Some of the nerves that descend from the brain cross over on their way to the body

335. In the foregoing two chapters we have made a slight acquaintance with the anatomy and functions of some few parts of the brain. A little more knowledge will enable us to think from correspondences about good and truth and the way these are represented by the right and left sides of the body and brain. Although we are given correspondences of parts of the body on the right and on the left, the chief concern is with the brain and nerves since life descends to the body through them. Some parts of the brain are more obviously separated into right and left halves than are others. In particular, the cerebrum is very deeply divided and the cerebellum has well marked right and left sides. The brain-stem, to which these parts are joined, is not so clearly divided. The cerebrum and cerebellum both have bands of fibres which connect one side to the other, besides the fibres that run down towards the body. The fibres that run down into the body are often in bands that are decussate (which means
X-shaped or intersecting). In anatomy, the word is used to describe the crossing-over of nerves or tracts of nerves from one side of the head or body to the other at a lower level. The most outstanding example is entitled "The Decussation of the Pyramids" and has no reference whatsoever to Egypt! (The pyramids are tracts of nerves in the medulla oblongata. They are wider at one end than at the other and this is the only way they resemble pyramids.) See Figure 19 which shows the decussation of the pyramids.

336. The decussation of the pyramids is responsible for the commonly observed fact that injuries to one side of the head often cause paralysis on the opposite side of the body. The connections have been known for a considerable time. Swedenborg refers to them in the Spiritual Diary.


The Decussations

       Decussation of the Pyramids. Scheme of the brain in coronal section at the level of the brain stem and major cortex, showing the crossover of nerve fibres in the medulla oblongata. The cut passes from the top downwards. Hence the intercerebral cleft can be seen. The section is not quite vertical, being farther forward at the top. The fibers descend from the cortex through the internal capsule, the cerebral peduncle, and the pons. The pyramids are medullary structures composed of bundles of these fibers, of which the majority (70-90%) cross over before the junction of the medulla and spinal cord.

Sources: Gardner, Fundamentals of Neurology, figs. 10-6, 7-15;
Anthony and Kolthoff, Textbook of Anatomy and Physiology, fig. 8-22; Clemente, Gray's Anatomy, Classic Collectors Edition, fig. 369.


An observation on decussation was made with the help of spirits

337. We read in the Spiritual Diary, "The contents of the left side of the brain correspond to the right portion of the body." We also read that when spirits acted on the left side of the brain Swedenborg felt sensations as if from the right nostril and the palm of the right hand (SD 1666). This is specially interesting because, although nerves to the arms and hands pass through the medulla oblongata where they usually cross over, the nerves to the nostrils (not the olfactory nerves) follow a direct route through the base of the skull. The neuron bodies of the sensory nerves are outside the brain and they send their axons (see No. 271) to groups of other neurons in the brain. These groups have fibres that connect them to the cerebral cortex (where consciousness is thought to reside). The connection is usually with the cerebral hemisphere of the opposite side, that is to say, the connecting fibres within the brain are decussate. The mapping of nerve tracts within the brain to produce this kind of
information is comparatively recent.
    As Swedenborg also moved his hand "from some unknown cause," we presume that both afferent and efferent nerve tracts, or rather their terminals in the brain, were activated. Although there are relays in the spinal cord and plexuses where nerve tracts branch and rejoin, none of these structures causes a crossing over from left to right.

A brief entry in the Spiritual Diary may lead to a misunderstanding of the correspondences

338. From AC 5725 we learn that an inundation of lusts "belongs to the will part, and is on the right side of the brain; but that of falsities belongs to the intellectual part and is on the left side of the brain." We also find, "the left side of the brain corresponds to rational or intellectual things, but the right to the affections or things of the will" (AC 3884). Thus, clearly, the right side of the brain is the home not, be it noted, of the will per se but of "things of the will" or affections. It will be well to adopt this as a general but quite firm statement of primary importance.

