G.J.C. Lokhorst & Timo T. Kaitaro. The originality of Descartes' theory about the pineal gland. Journal for the History of the Neurosciences, 10 (1): 6-18, 2001. ISSN 0964-704X.
Abstract. René Descartes thought that the pineal gland is the part of the body with which the soul is most immediately associated. Several prominent historians (such as Soury, Thorndike and Sherrington) have claimed that this idea was not very original. We re-examine the evidence and conclude that their assessment was wrong. We pay special attention to the thesis about the pineal gland which Jean Cousin defended in January, 1641.
René Descartes (1596-1650) maintained that the pineal gland is the part of the body with which the soul is most immediately associated. This theory is still widely known today. In this paper we will try to assess its originality.
Several historians of neurology have maintained that Descartes' theory was not very novel. The first one was Jules Soury, who claimed that "before Descartes, or at the same time as he, some of his contemporaries had already publicly defended the hypothesis which he eventually adopted" (Soury, 1899, vol. I, p. 374). Soury gave two references in support of this claim: first, a thesis defended by a certain Jean Cousin in 1641, according to which the pineal gland is the seat of the sensus communis, and second, Van Diemerbroeck's Anatomy of the human body of 1672, which states that many people were discussing the theory that the pineal gland is the seat of soul around that time. Béla Révész accepted Soury's verdict and said that Descartes' theory "was as it were in the air" when Descartes proposed it (Révész, 1917, p. 157). Pierre Mesnard (1937, pp. 210-211) later made a similar claim.
Half a century after Soury, Sir Charles Sherrington repeated Soury's conclusion and proposed two other precursors: Costa ben Luca (ca. 864-923 A.D.) and Jean Fernel (1497-1558). As Sherrington wrote,
the brain, despite its look of solidity, is a hollow organ; it has in it four large chambers containing watery fluid. Tradition regarded these as the reservoirs of the Galenical "spirits", which were generated at the base of the brain. The movement of the brain was taken to be the rhythmic charging of these reservoirs with "spirits". The fourth chamber, the hindmost, communicates with the three chambers in front by a narrow tunnel. The entrance to this tunnel is overhung by a small stalked gland. Certain anatomists taught that this gland acted as a valve controlling the passing of spirits backwards and forwards through the tunnel. Fernel himself took that view, describing how the expansion of the brain must raise the gland and free the passage, and the shrinking of the brain must allow the glandular valve to drop into place again and block the tunnel. The valve thus controlled the ebb and flow of spirits to the nerves of all parts. This view was not new. It existed already in the tenth century, in the Soul and Spirit of Costa ben Luca, latinized two centuries later by John of Spain, the physician who became Pope. The old tractate attributed the stooping habit of the head when thinking to an effect of that posture being to open the tunnel by lifting the valve. Descartes adopted this gland, and its traditional valvular action, as a key-structure for his scheme. It lay centrally in the brain, and a further supposition, current in Descartes' time, identified the gland with the "common sensorium" of Aristotle, making it a point of confluence of the animal spirits, coming hither and going thence in all directions. A control valve at such a meeting-place fitted the scheme which Descartes had in mind. (Sherrington, 1946, pp. 84-85.)
Sherrington based his account of Costa ben Luca's theory on a paraphrase given by Lynn Thorndike (1923-58, vol. I, p. 659) rather than Costa's own treatise, as is revealed by Sherrington's repetition of a mistake made by Thorndike: contrary to what Thorndike wrote, Costa associated thinking with a closed rather than an open valve, as we will see below.
Thorndike was of the same opinion as Sherrington, for he wrote that Descartes
repeated, without acknowledgement, Costa ben Luca's tenth century physiological explanation of thought as centring in the movement of the pineal gland. (Thorndike, 1953, p. 453; repeated in Thorndike, 1923-58, vol. VII, p. 555.)
In the present paper, we will argue that all these denials of originality on Descartes' part are wrong. Jean Cousin merely gave a summary of the ideas which Descartes had communicated to him, Van Diemerbroeck described the debate which took place after Descartes' views had been published, and both Costa ben Luca and Fernel were not referring to the pineal gland but to the vermis of the cerebellum.
