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This paper presents a survey of the cell masses in the brainstem of the Australian lungfish Neoceratodus forsteri, based ontransversely cut Bodian-stained serial sections, supplemented by immunohistochemical data from the recent literature. This study is intended to serve a double purpose. First it concludes and completes a series of publications on the structure of the brainstem in representative species of all groups of anamniote vertebrates. Within the framework of this comparative program the cell masses in the brainstem and their positional relations are analyzed in the light of the Herrick-Johnston concept, according to which the brainstem nuclei are arranged in four longitudinal, functional zones or columns, the boundaries of which are marked by ventricular sulci. The procedure employed in this analysis essentially involves two steps: first, the cell masses and large individual cells are projected upon the ventricular surface, and next, the ventricular surface is flattened out, that is, subjected to a one-to-one continuous topological transformation [J Comp Neurol. 1974;156:255–267]. The second purpose of the present paper is to complement our mapping of the longitudinal zonal arrangement of the cell masses in the brainstem of Neoceratoduswith a subdivision in transversely oriented neural segments. Five longitudinal rhombencephalic sulci – the sulcus medianus inferior, the sulcus intermedius ventralis, the sulcus limitans, the sulcus intermedius dorsalis and the sulcus medianus superior – and four longitudinal mesencephalic sulci – the sulcus tegmentalis medialis, the sulcus tegmentalis lateralis, the sulcus subtectalis and the sulcus lateralis mesencephali – could be distinguished. Two obliquely oriented grooves, present in the isthmic region – the sulcus isthmi dorsalis and ventralis – deviate from the overall longitudinal pattern of the other sulci. Although in Neoceratodus most neuronal perikarya are situated within a diffuse periventricular gray, 45 cell masses could be delineated. Ten of these are primary efferent or motor nuclei, eight are primary afferent or sensory centers, six are considered to be components of the reticular formation and the remaining 21 may be interpreted as “relay” nuclei. The topological analysis showed that in most of the rhombencephalon the gray matter is arranged in four longitudinal zones or areas, termed area ventralis, area intermedioventralis, area intermediodorsalis and area dorsalis. The sulcus intermedius ventralis, the sulcus limitans, and the sulcus intermedius dorsalis mark the boundaries between these morphological entities. These longitudinal zones coincide largely, but not entirely, with the functional columns of Herrick and Johnston. The most obvious incongruity is that the area intermediodorsalis contains, in addition to the viscerosensory nucleus of the solitary tract, several general somatosensory and special somatosensory centers. The isthmus region does not exhibit a clear morphological zonal pattern. The mesencephalon is divisible into a ventral, primarily motor zone and a dorsal somatosensory zone. The boundary between these zones is marked by the sulcus tegmentalis lateralis, which may be considered as an isolated rostral extremity of the sulcus limitans. The results of this study are summarized in a “classical” topological map, as well as in a “modernized” version of this map, in which neuromere borders are indicated.

This paper presents a survey of the cell masses in the brainstem of the Australian lungfish Neoceratodus forsteri, based ontransversely cut Bodian-stained serial sections, supplemented by immunohistochemical data from the recent literature. This study is intended to serve a double purpose. First it concludes and completes a series of publications on the structure of the brainstem in representative species of all groups of anamniote vertebrates. Within the framework of this comparative program the cell masses in the brainstem and their positional relations are analyzed in the light of the Herrick-Johnston concept, according to which the brainstem nuclei are arranged in four longitudinal, functional zones or columns, the boundaries of which are marked by ventricular sulci. The procedure employed in this analysis essentially involves two steps: first, the cell masses and large individual cells are projected upon the ventricular surface, and next, the ventricular surface is flattened out, that is, subjected to a one-to-one continuous topological transformation [J Comp Neurol. 1974;156:255-267]. The second purpose of the present paper is to complement our mapping of the longitudinal zonal arrangement of the cell masses in the brainstem of Neoceratoduswith a subdivision in transversely oriented neural segments. Five longitudinal rhombencephalic sulci - the sulcus medianus inferior, the sulcus intermedius ventralis, the sulcus limitans, the sulcus intermedius dorsalis and the sulcus medianus superior - and four longitudinal mesencephalic sulci - the sulcus tegmentalis medialis, the sulcus tegmentalis lateralis, the sulcus subtectalis and the sulcus lateralis mesencephali - could be distinguished. Two obliquely oriented grooves, present in the isthmic region - the sulcus isthmi dorsalis and ventralis - deviate from the overall longitudinal pattern of the other sulci. Although in Neoceratodus most neuronal perikarya are situated within a diffuse periventricular gray, 45 cell masses could be delineated. Ten of these are primary efferent or motor nuclei, eight are primary afferent or sensory centers, six are considered to be components of the reticular formation and the remaining 21 may be interpreted as "relay" nuclei. The topological analysis showed that in most of the rhombencephalon the gray matter is arranged in four longitudinal zones or areas, termed area ventralis, area intermedioventralis, area intermediodorsalis and area dorsalis. The sulcus intermedius ventralis, the sulcus limitans, and the sulcus intermedius dorsalis mark the boundaries between these morphological entities. These longitudinal zones coincide largely, but not entirely, with the functional columns of Herrick and Johnston. The most obvious incongruity is that the area intermediodorsalis contains, in addition to the viscerosensory nucleus of the solitary tract, several general somatosensory and special somatosensory centers. The isthmus region does not exhibit a clear morphological zonal pattern. The mesencephalon is divisible into a ventral, primarily motor zone and a dorsal somatosensory zone. The boundary between these zones is marked by the sulcus tegmentalis lateralis, which may be considered as an isolated rostral extremity of the sulcus limitans. The results of this study are summarized in a "classical" topological map, as well as in a "modernized" version of this map, in which neuromere borders are indicated.

