Evolution of Nervous Control from Primitive Organisms to Man A Symposium organized by the Section on Medical Sciences of the American Association for the Advancement of Science, and presented at the New York Meeting on December 29–30, 1956. Edited by Allan D. Bass. Pp. vii + 231. (Washington, D.C.: American Association for the Advancement of Science; London: Bailey Bros. and Swinfen, Ltd., 1959.) 52s.

The Central Nervous System

Analysis of data collected on 131 species of primates, bats, and insectivores showed that the sizes of brain components, from medulla to forebrain, are highly predictable from absolute brain size by a nonlinear function. The order of neurogenesis was found to be highly conserved across a wide range of mammals and to correlate with the relative enlargement of structures as brain size increases, with disproportionately large growth occurring in late-generated structures. Because the order of neurogenesis is conserved, the most likely brain alteration resulting from selection for any behavioral ability may be a coordinated enlargement of the entire nonolfactory brain.

https://science.sciencemag.org/content/sci/268/5217/1578.full.pdf

Linked regularities in the development and evolution of mammalian brains

Chemosensory receptors are essential for the survival of organisms that range from bacteria to mammals. Recent studies have shown that the numbers of functional chemosensory receptor genes and pseudogenes vary enormously among the genomes of different animal species. Although much of the variation can be explained by the adaptation of organisms to different environments, it has become clear that a substantial portion is generated by genomic drift, a random process of gene duplication and deletion. Genomic drift also generates a substantial amount of copy-number variation in chemosensory receptor genes within species. It seems that mutation by gene duplication and inactivation has important roles in both the adaptive and non-adaptive evolution of chemosensation.

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The evolution of animal chemosensory receptor gene repertoires: roles of chance and necessity.

A broad range of evidence regarding the functional organization of the vertebrate brain - spanning from comparative neurology to experimental psychology and neurophysiology to clinical data - is reviewed for its bearing on conceptions of the neural organization of consciousness. A novel principle relating target selection, action selection, and motivation to one another, as a means to optimize integration for action in real time, is introduced. With its help, the principal macrosystems of the vertebrate brain can be seen to form a centralized functional design in which an upper brain stem system organized for conscious function performs a penultimate step in action control. This upper brain stem system retained a key role throughout the evolutionary process by which an expanding forebrain - culminating in the cerebral cortex of mammals - came to serve as a medium for the elaboration of conscious contents. This highly conserved upper brainstem system, which extends from the roof of the midbrain to the basal diencephalon, integrates the massively parallel and distributed information capacity of the cerebral hemispheres into the limited-capacity, sequential mode of operation required for coherent behavior. It maintains special connective relations with cortical territories implicated in attentional and conscious functions, but is not rendered nonfunctional in the absence of cortical input. This helps explain the purposive, goal-directed behavior exhibited by mammals after experimental decortication, as well as the evidence that children born without a cortex are conscious. Taken together these circumstances suggest that brainstem mechanisms are integral to the constitution of the conscious state, and that an adequate account of neural mechanisms of conscious function cannot be confined to the thalamocortical complex alone.

http://www.summer12.isc.uqam.ca/page/docs/readings/Merker-Bjorn/Merker-Consciousness%20without%20a%20cerebral%20cortex.pdf

Consciousness without a cerebral cortex: a challenge for neuroscience and medicine.

Animals use the geomagnetic field in many ways: the magnetic vector provides a compass; magnetic intensity and/or inclination play a role as a component of the navigational ‘map’, and magnetic conditions of certain regions act as ‘sign posts’ or triggers, eliciting specific responses. A magnetic compass is widespread among animals, magnetic navigation is indicated e.g. in birds, marine turtles and spiny lobsters and the use of magnetic ‘sign posts’ has been described for birds and marine turtles. For magnetoreception, two hypotheses are currently discussed, one proposing a chemical compass based on a radical pair mechanism, the other postulating processes involving magnetite particles. The available evidence suggests that birds use both mechanisms, with the radical pair mechanism in the right eye providing directional information and a magnetite-based mechanism in the upper beak providing information on position as component of the ‘map’. Behavioral data from other animals indicate a light-dependent compass probably based on a radical pair mechanism in amphibians and a possibly magnetite-based mechanism in mammals. Histological and electrophysiological data suggest a magnetite-based mechanism in the nasal cavities of salmonid fish. Little is known about the parts of the brain where the respective information is processed.

/pdf/magnetic-orientation-and-magnetoreception-in-birds-and-other-3ifs8uqbja.pdf

Magnetic orientation and magnetoreception in birds and other animals

The neural substrate subserving magnetic orientation is largely unknown in vertebrates and unstudied in mammals. We combined a behavioral test for magnetic compass orientation in mole rats and immunocytochemical visualization of the transcription factor c-Fos as a marker of neuronal activity. We found that the superior colliculus of the Zambian mole rat (Cryptomys anselli) contains neurons that are responsive to magnetic stimuli. These neurons are directionally selective and organized within a discrete sublayer. Our results constitute evidence for the involvement of a specific mammalian brain structure in magnetoreception.

https://science.sciencemag.org/content/sci/294/5541/366.full.pdf

Neuroanatomy of Magnetoreception: The Superior Colliculus Involved in Magnetic Orientation in a Mammal

