Regional Brain Morphometry and Lissencephaly in the Sirenia

Reep, Roger L.; O’Shea, Thomas J.

doi:10.1159/000115866

Cited by 47 publications

(17 citation statements)

References 19 publications

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“…Measurements of total brain volume, cerebellar volume, and body mass for 14 orders of extant mammals were assembled from the literature, including Monotremata (16), Marsupalia (16,17), Insectivora, Macroscelidae and Scandentia (18), Chiroptera (19), Rodentia (17), Edentata (20), Lagomorpha (21), Cetacea (22,23), Proboscidea (24), Sirenia (25), Rodentia (17), Artiodactyla (26), Carnivora (17,21), and Primates (12-14, 18, 21, 27).…”

Section: Methodsmentioning

confidence: 99%

Reciprocal evolution of the cerebellum and neocortex in fossil humans

Weaver

2005

Proc. Natl. Acad. Sci. U.S.A.

177

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Human brain evolution involved both neurological reorganization and an increase in overall brain volume relative to body mass. It is generally difficult to draw functional inferences about the timing and nature of brain reorganization, given that superficial brain morphology recorded on fossil endocasts is functionally ambiguous. However, the cerebellum, housed in the clearly delineated posterior cranial fossa, is functionally and ontologically discrete. The cerebellum is reciprocally connected to each of 14 neocortical regions important to human cognitive evolution. Cerebellar volume varies significantly relative to overall brain volume among mammalian orders, as well as within the primate order. There is also significant diachronic variation among fossil human taxa. In the australopithecines and early members of the genus Homo, the cerebral hemispheres were large in proportion to the cerebellum, compared with other hominoids. This trend continued in Middle and Late Pleistocene humans, including Neandertals and CroMagnon 1, who have the largest cerebral hemispheres relative to cerebellum volume of any primates, including earlier and Holocene humans. In recent humans, however, the pattern is reversed; the cerebellum is larger with respect to the rest of the brain (and, conversely, the cerebral hemispheres are smaller with respect to the cerebellum) than in Late Pleistocene humans. The cerebellum and cerebral hemispheres appear to have evolved reciprocally. Cerebellar development in Holocene humans may have provided greater computational efficiency for coping with an increasingly complex cultural and conceptual environment.human evolution ͉ Plio-Pleistocene hominins ͉ Upper Paleolithic transition P aleoneurologists agree that increased encephalization is an important dynamic of human brain evolution. However, brain evolution involved more than brain expansion. It also involved reorganization to support specific, uniquely human cognitive tasks, including those involved in linguistic processing and a highly developed facility for manufacturing and manipulating tools. Nevertheless, despite more than a century of effort, there is little consensus about how and when such reorganization occurred.One approach to exploring functional reorganization of the brain in humans has been the analysis of impressions of the brain's surface convolutions (sulci and gyri) on the inner table of the endocranium. However, endocranial markings are notoriously difficult to identify reliably (1, 2). Even where the impressions are fairly clear, taphonomic processes may distort the evidence. In addition, the functional correlates of the brain's surface convolutions, especially in fossils, are literally superficial. Cognitive functions occur through internal connections among brain regions, as well as through the distribution of neuroreceptors that cannot be detected by examining the surface of the brain, let alone from endocranial markings. Therefore, functional inferences based on sulcal patterns are problematic.Another approach to endocran...

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Section: Methodsmentioning

confidence: 99%

Reciprocal evolution of the cerebellum and neocortex in fossil humans

Weaver

2005

Proc. Natl. Acad. Sci. U.S.A.