During the period extending from 1910 to 1970, Oscar and Cécile Vogt and their numerous collaborators published a large number of myeloarchitectonic studies on the cortex of the various lobes of the human cerebrum. In a previous publication [Nieuwenhuys et al (Brain Struct Funct 220:2551-2573, 2015; Erratum in Brain Struct Funct 220: 3753-3755, 2015)], we used the data provided by the Vogt-Vogt school for the composition of a myeloarchitectonic map of the entire human neocortex. Because these data were derived from many different brains, a standard brain had to be introduced to which all data available could be transferred. As such the Colin 27 structural scan, aligned to the MNI305 template was selected. The resultant map includes 180 myeloarchitectonic areas, 64 frontal, 30 parietal, 6 insular, 17 occipital and 63 temporal. Here we present a supplementary map in which the overall density of the myelinated fibers in the individual architectonic areas is indicated, based on a meta-analysis of data provided by Adolf Hopf, a prominent collaborator of the Vogts. This map shows that the primary sensory and motor regions are densely myelinated and that, in general, myelination decreases stepwise with the distance from these primary regions. The map also reveals the presence of a number of heavily myelinated formations, situated beyond the primary sensory and motor domains, each consisting of two or more myeloarchitectonic areas. These formations were provisionally designated as the orbitofrontal, intraparietal, posterolateral temporal, and basal temporal dark clusters. Recently published MRI-based in vivo myelin content mappings show, with regard to the primary sensory and motor regions, a striking concordance with our map. As regards the heavily myelinated clusters shown by our map, scrutiny of the current literature revealed that correlates of all of these clusters have been identified in in vivo structural MRI studies and appear to correspond either entirely or largely to known cytoarchitectonic entities. Moreover, functional neuroimaging studies indicate that all of these clusters are involved in vision-related cognitive functions.

Causal analysis of molecular patterning at neural plate and early neural tube stages has shown that the central nervous system (CNS) of vertebrates is essentially organized into transverse neural segments or neuromeres and longitudinal zones which follow the curved axis of the brain. The intersection of the longitudinal and transverse patterning processes in the embryonic brain leads to the formation of a checkerboard pattern of distinct progenitor domains called “fundamental morphological units” (FMUs). The topologically invariant pattern formed by the ventricular surfaces of the FMUs of a given taxon represents the “Bauplan” or “blueprint” of the brain of that taxon. The FMUs initially represent thin epithelial fields; during further development they are transformed into three-dimensional radial units, extending from the ventricular surface to the meningeal surface. It is of note that the boundaries of the neuromeres, longitudinal zones, and radial units all strictly adhere to a non-Cartesian coordinate system inherent to the CNS of all vertebrates. The major neural histogenetic processes, including cellular proliferation, radial migration, and differentiation, as well as the formation of grisea (cell masses, nuclei, and cortices), occur principally within the confines of the FMUs, although tangential migration may also take cells to distant sites. Hence, recognition and delimitation of these units is essential for the identification and interpretation of grisea. An outline of the procedure to be followed in these processes of identification and interpretation is presented, and a list of the pertinent homology criteria is provided.

The human cerebral cortex contains numerous myelinated fibres, the arrangement and density of which is by no means homogeneous throughout the cortex. Local differences in the spatial organization of these fibres render it possible to recognize areas with a different myeloarchitecture. The neuroanatomical subdiscipline aimed at the identification and delineation of such areas is known as myeloarchitectonics. During the period extending from 1910 to 1970, Oscar and Cécile Vogt and their numerous collaborators (The Vogt-Vogt school) published a large number of myeloarchitectonic studies on the cortex of the various lobes of the human cerebrum. Recently, one of us (Nieuwenhuys in Brain Struct Funct 218: 303-352, 2013) extensively reviewed these studies. It was concluded that the data available are adequate and sufficient for the composition of a myeloarchitectonic map of the entire human neocortex. The present paper is devoted to the creation of this map. Because the data provided by the Vogt-Vogt school are derived from many different brains, a standard brain had to be introduced to which all data available could be transferred. As such, the colin27 structural scan, aligned to the MNI305 template was selected. The procedure employed in this transfer involved computer-aided transformations of the lobar maps available in the literature, to the corresponding regions of the standard brain, as well as local adjustments in the border zones of the various lobes. The resultant map includes 180 myeloarchitectonic areas, 64 frontal, 30 parietal, 6 insular, 17 occipital and 63 temporal. The designation of the various areas with simple Arabic numbers, introduced by Oscar Vogt for the frontal and parietal cortices, has been extended over the entire neocortex. It may be expected that combination of the myeloarchitectonic data of the Vogt-Vogt school, as expressed in our map, with the results of the detailed cytoarchitectonic and receptor architectonic studies of Karl Zilles and Katrin Amunts and their numerous associates, will yield a comprehensive 'supermap' of the structural organization of the human neocortex. For the time being, i. e., as long as this 'supermap' is not yet available, our map may provide a tentative frame of reference for (a) the morphological interpretation of the results of functional neuroimaging studies; (b) the selection of starting points (seed voxels, regions-of-interest) in diffusion tractography studies and

