A Hole in the Head

by Charles G Gross

  A friend of mine, that for a few days had been suffering from a headache, was struck after lunch with an apoplectic stroke, and although there was complete paralysis of the right side of his body, and perfect sight in the corresponding eye, his mind was free, but not his speech. He lived for 4 days maintaining his intellectual faculties, that only slightly began to vanish in the last 12 [hours] of life. In the sections we did not find accumulation of blood nor any fluid in any part of the brain, nor infection in the large or small blood supply. There appeared instead a softening of [the] left hemisphere and in particular in the optic thalamus. In the posterior and superior parts of the cerebral circumvolutions we found a very notable softening, confirmed by all persons present at the examination of the cadaver, among which was my learned colleague and friend Professor Platner: the comparison with the analogous parts in the other hemisphere left no doubt in this regard. The quadrigeminal eminence and the optic nerve were in a normal state.

  To summarize what I have said so far on the origin of the optic nerve in the three classes of animals, fish, birds, and mammals, the results showed that:

  1. In fish the formation of the optic nerve is contributed little by the anterior lobe, much by the hollow lobe, and within the internal objects of this the corpus striatum and the above placed eminence.

  2. In the lobe and optic thalamus of birds, some fibrous fascia of the hemispheres alongside the peduncle join to the thalamus and, therefore, the optic nerve, as well as the radiating lamina of the internal wall of the cerebral hemisphere, lamina that with its nervous fascia intersect in part the optic nerve and in part the external extreme of the same optic thalamus (all contribute to the origin of the optic nerve).

  3. In mammals the quadrigeminal eminence (especially the nates), the optic thalamus, the fibrous fascia that originate in the posterior cerebral circumvolutions, and also the tuber cinereum and the substance of the lateral wall of the infundibulum of the third ventricle (all contribute to the origin of the optic nerve).

  From the things said up to now, what follows are some considerations that should be noted.

  If a bird, or a suckling just born, loses sight in one eye and lives then a normal development, this will result in a major elevation of the skull and of the brain on the side of the blind eye. If you look at Figure 20, Table VIII [here, figure 9.1], that shows the head of a chicken in which I blinded the left eye while it was still a chick of a few days old: killed after 1 year, the skull showed an elevation on the left side, and I similarly found more prominent in the brain the hemisphere and the optic lobe on the left side, as is seen in Figure 21, Table VIII, or better still in Figures 22a and b, of Table VIII. The same experiment was performed on ducks a few days old that, along with a perfect development, also showed a skull (Table VIII, Figure 24) that was more prominent on the left side, as well as a more prominent left cerebral hemisphere (Table VIII, Figure 25a). Figure 26 (the inferior surface of the same brain) shows considerable development of the right nerve, and of the hemisphere and optic lobe on the left, while showing atrophy of the left optic nerve and the right optic lobe. Following blindness of the left eye on many lactating rabbits and dogs that were then sacrificed after 1 year, I could reveal a more or less normal development of the skull and brain corresponding to the good eye. The third figure of the ninth Table shows the left part of the skull of a dog that is more developed (letter a), as was the cerebral hemisphere maximally at the posterior lateral portion. The internal parts can be seen in the fourth figure that shows the enlargement of the corpus striatum, of the left optic thalamus, of its external geniculate body, and of the bigeminal eminence (letters a–c). The fifth figure shows the change of the optic nerve in front and also posteriorly to the aja. I do not believe, however, that in birds one can replicate the major elevation of the cerebral hemisphere by just increasing the lobe or optic thalamus; a lot is due to the development of the fibrous apparatus of the optic thalamus, that, uniting with the medullary fascia of the cerebral peduncle, expands in the cerebral hemisphere, so much so that it is notable on the side of the good eye as a major development of the optic thalamus and of the corresponding corpus striatum; these two bodies should be considered the center of the emanations of the fibrous apparatus that is part of the cerebral circumvolutions, particularly of the posterior part.