339. It had been thought (Berridge, 1981, p. 35; Worcester, 1889, p. 422) that the entry in SD 1667 (quoted below) is at variance with this teaching from the Arcana (quoted just above). It is necessary to examine the supposed discrepancy. Spirits from Jupiter said that the intellectual principle was on the right side of the cerebrum, etc. This is not stating that the right cerebral hemisphere is the home of the intellect, but merely that there is an "intellectual principle" there. As will be seen below (No. 352), principles of good, which are dominant in the right hemisphere, do not preclude truth and understanding. Indeed it is made clear in many places that celestial angels understand truth very well. However, the entry in the Spiritual Diary (n. 1667) continues, "[From this it is to be inferred] that the right part of the brain is the seat of the intellectuals, and the left of affections." The square brackets indicate a suggestion by the translator which gives the impression that Swedenborg was still in the process of learning. An earlier passage (SD 1027) is similar, but includes the words, "I was told." One may thus incline to the belief that these ideas were tentatively held, but further study will show that it is not really necessary to adopt such an opinion. Indeed, these sources differ only when we misunderstand them by instituting a divorce between intellect and will or between faith and love.

Decussation is accepted in the Spiritual Diary but ignored in parts of Arcana Coelestia

340. The passages in the SD considered just above include a reference to a decussation of the optic nerves and suggest from that a similar crossing over between the brain and the whole body. The eyes, however, constitute a special case which will be considered in a later chapter (Nos. 368 and 369). For the present we note that a general decussation is assumed or deduced in SD but it appears to be denied in parts of AC. We have noted above that the right side of the brain corresponds to things of the will and we find (AC 9556) that "by the things which are in the right side of the body are signified goods" (which are of course things of the will). Also "those things which are on the right side of the man correspond to celestial good" (AC 9511) which must be of love or the will. Thus a crossing over between the brain and the rest of the body including the eyes is envisaged in the Diary but not in these parts of AC. In AC 1270, however, a decussation is clearly indicated, for
antediluvian spirits were allowed to flow into the right side of Swedenborg's head, "and from the right side of the head into the left side of the chest." We have, therefore, some passages for, and some against decussation; but we know that it does occur and it is instructive to find out why it is sometimes ignored. To do this we consider first what some other parts of the Writings say about the right and left hands and sides of the body.

The correspondences of right and left sides are complex

341. For the sake of clarity we begin with the right side only and select simple statements. One such statement is that the right hand or right side denotes good. For example, "by the right is signified good" (AE 600:8). Similarly, the right hand signifies everything pertaining to the will and affection thence. Even the right eye has connections with good, as explained here (AE 600:8), although the eye signifies everything pertaining to the understanding and thought therefrom. However, if good is to be anything, it requires truth as a means to its ends; thus it produces, or finds, or gives life to truth. It follows that the good which is denoted by the right or the right hand is good from which is truth, as follows: "All those things in man which belong to his right side have reference to good from which is truth" (AE 1120:2, similarly AC 9604, 10061).

342. These meanings are in obvious agreement, but as one continues the study, apparent discrepancies occur. For example, we read in AE 336:6 that the right hand signifies the truth of good (rather than good from which is truth). Many other examples are given in AE 600 where one may find also the explanations that are necessary to harmonize truths that look different at first sight. But in spite of the explanations some readers might feel that the significations are distressingly different. We find, for example, that only just over half the references given in AE 600 are in obvious agreement with what we have already learned, i.e., that the right signifies good from which is truth.

343. Some of the other meanings of right are as follows:

1.     the south in the spiritual world (from which other meanings are derived),
2.     the clear light of truth from good (AE 600:9) (this is notable because the left often corresponds to truth from good),
3.     truth in light,
4.     the good of charity and of faith therefrom (rather than good of charity from which is faith),
5.     truth of the understanding (because in this case it is "the eye of his right side"), and
6.     Divine Truth in light, intelligence, and thence power.

