Original Article

Brain Structure and Function

, Volume 220, Issue 1, pp 361-383

In contrast to many other mammals, cetaceans have relatively small hippocampi that appear to lack adult neurogenesis

  • Nina PatzkeAffiliated withSchool of Anatomical Sciences, University of the Witwatersrand
  • , Muhammad A. SpocterAffiliated withSchool of Anatomical Sciences, University of the WitwatersrandDepartment of Anatomy, Des Moines University
  • , Karl Æ. KarlssonAffiliated withBiomedical Engineering, Reykjavik University
  • , Mads F. BertelsenAffiliated withCentre for Zoo and Wild Animal Health, Copenhagen Zoo
  • , Mark HaagensenAffiliated withDepartment of Radiology, Donald Gordon Medical Centre, University of the Witwatersrand
  • , Richard ChawanaAffiliated withSchool of Anatomical Sciences, University of the Witwatersrand
  • , Sonja StreicherAffiliated withDepartment of Zoology and Entomology, University of Pretoria
  • , Consolate KasweraAffiliated withFaculté des Sciences, University of Kisangani
  • , Emmanuel GilissenAffiliated withSchool of Anatomical Sciences, University of the WitwatersrandDepartment of African Zoology, Royal Museum for Central AfricaLaboratory of Histology and Neuropathology, Université libre de BruxellesDepartment of Anthropology, University of Arkansas
    • , Abdulaziz N. AlagailiAffiliated withSchool of Anatomical Sciences, University of the WitwatersrandKSU Mammals Research Chair, Department of Zoology, King Saud University
    • , Osama B. MohammedAffiliated withSchool of Anatomical Sciences, University of the WitwatersrandKSU Mammals Research Chair, Department of Zoology, King Saud University
    • , Roger L. ReepAffiliated withSchool of Anatomical Sciences, University of the WitwatersrandDepartment of Physiological Sciences, University of Florida
    • , Nigel C. BennettAffiliated withSchool of Anatomical Sciences, University of the WitwatersrandDepartment of Zoology and Entomology, University of PretoriaKSU Mammals Research Chair, Department of Zoology, King Saud University
    • , Jerry M. SiegelAffiliated withSchool of Anatomical Sciences, University of the WitwatersrandNeurobiology Research, 151A3, Department of Psychiatry, Brain Research Institute, UCLA School of Medicine, Sepulveda VA Medical Centre
    • , Amadi O. IhunwoAffiliated withSchool of Anatomical Sciences, University of the Witwatersrand
    • , Paul R. MangerAffiliated withSchool of Anatomical Sciences, University of the Witwatersrand Email author 

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Abstract

The hippocampus is essential for the formation and retrieval of memories and is a crucial neural structure sub-serving complex cognition. Adult hippocampal neurogenesis, the birth, migration and integration of new neurons, is thought to contribute to hippocampal circuit plasticity to augment function. We evaluated hippocampal volume in relation to brain volume in 375 mammal species and examined 71 mammal species for the presence of adult hippocampal neurogenesis using immunohistochemistry for doublecortin, an endogenous marker of immature neurons that can be used as a proxy marker for the presence of adult neurogenesis. We identified that the hippocampus in cetaceans (whales, dolphins and porpoises) is both absolutely and relatively small for their overall brain size, and found that the mammalian hippocampus scaled as an exponential function in relation to brain volume. In contrast, the amygdala was found to scale as a linear function of brain volume, but again, the relative size of the amygdala in cetaceans was small. The cetacean hippocampus lacks staining for doublecortin in the dentate gyrus and thus shows no clear signs of adult hippocampal neurogenesis. This lack of evidence of adult hippocampal neurogenesis, along with the small hippocampus, questions current assumptions regarding cognitive abilities associated with hippocampal function in the cetaceans. These anatomical features of the cetacean hippocampus may be related to the lack of postnatal sleep, causing a postnatal cessation of hippocampal neurogenesis.

Keywords

Adult hippocampal neurogenesis Hippocampus Doublecortin Memory Mammalia Cognition