  For the purposes of a demonstration, let us make, in the brain of a human, dog, or rabbit, a longitudinal cut that divides the corpus callosum into two symmetrical parts and continue to cut to the base of the brain so as to separate the brain into two equal portions. In each of these we lift up the corresponding part of the corpus callosum and vault with three columns so as to uncover the external contours of the corpus striatum, the optic thalamus, and of the digital cavity; then we graze with a knife blade the medullary substance outside the margins indicated above and immediately one will see appear the considerable nervous fascia exiting from the aforementioned bodies; fascia that by spreading they extend toward the periphery of the cerebral hemispheres, then to their circumvolutions, and those of the posterior contours of the optic thalamus to the posterior superior circumvolutions. It is the existence of these nervous fascia that suggests an explanation for the above phenomenon, that even a light lesion to the periphery of the cerebral hemisphere, if it reaches the fibrous substance, always results in blindness of the opposite eye, or complete blindness if the same lesion is made in both hemispheres, without causing disorders of other cerebral functions.

  The above observations suggest another consideration, that is, that one part of the brain located even at the base can give indication of its greater swelling in the superior surface of the skull if this swelling occurs while the brain is still developing. In [the case of ] swelling, for example, of the optic lobe, the thalamus can do no less than occupy the space that belongs to the overlying part, and this should be pushed above the normal limits so that, coming in contact against the flexible walls of the skull, [it] will join handin-hand to alter its good form, thus breaking its symmetrical disposition. Therefore, if it is right to consider the brain as a complex of organs, it is not as easy to determine their number, the seat of each one, and their respective functions, and I believe that in this serious subject we are a long way from having an absolute and decisive language. In my opinion, in-depth studies are still required on the brain organization of humans and brutes; and these should be carried out considering the development and improvement of its parts, and the relation of these to the various intellectual and moral manifestations. In fact, we should continue emphasis on anatomical studies, and especially on the comparative examination of the brain; carrying out careful studies on live animals with interest in the various brain parts, observing closely what happens to them, and considering the various pathological cases, we may be able to clarify some of the many principles of the physiology of the brain that are still unclear, and we can better reach this goal, when we make more scrupulous and serious observations of all principles investigated.

  From the research carried out on the origins of the optic nerve, of that which is described in this paper, the results demonstrated that the optic nerve, in contrast to other cranial nerves, rather than having a unique origin, is composed of fibers originating from various points of the brain mass, of which the more important ones find themselves far from the openings at which the nerve is destined to exit from the skull, thus it must extend over a considerable section of this cavity, along which it comes into contact with various objects forming the cerebral mass. From this we could argue that, regarding a nerve that has an important part in intellectual development, that furnishes many precious materials in this exercise above all other noble faculties, to be, as it has been said, the mirror of the soul, nature wanted to put it in contact with a great number of the organs required for intelligence. We could object that another nerve, that has a duty no less important, for example the acoustic nerve, originates from a singularly narrow tract of the brain, while everybody knows that in this point regard
ing the origin of the acoustic nerve the fibers come from more noble parts of nervous centers, such that this nerve collects information from other organs, which are tied to the life and all of its attributes. But, also disregarding these arguments, one cannot deny that the various origins of the optic nerve explains the observed phenomenon in birds as well as mammals, that after an injury of even a small and superficial part of the brain at the anterior extremity and especially posteriorly at the corpus striatum or the optic thalamus, the sight of the opposite eye is always damaged, without any other damage to motion, the senses, and intelligence.

  The research on the optic nerve gave me new motivation to examine closely the manner in which the optic nerve behaves in the chiasm, in other words how the two nerves unite. We know that some opinions are that the optic nerves do nothing but connect one to the other; others admit total crossing, that is, the one on the right side crosses to the left side after the chiasm. Many others, and they are the most, maintain that there is only a partial decussation, a crossing of the major parts of the fibers, and especially of the internal ones, that pass to the opposite sides, while the external fibers of each nerve continue their path without penetrating into the aja, favoring only the curve of the external side of the nerve.