344. In AE 600 there is clearly a majority of references where right signifies good, usually good from which is truth. But correspondences and the significations of passages in the Word may not be counted in natural numbers, nor balanced one against another for they form a harmonious whole. So if disagreements appear, though they be only apparent and few in number they are like discords in music. One cannot enjoy them until they are resolved.

345. It will be clear from a perusal of the whole of AE 600 that each individual item that appears at first to be in discord is reconciled with the main theme by means of suitable related truths; thereby, the rational mind can assent to them and enjoy a great increase in enlightenment. However, although the rational might be convinced, the mind as a whole might still not see the subject clearly and be able to confirm it to the extent of faith. Such a mental state has been mentioned in DLW 405, where confirmation is given by thinking from correspondences; in that case, correspondences with the heart and lungs. Here we will make bold to consider a few more details about the central nervous system in the hope of enabling the mind to see the spiritual teaching more clearly.

The anatomy of the brain illustrates the relationship between the right and left sides and shows how complex it is

346. A little information about brain cells, especially neurons, has already been given (no. 271). To this we now add the following. The neuron bodies are massed on the outer surfaces of the cerebrum and cerebellum forming the grey (or cineritious) matter, and most of the axons and dendrites are within, forming the white matter. This, however, is only a very general description. There are, in addition, various other neurons that are organized into groups or nuclei with specific purposes, often connected with the control of the body. These groups are also part of the grey matter. Between them is white matter consisting of their own very numerous fibres, forming a communication system between different nuclei and between nuclei and the cortex. There are also regions where grey and white matter, that is, neuron bodies and connecting fibres, are mixed in what seems to be a random fashion. The complexity of the system has already been mentioned but it is especially noticeable when the
decussations are studied.

347. If the student of anatomy wishes to know whether the right eye communicates with the left hemisphere as indicated in SD 1667, or with the right as deducible from AC 9511 and 9556, he finds that it communicates with both (see no. 369). If he turns his attention to the ear he finds at least four sites in the brain where nerve impulses may be passed on to either or both sides. When he comes to consider the body, the right hand, for example, he finds a massive crossing-over of nerves from the left cerebrum to the right side of the spinal chord (the decussation of the pyramids). But when he looks at the detail he finds that in most individuals more than thirty percent of the nerves do not cross over (but in some cases the proportion may sink to ten percent). Still he has problems because, throughout the spinal chord itself there are bands of nerves which provide communication between opposite sides. Nor has he finished yet, because in the brain there are, as already mentioned, many
regions consisting of a more diffusely ordered mixture of white and grey matter having the appearance of a network. It is hence called the reticular formation. This formation is closely associated functionally with the more distinct parts and its interest for us at present is that within it the nerve pathways form many junctions. These include ascending (i.e., towards the cerebrum) and descending components, some of which cross over to the opposite side (decussate) while others make connections on the same side. The reticular formation receives convergent information from all principal parts of the nervous system and projects directly or indirectly back to all these regions including the cerebral cortex.

348. There are also various other nerve tracts in the brain which connect one side with the other. An example is the Corpus Callosum which connects the cerebral hemispheres, although this is not a decussation but a connection at the same level.

349. These facts of anatomy indicate that what happens on one side of the brain can usually only be partially separated from the other side. Though one side may be dominant, it is still one brain, for a vast number of parts of one hemisphere are connected to parts of the other. So many parts of one hemisphere are in mediate or immediate connection with one another that it is difficult to think that any significant portion of the brain cannot be reciprocally connected with a part on the opposite side. Thus, although what is on the right is certainly different and distinguishable from what is on the left, the connections are so multifarious that an activation of parts on the right may in some cases lead to greater activity on the left, and what is really right may seem like left. The situation is not actually confused; the brain works wonderfully well, but it is so complex that the student may become confused.