The Actinopterygii or ray-finned fishes comprise, in addition to the large superorder of teleosts, four other superorders, namely the cladistians, the chondrosteans, the ginglymodes, and the halecomorphs, each with a limited number of species. The telencephalon of actinopterygian fishes differs from that in all other vertebrates in that it consists of a pair of solid lobes. Lateral ventricles surrounded by nervous tissue are entirely lacking. At the end of the nineteenth century, the theory was advanced that the unusual configuration of the forebrain in actinopterygians results from an outward bending or eversion of its lateral walls. This theory was accepted by some authors, rejected or neglected by others, and modified by some other authors. The present paper is based on the data derived from the literature, complemented by new observations on a large collection of histological material comprising specimens of all five actinopterygian superorders. The paper consists of three parts. In the first, a survey of the development of the telencephalon in actinopterygian fishes is presented. The data collected show clearly that an outward bending or eversion of the pallial parts of the solid hemispheres is the principal morphogenetic event in all five actinopterygian superorders. In all of these superorders, except for the cladistians, eversion is coupled with a marked thickening of the pallial walls. In the second part, some aspects of the general morphology of the telencephalon in mature actinopterygians are highlighted. It is pointed out that (1) the degree of eversion varies considerably among the various actinopterygian groups; (2) eversion leads to the transformation of the telencephalic roof plate into a wide membrane or tela choroidea, which is bilaterally attached to the lateral or ventrolateral aspect of the solid hemispheres; (3) the lines of attachment or taeniae of the tela choroidea form the most important landmarks in the telencephalon of actinopterygians, indicating the sites where the greatly enlarged ventricular surface of the hemispheres ends and its reduced meningeal surface begins; (4) the meningeal surface of the telencephalon shows in most actinopterygians bilaterally a longitudinally oriented sulcus externus, the depth of which is generally positively correlated with the degree of eversion; (5) a distinct lateral olfactory tract, occupying a constant topological position close to the taenia, is present in all actinopterygians studied; and (6) this tract is not homologous to the tract of the same name in the evaginated and inverted forebrains of other groups of vertebrates. In the third and final section, the concept that the structural organization of the pallium in actinopterygians can be fully explained by a simple eversion of its walls, and the various theories, according to which the eversion is complicated by extensive shifts of its constituent cell groups, are discussed and evaluated. It is concluded that there are no reasons to doubt that the pallium of actinopterygian fishes is the product of a simple and complete eversion.

The forebrain of actinopterygian fishes differs from that of other vertebrates in that it consists of a pair of solid lobes. Lateral ventricles surrounded by nervous tissue are entirely lacking. This peculiar configuration of the actinopterygian forebrain results from an outward bending or eversion of its lateral walls during ontogenesis. Due to this eversion, the telencephalic roof plate is transformed into a wide, membranous structure that surrounds the dorsal and lateral parts of the solid lobes and is attached to their lateral or ventrolateral aspects. Another effect of the eversion is that the ventricular surface of the telencephalic lobes is very extensive, whereas their meningeal surface is small. In many recent publications on the forebrain of actinopterygian fishes, these structures are presented as solid lobes, without any reference to the fact that they are the product of an eversion process, and without any indication concerning the location and extent of their ventricular and meningeal surfaces. It is explained here that, in light of current concepts concerning the histogenesis of the brain, these omissions are intolerable. It is also strongly recommended that the location and extent of these surfaces should always be clearly indicated in brain sections in general, because the simple notion that in the brain of vertebrates the ventricular surface is on the inside and the meningeal surface on the outside has numerous and notable exceptions.

During the 2008 Karger Workshop considerable progress was made towards defining a model or structural plan, valid for the prosencephalon of all vertebrates. The presentations demonstrated that the following features, which are valid for tetrapods, also hold true for most groups of fish: (1) The diencephalon proper is clearly composed of three neuromeres, p1–p3; (2) in the pallium four, rather than three, fundamental longitudinal zones can be distinguished; (3) during ontogenesis, numerous GABA-ergic elements migrate tangentially from the subpallium to the pallium.

It has already been discussed that the brain is essentially a tube to which a long axis can be attributed.

Let us begin our discussion of the neural tube and its regional differentiation by looking at some historic pictures, one from His (1893b), and three from Karl Von Kupffer (1906).

Plate 17 presents dorsal views of early frog and human embryos (Fig. A, B). In the frog embryo, the neural plate is surrounded by a distinct ridge (neural fold). In the human embryo, such a demarcation is lacking and the neural plate can only be arbitrarily delimited morphologically from the remainder of the external germ layer, though a precise neural versus non-neural boundary is visible with molecular markers. The apparent lack of a border can also be observed in the transverse section through the human embryonic disk, shown in Plate 17, Fig. C.

The centres or grisea in the brain discussed in the previous section are interconnected by fibres, which commonly assemble in fibre systems, bundles or tracts.

At the beginning of this new section it may be recalled that: 1. The CNS consists of fundamental morphological units (FMUs), which are centres of neuronal and glial proliferation, migration and differentiation (Plate 93, Fig. A). 2. All of these FMUs are radial entities, the ventricular/ependymal surfaces of which occupy a specific area of the ventricular surface of the neural tube.