  Generally, in fish the optic nerves overlap one another, remaining united with the thick cellular texture. In some reptiles, such as Coluber viridflavus25 (Table IX, Figure 10), each nerve divides into two fascia, one that passes in the middle of the hole left by the other. In the brain of the chameleon (Table IX, Figure 11) at the crossing the nerve divides into small fascia, which truly entwine with the small fascia of the other nerve without mixing, like what happens when you cross the fingers of the hand (Table IX, Figure 11a). In birds, such as the crow, chickens, and in palmipeds, clearly you can see the decussation and the interlacing of the right fibers with the left ones (Table IX, Figures 12–14). These observations are confirmed by the examination of the pathological pieces collected from chickens in which one eye was blinded.

  While the total decussation is clear in the above-mentioned animals, examining this point is difficult in mammals and, therefore, in humans. In the works of many learned authors we find the representative figure, in which [we] see the partial crossing of the internal fibers of each nerve, while the external ones follow the primitive way directing themselves to the corresponding orbit without mixing with the fibers of the other. After a close examination of a series of preparations, I am able to accept that the external margin of the aja does not consist of portions of the nerve that continues, but from fibrous fascia that are directed, some superficial, others deep, but in a way that does not continue to the external margin of the nerve. In fact I noticed a completely different direction, and, therefore, I traced Figures 15 and 16, Table IX. As a result of this, at the joining of the optic nerve at the aja, some of its fascia, particularly the deep ones, cross diagonally and emerge from the opposite side, the others run along the external margin, but sooner or later they wrap around it, to also end up on the opposite side, therefore, completing a perfect decussation: in other words I saw that from the two lateral lamina of the infundibulum of the third ventricle exit some medullary fascia that expand into the superficial surface of the aja directing themselves from back to front, and in this way at the inferior surface of the aja I noticed longitudinal fibers that derive from the tuber cinereum. These anatomical observations favor perhaps the opinion that there is a complete decussation of the optic nerve even in humans, opinions that make it easy to understand the pathological phenomenon noted by all, that after cerebral damage you almost always have perfect blindness of one eye, while the other remains perfectly normal, a phenomenon that would remain inexplicable given just a partial decussation.

  On the richness and distribution of the blood vessels in the chiasm, and the particularities of the structure of the optic nerves, up to the square aja and after, with respect to the form and the distribution of the large and small nervous granulations, I will speak on another occasion.

  Notes

  This paper was originally published in Behavioural Brain Research (58: 529–539 [2002], M. Colombo, A. Colombo, and C. G. Gross, “Bartolomeo Panizza’s Observations on the Optic Nerve [1855]”). Dr. M. Colombo is in the Department of Psychology and the Centre for Neuroscience, University of Otago, Dunedin, New Zealand, and A. Colombo is his father. Professor M. Bentivogio, University of Verona, helped with the older Italian terms.

  1. Broca, 1960; Fritsch and Hitzig, 1960.

  2. Panizza, 1855. This was republished as Panizza, 1856, and it was from the latter that the two sets of illustrations (labeled in the original and referred to in the text as Table VIII and Table IX, here shown as figures 9.1 and 9.2) were reproduced.

