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Wright AK, Theilmann RJ, Ridgway SH, Scadeng M. Diffusion tractography reveals pervasive asymmetry of cerebral white matter tracts in the bottlenose dolphin (Tursiops truncatus). Brain Struct Funct 2017; 223:1697-1711. [PMID: 29189908 PMCID: PMC5884918 DOI: 10.1007/s00429-017-1525-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2016] [Accepted: 07/06/2017] [Indexed: 12/18/2022]
Abstract
Brain enlargement is associated with concomitant growth of interneuronal distance, increased conduction time, and reduced neuronal interconnectivity. Recognition of these functional constraints led to the hypothesis that large-brained mammals should exhibit greater structural and functional brain lateralization. As a taxon with the largest brains in the animal kingdom, Cetacea provides a unique opportunity to examine asymmetries of brain structure and function. In the present study, diffusion tensor imaging and tractography were used to investigate cerebral white matter asymmetry in the bottlenose dolphin (Tursiops truncatus). Widespread white matter asymmetries were observed with the preponderance of tracts exhibiting leftward structural asymmetries. Leftward lateralization may reflect differential processing and execution of behaviorally variant sensory and motor functions by the cerebral hemispheres. The arcuate fasciculus, an association tract linked to human language evolution, was isolated and exhibited rightward asymmetry suggesting a right hemisphere bias for conspecific communication unlike that of most mammals. This study represents the first examination of cetacean white matter asymmetry and constitutes an important step toward understanding potential drivers of structural asymmetry and its role in underpinning functional and behavioral lateralization in cetaceans.
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Affiliation(s)
- Alexandra K Wright
- Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California-San Diego, La Jolla, CA, 92093, USA.
| | - Rebecca J Theilmann
- Department of Radiology, University of California-San Diego, La Jolla, CA, 92093, USA
| | - Sam H Ridgway
- National Marine Mammal Foundation, San Diego, CA, 92106, USA
| | - Miriam Scadeng
- Center for Functional MRI, Department of Radiology, University of California-San Diego, La Jolla, CA, 92093, USA
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Abstract
AbstractX-ray computed tomography (CT) provides a nondestructive means of studying the inside and outside of objects. It allows accurate visualization and measurement of internal features, that are otherwise impossible to obtain nondestructively, and is a lasting digital record that can be made available to future researchers, museums, and the general public. Here, an overview of CT scanning methodologies and protocol is provided, as well as some recent examples of how this technology is allowing paleontologists to make new inroads into understanding the ecology, evolution, and development of both extant and extinct organisms. Lastly, some frontiers and outstanding questions in the acquisition, processing, and storage of digital 3-D morphological data are highlighted.
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Neuroanatomy of the killer whale (Orcinus orca): a magnetic resonance imaging investigation of structure with insights on function and evolution. Brain Struct Funct 2016; 222:417-436. [PMID: 27119362 DOI: 10.1007/s00429-016-1225-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2015] [Accepted: 04/07/2016] [Indexed: 12/18/2022]
Abstract
The evolutionary process of adaptation to an obligatory aquatic existence dramatically modified cetacean brain structure and function. The brain of the killer whale (Orcinus orca) may be the largest of all taxa supporting a panoply of cognitive, sensory, and sensorimotor abilities. Despite this, examination of the O. orca brain has been limited in scope resulting in significant deficits in knowledge concerning its structure and function. The present study aims to describe the neural organization and potential function of the O. orca brain while linking these traits to potential evolutionary drivers. Magnetic resonance imaging was used for volumetric analysis and three-dimensional reconstruction of an in situ postmortem O. orca brain. Measurements were determined for cortical gray and cerebral white matter, subcortical nuclei, cerebellar gray and white matter, corpus callosum, hippocampi, superior and inferior colliculi, and neuroendocrine structures. With cerebral volume comprising 81.51 % of the total brain volume, this O. orca brain is one of the most corticalized mammalian brains studied to date. O. orca and other delphinoid cetaceans exhibit isometric scaling of cerebral white matter with increasing brain size, a trait that violates an otherwise evolutionarily conserved cerebral scaling law. Using comparative neurobiology, it is argued that the divergent cerebral morphology of delphinoid cetaceans compared to other mammalian taxa may have evolved in response to the sensorimotor demands of the aquatic environment. Furthermore, selective pressures associated with the evolution of echolocation and unihemispheric sleep are implicated in substructure morphology and function. This neuroanatomical dataset, heretofore absent from the literature, provides important quantitative data to test hypotheses regarding brain structure, function, and evolution within Cetacea and across Mammalia.