We have already pointed out that the orthogonal or Cartesian coordinate system (Plate 64, Fig. A) used in descriptive anatomy and adult brain stereotaxis, is fully inadequate to characterize the true morphological directional and positional relations within developing and adult brains, due to various accumulated morphogenetic deformations which start with the closure of the neural tube itself (Sect. 1.5; Plate 13).

By way of introduction, we present here two figures that have been shown before (see Plates 24 and 34).

The transformation of the neural plate into the neural tube is known as neurulation. During this process, the bilateral outer borders of the neural plate fuse together point-to-point along the median line, forming the roof plate. The neural crest population is released into the mesenchyme at the same time, and the skin also fuses, covering the whole.

All fundamental morphological units (FMUs) in the CNS occupy their own, specific locus at the ventricular surface of the neural tube, and hence their position can be fully characterized in flat maps of the ventricular surface of the CNS (see Plate 68). However, the CNS is a three-dimensional structure and so are the FMUs. The third dimension, which is (topologically) oriented perpendicularly to the ventricular surface, is represented by the thickness of the neural wall. This thickness increases steadily during ontogeny and may attain amazing proportions (10 cm or more).

Most of you will know that the human brain begins as a tiny epidermal plate, called the ‘neural plate’, whose lateral edges rise upward, approach each other and finally fuse, so that the originally flat neural plate is transformed into a hollow neural tube with a fused roof plate (left panel). Note that this closing process does not occur synchronously over the length of the developing central nervous system (CNS). It begins in the future cervical (neck) region and proceeds from there anteriorly and posteriorly, so that the initially large anterior and posterior neural openings or ‘neuropores’ become progressively smaller and finally disappear. Experimental fate-mapping has shown that the rostralmost closing point lies at the locus of the future anterior commissure.

The living deuterostomes comprise six monophyletic groups: (1) echinoderms + hemichordates, (2) tunicates, (3) cephalochordates, (4) myxinoids, (5) petromyzontoids, and (6) gnathostomes. The morphotype of the craniote (myxinoids + petromyzontoids + gnathostomes) central nervous system (CNS) comprises a fixed number of histogenetic units, formed by the intersection of transversely oriented neuromeres and longitudinally arranged zones. A well-developed built-in, natural coordinate system adds the third dimension to this morphotype. The classical subdivisions of the craniote CNS: prosencephalon (P), mesencephalon (M), rhombencephalon (R), and spinal cord (S) are each composed of a number of neuromeres. Chordates (larval tunicates + cephalochordates + craniotes) share a highly characteristic axial complex, encompassing a dorsal tubular CNS, a notochord and bilateral series of segmental muscles. In all chordates the CNS can be divided into a rostral (P-like + M-like), an intermediate (R-like) and a caudal (S-like) sector, and sets of homologous developmental genes play a role in this tripartitioning. There are no indications for the presence of olfactory or other telencephalic regions in the brain of non-craniote chordates. Convincing evidence that parts of the chordate CNS are homologous to parts of the larval or adult CNS of non-chordate deuterostomes (echinoderms + hemichordates) is lacking. The dorsal tubular CNS is most probably a chordate autapomorphy.

The human cerebral cortex contains numerous myelinated fibres, many of which are concentrated in tangentially organized layers and radially oriented bundles. The spatial organization of these fibres is by no means homogeneous throughout the cortex. Local differences in the thickness and compactness of the fibre layers, and in the length and strength of the radial bundles renders it possible to recognize areas with a different myeloarchitecture. The neuroanatomical subdiscipline aimed at the identification and delineation of such areas is known as myeloarchitectonics. There is another, closely related neuroanatomical subdiscipline, named cytoarchitectonics. The aims and scope of this subdiscipline are the same as those of myeloarchitectonics, viz. parcellation. However, this subdiscipline focuses, as its name implies, on the size, shape and arrangement of the neuronal cell bodies in the cortex, rather than on the myelinated fibres. At the beginning of the twentieth century, two young investigators, Oskar and Cécile Vogt founded a centre for brain research, aimed to be devoted to the study of the (cyto + myelo) architecture of the cerebral cortex. The study of the cytoarchitecture was entrusted to their collaborator Korbinian Brodmann, who gained great fame with the creation of a cytoarchitectonic map of the human cerebral cortex. Here, we focus on the myeloarchitectonic studies on the cerebral cortex of the Vogt-Vogt school, because these studies are nearly forgotten in the present attempts to localize functional activations and to interprete findings in modern neuroimaging studies. Following introductory sections on the principles of myeloarchitectonics, and on the achievements of three myeloarchitectonic pioneers who did not belong to the Vogt-Vogt school, the pertinent literature is reviewed in some detail. These studies allow the conclusion that the human neocortex contains about 185 myeloarchitectonic areas, 70 frontal, 6 insular, 30 parietal, 19 occipital, and 60 temporal. It is emphasized that the data available, render it possible to compose a myeloarchitectonic map of the human neocortex, which is at least as reliable as any of the classic architectonic maps. During the realization of their myeloarchitectonic research program, in which numerous able collaborators were involved, the Vogts gradually developed a general concept of the organization of the cerebral cortex. The essence of this concept is that this structure is composed of about 200 distinct, juxtaposed 'Rindenfelder' or 'topistische Einheiten', which represent fundamental structural as well as functional entities. The second main part of this article is devoted to a discussion and evaluation of this 'Vogt-Vogt concept'. It is concluded that there is converging quantitative cytoarchitectonic, receptor architectonic, myeloarchitectonic, hodological, and functional evidence, indicating that this concept is essentially correct. The third, and final part of this article deals with the problem of relating particular cortical functions, as determined with neuroimaging techniques, to particular cortical structures. At present, these 'translation' operations are generally based on adapted, three-dimensional versions of Brodmann's famous map. However, it has become increasingly clear that these maps do not provide the neuroanatomical precision to match the considerable degree of functional segregation, suggested by neuroimaging studies. Therefore, we strongly recommend an attempt at combining and synthesizing the results of Brodmann's cytoarchitectonic analysis, with those of the detailed myeloarchitectonic studies of the Vogt-Vogt school. These studies may also be of interest for the interpretation of the myeloarchitectonic features, visualized in modern in vivo mappings of the human cortex.

