Elsevier

Brain Research Bulletin

Volume 70, Issue 2, 30 June 2006, Pages 124-157
Brain Research Bulletin

Elephant brain: Part I: Gross morphology, functions, comparative anatomy, and evolution

https://doi.org/10.1016/j.brainresbull.2006.03.016Get rights and content

Abstract

We report morphological data on brains of four African, Loxodonta africana, and three Asian elephants, Elephas maximus, and compare findings to literature. Brains exhibit a gyral pattern more complex and with more numerous gyri than in primates, humans included, and in carnivores, but less complex than in cetaceans. Cerebral frontal, parietal, temporal, limbic, and insular lobes are well developed, whereas the occipital lobe is relatively small. The insula is not as opercularized as in man. The temporal lobe is disproportionately large and expands laterally. Humans and elephants have three parallel temporal gyri: superior, middle, and inferior. Hippocampal sizes in elephants and humans are comparable, but proportionally smaller in elephant. A possible carotid rete was observed at the base of the brain. Brain size appears to be related to body size, ecology, sociality, and longevity. Elephant adult brain averages 4783 g, the largest among living and extinct terrestrial mammals; elephant neonate brain averages 50% of its adult brain weight (25% in humans). Cerebellar weight averages 18.6% of brain (1.8 times larger than in humans). During evolution, encephalization quotient has increased by 10-fold (0.2 for extinct Moeritherium, ∼2.0 for extant elephants). We present 20 figures of the elephant brain, 16 of which contain new material. Similarities between human and elephant brains could be due to convergent evolution; both display mosaic characters and are highly derived mammals. Humans and elephants use and make tools and show a range of complex learning skills and behaviors. In elephants, the large amount of cerebral cortex, especially in the temporal lobe, and the well-developed olfactory system, structures associated with complex learning and behavioral functions in humans, may provide the substrate for such complex skills and behavior.

Introduction

Despite the attention of the public to elephants and popularity of these animals, many aspects of elephant biology have been incompletely studied. In particular, detailed studies of the nervous system have been limited, notwithstanding a literature dating from the early 19th century. A recent paper brought to light the paucity of information on elephant brain research and provided a stimulus to publish our findings [22]. In the present investigation, we provide a summary of findings on the gross anatomy of elephant brains.

We studied elephant brains and compared them to other mammalian brains, with the objective to collect data on elephant brain gross morphology. Evolutionary inferences were made based on our examination of ontogenetic stages of elephant brains, from endocasts, and from structures preserved in cranial cavities of extinct proboscideans.

Section snippets

Materials and methods

Our data are based on direct observations of seven elephant brains, three Asian and four African elephants, Elephas maximus and Loxodonta africana, respectively (Table 1A). Elephant brains listed in Table 1A were obtained within 12–24 h after death. They were removed with tools, such as chain saw, chisels, and hammers for adult elephants, or with a Stryker electric handsaw or a hacksaw for a newly born elephant (Fig. 1A and B). Specimens were originally fixed in formaldehyde or

General observations

Six of the seven captive elephant brains available for our study (Table 1A) were females. African elephants (L. africana) brains comprised 13/22 of all the brains listed in Table 1A and B; the remaining eight brains were of Asian elephant (E. maximus), plus one of unknown genus.

Encased in the bony braincase, the brain of an adult elephant is well protected (Fig. 1A, top). In adult elephants, the sidewalls and roof of the braincase are not all solid bones; they are pneumatized, extensively

Historical and current perspectives

Anatomical studies of elephant brains were conducted by various investigators [1], [10], [19], [32], [44], [45], [46], [55], [61], [62], [63], [72], [73], [74], [77], [79], [80], [81], [87], [99], [109], [119], [122], [129], [130], [131]. Each of these investigators focused on certain areas, or made general observations; the study of Dexler [32] was the most comprehensive. The recent review by Cozzi et al. [22] brought to light the paucity of basic detailed research on elephant brains. The

Acknowledgements

Credits for the brains (or parts of them) of specimens A–G are given in Table 1. These individuals deserve special acknowledgments: veterinarians Dalen Agnew, Ann Duncan, and Cindy Stadler (all from the Detroit Zoological Institute), veterinarians Richard J. Montali (National Zoological Park) and Wynona Schallenberger (Toledo Zoo), and Bucky Steele (Seagoville, Texas)—for providing brain specimens. Charles R. Chaff (Museum of Comparative Zoology, MCZ, at Harvard University, Cambridge, MA, USA)

References (144)

  • J. Anthony

    Le névraxe de mammifères

  • M.A. Baker

    A brain-cooling system in mammals

    Sci. Am.

    (1979)
  • M.A. Baker

    Brain cooling in endotherms in heat and exercise

    Ann. Rev. Physiol.

