John Irwin Johnson

Barrels in cerebral cortex altered by receptor disruption in newborn, but not in five-day-old mice (Cricetidae and Muridae)

Fig. 1. Photographs and graphic reconstructions of normal and disrupted barrel fields in cerebral cortices of Cricetid deer mice Peromyscus leucopus, compared with the arrangement of vibrissa follicles and a peripheral lesion. Top right : diagram of the arrangement of vibrissa follicles. Large follicles form 5 postero-anterior rows, here labeled A, B, C, D, E, and at least 4 complete columns, two of which are labeled 1 and 2. Four posteriormost follicles, labeled a,/3, ~,, 6, straddle the 5 rows. The pattern shown here is consistently seen in Peromyscus leucopus, and appears to be the same as that seen in Murid house mice Mus musculus 18. The cross-hatched area indicates the follicles lesioned at birth on the snout of the animal whose contralateral cortical barrel field is pictured at the bottom of this figure. Center: Normal barrel field, postero-medial portion. The photomicrograph at left is a tangential 18 section through layer IV of a cerebral cortex fixed on the tenth postnatal day. The diagram at right depicts in heavy lines the barrels visible in the photograph; lighter lines show reconstruction of barrels visible in neighboring sections. Like the follicles, barrels are arranged in 5 rows labeled A through E, and in columns two of which are labeled 1 and 2, and 4 posteriormost barrels labeled c~,/3, T, 6, straddle the 5 rows. Barrels in Mus is closely resemble these in size and arrangement but are not so nearly square in shape. This pattern of barrels was seen in all normal animals, in cortices ipsilateral to lesioned follicles (i.e., contralateral to non-lesioned sides), and in both hemispheres of animals whose vibrissae were removed daily, and of animals whose follicles were lesioned 5 days postnatally. Bottom: disrupted barrel field in cerebral cortex contralateral to follicles lesioned on the first postnatal day as indicated in diagram at top right, fixed at 11 days after birth. Heavy lines in diagram at right indicate structural features visible in photomicrograph at left, finer lines indicate features reconstructed from neighboring sections. Greatly enlarged barrel-like formations mark the position normally occupied by barrel rows A-E in columns 1-4.

Manatee cerebral cortex: cytoarchitecture of the frontal region in Trichechus manatus latirostris

Members of the order Sirenia are unique among mammals in being the only totally aquatic herbivores. They display correspondingly specialized physiological, behavioral and anatomical features. There have been few reports concerning sirenian neuroanatomy, and most of these have consisted of gross anatomical observations. Our interest in Sirenia stems from the desire to understand neuroanatomical specializations in the context of behavior and the effort to elucidate trends in mammalian brain evolution. The architecture of frontal regions of cerebral cortex was investigated in several brains of the Florida manatee, Trichechus manatus latirostris. Through observation of sections stained for Nissl substance or myelinated fibers, several distinct cortical areas were identified on the basis of laminar organization. These range from areas with poorly defined laminae to those having 6 well-defined layers, some of which exhibit sublayers. Two cortical areas exhibit pronounced cell clusters in layer VI, and these stain positively for acetylcholinesterase and cytochrome oxidase. We hypothesize that these clusters may be involved in perioral tactile bristle function. Certain of our findings are consistent with previous observations in the literature on the brains of dugongs. On the basis of their lamination patterns, these frontal cortical areas appear to be organized into concentric zones of allocortex, mesocortex and isocortex.

Phylogeny through Brain Traits: More Characters for the Analysis of Mammalian Evolution