We will also pay attention to a tenth-century theory that has so far been overlooked in this context. It is closer to Descartes' account than Costa ben Luca's theory, but there are nevertheless considerable differences.
In seventeenth-century France, the length of medical studies was from six to seven years. The examinations often consisted of theses defended before an audience of professors and students (Lebrun, 1995, p. 29). On Thursday, 24 January 1641, Jean Cousin defended such a thesis in the series of matutinal quodlibetal disputations of the École de médecine in Paris. The title of his thesis was An (Greek ->) kwna'rion (<- Greek) sensus communis sedes? (Is the pineal gland the seat of the sensus communis?) He gave an affirmative answer to this question: Ergo (Greek ->) kwna'rion (<- Greek) sensus communis sedes (Therefore the pineal gland is the seat of the sensus communis) (Cousin, 1641).
Not much is known about Jean Cousin. He is not mentioned in the large biographical dictionaries (Michaud et al., 1811-64; Hoefer, 1855-66; Bradley, 1987). In 1642, he defended two other theses, Theriac is a remedy for hypercatharsis (Cousin, 1642a) and Warm and moist food is good for the elderly (Cousin, 1642b). He may also have written a book (Cousin, 1673).
The poster which contained Cousin's thesis and announced its public defence has been preserved (Fig. 1). (See illustration at end.) Most of the thesis is nothing but a recapitulation of points made by Aristotle and Galen. The closing paragraph is, however, of interest.
Cerebrvm facultatum animalium sedes, meningibus & osseis muris vndiquaque munitum, frigidâ & humidâ temperie donatum fuit, pluribúsque distinctum partibus, quibus vt à se inuicem disjunctae sunt, insiderent. Inter illas glandula obseruatur (Greek ->) kwna'rion (<- Greek) appellata, velut centrum in medio ventriculorum sita, ad quam ex sensibus externis, quasi è circumferentia ductae lineae concurrunt; cúmque vnica sit, plexu choroide suffulta, elaboratis spiritibus semper turgens, in ea sola duae tùm oculis, tùm auribus exceptae species vniri possunt ac debent: (Greek ->) e)'sti me`n ga`r mi'a ai)'sqhsis, kai` to` ku'rion ai)sqhqh'rion e('n (<- Greek). Propterea malè Aristoteles sensum communem in corde, malè Arabes in anteriore cerebri parte, malè Metoposcopi in fronte & eius lineis positum voluêrunt.
The brain--the seat of the psychic faculties--is protected by membranes and bony walls on all sides, has a cold and moist temperament, and is divided into several parts, which reside in it as if they were not attached to each other. Among them one may observe a gland, called the pineal gland, which is situated like a centre in the middle of the ventricles, and which is the meeting point of threads coming from the external senses as if from the circumference; and because it is unique, supported by the choroid plexus and permanently inflated by the spirits which have been elaborated, it is only in this gland that the double appearances received by both the eyes and the ears can and must be united: "for there is one sense-faculty, and one paramount sense organ." Aristotle was therefore mistaken when he located the common sense in the heart, the Arabs were mistaken when they located it in the anterior part of the brain, and the Metoposcopists were mistaken when they located it in the forehead and its wrinkles.
Some clarification may be in order. First, both Aristotle and Galen viewed the brain as cold and moist. Second, the quote about the uniqueness of the faculty of perception and its paramount organ comes from Aristotle's On sleep (Bekker, 1831-70, 455a21). Third, Aristotle located the sensus communis in the heart in On sleep (Bekker, 1831-70, 456a1) and On youth (Bekker, 1831-70, 469a10). Fourth, "the Arabs" refers to Avicenna and his followers (Sudhoff, 1913). Fifth, "the Metoposcopists" refers to the adherents of the pseudo-science of metoposcopy or physiognomy, which was very popular in the sixteenth and seventeenth centuries (Thorndike, 1923-58, vols. V-VIII).
The remarks about the pineal gland are the most interesting ones from our point of view. Did Cousin think them up by himself? Or were they somehow inspired by Descartes' similar views from around the same time? In order to answer these questions, we turn to the correspondence between Descartes and the Parisian polymath Marin Mersenne (1588-1648).