177

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“…As the only portion available of the insula of the Florida manatee was the most rostral region, we only investigated the anterior part of the insula in our specimen and refer to Marshall and Reep (1995) for the structure of the posterior insula in this species. The brain of sirenians represents an important departure from the general Bauplan of the mammalian brain as it is characterized by a pronounced lissencephaly except for a deep and extremely wide lateral (pseudosylvian) fissure and two additional fissures originating at its dorsal end and extending caudally (Reep and O'Shea 1990). The width of the lateral fissure results in the lack of hidden cortex that, combined with the lissencephalic condition, makes the Fig.…”

Section: Sireniansmentioning

confidence: 99%

The insular cortex: a comparative perspective

2010

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The human insular cortex is involved in a variety of viscerosensory, visceromotor, and interoceptive functions, and plays a role in complex processes such as emotions, music, and language. Across mammals, the insula has considerable morphologic variability. We review the structure and connectivity of the insula in laboratory animals (mouse, domestic cat, macaque monkey), and we present original data on the morphology and cytoarchitecture of insular cortex in less common species including a large carnivore (the Atlantic walrus, Odobenus rosmarus), two artiodactyls (the pigmy hippopotamus, Hexaprotodon liberiensis, and the Western bongo, Tragelaphus eurycerus), two cetaceans (the beluga whale, Delphinapterus leucas, and the minke whale, Balaenoptera acutorostrata), and a sirenian (the Florida manatee, Trichechus manatus latirostris). The insula shows substantial variability in shape, extent, and gyral and sulcal patterns, as well as differences in laminar organization, cellular specialization, and structural association with the claustrum. Our observations reveal that the insular cortex is extremely variable among mammals. These differences could be related to the role exerted by specific and selective pressures on cortical structure during evolution. We conclude that it is not possible to identify a general model of organization for the mammalian insular cortex.

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“…Sirenians, which include manatees and dugongs, are unusual members of Afrotheria because they have adapted to an entirely aquatic lifestyle and have a highly unusual, lissencephalic brain for their relatively large body size [Edinger, 1933[Edinger, , 1939Reep et al, 1989;Reep and O'Shea, 1990] ( fig. 1 ).…”

Section: Introductionmentioning

confidence: 99%

Golgi Analysis of Neuron Morphology in the Presumptive Somatosensory Cortex and Visual Cortex of the Florida Manatee <b><i>(Trichechus manatus latirostris)</i></b>

Reyes

Harland²,

Reep³

et al. 2016

Brain Behav Evol

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The current study investigates neuron morphology in presumptive primary somatosensory (S1) and primary visual (V1) cortices of the Florida manatee (Trichechus manatus latirostris) as revealed by Golgi impregnation. Sirenians, including manatees, have an aquatic lifestyle, a large body size, and a relatively large lissencephalic brain. The present study examines neuron morphology in 3 cortical areas: in S1, dorsolateral cortex area 1 (DL1) and cluster cortex area 2 (CL2) and in V1, dorsolateral cortex area 4 (DL4). Neurons exhibited a variety of morphological types, with pyramidal neurons being the most common. The large variety of neuron types present in the manatee cortex was comparable to that seen in other eutherian mammals, except for rodents and primates, where pyramid-shaped neurons predominate. A comparison between pyramidal neurons in S1 and V1 indicated relatively greater dendritic branching in S1. Across all 3 areas, the dendritic arborization pattern of pyramidal neurons was also similar to that observed previously in the afrotherian rock hyrax, cetartiodactyls, opossums, and echidnas but did not resemble the widely bifurcated dendrites seen in the large-brained African elephant. Despite adaptations for an aquatic environment, manatees did not share specific neuron types such as tritufted and star-like neurons that have been found in cetaceans. Manatees exhibit an evolutionarily primitive pattern of cortical neuron morphology shared with most other mammals and do not appear to have neuronal specializations for an aquatic niche.

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Regional Brain Morphometry and Lissencephaly in the Sirenia

Cited by 47 publications

References 19 publications

Reciprocal evolution of the cerebellum and neocortex in fossil humans

Reciprocal evolution of the cerebellum and neocortex in fossil humans

The insular cortex: a comparative perspective

Golgi Analysis of Neuron Morphology in the Presumptive Somatosensory Cortex and Visual Cortex of the Florida Manatee <b><i>(Trichechus manatus latirostris)</i></b>

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