The human insular cortex forms a distinct, but entirely hidden lobe, situated in the depth of the Sylvian fissure. Here, we first review the recent literature on the connectivity and the functions of this structure. It appears that this small lobe, taking up less than 2% of the total cortical surface area, receives afferents from some sensory thalamic nuclei, is (mostly reciprocally) connected with the amygdala and with many limbic and association cortical areas, and is implicated in an astonishingly large number of widely different functions, ranging from pain perception and speech production to the processing of social emotions. Next, we embark on a long, adventurous journey through the voluminous literature on the structural organization of the insular cortex. This journey yielded the following take-home messages: (1) The meticulous, but mostly neglected publications of Rose (1928) and Brockhaus (1940) are still invaluable for our understanding of the architecture of the mammalian insular cortex. (2) The relation of the insular cortex to the adjacent claustrum is neither ontogenetical nor functional, but purely topographical. (3) The insular cortex has passed through a spectacular progressive differentiation during hominoid evolution, but the assumption of Craig (2009) that the human anterior insula has no homologue in the rhesus monkey is untenable. (4) The concept of Mesulam and Mufson (1985), that the primate insula is essentially composed of three concentrically arranged zones, agranular, dysgranular, and granular, is presumably correct, but there is at present much confusion concerning the more detailed architecture of the anterior insular cortex. (5) The large spindle-shaped cells in the fifth layer of the insular cortex, currently known as von Economo neurons (VENs), are not only confined to large-brained mammals, such as whales, elephants, apes, and humans, but also occur in monkeys and prosimians, as well as in the pygmy hippopotamus, the Atlantic walrus, and Florida manatee. Finally, we point out that the human insula presents a unique opportunity for performing an in-depth comparative analysis of the relations between structure and function in a typical sensory and a typical cognitive cortical domain.

The human insular cortex forms a distinct, but entirely hidden lobe, situated in the depth of the Sylvian fissure. Here, we first review the recent literature on the connectivity and the functions of this structure. It appears that this small lobe, taking up less than 2% of the total cortical surface area, receives afferents from some sensory thalamic nuclei, is (mostly reciprocally) connected with the amygdala and with many limbic and association cortical areas, and is implicated in an astonishingly large number of widely different functions, ranging from pain perception and speech production to the processing of social emotions. Next, we embark on a long, adventurous journey through the voluminous literature on the structural organization of the insular cortex. This journey yielded the following take-home messages: (1) The meticulous, but mostly neglected publications of Rose (1928) and Brockhaus (1940) are still invaluable for our understanding of the architecture of the mammalian insular cortex. (2) The relation of the insular cortex to the adjacent claustrum is neither ontogenetical nor functional, but purely topographical. (3) The insular cortex has passed through a spectacular progressive differentiation during hominoid evolution, but the assumption of Craig (2009) that the human anterior insula has no homologue in the rhesus monkey is untenable. (4) The concept of Mesulam and Mufson (1985), that the primate insula is essentially composed of three concentrically arranged zones, agranular, dysgranular, and granular, is presumably correct, but there is at present much confusion concerning the more detailed architecture of the anterior insular cortex. (5) The large spindle-shaped cells in the fifth layer of the insular cortex, currently known as von Economo neurons (VENs), are not only confined to large-brained mammals, such as whales, elephants, apes, and humans, but also occur in monkeys and prosimians, as well as in the pygmy hippopotamus, the Atlantic walrus, and Florida manatee. Finally, we point out that the human insula presents a unique opportunity for performing an in-depth comparative analysis of the relations between structure and function in a typical sensory and a typical cognitive cortical domain.

Total neuron numbers in the amygdala and in eight of its subnuclei were determined in 9 cases of Alzheimer's disease (AD) and in 6 age-matched controls (AMC). Total neuron numbers were obtained using the fractionator. A neuron loss of 56.3% for the left amygdala and 50.5% for the right amygdala in AD was found, being more severe than previously reported. The subdivisions showed a differential neuron loss ranging from 35.5% in nucleus lateralis of the right amygdala to 70.4% in the nucleus basalis accessorius of the right amygdala. Moreover, a shift in size distribution to smaller neurons could be demonstrated. No left-right hemispheric differences were detected in total neuron numbers in AD and AMC.