As Berthier (1914, p. 70) and Souques (1938a; 1938b, p. 235) have pointed out, Descartes had already described his pineal gland hypothesis in several letters by the time Cousin defended it. However, they did not recognize the special role played by the letter which Descartes wrote to Mersenne on Monday, 24 December 1640, exactly a month before Cousin defended his thesis. This letter starts as follows:
I have received your letters only one or two hours before the Messenger has to return; this is the reason that I cannot punctually respond to everything this time. But because the difficulty which you propose for the pineal gland seems to be the most pressing one and because he who wants to defend in public what I have said about it in my Dioptrique does me so much honour that I am obliged to try to satisfy him, I do not want to wait to the next dispatch to say to you that, even though the pituitary gland has some similarity with the pineal gland in that it is situated, like the latter, between the carotids and on the straight line along which the spirits travel from the heart to the brain, one cannot infer from this that it has the same function, because it is not, like the other one, in the brain, but beneath it, and completely separated from its mass in a concavity of the sphenoid bone, which is expressly made to contain it, even under the dura mater, if I remember correctly; apart from this it is completely immobile, whereas we experience, when imagining, that the seat of the sensus communis, that is to say, the part of the brain in which the soul executes all of its principal operations, has to be mobile. Now, it is not surprising that this pituitary gland is to be found in the place where it is, between the heart and the pineal gland, because one finds a great quantity of small arteries in this place, which constitute the plexus mirabilis, and which by no means go all the way to the brain; for it is like a general rule throughout the body that there are glands wherever several branches of veins or arteries meet each other. And it is not surprising either that the carotids send several branches to that area; for these are needed to nourish the bones and the other parts, and also to separate the grossest parts of the blood from the most subtle ones, which are the only ones to ascend, through the straightest branches of these carotids, to the inside of the brain, where the pineal gland is located. And one should not assume that this separation takes place in any other than a purely mechanical manner, just as, when reeds and foam float on a stream which divides itself somewhere in two branches, one will see that all these reeds and this foam will go to the branch where the water travels in the least straight line. Now, it is with good reason that the pineal gland is similar to a gland, since it is the primary function of the glands to receive the most subtle portions of the blood which are exhaled from the vessels which surround them, while it has the primary function to receive the psychic spirits in the same way. And since it is the only solid part of the whole brain which is unique, it is necessary that it is the seat of the sensus communis, that is to say, that of thought, and as a consequence that of the soul; for the one cannot be separated from the other. Otherwise one would have to admit that the soul is not immediately united with any solid part of the body, but only with the psychic spirits which are in the concavities, and which continually enter and leave them like the water of a river, which would be too absurd. Besides this, the position of the pineal gland is such that one may very well understand how the images which come from the two eyes, or the sounds which enter through the two ears, and so on, have to be combined at the place where it is: which they would not be able to do in the concavities, unless it were in the middle one, or in the passage above which the pineal gland is located, which would, however, not suffice, because these concavities are not at all different from the others where the images are necessarily double. If I can do anything else for him who has proposed this to you, I beg you to assure him that I would very gladly do whatever I can to satisfy him. (Descartes, 1640d.)
The passage in the Dioptrique (Descartes, 1637) to which Descartes refers is very short. It only says that each eye projects an image onto the wall of "the concavities of the brain" which may "then be followed to a small gland, which is located approximately in the middle of those concavities, and is in fact the seat of the sensus communis" (Adam & Tannery, 1964-74, vol. VI, p. 129). Descartes was hardly more explicit in his Meditations, which appeared in August 1641 (Descartes, 1641c): "the mind is not immediately affected by all parts of the body but only by the brain, particularly by one very small part of it, namely that in which the sensus communis is said to reside" (Adam & Tannery, 1964-74, vol. VII, p. 86). It was not until 1649 that he published a detailed description of his pineal gland theory (Descartes, 1649).
When we compare Cousin's thesis with Descartes' letter, it immediately becomes clear that the passage about the pineal gland in Cousin's thesis is nothing but a summary of the views expressed by Descartes. All of Cousin's statements about the pineal gland are to be found in Descartes' letter, and Cousin did not add any original claim of his own.