    (1982)
  • R. Barone

    Appareil circulatoire

  • F.E. Beddard

    On the brain of the African elephant

    Proc. Zool. Soc. Lond.

    (1893)
  • F.G. Benedict

    The Physiology of the Elephant

    (1936)
  • J.E.V. Boas et al.

    The Elephant's Head: Studies in the Comparative Anatomy of the Organs of the Head of the Indian Elephant and Other Mammals. Part II

    (1925)
  • C. Braden

    Not so dumbo: should elephants be moved to near the top of the animal-intelligence list?

    BBC Wildl.

    (2003)
  • L.E. Bregmann

    Neue Untersuchungen zur Kenntnis der Pyramidenbahn. 2. Die Oblongatapyramide des Elephanten

    Anat. Anz.

    (1915)
  • R. Brummelkamp

    Das Wachstum der Gehirnmasse mit kleinen cephalisierungssprüngen (sog. √ 2-Sprüngen) bei den Ungulaten

    Acta Neerlandica Morph. Norm. et Path.

    (1939)
  • C.D. Clemente

    Anatomy: A Regional Atlas of the Human Body

    (1987)
  • G. Cole et al.

    The brain in aged elephants

    J. Neuropathol. Exp. Neurol.

    (1990)
  • P. Cottereau

    Elephant memory

    Bulletin de l’Academie Veterinaire de France

    (1969)
  • E.W. Count

    Brain and body weight in man: their antecedents in growth and evolution

    Ann. N. Y. Acad. Sci.

    (1947)
  • G. Crile et al.

    A record of the body weight and certain organ and gland weights of 3690 animals

    Ohio J. Sci.

    (1940)
  • E.C. Crosby et al.

    Correlative Anatomy of the Nervous System

    (1962)
  • C. de Lacoste-Utamsing et al.

    Sexual dimorphism in the human corpus callosum

    Science

    (1982)
  • T.W. Deacon

    Primate brains and senses

  • H.-D. Dellmann et al.

    Central nervous system

  • H.-D. Dellmann et al.

    Equine nervous system

  • H.-D. Dellmann et al.

    Ruminant nervous system

  • H.-D. Dellmann et al.

    Porcine nervous system

  • H.-D. Dellmann et al.

    Carnivore neurology

  • H. Dexler

    Zur Anatomie des Zentralnervensystems von Elephas indicus

    Arb. Neurol. Inst. Wein

    (1907)
  • R. Diepen et al.

    Recherches sur le cerveau de l’éléphant d’Afrique (Loxodonta africana Blum) ll—Données sur l’hypothalamus

    Acta Neurol. Psychiatr. Belg.

    (1956)
  • I. Douglas-Hamilton et al.

    Among the Elephants

    (1975)
  • L. DuBreuil-Chambardel

    Deux cas de duplicité du tronc basilaire

    Bull. Soc. Anat. Paris

    (1923)
  • N.B. Eales

    The anatomy of the head of a foetal African elephant, Elephas africanus (Loxodonta africana)

    Trans. R. Soc. Edinburgh

    (1926)
  • R. Eckert et al.

    Animal Physiology: Mechanisms and Adaptations

    (1988)
  • H. Eichenbaum

    How does the brain organize memories?

    Science

    (1997)
  • J.F. Eisenberg

    The Mammalian Radiation

    (1981)
  • J.F. Eisenberg et al.

    Relative brain size and demographic strategies in didelphid marsupials

    Am. Natur.

    (1981)
  • B.L. Finlay et al.

    Linked regularities in the development and evolution of mammalian brains

    Science

    (1995)
  • R. Fléaux

    Histoire d’une merveille d’ingénierie mécanique: Genèse de la trompe

    Sci. Avenir

    (1998)
  • F. Frade

    Ordre des proboscidiens (Proboscidea Illiger, 1811)

  • M. Friant

    Le premier stade de l’évolution ontogenique du cerveau chez l’éléphant

    Rev. Zool. Bot. Afr.

    (1944)
  • M. Friant

    Deux stades de l’évolution du cerveau (télencephale) de l’éléphant (Loxodonta africana Blum.)

    Acta Univ. Lund N. F. Adv.

    (1951)
  • M. Friant

    Développement et morphologie du cerveau d’un proboscidien, l’ éléphant d’Afrique (Loxodonta africana Blum.)

    Acta Neurol. Psychiatr. Belg.

    (1969)
  • J.-H. Gao et al.

    Cerebellum implicated in sensory acquisition and discrimination rather than motor control

    Science

    (1996)
  • W. Gilchrist

    A Practical Treatise on the Treatment of the Diseases of the Elephant, Camel, and the Horned Cattle with Instructions for Preserving their Efficiency

    (1851)
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