  3. Finger, 1994; Gross, 1998a.

  4. Gross, 1998a, 1999d.

  5. Gross, 1998a, 1999d; Young, 1970.

  6. Broca, 1960.

  7. Fritsch and Hitzig, 1960

  8. Gross, 1998a; Young, 1970.

  9. Manni and Petrosini, 1994.

  10. Manni and Petrosini, 1994; Mazzarello and Della Sala, 1993; Zago et al., 2000.

  11. Von Gudden, 1870.

  12. Munk, 1878; Luciani and Tamburini, 1879; Munk, 1881.

  13. Tamburini, 1880; Polyak, 1957.

  14. Finger, 1994; Polyak, 1957; Manni and Petrosini, 1994; Mazzarello and Della Sala, 1993; Zago et al., 2000.

  15. Zago et al., 2000.

  16. Panizza, 1855.

  17. Throughout the manuscript Panizza refers to “eminenze bigemine.” Ranson, 1920, states: “In the lower vertebrates there are but two elevations in the roof, the optic lobes or corpora bigemina, and these, which correspond in a general way to the superior colliculi, are visual centers” (p. 165). It is clear that the “eminenze bigemine” refer to the optic tectum in fish, also known as the superior colliculi in mammals. To maintain as close a wording as possible to the original document we have translated “eminenze bigemine” into “bigeminal eminence.”

  18. In most nonmammalian vertebrates, the third ventricle extends into the optic lobe, where it is referred to as the tectal ventricle (see Butler and Hodos, 1996). Hence, “hollow lobe” refers to the optic tectum.

  19. Medullary refers to white matter.

  20. The term “corpo striato” refers to the “corpus striatum,” which consists of the caudate nucleus, putamen, and globus pallidus. The fact that at one time the optic thalamus and the corpus striatum were considered both part of the basal ganglia (Whitaker, 1887; Whitehead, 1900), and the fact that they lie in close proximity to each other in the brain, might explain why in many cases Panizza makes reference to either the optic thalamus or corpus striatum.

  21. The term “eminenze quadrigemelle” refers to the superior and inferior colliculi. The actual translation would be “corpora quadrigemina.” Again, to maintain as close a wording as possible to the original document, we have translated “eminenze quadrigemelle” to “quadrigeminal eminence.”

  22. Aja and aja quadrata refer to the immediate area around the optic chiasm. We have translated “aja quadrata” into “square aja.”

  23. Nates are buttocks and refer to the superior colliculi. It was common to name brain parts after sexual organs they supposedly looked like. Whitaker (1887) states, “The corpora Quadrigemina are four rounded tubercles separated from each other by two grooves, the one longitudinal, the other transverse. They are placed in pairs, on each side of the middle line, behind the pineal gland and above the aqueduct of Sylvius; the anterior pair are called the nates, the posterior pair, the testes.” The testes in this case are the inferior colliculi.

  24. A line is approximately 1/12 of an inch.

  25. A member of the colubridae family also known as a common racer snake.

  10

  JOSEPH ALTMAN AND ADULT NEUROGENESIS: THE DOGMA OF “NO NEW NEURONS” IN THE ADULT MAMMALIAN BRAIN

  From the beginning of the neuron doctrine in the late nineteenth century until the earl
y 1990s a central dogma in neuroscience was that “no new neurons are added to the adult mammalian brain.”1 By the end of the nineteenth century, the idea that the brain of the adult mammal remains structurally constant was already universally held by the neuroanatomists of the time. Koelliker, His, and others had described in detail the development of the central nervous system of humans and other mammals.2 They found that the structure of the brain remained fixed from soon after birth. Because the elaborate architecture of the brain remained constant in appearance, the idea that neurons were continually added to it was, understandably, inconceivable. Similarly, Ramón y Cajal and others had described the different phases in the development of the neuron, terminating with the multipolar structure characteristic of the adult.3 As neither mitotic figures nor preadult developmental stages had been seen in the adult brain, the possibility of continuing neuronal addition to the adult brain was rarely, if ever, seriously entertained. As Ramón y Cajal put it, “In the adult centers the nerve paths are something fixed, ended and immutable. Everything may die, nothing may be regenerated.”4

  In the first half of the twentieth century, there were occasional reports of postnatal neurogenesis in mammals but these were usually ignored by textbooks and rarely cited.5 Presumably this was because of the weight of authority opposed to the idea and the inadequacy of the available methods both for detecting cell division and for determining whether the apparently new cells were glia or neurons.6