Was Descartes Cousin's immediate source? We think there can be no doubt about this. In the second sentence of the letter, Descartes refers to someone "who wants to defend in public what I have said about it in my Dioptrique." At the end of quoted passage, he describes him as the person "who has proposed this to you." To whom does this refer? De Waard did not know (Tannery & de Waard, 1932-88, vol. X, p. 341, n. 1). Bitbol-Hespéries (1993, p. 49, n. 14) suggested that Mersenne himself was uncertain whether Descartes was referring to the pineal gland. But this is unlikely because, by December 1640, Mersenne had already received five letters in which this had been pointed out (Descartes, 1640a, 1640b, 1640c; Villiers, 1640; Meyssonnier, 1640). Furthermore, Descartes refers to "him who has proposed this to you." He would not have done so if Mersenne was putting forward his own question. The solution is very simple: Descartes was referring to Jean Cousin.
If this is correct, the course of events was as follows. Cousin read the Dioptrique (or heard about its contents), wondered whether Descartes was referring to the pineal gland or the pituitary gland, and decided to ask Descartes himself through Mersenne. Descartes gave an answer that was probably more detailed than Cousin had expected, and Cousin then gratefully used this for the preparation of his thesis.
How did Cousin's audience react? We have reason to think that Mersenne wrote a letter about this to Descartes. But Descartes never received this letter and it seems to have been lost. On Monday, 4 March 1641 (less than forty days after Cousin defended his thesis), Descartes wrote to Mersenne:
I have received letters from you in the last two deliveries, but it nevertheless seems to me that you have sent me more than I have received, for in the letter which arrived eight hours ago, you ask me whether I have seen the objections which have been made in the dispute about the pineal gland [la dispute du conarium], which I have, however, not seen in any way. (Descartes, 1641a.)
On 21 April 1641, Descartes made the same point:
The letter in which you have previously described the Objections about the pineal gland for me must have been lost, if you have not forgotten to write them down; for I do not have them, apart from what you have since written about this to me, namely that no nerve goes to the pineal gland and that it is too mobile to be the seat of the sensus communis. (Descartes, 1641b.)
De Waard did not know to which dispute Descartes was referring in these letters (Tannery & de Waard, 1932-88, vol. X, p. 523, nn. 1-2, and vol. X, p. 585, n. 2). Berthier (1914, p. 70, n. 2) thought that the letter of 4 March 1641 referred to several disputes, but it clearly refers to only one. Which dispute could this be? There is only one candidate: the dispute about Cousin's thesis on 24 January 1641.
In support of their claim that Descartes was not the first or only one to defend the view that the pineal gland is the principal seat of the soul, Soury (1899, vol. I, p. 373) and Révész (1917, p. 157) referred not only to Cousin, but also to the Utrecht professor Ysbrand van Diemerbroeck (1609-1674). This reference, however, is less interesting than the reference to Cousin. Van Diemerbroeck wrote:
Opinions vary as to the function of this gland. Some believe that it serves to secure the choroid plexus. Others say, with Galen, that it functions as a valve which closes the foramen of the canal between the third and the fourth ventricle. Others enclose the Soul itself in its confines, as in a capsule (perhaps so that it does not stray too far away into the infinite nooks and crannies of the whole microcosm, and sometimes forgets its whereabouts and then can no longer find its way home when the need arises); and these think that in this gland, which is as it were located in the centre of the brain, the ideas supplied by the five senses are combined, apprehended and discerned, and that from here even the psychic spirits are sent to definite parts through these or those nerves: the latter opinion is vigorously defended by some and strongly attacked by others. (Van Diemerbroeck, 1672, p. 592.)
He then discussed the opinions of Descartes (1649), Regius (1657) and La Forge (Descartes, 1664), who defended the latter view, as well as those of Le Boë Sylvius (1663) and Wharton (1656), who rejected it. He drew the following conclusion:
And so the problem of the function of this gland is still undecided. Everybody may have his own opinion, but I think that its function is rather unknown and obscure and that nothing can be stated about it except by mere conjecture on the basis of uncertain arguments, and I therefore think that everybody's ingenious speculations about this matter are praiseworthy but that it is not necessary to accept them as the sacred gospel or the articles of faith. (Van Diemerbroeck, 1672, p. 593.)
Three points may be made in connection with Van Diemerbroeck's discussion.