We have assembled data on nine brain traits, in addition to the fifteen we have previously described, which provide new evidence for assessing mammalian relationships. States of these characters are tabulated as they occur in each of 152 mammalian species, providing data in numerically ordered form, useful for multiple analyses of phylogenetic relationships in programs which take into account variations in several different characters simultaneously. Derived states of each of the nine traits are characteristic of certain restricted groups of mammals; (1) mirroring of the complete SI body representation in isocortex (anthropoid primates); (2) loss of the accessory olfactory bulbs (sirenians, cetaceans, most bats, catarrhine primates); (3) Rindenkerne, clumps of cell bodies in layer 6 of cerebral cortex (sirenians); (4) posteriorly-pointing digits in the SI body representation (bats, both mega- and micro-); (5) equivalent tectopetal connections to the anterior colliculus of one side from both retinas, rather than predominantly from the contralateral retina (primates and megabats); (6) loss of lamination in dorsal cochlear nuclei (anthropoid primates, bats, seals, sirenians, cetaceans); (7) separation of claustrum from cerebral cortex (diprotodont marsupials, carnivores, artiodactyls, perissodactyls, hyracoids, cetaceans and primates), (8) presence of a complete secondary (SII) somatic sensory region of cerebral cortex (therians-all extant mammals other than monotremes), and (9) presence of a distinct external cuneate nucleus among the nuclei of the dorsal columns (all mammalian groups except monotremes and sirenians). Two examples of phylogenetic trees derived from these data are presented. These sample trees maintain the segregation of the monotremes and the marsupials, and the basic dichotomy of placentals seen in our earlier trees based entirely on brain data. They also show: an orderly sequence of bifurcations (rather than the commonly seen multifurcation near the base of the radiation) in the reconstruction of placental relationships; extremes of derivation for the Cetacea, the Chiroptera, and the Sirenia (in concordance with trees based on other data); a ferungulate association of Carnivora, Perissodactyla, Artiodactyla, Hyracoidea and Sirenia; and an assemblage of related Dermoptera, Primates, Scandentia, and Chiroptera which in this model also includes Insectivora and Macroscelidea. Analyses based on brain characters can reinforce conclusions based on other data, while at the same time introducing new ideas about relationships. Neural traits provide a source of data independent of those commonly used in phylogenetic analysis, and are extremely valuable for testing old hypotheses and for introducing new ones.(ABSTRACT TRUNCATED AT 400 WORDS)

Phylogeny through Brain Traits: The Distribution of Categorizing Characters in Contemporary Mammals

The varying states of 15 characters of the central neural organization are tabulated as they occur in each of 147 mammalian species. For each character and species, scores are entered designating the primitive or derived state of the character as it is observed in that species. This tabulation provides data in numerically ordered form for multiple analyses of possible phylogenetic relationships which take into account variations in several different characters simultaneously.

Anatomy and three-dimensional reconstructions of the brain of a bottlenose dolphin (Tursiops truncatus) from magnetic resonance images.

Cetacean (dolphin, whale, and porpoise) brains are among the least studied mammalian brains because of the formidability of collecting and histologically preparing such relatively rare and large specimens. Magnetic resonance imaging offers a means of observing the internal structure of the brain when traditional histological procedures are not practical. Furthermore, internal structures can be analyzed in their precise anatomic positions, which is difficult to accomplish after the spatial distortions often accompanying histological processing. In this study, images of the brain of an adult bottlenose dolphin, Tursiops truncatus, were scanned in the coronal plane at 148 antero‐posterior levels. From these scans a computer‐generated three‐dimensional model was constructed using the programs VoxelView and VoxelMath (Vital Images, Inc.). This model, wherein details of internal and external morphology are represented in three‐dimensional space, was then resectioned in orthogonal planes to produce corresponding series of virtual sections in the horizontal and sagittal planes. Sections in all three planes display the sizes and positions of major neuroanatomical features such as the arrangement of cortical lobes and subcortical structures such as the inferior and superior colliculi, and demonstrate the utility of MRI for neuroanatomical investigations of dolphin brains. Anat Rec 264:397–414, 2001.

Identification of motoneurons innervating the tensor tympani and tensor veli palatini muscles in the cat

The somatotopic arrangement of the motoneurons associated with the two non-masticatory muscles innervated by the trigeminal motor nerve, tensor tympani (TT) and tensor veli palatini (TVP), was determined in the cat using retrograde transport of horseradish peroxidase. The motoneurons of the TT are distinct and separate, ventral and ventral-lateral to the rostral two-thirds of the trigeminal motor nucleus. The cells are smaller than those of the motor nucleus and constitute a parvocellular division. Based on functional and morphological criteria, TT motoneurons may be considered as an accessory trigeminal nucleus. The somatotopic arrangement of TVP motoneurons has been described for the first time. These motoneurons are located in the rostral two-thirds of the ventromedial division of the cat trigeminal motor nucleus. The location of motoneurons associated with TT and TVP does not fit the parcellation of the cat trigeminal motor nucleus as described by previous investigators. The motoneurons of these muscles can now be assigned to areas either within (TVP) or adjacent to (TT) the rostral two-thirds of the motor nucleus.

Magnetic resonance imaging and three-dimensional reconstructions of the brain of a fetal common dolphin, Delphinus delphis

To demonstrate the kinds of data that can be obtained non-destructively and non-invasively from preserved museum specimens using modern imaging technology the head region of a whole body fetal specimen of the common dolphin, Delphinus delphis, aged 8–9 months post-conception, was scanned using Magnetic Resonance Imaging (MRI). Series of scans were obtained in coronal, sagittal and horizontal planes. A digital three-dimensional reconstruction of the whole brain was prepared from the coronal series of scans. Sectional areas and three-dimensional volumes were obtained of the cerebral hemispheres and of the brainstem-plus-cerebellum. Neuroanatomical features identified in the scans include the major sulci of the cerebral hemispheres, well-differentiated regions of gray and white matter, the mesencephalic, pontine, and cervical flexures, the ”foreshortened’’ appearance of the forebrain, and the large auditory inferior colliculi. These findings show that numerous features of the fetal common dolphin brain can be visualized and analyzed from MRI scans.