According to Wilhelm His (1891, 1893) the brainstem consists of two longitudinal zones, the dorsal alar plate (sensory in nature) and the ventral basal plate (motor in nature). Johnston and Herrick indicated that both plates can be subdivided into separate somatic and visceral zones, distinguishing somatosensory and viscerosensory zones within the alar plate, and visceromotor and somatomotor zones within the basal plate. To test the validity of this ‘four-functional-zones’ concept, I developed a topological procedure, surveying the spatial relationships of the various cell masses in the brainstem in a single figure. Brainstems of 16 different anamniote species were analyzed, and revealed that the brainstems are clearly divisible into four morphological zones, which correspond largely with the functional zones of Johnston and Herrick. Exceptions include (1) the magnocellular vestibular nucleus situated in the viscerosensory zone; (2) the basal plate containing a number of evidently non-motor centres (superior and inferior olives). Nevertheless the ‘functional zonal model’ has explanatory value. Thus, it is possible to interpret certain brain specializations related to particular behavioural profiles, as ‘local hypertrophies’ of one or two functional columns. Recent developmental molecular studies on brains of birds and mammals confirmed the presence of longitudinal zones, and also showed molecularly defined transverse bands or neuromeres throughout development. The intersecting boundaries of the longitudinal zones and the transverse bands appeared to delimit radially arranged histogenetic domains. Because neuromeres have been observed in embryonic and larval stages of numerous anamniote species, it may be hypothesized that the brainstems of all vertebrates share a basic organizational plan, in which intersecting longitudinal and transverse zones form fundamental histogenetic and genoarchitectonic units.

Il termine gangli della base si riferisce a un gruppo di nuclei strettamente connessi che formano un continuum che si estende dalla base del telencefalo, attraverso la parte centrale del diencefalo, nel tegmento mesencefalico. Questo complesso, secondo la definizione classica, risulta composto dallo striato (nucleo caudato e putamen), dal globo pallido, dal nucleo subtalamico e dalla substantia nigra.

Herrick [9, 10] ha diviso il diencefalo in quattro zone longitudinali: l’epitalamo, il talamo dorsale, il talamo ventrale e l’ipotalamo. Questa suddivisione e stata ampiamente condivisa dalla comunita scientifica ed e stato asserito che poteva essere applicata a tutte le classi di vertebrati, inclusi i mammiferi [3, 27] e l’uomo [5, 11, 12, 26]. Sebbene attualmente sia noto (vedi Cap. 2) che due delle zone di Herrick, ovvero il talamo dorsale e quello ventrale, derivino direttamente dai neuromeri, e che il loro orientamento topografico orizzontale sia dovuto alla forte curvatura della parte rostrale dell’encefalo, non si puo negare che la suddivisione di Herrick costituisca un conveniente punto di partenza per una discussione relativa alle diverse masse cellulari diencefaliche e alle loro connessioni. Per questa ragione pratica, nei successivi capitoli sara utilizzata la stessa suddivisione.

Nell’uomo, la maggior parte della superficie mediale degli emisferi cerebrali e occupata dalla neocortex notevolmente espansa. Comunque, su questo lato dell’encefalo, sono presenti anche numerose strutture che non sono neocorticali. Due di queste, il sistema olfattorio centrale e il setto, occupano una posizione superficiale, mentre altre due, il complesso amigdaloideo e la formazione ippocampale, sono per la maggior parte nascoste nella struttura degli emisferi. A seguito del cospicuo sviluppo della neocortex e della relativa espansione del lobo temporale, i principali sistemi efferenti del complesso amigdaloideo e della formazione dell’ippocampo risultano espansi in lunghi fasci arciformi che, rispettivamente, costituiscono la stria terminalis e il fornice (Figg. 23.1–23.4). Il setto, l’amigdala, la formazione ippocampale e i loro fasci efferenti costituiscono, nell’insieme, la zona piu mediale dell’emisfero a forma di anello (Figg. 23.3, 23.5). Questa zona e per gran parte circoscritta da una seconda zona che, nei primati, comprende due circonvoluzioni, il giro cingolato e il giro paraippocampale (Figg. 23.1, 23.3, 23.5). Nel 1878, Broca [17] denomino questi due giri, nell’insieme, come le grand lobe limbique (‘il grande lobo limbico’). Egli fece notare di aver coniato questo termine allo scopo di definire una struttura anatomica e non un’unita funzionale. Durante gli ultimi due decenni del diciannovesimo e i primi due decenni del ventesimo secolo, in generale, e stato ritenuto che la maggior parte delle strutture comprese nel lobo limbico di Broca, se non tutte, e dominata dalle proiezioni olfattorie e, pertanto, costituisce parte del rinencefalo. Open image in new window Fig. 23.1. Sintesi del complesso limbicoipotalamico. Suddivisione dell’area in unita centrali e anelli. H, ipotalamo; LMA, arealimbica mesencefalica; PO), regione preottica; S, setto; anello (limbico) interne in rosso scuro; anello (paralimbico) esterno in rosso chiaro Open image in new window Fig. 23.2. Le principali vie del sistema limbico e del rinencefalo Open image in new window Fig. 23.3. La struttura dei sistemi limbico e olfattorio e alcune vie afferenti-efferenti come visibili in proiezione mediale (3/2 ×). Un certo spostamento delle strutture serve per rendere visibili altre strutture. I,e pareti del terzo ventricolo e il tronco encefalico sono stati quasi completamente omessi; del talamo sono raffigurati solo i nuclei anteriore, mediodorsale e abenulari Open image in new window Fig. 23.4. La parte centrale dell’area limbica; proiezione mediale dei nuclei e dei tratti (5/2 ×) Open image in new window Fig. 23.5. Proiezione mediale dell’eneefalo umano. Sono schematicamente indicate le posizioni di giro cingolato (G CINGULI), giro paraippocampale (GPH), setto (S), fornice + stria terminalis (f+st), ipotalamo (Hy), ippocampo (H), amigdala (A), core + paracore laterale (C+LPC) e paracore mediano (MPC)

