Quantitative neuroanatomy of the brain of the La Plata dolphin, Pontoporia blainvillei

Abstract

The brain of the La Plata dolphin, Pontoporia blainvillei, was studied with methods of quantitative morphology. The volumes and the progression indices of the main brain structures were determined and compared with corresponding data of other Cetacea, Insectivora and Primates. In Pontoporia, encephalization and neocorticalization are clearly greater than in primitive ("basal") Insectivora. The indices are in the lower part of the range for simian monkeys. The paleocortex is regressive in accordance with the total reduction of the olfactory bulb and olfactory tract. In contrast to the situation in primates, the septum, schizocortex and archicortex are not progressive in Pontoporia. The striatum and cerebellum are strongly progressive, corresponding to the efficiency and importance of the motor system in the three-dimensional habitat. The diencephalon, mesencephalon and medulla oblongata show considerable progression. Obviously, this is correlated with the extensive development of structures of the acoustic system. The superficial correspondence of the brains of dolphins and primates in relative size and in the degree of gyrencephaly is rather a rough morphological convergence than a sign of functional equivalence. It is coupled to a strongly divergent development of the various functional systems in the two mammalian orders according to their specific evolution.

Cetacean brains: How aquatic are they?

“…The loss of olfactory input in odontocetes has resulted in a substantial reduction in the hippocampus (archicortex), fornix, and mammillary bodies (Jacobs et al, 1979;Morgane et al, 1980) in odontocetes. On the other hand, the amygdala is large and welldeveloped in odontocetes and other cetaceans (Schwerdtfeger et al, 1984), reflecting the maintenance of substantial nonolfactory sources of input to this structure. The reduction of the hippocampus and related structures in odontocetes is particularly striking in light of the fact that odontocetes possess robust memory and learning skills (Mercado et al, 1998(Mercado et al, , 1999 which, in other mammals, depend highly on the hippocampus.…”

Morphology and Evolutionary Biology of the Dolphin (<i>Delphinus</i> sp.) Brain – MR Imaging and Conventional Histology

“…This is most impressive in the smaller species of the delphinid toothed whales (Odontoceti) with an unexpectedly high brain mass which, in relation to body mass, is second only to that of the human [Schwerdtfeger et al, 1984;Oelschläger and Oelschläger, 2002;Manger, 2006].…”

“…Structures of the dolphin brain were labeled in cresyl violet sections from coronal, horizontal, and sagittal microslide series following the nomenclature of Ogawa and Arifuku [1948], Jansen and Jansen [1969], McFarland et al [1969], Dailly [1972], Morgane and Jacobs [1972], Morgane et al [1980], Pilleri et al [1980], Schwerdtfeger et al [1984], Oelschläger and Oelschläger [2002] as well as Terminologia Anatomica [1998] and Schaller [1992]. Structures of gray substance are in capitals, white substance and cortical sulci in lower case, cranial nerves in Arabic numerals and ventricular spaces in lower case and Roman numerals.…”

Anatomy and three‐dimensional reconstructions of the brain of the white whale (Delphinapterus leucas) from magnetic resonance images

“…Although there are a number of published descriptions of cetacean neuroanatomy (see Morgane et al, 1986;Ridgway, 1990; for reviews of this literature) there are only a handful of studies in which morphometric analyses were conducted in a systematic way permitting quantitative comparative analysis with other mammals (Jacobs et al, 1984;Johnson et al, 1984;Schwerdtfeger et al, 1984;Garey and Leuba, 1986;Johnson et al, 1994;Tarpley and Ridgway, 1994;Manger et al, 1998;Marino, 1998). Furthermore, with the exception of Morgane et al (1980), Ridgway and Brownson (1984), Haug (1987), and Tarpley and Ridgway (1994) there are no systematic anatomical descriptions of whole cetacean brains and substructures at the qualitative level.…”