The anterior border zones of primary somatic sensory (SI) neocortex and their relation to cerebral convolutions, shown by micromapping of peripheral projections to the region of the fourth forepaw digit representation in raccoons

In raccoons the somatic sensory neocortex is greatly expanded, with separate gyral crowns devoted to and intervening sulci separating, sensory representations of separate body parts, most strikingly those of the volar surfaces of individual forepaw digits. Most of the cortex in this region is buried in widely ramifying sulcal walls, wherein sensory projections have not been studied. We have determined mechanosensory projections to the fourth digit representation region including all neighboring sulcal walls, using tungsten microelectrodes for 3-dimensional micromapping. We found no significant alteration in the location and pattern of projections when the following different anesthetics were used: dial-urethane, chloralose, or methoxyflurane with nitrous oxide. The precisely organized somatotopic representation of the distal volar surface of the fourth digit, on the causal aspect of its gyral crown, continues down the anterior bank of the triradiate sulcus. This meets, at the fundus, projections from the proximal volar surface of the digit which occupy the posterior sulcus wall; they in turn meet projections from the volar palm at the gyral crown. In the anterior part of the crown containing the representation of the distal volar digit, across the crown. In the anterior part of the crown containing the representation of the distal volar digit, across the crown of the gyral bridge intervening between the medial and lateral segments of the central sulcus, throughout the posterior walls of the central sulci, and in the walls of the interbrachial sulcus, we found a distinctive border-zone of projections from heterogeneous receptive fields. Within a roughly somatotopic basic pattern of organization we found intermingled projections from single and multiple claws and dorsal hairy surfaces of digits and proximal hand, along with additional projections from volar surfaces. These projections can be construed as forming something of a distorted mirror-image of the representation of the volar hand. Beyond this was a second zone of distinctive projections from afferents of the forelimb muscles, in the anterior walls of the central sulci. These projections are interrupted where the sulci are interrupted. The zone of muscle afferent projections corresponds to those seen between sensory and motor regions in other species; its strict association with sulcal folding here and in other species suggests a general relationship of these projections to central sulci. The zone of heterogeneous projections resembles similar zones seen at other levels of this system in raccoons, in the cortex of other species, and it may relate to some of the multiple representation reported in other species. It also may be related to the formation of sulci in this region and may be a specialized zone for cortico-cortical connections.

Anatomy and Three-Dimensional Reconstructions of the Brain of the White Whale (Delphinapterus leucas) From Magnetic Resonance Images

Magnetic resonance imaging offers a means of observing the internal structure of the brain where traditional procedures of embedding, sectioning, staining, mounting, and microscopic examination of thousands of sections are not practical. Furthermore, internal structures can be analyzed in their precise quantitative spatial interrelationships, which is difficult to accomplish after the spatial distortions often accompanying histological processing. For these reasons, magnetic resonance imaging makes specimens that were traditionally difficult to analyze, more accessible. In the present study, images of the brain of a white whale (Beluga) Delphinapterus leucas were scanned in the coronal plane at 119 antero‐posterior levels. From these scans, a computer‐generated three‐dimensional model was constructed using the programs VoxelView and VoxelMath (Vital Images, Inc.). This model, wherein details of internal and external morphology are represented in three‐dimensional space, was then resectioned in orthogonal planes to produce corresponding series of “virtual” sections in the horizontal and sagittal planes. Sections in all three planes display the sizes and positions of such structures as the corpus callosum, internal capsule, cerebral peduncles, cerebral ventricles, certain thalamic nuclear groups, caudate nucleus, ventral striatum, pontine nuclei, cerebellar cortex and white matter, and all cerebral cortical sulci and gyri. Anat Rec 262:429–439, 2001.

Morphological Correlates of Specialized Elaborations in Somatic Sensory Cerebral Neocortex

More engaging and frivolous titles for this review might be “Bumps and Barrels, Brains and Behaviors” or “The New Phrenology.” As with the Old Phrenology, the subject matter here is the correlation of morphological characters—growth and bumps—with “mental faculties and traits of character,” behavioral character, the probabilities of occurrence of specific kinds of actions. The Old Phrenology restricted its concern to humans, and failed because of its flawed premise that brain growths could be detected through faithfully correlated protuberances in the overlying bone. Our New Phrenology looks at the brain directly, and, by widening its attention to consider all mammals, it succeeds in discovering correlations between the observed morphology and the predictive probabilities of behavior.