The unity in diversity of the brain illustrates the marriage of love and wisdom or of good and truth

350. The anatomy of the brain suggests by correspondence that there is no type or kind of genuine good which cannot be reciprocally connected with a suitable truth; nor can such good avoid activating truth. The anatomical facts thus emphasize the closeness of the union between truth and good. We have seen how nerve impulses occurring on one side of the body or brain may be radiated to the other side, or perhaps even pass from side to side and back on their journeys between various centres of the brain, and on their way from the brain to the body. Retaining the simple notion of the right side being good and the left truth we can now see how, in the living soul, and in Heaven or the Grand Man, good or love radiates itself to innumerable connected truths. These truths, in turn, can reflect back into good at the same or at a lower or even a higher level. We can also see that all the living truths and goods are more or less directly connected with each other and organized into a whole
by means of these connections. So it is that whether you start from good, (the right) or truth (the left), the whole man is activated as to both. So it is also that a rigid mechanical division between good and truth is no more possible than a complete dissociation of each side of the body-brain unit.

The apparently variable correspondences of right and left reflect the true situation

351. Looking back upon the significations of right and left mentioned earlier, one may perhaps feel that their apparently contradictory nature is dispelled by their true internal harmony, so much so that the following thoughts occur: How could any man of Sweden-borg's standing have had the audacity to present such an apparently variable and inconsistent interpretation had he not been instructed by the Lord by means of experience? And further, how privileged we are now to have confirmation by scientific knowledge. We can now see that it is only the apparently inconsistent interpretation that corresponds to the facts of anatomy.

Correspondences of the brain suggest four angelic categories related to two ways of receiving good and two ways of receiving truth

352. Having studied the correspondences so far we now return to the Writings and find the following in AC 4052:

that those [in the Grand Man] who are in the first principles or beginnings of good have relation to those things in the brain that are the beginnings and are called the glands or cortical substances; whereas they who are in the first principles of truth relate to those things in the brains that flow out from these beginnings and are called fibres; and yet with this difference--that those who correspond to the right side of the brain are those who are in the will of good and thereby in the will of truth; whereas those who correspond to the left side of the brain are those who are in the understanding of good and truth and thereby in the affection of them.
Since there are cortical substances and fibres on both sides, we have four categories. Two of them are easy to understand, namely:

1.     cortical substances on the right corresponding to first principles of good and the will of good, and
2.     fibres on the left corresponding to first principles of truth and the understanding of good and truth.

The other two are less obvious, namely:

3.     cortical substances on the left, corresponding to the first principles of good and the understanding of good and truth, and
4.     fibres on the right corresponding to first principles of truth and the will of good.

It follows that first principles of good do not preclude understanding, and first principles of truth do not preclude will. This must be so even though spiritual space is non-Euclidean and even if ordinary mathematics do not apply in heaven.

The anatomy of the brain shows that angels who are in good rely on those in truths for confirmation

353. It is worth emphasizing here that every fibre is a living outgrowth from a neuron body. The cortical substances are either neuron bodies or those parts where the cell bodies of the neurons are most numerous, but as "glands" are also mentioned we tend to equate them with individual cell bodies of neurons. This, of course, is all in agreement with the clear teaching that there is really no such thing as genuine truth without good; indeed it indicates that it is the good which produces the truth as a means of communication. It would also seem reasonable to believe that no category in which truth or good is predominant is actually exclusive. But this belief is unimportant because we are considering the Grand Man, or Heaven, and there is full communication between all in Heaven. This is reflected in the anatomy of the brain, in which it appears that all neurons receive communicating fibres from other neurons (see above). If translated into spiritual terms, this means that all those who are in the first principles of good are in communication with each other through those in the first principles of truth.

354. These considerations also show that the distinction between right and left and between good and truth is not a simple exclusive one; though they are distinct, yet they are one.

355. For a final word we read from DLW:

The right of these [various organs] relate to the goodness belonging to truth, and the left to the truth belonging to goodness; or what is the same, the right has relation to the goodness of love from which comes the truth of wisdom, and the left to the truth of wisdom which comes from the good of love. And because the union of good and truth is reciprocal, and by means of that union they become as it were one, the effect in man is that these pairs act together and jointly in their functions, movements, and sensations. (DLW 384)

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