L’amigdala, o corpo amigdaloideo, e un grande complesso nucleare situato nella parte dorsomediale del lobo temporale, dove costituisce parte delle pareti rostromediale e rostrodorsale del corno inferiore del ventricolo laterale (Fig. 5.6, 5.7, 5.23, 5.24, 6.39–6.41). Il termine deriva dal Greco (amygdalon) o dal Latino (amygdalum) che significa mandorla, cui Burdach [28] paragono questo complesso per la forma agli inizi del diciannovesimo secolo. Il volume dell’amigdala umana, come stabilito dagli studi condotti mediante RMN in soggetti normali, e di circa 1700 mm3 [22].

Il midollo spinale con i suoi rivestimenti meningei e accolto nel canale vertebrale (Figg. 4.30–4.32). Il limite tra midollo spinale e tronco encefalico e fissato rostralmente all’origine del primo nervo cervicale, a livello della decussazione delle piramidi. Comunque, il passaggio dai nuclei motori e sensoriali del midollo alle corrispondenti strutture della parte caudale del tronco encefalico (responsabili dell’innervazione di strutture originate dai somiti occipitali, vedi Cap. 2) avviene in maniera graduale.

In questo capitolo, saranno trattati l’ippocampo e due relative strutture telencefaliche, il lobo limbico e il setto precommissurale. L’ippocampo, che si sviluppa dal pallio mediale (Figg. 2.24B, 2.25, 11.1), fa la sua comparsa durante la sesta settimana di gestazione. Negli ultimi stadi della vita embrionale questa struttura occupa una considerevole parte della parete mediale dell’emisfero (Fig. 12.1A) ma, durante il successivo sviluppo, e piu volte sopravanzato dal neopallio in espansione [80]. Dal quarto mese in poi, le parti rostrali del primordio ippocampale vanno incontro a modificazioni regressive e gradualmente si riducono a uno stretto rudimento a forma di nastro (Fig. 12.1B, C). La parte morfologicamente caudale dell’abbozzo ippocampale segue la curvatura ventrale dell’emisfero che si sviluppa e viene incorporata nel lobo temporale. Con il procedere dello sviluppo, questa parte temporale dell’ippocampo si avvolge su se stessa lungo un solco longitudinale, la fessura ippocampale [80]. A seguito di questa „internalizzazione„, solo parti relativamente piccole dell’ippocampo mantengono, nella vita adulta, la loro iniziale posizione superficiale (Fig. 3.6). Open image in new window Fig. 12.1 Proiezioni mediali schematiche dcll’emisfero cerebrale di destra di un embrione umano di 7 settimane (A); un feto umano di 12 settimane (B); uomo adulto (C); un istrice, Erinaceus europaeus (D) e un galagone di Demidoff, Galago demidovii (E), che mostrano la forma e l’estensione dell’ippocampo e del suo abbozzo. In C la parte ventrale dell’ippocampo, che e ampiamente immersa nel lobo temporale, e stata proiettata sulla superficie mediale. L’ippocampo e raffigurato in rosso, il corpo calloso in grigio. A e B sono basate sul lavoro di O’Rahilly e Muller [158]; D ed E sono tratte e semplificate da Stephan [214]

La percezione cosciente della sensibilita cutanea e propriocettiva e del gusto dipendono dalle vie di conduzione che connettono i recettori periferici con i centri a livello del diencefalo e del telencefalo. La maggior parte di queste connessioni, a eccezione delle vie per il gusto, e crociata. L’elaborazione iniziale dell’informazione sensoriale avviene nel midollo spinale e nei nuclei delle colonne dorsali per le informazioni relative al tronco e alle estremita, e nei nuclei sensoriali del nervo trigemino per quelle della faccia. Il primo rele per il gusto e situato nel nucleo del tratto solitario nel segmento inferiore del tronco encefalico. Le vie di conduzione spinale sono costituite dal fascicolo anterolaterale e dalla via delle colonne dorsali-lemnisco mediale. Entrambi questi sistemi sono crociati. Le vie corrispondenti traggono origine dai nuclei sensoriali del nervo trigemino.

Nel corso dell’ontogenesi, gli emisferi telencefalici evaginano bilateralmente dalla parte piu dorsale della lamina alare del prosencefalo secondario (Figg. 2.2C, 2.3C, 2.4, 2.5B, C). Esistono due principali divisioni degli emisferi telencefalici: il tetto o pallio e la base o sub pallio. Classicamente, il pallio e diviso in tre zone longitudinali, mediale, dorsale e laterale. Durante lo sviluppo, i neuroblasti migrano verso l’esterno dalla matrice ventricolare per partecipare alla formazione delle strutture corticali in tutte le zone del pallio. Il pallio mediale si sviluppa dando origine alla formazione ippocampale, nella quale, tra i due strati plessiformi, periventricolare e subpiale, e racchiuso un compatto strato di cellule. Una struttura a tre strati si forma anche nel pallio laterale. Qui riscontriamo uno strato molecolare superficiale, contenente un relativo scarso numero di cellule sparse, uno strato intermedio a elevata densita cellulare e uno strato profondo, che mostra una moderata densita cellulare. La formazione corticale, che si sviluppa dal pallio laterale, riceve proiezioni dirette dal bulbo olfattorio.