First, Van Diemerbroeck described the debate which followed the publication of The passions of the soul (Descartes, 1649). He did not refer to contemporaries of Descartes who had independently proposed the same views. His book therefore offers no support for Soury's and Révész's claim that Descartes' theory was already "in the air" when Descartes proposed it.
Second, there were many more critics of Descartes' theory than Van Diemerbroeck indicated. The most important critics were Bartholinus (1651) (who was in his turn La Forge's main target), More (1653, 1659), Willis (1664) and Steensen (1669). This widespread opposition to Descartes' theory, which even began when he was still alive (Villiers, 1640; Meyssonnier, 1640; Digby, 1644), again shows that his theory was not "in the air" when he proposed it.
Third, Van Diemerbroeck's remark about Galen is incorrect. Galen had emphatically denied that the pineal gland acts as a valve, as we will now see, leaving the seventeenth century and going back some fourteen centuries in time.
In Galen's (129-ca. 210 A.D.) On the usefulness of the parts of the body we find the following passage about the function of the pineal gland:
I believe that this gland resembling a pine cone and filling up the bifurcation of the large vein [v. cerebri magna (Galeni)] from which nearly all the choroid plexuses of the anterior ventricles arise was formed for the same usefulness as other glands that support veins as they divide. Indeed, its position is the same in every respect as that of such glands, for its apex is firmly established at those parts of the vein where it first divides [beneath the splenium of the corpus callosum]; all the rest of it increases in size to correspond with the distance between the vessels [vv. cerebri internae, veins of Galen] resulting from the division; and it proceeds as far as the vessels extend in a suspended condition. As soon as these veins pass onto the body of the encephalon itself [at the posterior boundary of the third ventricle], the pineal body abandons them, and the body of the encephalon in this region becomes a support for both the pineal body itself and the veins.
The notion that the pineal body is what regulates the passage of the pneuma is the opinion of those who are ignorant of the action of the vermiform epiphysis [vermis superior cerebelli] and who give more than due credit to this gland. Now if the pineal body were a part of the encephalon itself, as the pylorus is part of the stomach, its favourable location would enable it alternately to open and close the canal because it would move in harmony with the contractions and expansions of the encephalon. Since this gland, however, is by no means a part of the encephalon and is attached not to the inside but to the outside of the ventricle, how could it, having no motion of its own, have so great an effect on the canal? But perhaps some one will say, "What is to prevent it from having a motion of its own?" What, indeed, other than that if it had, the gland on account of its faculty and worth would have been assigned to us as an encephalon, and the encephalon itself would be only a body divided by many canals and would be like an instrument that was suited to be of service to a part formed by Nature to move and capable of doing so? Why need I mention how ignorant and stupid these opinions are? For this part, which people imagine must be a part of the encephalon itself near the canal, this part which must be such as to control and govern the passage of the pneuma and which they cannot discover, is not the pineal body but the epiphysis [vermis superior cerebelli] that is very like a worm and is extended along the whole canal. (Book VIII, ch. 14; May, 1968, vol. I, pp. 419-420.)
Thus, Galen regarded the pineal gland as a support for the blood vessels in its neighbourhood. This idea was widely accepted until the eighteenth century. Even Vesalius (1543, p. 638) did not object to it.
The idea that the vermis regulates the flow of spirit in the "canal" between the third and fourth ventricles was also accepted for a very long time. It fell out of favour after Vesalius (1543, p. 216, p. 639) had rejected it.
Galen unfortunately did not mention the names of those who where so stupid as to regard the pineal gland as a valve. There is one book from around the same time which mentions the pineal gland and the flow of spirit in its neighbourhood, namely The refutation of all heresies by Saint Hippolytus of Rome (ca. 170-235 A.D.), the first Anti-Pope. But in this book, the pineal gland seems to play a purely passive role.
...the brain, on being dissected, has within it what may be called a vaulted chamber. And on either side of this are thin membranes, which they term little wings. Now these are gently moved by the spirit, and in turn propel towards the cerebellum the spirit, which, careering through a certain blood-vessel like a reed, advances towards the pineal gland [epi to kônarion]. And near this is situated the entrance of the cerebellum, which admits the current of spirit, and distributes it into what is styled the spinal marrow. But from them the whole frame participates in the spiritual energy, inasmuch as all the arteries, like a branch, are fastened on from this blood-vessel, the extremity of which terminates in the genital blood-vessels, whence all the (animal) seeds proceeding from the brain through the loin are secreted (in the seminal glands). The form, however, of the cerebellum is like the head of a serpent, respecting which a lengthened discussion is maintained by the professors of knowledge, falsely so named, as we shall prove. (Book IV, ch. 51; Marcovich, 1986, p. 139; translation from Roberts & Donaldson, 1885-96, vol. V, p. 46; a mistake in the translation has been corrected.)
