Elsevier

Brain Research Bulletin

Volume 54, Issue 2, 15 January 2001, Pages 219-227
Brain Research Bulletin

An overview of the central nervous system of the elephant through a critical appraisal of the literature published in the XIX and XX centuries

https://doi.org/10.1016/S0361-9230(00)00456-1Get rights and content

Abstract

The two species of elephants (Indian: Elephas maximus and African: Loxodonta africana) possess the largest brain among land mammals. Due to its size, the elephant brain is discussed in virtually every paper dealing with the evolution of the central nervous system of mammals and comparative brain size. Studies on the social habits of elephants also deal with the skills and the “intelligence” and brain size of these species. Yet most of the descriptions and conclusions reported in comparative studies rely on second-hand data derived from investigations performed several decades before, often dating as far back as the XIX century. Furthermore, many of the original papers actually describing gross and detailed features of the brain of elephants are either no longer available, are written in languages other than English, or are difficult to trace. The present study gives a short description of the anatomy of the central nervous system of elephants, with special attention to its distinctive features, reports all available literature on the subject, and briefly discusses its origins and rationale.

Introduction

The African elephant (Loxodonta africana) and the Indian elephant (Elephas maximus) possess the largest brain among land mammals. The development of the central nervous system in mammals, the relationships between brain and body weights, and the thickness of the neocortex have all been studied to evaluate the evolution of the brain in different Orders and between Families of mammals 12, 17, 29, 34, 36, 52, 53, 55, 57, 58, 59, 60, 62, 77, 80, 105, 107, 114, 117, 119, 120, 128, 130. For recent and comprehensive reviews see [120] and [128]. Due to these studies it is widely known that the brains of the two species of elephant rank among the highest for absolute and relative mass, cortical expansion, and complexity, features comparable only to those of some Cetacea and man 29, 77, 128, 130.

However, a close scrutiny of comparative studies of brain evolution reveals that data relative to the brain of the elephant seldom rely on original investigations and rarely (if ever) discriminate between Loxodonta and Elephas. It appears that the values relative to brain size and architecture are mostly taken from few original investigations, or quoted second-handedly from the original studies.

The literature on the brain of the Order Proboscidea is not abundant or easy to access. We started this study with the intent of collecting the largest possible body of literature on the brain of elephants, and to make it available to investigators wishing to study the subject. In the present paper we also briefly outline the main features of the brain of elephants, with special attention to the relevant differences with the general mammalian plan. Furthermore we analyzed the literature to understand the reasons for the relatively scarce development of the investigations, also taking into account the growing interest in other large mammals.

Section snippets

Materials and methods

We started our investigation by use of conventional electronic data banks, and specifically Medline and Current Contents (courtesy of the Universities of Milan and Padua, Italy) checking key words related to elephants.

We then proceeded to search the Zoological Record (printed version, courtesy of the Museum of Natural History of Milan, Italy) for any reference relative to elephants dating to the years preceding the use of electronic data banks in science.

References 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

Brain weight

The elephant brain has a weight of 4.5 to 6.5 kg 2, 6, 14, 86, 119 (Elephas’s brain is up to 5.5 kg, while Loxodonta’s is slightly heavier and larger).

Telencephalon

The most striking features of the elephant forebrain are the complexity and depth of gyri, the development of the parietal and temporal lobes and the large cerebellum (Fig. 1 A–C). Rostrocaudal diameter is compressed, while the lateral one is enlarged [78]. The general outline of the telencephalon is reminiscent of that of Cetacea, and

Discussion

Our data indicate that the literature dedicated to the brain of Proboscidea is scarce. In relatively recent years, the elephant brain has been taken into account only as comparison in brain-body weight ratios and evolutionary studies. Most of the articles dealing with the neuroanatomy of Proboscidea discuss the brain of the elephant in general (n = 26 out of 52), or describe features specific of the Indian elephant brain (n = 17). Direct references to the neuroanatomy of Loxodonta africana are

Acknowledgements

We wish to thank Dr. Luigi Cagnolaro and Dr. Michela Podestà, Director and Curator, respectively, of the Museum of Natural History of Milan, Italy, for their precious help with the specific literature. A special thanks goes to Andrew Berman of New York, NY, USA, for critical revision of the manuscript. A special thanks also goes to Professor Antonio Barasa of the University of Turin, Italy, who kindly allowed us to use a drawing of a pyramidal neuron from one of his preparations of the brain of

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