L’area che occupa la porzione centrale del tronco e nota come formazione reticolare. Per gran parte della sua estensione, questa area e occupata da aggregati di cellule sparse, diverse per tipo e dimensioni, e i sistemi di fibre che attraversano questo territorio sono parimenti organizzati in maniera alquanto diffusa. Il termine “formazione reticolare” si riferisce al fatto che i dendriti delle cellule in questa area sono disposti in fasci che insieme formano una struttura a forma di rete [161]. I sistemi di fibre che la attraversano decorrono negli interstizi di questa rete. La formazione reticolare e circondata dai nuclei dei nervi cranici, dai nuclei di proiezione sensoriale e dai lunghi sistemi di fibre ascendenti e discendenti. Per motivi di citoarchitettonica, di chemoarchitettonica e funzionali, la formazione reticolare del bulbo e del ponte e stata divisa in tre zone longitudinali [29] (Figg. 22.1, 22.2): 1. Una zona mediana e paramediana, costituita dai nuclei del rafe. I neuroni serotoninergici dei gruppi B1–B9 di Dahlstrom e Fuxe [43, 44] sono disposti nei nuclei del rafe e nell’adiacente formazione reticolare. 2. Una zona mediale, che contiene numerose cellule di grandi dimensioni, nota come campo tegmentale mediale. 3. Una zona laterale, una zona ampiamente parvocellulare, nota come campo tegmentale laterale. Open image in new window Fig. 22.1. La formazione rcticolare. Rapprcsentazione scmischcmatica in proiczione dorsale del tronco encefalico. Sinistra, citoarchitettura; destra, suddivisioni della formazione reticolare (campo tegmentale mediale, grigio chiaro; campo tegmentale latcralc, grigio scuro), i nuclei del rafe (rosso), i gruppi cellulari noradrencrgici A1–A6 (rosso chiaro), i gruppi adrenergici C1 e C2 (rosso media) e i gruppi cellulari colinergici Ch5 e 6 (grigio). AMB, nucleo ambiguo Open image in new window Fig. 22.2 A–D. La formazionc rcticolare. Sezioni schematichc trasverse condotte a livello della parte caudalc (A) e rostrale (B) del bulbo. La parte rostrale del tegmento pontino (C) e del mesencefalo (D), per mostrare la posizione del campo tcgmcntale mediale (grigio chiaro) e il campo tegmentale laterale (grigio scuro), i nuclei del rafe (rosso), i gruppi cellular! noradrenergici A1–A7 (rosso chiaro), i gruppi cellular! adrenergici Cl e S2 (rosso rnedio) e i gruppi cellular! colinergici Ch5 e Ch6 (grigio). A1–A7, gruppi cellulari noradrenergici A1–A7; AMB, nucleo ambiguo; Cl, C2, gruppi cellulari adrenergici C1, C2; Cocl, nuclei cocleari; CUI, nucleo cuneato laterale; CUm, nucleo cuneato mediale; FLM, fascicolo longitudinale mediale; GRAC, nucleo gracile; LRN, nucleo reticolare laterale; MesV, tratto mesencefalico del nervo trigemino; Nucleo subcoer., nucleo subcoeruleus; NRTP, nucleo reticolare del tegmento pontino; PAG, grigio periacqueduttale; Prep, nucleo preposito dell’ipoglosso; Rest.b, corpo restiforme; SOL, nucleo del tratto solitario; V spin, tratto spinale del nervo trigemino; Vest, nuclei vestibolari; VMS, velo midollare superiore; X, nucleo dorsale del vago; XII, nucleo del nervo ipoglosso

Il talamo e un grande complesso nucleare di forma ovoidale situato nella parete del diencefalo caudalmente al forame interventricolare (Figg. 3.19, 3.20). Lateralmente, un sottile strato di fibre mieliniche, la lamina midollare esterna, divide il corpo principale del talamo dal nucleo reticolare talamico. La principale massa del talamo costituisce il talamo dorsale. Il nucleo reticolare talamico e alcune strutture adiacenti fanno parte del talamo ventrale(vedi in seguito). I termini talamo dorsale e ventrale derivano dalla loro disposizione topografica nella parete laterale del diencefalo durante lo sviluppo (vedi Cap. 2)

Il talamo ventrale occupa una zona relativamente stretta del diencefalo interposta tra il talamo dorsale e l’ipotalamo. I suoi principali gruppi nucleari sono rappresentati dal nucleo reticolare, dalla zona incerta, dal nucleo pregenicolato e dal corpo o nucleo subtalamico (Figg. 6.36, 6.37). E importante notare che Kahle [20] e Richter [52, 53] asseriscono che il nucleo subtalamico forma parte di una zona, subtalamica, separata. Comunque, la maggior parte degli autori non fa questa distinzione e tratta subtalamo e talamo ventrale come sinonimi.