...For a proof of this, they adduce the anatomy of the brain, assimilating, from the fact of its immobility, the brain itself to the Father, and the cerebellum to the Son, because of its being moved and being of the form of (the head of) a serpent. And they allege that this (cerebellum), by an ineffable and inscrutable process, attracts through the pineal gland [dia tou kônariou] the spiritual and life-giving substance emanating from the vaulted chamber. And on receiving this, the cerebellum in an ineffable manner imparts the ideas, just as the Son does, to matter; or, in other words, the seeds and the genera of the things produced according to the flesh flow along into the spinal marrow. (Book V, ch. 12; Marcovich, 1986, p. 187; translation from Roberts & Donaldson, 1885-96, vol. V, p. 64; a misleading comment has been omitted.)
These passages are not only interesting because of their references to the pineal gland, but also because they tell us something about the context in which the Christian doctrines about the Holy Spirit (to hagion pneuma) and the Blessed Trinity took shape.
The Christian Syrian physician and philosopher Costa ben Luca (ca. 864-923 A.D.)--the author to whom Sherrington and Thorndike referred, as we have seen in the Introduction--was one of the many people who accepted Galen's theory about the regulatory function of the vermis. In his On the difference between spirit and the soul, which was extraordinarily influential (Wilcox, 1985), he combined this theory with the ventricular localization theory proposed by Posidonius of Byzantium (Olivieri, 1950, book 6, ch. 2, p. 125) and Bishop Nemesius of Emesa (Morani, 1987, chs. 6, 8, 11-13, 27) around 400 A.D. In this way he arrived at the following view about the role of the vermis in thinking and recollection.
The brain is divided into two parts, an anterior part, which is the larger one, and a posterior part. In the anterior part there are two ventricles which have an entrance to a common space in the middle of the brain. In the posterior part however there is one ventricle which is connected with the just-mentioned space which is common to both ventricles in the anterior part of the brain. When the delicate pulses sent from the net below the brain [i.e., the rete mirabile] arrive in the interior of the brain, they propel the vital spirit to the ventricle in the anterior part, and from there it travels to the other ventricle where it becomes finer and is purged and prepared to receive the power of the soul, which as it were digests it and converts it into a finer and clearer spirit. From there it travels, passing from one space into the other, to the posterior ventricle, following the canal from the common space in the middle of the brain to that ventricle.
And in this passage and canal, that is, in this entrance, traversed by the spirit, there is a certain space and a certain small part of the substance of the brain, similar to a worm, which moves upwards and downwards in its path. When this small part is in its top position, the foramen between the common space which connects the ventricles (on the one hand) and the ventricle in the posterior part of the brain (on the other) is open; but when it is down, the foramen is closed. When the foramen is open the spirit goes from the anterior part of the brain to the posterior part, but this does not occur unless it is necessary to remember something which has passed into oblivion, at a time when one is thinking about the past. If the foramen is not open, however, there is no flow of spirit to the posterior part of the brain and the person does not remember and will not respond to the questions he is asked. This opening of the foramen which occurs when that body which resembles a worm is raised, differs in quickness and slowness between people. For it is slower in some, which causes a slow memory and slow responses in those who have to think hard. This also explains why someone who wants to remember something lifts his head and tilts it backwards and looks upwards with staring eyes, because this position or posture facilitates the opening of the just-mentioned foramen and the upward motion of the worm-like body.
