpretation does not ultimately seem sustainable. La Mettrie, after all, had his own ax to grind. A reading of the whole of Descartes Oeuvre leaves little doubt that his intention was to support ecclesiastical authority. The Galilean contretemps must have seemed a catastrophe. In his withdrawal and reappraisal after 1633 we should rather see (I believe) prudence and a wish for a quiet life. Only at the insistence of Queen Christina in their early morning tutorials did he rummage in his trunk for Le Monde (Baillet, 1691). The complex, speculative, iatrohydraulics of his earthen machine can thus be seen as a ‘‘likely story’’ with which the nonspatial, immortal, ‘‘thinking substance’’ can (it is true rather shakily) be united. For Descartes, animals were conscious automata. They saw, heard, and ‘‘emoted’’ without ‘‘knowing’’ that they were so doing. Habitual commuters, long-distance lorry drivers, and, perhaps, patients with ‘‘blindsight’’ know that this is fully possible. It is thus, in spite of the common opinion, unCartesian to treat animals as unfeeling machines. The rational soul somehow grafted into the machine allows humans to go one step further: not only to know but also to ‘‘know that they know.’’ It also provides our introspective conviction of volitional freedom. Humans, in other words, differ from animals in being ‘‘self-conscious.’’ It was not, however, until Darwin that we began to have an inkling of how this phenomenon might be given a naturalistic explanation. References Adam, C., & Tannery, P. Eds. 1897–1913. Oeuvres de Descartes, Paris: L. Cerf. Aranzi, J. C. 1595. De humano foetu; anatomicarum observationum; etc. Carampellum; Venetis. Baillet, A. 1691. La vie de Monsieur Descartes. Paris: D. Horthemels. [Facsimile reprint, Geneva, 1970; trs. by S. R. London, 1693]. Bauhin, C. 1605/1621. Theatrum anatomicum. Frankfurt: Matthaei Bekeripp. Bitpol-Hesperies, A. 1990. Le principle de vie chez Descartes. Paris: Vrin. Cohen, I. B. 1972. in T. S. Hall, 1972. Treatise of Man, Cambridge, MA: Harvard Univ. Press. Pp. xiii–xiv. Crick, F. H. C. 1994. The astonishing hypothesis. London: Simon & Schuster. Crooke, H. 1631. Mikrosmographie: A description of the body of man. 2nd ed. London: T. and R. Cotes. Cottingham, J., Stoothoff, R., & Murdoch, D. 1984. The philosophical writings of Descartes. Cambridge, UK: Cambridge Univ. Press. Foster, M. 1970. Lectures on the history of physiology in the sixteenth, seventeenth and eighteenth centuries. New York: Dover. Hall, T. S. 1972. Treatise of man. Cambridge, MA: Harvard Univ. Press. Kenny, A. 1970. Descartes: Philosophical letters. Oxford: Clarendon.
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Kepler, J. 1604. Ad Vitellionem Paralipomena quibus Astronomiae pars optica Eraditur . . . : Francofurti. La Forge, L. 1664. L’homme de Rene´ Descartes et un traite´ de la formation du foetus du meˆme autheur. Paris: S. Jaques. La Mettrie, J. O. de. 1748. L’homme machine. Leyden. Marion, J.-L. 1981. Sur la the´ologie blanche de Descartes. Paris: Presses Univ. France. May, M. T. 1968. [trs. Galen] De usu partium: On the usefulness of the parts of the body. New York: Cornell Univ. Press. Mourant, J. A. 1979. The cogitos: Augustinian and Cartesian. Augustinian Studies, 10, 27– 42. O’Daley, G. 1987. Augustine’s philosophy of mind. London: Duckworth. Risner. 1572. Opticae thesaurus. Basel. Reisch, G. 1504. Margarita Philosophica. Basiliae. Rosenfield, L. G. 1968. From beast-machine to man-machine. New York. Octagon Books. Schiller, F. 1995. Pineal gland, perennial puzzle. Journal of the History of the Neurosciences, 4, 155–165. Sherrington, C. S. 1951. Man on his nature. Harmondsworth: Penguin. Singer, C. 1956. [trs. Galen] On anatomical procedures. London: Oxford Univ. Press. St. Augustine, De genesi ad litteram libri duodecim, Bibliotheque Augustinienne, Vol. 48, Paris: Descle´e de Brouwer, 1972. Vesalius, A. 1543. De humani corporis fabrica. Basiliae. [Facsimile reprint by Culture et Civilisation, Bruxelles, 1964] Wilson, C. 1989. Liebniz’s metaphysics. Manchester: Manchester Univ. Press.