SUMMARY The forelimb of whales and dolphins is a flipper that shows hyperphalangy (numerous finger bones). Hyperphalangy is also present in marine reptiles, including ichthyosaurs and plesiosaurs. The developmental basis of hyper-phalangy is unclear. Kukenthal suggested that phalanx anlagen split into three pieces during cetacean development, thereby multiplying the ancestral number. Alternatively, Holder suggested that apical ectodermal ridge (AER)-directed limb outgrowth might be prolonged by a timing shift (heterochrony), leading to terminal addition of extra phalanges. We prepared a series of whole mounted and serially sectioned embryonic flipper buds of the spotted dolphin Stenella attenuata. This cetacean shows marked hyperphalangy on digits II and III. We confirm previous reports that the proximodistal laying down of phalanges is prolonged in digits II and III. Histology showed that the apical ectoderm was thickened into a cap. There was a weak ridge-like structure in some embryos. The cap or ridge formed part of a bud-like mass that persisted on digits II and III at stages when it had disappeared from other digits. Thus the dolphin differs from other mammals in showing a second period of limb outgrowth during which localized hyperphalangy develops. New phalanges only formed at the tip of the digits. These findings are consistent with a model in which heterochrony leads to the terminal addition of new phalanges. Our results are more easily reconciled with the progress zone model than one in which the AER is involved in the expansion of a prepattern. We suggest that patterning mechanisms with a temporal component (i.e., the “progress zone” mechanism) are potential targets for heterochrony during limb evolution.

Time, pattern, and heterochrony: a study of hyperphalangy in the dolphin embryo flipper.

Serial sections of 13 embryos and fetuses of the harbor porpoise from 10 mm crown-rump length up to 167 mm total length were studied. Unlike the adult animals, ontogenetic stages of 18-27 mm crown-rump length still show a typical mammalian olfactory bulb. The olfactory bulb primordium is penetrated by olfactory nerve fibers, the latter passing through the cribriform plate. However, the olfactory bulb anlage is gradually reduced in later stages, its placodal component being largely uncoupled from the telencephalon. As a ganglionlike structure, the remains of the placodal component stay in contact with the nasal septum and mucosa via thin bundles of nerve fibers. The ganglion and plexus can be traced within the meninges until the adult stage of the porpoise. There is strong evidence that they represent the material of the terminalis system, which cannot be distinguished from the olfactory system in earlier stages. A vomeronasal organ could not be detected in the embryonal and fetal material investigated.

Development and rudimentation of the peripheral olfactory system in the harbor porpoise Phocoena phocoena (Mammalia: Cetacea)

Cetaceans are the most fascinating creatures in the animal kingdom. They adapted so perfectly to their aquatic habitat that it is hard to imagine they originated from typical tetrapod land mammals. Naturally, this change to an extremely different habitat brought about profound modifications and specializations in the cetacean sensory world. Dolphins have a fairly effective visual system, which allows good sight above and below the water surface (Nachtigall, 1986; Dral, 1987). The peripheral olfactory system is reduced totally, but still occurs during early ontogenesis (Jacobs et al., 1971; Oelschlager and Buhl, 1985a, b) while the taste organ, in principle, is retained (Nachtigall and Hall, 1984). Cutaneous sensitivity seems to be fairly good in cetaceans (Herman and Tavolga, 1980) and there are indications that dolphins may possess a magnetic sense (Zoeger et al., 1981; Bauer et al., 1985; Kirschvink et al., 1986; Credle, 1988). However, it is the acoustic system, which is clearly dominant and optimized by a highly efficient ultrasound transmitter for echolocation. The latter may be connected functionally with the unusually well-developed terminalis system (Demski et al., 1985; Buhl and Oelschlager, 1986; Oelschlager et al., 1987; Ridgway et al., 1987; Oelschlager, 1989). Some toothed whales presumably can...,“emit sounds so intense that their prey is debilitated and capture made easier” (Norris and Mohl, 1983).

Evolutionary Morphology and Acoustics in the Dolphin Skull

The early ontogenesis and topography of the mammalian terminalis system was investigated in 43 microslide series of toothed whale and human embryos and fetuses. In early embryonal stages the development of the nasal pit, the olfacto-terminalis placode, and the olfactory bulb anlage is rather similar in toothed whales and humans. However, toothed whales do not show any trace of the vomeronasalis complex. In early fetal stages the olfactory bulb anlage in toothed whales is reduced and leaves the isolated future terminalis ganglion (ganglia) which contains the greatest number of cells within Mammalia. The ganglion is connected with the nasal mucosa via peripheral fiber bundles and with the telencephalon via central terminalis rootlets. The functional implications of the terminalis system in mammals and its evolution in toothed whales are discussed. Obviously, the autonomic component has been enlarged in the course of perfect adaptation to an aquatic environment.

Helmut H.A. Oelschläger

Papers

Neuroanatomy of Magnetoreception: The Superior Colliculus Involved in Magnetic Orientation in a Mammal

Time, pattern, and heterochrony: a study of hyperphalangy in the dolphin embryo flipper.

Development and rudimentation of the peripheral olfactory system in the harbor porpoise Phocoena phocoena (Mammalia: Cetacea)

Evolutionary Morphology and Acoustics in the Dolphin Skull

Development of the Nervus Terminalis in Mammals Including Toothed Whales and Humans