Understanding and thinking and looking ahead and cognition are however mediated by the spirit which is in the ventricle which forms part of the two ventricles which are in the anterior part of the brain. When somebody thinks or foresees something, it is necessary that the canal--that is, the route and the foramen--between the common space which connects the two ventricles in the anterior part of the head (on the one hand) and the ventricle in its posterior part (on the other) is closed; in this way the spirit in the common space can rest, become stronger and increase its power to think and understand. This explains why someone who thinks bends his head towards the earth and watches it intently and stoops forward, as if he were writing some document and drawing some figures on it, because this as it were facilitates the downward motion of that body which we have described as being similar to a small worm, and which is positioned above the foramen through which the spirit passes on its route towards the posterior parts of the head.
The spirit in this space in the middle ventricle differs between people. It is subtle and clear in some, and these people are rational, of a thoughtful disposition and intelligent. But in some people it has a bad quality, and these are insane, irrational, shallow and stupid. (Barach, 1878, pp. 124-127.)
Costa ben Luca's theory is illustrated in Fig. 2. (See illustration at end.)
Costa ben Luca made it very clear that he was talking about the vermis of the cerebellum, not the pineal gland. Thus, Sherrington's and Thorndike's claim that Descartes "repeated, without acknowledgement, Costa ben Luca's tenth century physiological explanation of thought as centring in the movement of the pineal gland" is false. They made the same mistake with respect to Costa ben Luca as Van Diemerbroeck did with respect to Galen.
Van Diemerboeck was not the first author who confused the vermis with the pineal gland. In his Treatise on forgetfulness and its treatment, Ibn al-Jazzar (ca. 900-980 A.D.) applied Costa ben Luca's theory to the pineal gland, with the result that he described this gland as playing a role in recollection.
The excellent doctors agree that the activities of the intellect are threefold: imagination, thought and memory; that the brain consists of two parts: anterior and posterior; and that the anterior part consists of two parts, each of which is more sizable in general than the posterior part. The doctors further agree that, since the anterior part corresponds to the posterior and since it is necessary that both parts of the anterior are connected with the posterior, both anterior chambers open into another part, namely, a common vacuum.
Some anatomists call this place the fourth ventricle and (say that) the two anterior chambers produce and distribute the air, and prepare from it the psychical pneuma for the brain, which causes the sensations of sight, hearing, smell, taste and touch, and additionally causes the imagination. (They go on to say that) the two anterior chambers open into a common vacuum in the middle of the brain. Here the psychical pneuma penetrates and becomes finer, subtler and purer than in the anterior part of the brain. Thus, here we have the source of thought, understanding, reflection, discrimination and intelligence. Then that pneuma penetrates into the posterior ventricle of the brain, where it causes recollection, retention and voluntary movement.
Proclus states that the posterior ventricle is the noblest ventricle of the brain, since the psychical pneuma reaches it only after it has become fine and subtle, for recollection and retention need a high degree of fineness and subtleness to remember things past and gone.
Near the beginning of the protuberance between the middle and posterior ventricles, a brain-fragment is situated resembling a worm, named by the anatomists the pineal (gland). This gland moves up and down the passage; when it moves up, the hole between the common roof of the ventricles and the passage is opened, but when it moves down, the hole is closed. When the worm-like fragment opens the hole, the psychical pneuma passes from the anterior to the posterior part of the brain. But this happens only when trying to remember things forgotten or thinking about the past. If, however, this passage is not opened and the pneuma thus fails to reach the posterior part of the brain, one cannot remember anything, and the answer to what one was asked does not come to one's mind. The pineal form is situated at the beginning of the passage which brings the psychical pneuma from the middle to the posterior ventricle of the brain where it collects, deposits, preserves and distributes the amount of pneuma which penetrates that passage. For this reason, as regards the opening of this passage, there are differences between people, for instance, in speed and slowness; with some people it goes fast and because of that these people are sharp-witted and quick at repartee. However, in other people it goes slowly, and therefore they remember and answer slowly and need to think for a long time. (Bos, 1995, pp. 37-38.)
Ibn al-Jazzar's treatise was translated into Latin in the eleventh century (Bos, 1994; Burnett, 1994). This translation was published in 1515 (Constantine the African, 1515), so Descartes could, in principle, have read it, but there is no evidence that he did.
Although Descartes' theory is reminiscent of that of Ibn al-Jazzar (and certainly closer to the latter than to Costa ben Luca's account), there are considerable differences. First, Descartes did not regard the pineal gland as a valve which could open or close the canal between the third and fourth ventricles: he thought that it made small movements in all directions. Second, Descartes did not think that the pineal gland is only involved in recollection: he thought that it plays an important role in connection with all psychic faculties. Third, Descartes did not think that all psychic faculties are primarily associated with the spirit in the ventricles: he thought that they are primarily associated with the pineal gland. Fourth, Descartes did not think that physical memory traces are located in the spirit in the ventricles: he located them in the substance of the brain. Fifth, Ibn al-Jazzar did not explain why he modified Costa ben Luca's theory and let the pineal gland rather than the vermis play the role of a valve. But Descartes did explain his preference for the gland:
Because our soul is not double but simple and indivisible, it seems to me that the part of the body with which it is most immediately united must also be simple and not divided into two similar parts, and I find nothing of the sort in the whole brain except this gland. For as to the Cerebellum, it is only simple as far as its surface and name are concerned; and it is certain that even its vermiform appendage, which resembles a simple body to the greatest extent, is divisible into two halves. (Descartes, 1640c.)
This desire to associate the soul with a single point of the body was unprecedented. Before Descartes, the soul had always been associated with extended areas of the body, either in the head or elsewhere.
As an aside, we may note that the vermis was not only confused with the pineal gland, but also with the choroid plexus in the passage between the lateral ventricles and the third ventricle. Mondino dei Luzzi made this mistake in his Anothomia of 1316 (Wickersheimer, 1926, p. 43). Since this was the standard textbook of anatomy until Vesalius' Fabrica appeared in print, it is this theory which is represented in most drawings and engravings of the brain made between 1316 and 1543 (Clarke & Dewhurst, 1972, ch. 2).
Finally, let us consider Jean Fernel (1497-1558). As we have seen in the Introduction, Sherrington wrote that Fernel described "how the expansion of the brain must raise the gland and free the passage, and the shrinking of the brain must allow the glandular valve to drop into place again and block the tunnel." But Sherrington made the same mistake here as in his description of Costa ben Luca's views.
Fernel did not regard the pineal gland as a valve which opens and closes the canal between the third and fourth ventricles: he ascribed this function to the vermis. He regarded the pineal gland as a support for the blood vessels in its neighbourhood. Moreover, he thought that the vermis moves of its own accord; he did not say that it merely follows the "expansion and shrinking of the brain." His account was therefore hardly different from Galen's (Fernel, 1581, vol. I, Physiologia, lib. I, cap. IX, pp. 52-53).
Sherrington's mistake was repeated by Grüsser (1990, p. 82), who wrote that "Fernel gave the pineal gland the function of a valve which controls the flow of spiritus animalis from the third to the fourth cerebral ventricle."
Was there anyone in the sixteenth or the seventeenth century who defended the theory which Sherrington and Grüsser ascribed to Fernel? This is unlikely, because such a theory would have flown into the face of everything that Galen and Vesalius had taught. Van Diemerbroeck (1672, p. 592) and Bitbol-Hespéries (Descartes, 1996, pp. 197-198) have made the opposite suggestion. But the former gave not a single reference, while the latter mentioned only authors who either followed Galen (Dubois, 1555; Du Laurens, 1600; Bauhin, 1605, 1621) or did not say a word about the pineal gland (Fracastoro, 1555, fol. 203r-205v). So it cannot be said that they have presented their case in a convincing manner.
The attempts of Soury, Révész, Sherrington, Thorndike and others to cast doubt on the originality of Descartes' pineal gland theory have failed. Furthermore, we have not found any anticipation of this theory which they overlooked. We therefore want to propose the hypothesis that Descartes' theory that the soul is primarily associated with the pineal gland is more original than is usually supposed.
The authors are grateful to Dr Han van Ruler (Erasmus University Rotterdam) for his useful advice.
Fig. 1. Announcement of the disputation about Jean Cousin's question whether the pineal gland is the seat of the sensus communis (Paris, Thursday 24 January 1641). Photograph provided by the Bibliothèque Nationale, Paris. Reprinted with permission.
Fig. 2. Costa ben Luca's theory. Memories are stored in the fourth ventricle. The vermis acts as a valve. Recollection can only occur when the head is raised and the valve is open (left). Stooping the head closes the valve and makes concentrated thinking possible (right). The pineal gland plays no role in this theory.
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