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Anterior commissure versus corpus callosum: A quantitative comparison across mammals. ZOOLOGY 2016; 119:126-136. [DOI: 10.1016/j.zool.2016.02.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 01/11/2016] [Accepted: 02/22/2016] [Indexed: 11/20/2022]
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Ridgway S, Samuelson D, Van Alstyne K, Price D. On doing two things at once: dolphin brain and nose coordinate sonar clicks, buzzes, and emotional squeals with social sounds during fish capture. J Exp Biol 2015; 218:3987-95. [DOI: 10.1242/jeb.130559] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2015] [Accepted: 10/13/2015] [Indexed: 11/20/2022]
Abstract
Dolphins fishing alone in open waters may whistle without interrupting their sonar clicks as they find and eat or reject fish. Our study is the first to match sound and video from the dolphin with sound and video from near the fish. During search and capture of fish, free-swimming dolphins carried cameras to record video and sound. A hydrophone in the far field near the fish also recorded sound. From these two perspectives, we studied the time course of dolphin sound production during fish capture. Our observations identify the instant of fish capture. There are three consistent acoustic phases: sonar clicks locate the fish; bout 0.4 sec before capture, the dolphin clicks become more rapid to form a second phase, the terminal buzz; at or just before capture, the buzz turns to an emotional squeal-the victory squeal, which may last 0.2 to 20 sec after capture. The squeals are pulse bursts that vary in duration, peak frequency, and amplitude. The victory squeal may be a reflection of emotion triggered by brain dopamine release. It may also affect prey to ease capture and or it may be a way to communicate the presence of food to other dolphins.
Dolphins also use whistles as communication or social sounds. Whistling during sonar clicking suggests that dolphins may be adept at doing two things at once. We know that dolphin brain hemispheres may sleep independently. Our results suggest that the two dolphin brain hemispheres may also act independently in communication.
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Affiliation(s)
- Sam Ridgway
- National Marine Mammal Foundation, 2240 Shelter Island Drive, Ste 200, San Diego, CA 92106, USA
| | - Dianna Samuelson
- National Marine Mammal Foundation, 2240 Shelter Island Drive, Ste 200, San Diego, CA 92106, USA
| | - Kaitlin Van Alstyne
- National Marine Mammal Foundation, 2240 Shelter Island Drive, Ste 200, San Diego, CA 92106, USA
| | - DruAnn Price
- National Marine Mammal Foundation, 2240 Shelter Island Drive, Ste 200, San Diego, CA 92106, USA
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Mortensen HS, Pakkenberg B, Dam M, Dietz R, Sonne C, Mikkelsen B, Eriksen N. Quantitative relationships in delphinid neocortex. Front Neuroanat 2014; 8:132. [PMID: 25505387 PMCID: PMC4244864 DOI: 10.3389/fnana.2014.00132] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2014] [Accepted: 10/29/2014] [Indexed: 12/04/2022] Open
Abstract
Possessing large brains and complex behavioral patterns, cetaceans are believed to be highly intelligent. Their brains, which are the largest in the Animal Kingdom and have enormous gyrification compared with terrestrial mammals, have long been of scientific interest. Few studies, however, report total number of brain cells in cetaceans, and even fewer have used unbiased counting methods. In this study, using stereological methods, we estimated the total number of cells in the neocortex of the long-finned pilot whale (Globicephala melas) brain. For the first time, we show that a species of dolphin has more neocortical neurons than any mammal studied to date including humans. These cell numbers are compared across various mammals with different brain sizes, and the function of possessing many neurons is discussed. We found that the long-finned pilot whale neocortex has approximately 37.2 × 109 neurons, which is almost twice as many as humans, and 127 × 109 glial cells. Thus, the absolute number of neurons in the human neocortex is not correlated with the superior cognitive abilities of humans (at least compared to cetaceans) as has previously been hypothesized. However, as neuron density in long-finned pilot whales is lower than that in humans, their higher cell number appears to be due to their larger brain. Accordingly, our findings make an important contribution to the ongoing debate over quantitative relationships in the mammalian brain.
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Affiliation(s)
- Heidi S Mortensen
- Research Laboratory for Stereology and Neuroscience, Bispebjerg and Frederiksberg University Hospitals Copenhagen, Denmark ; Research Department, Environment Agency Torshavn, Faroe Islands
| | - Bente Pakkenberg
- Research Laboratory for Stereology and Neuroscience, Bispebjerg and Frederiksberg University Hospitals Copenhagen, Denmark
| | - Maria Dam
- Research Department, Environment Agency Torshavn, Faroe Islands
| | - Rune Dietz
- Department of Bioscience, Institute for Bioscience - Arctic Research Centre, Roskilde, University of Aarhus Roskilde, Denmark
| | - Christian Sonne
- Department of Bioscience, Institute for Bioscience - Arctic Research Centre, Roskilde, University of Aarhus Roskilde, Denmark
| | | | - Nina Eriksen
- Research Laboratory for Stereology and Neuroscience, Bispebjerg and Frederiksberg University Hospitals Copenhagen, Denmark
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Racicot RA, Colbert MW. Morphology and Variation in Porpoise (Cetacea: Phocoenidae) Cranial Endocasts. Anat Rec (Hoboken) 2013; 296:979-92. [DOI: 10.1002/ar.22704] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2012] [Accepted: 03/20/2013] [Indexed: 11/09/2022]
Affiliation(s)
- Rachel A. Racicot
- Department of Geology and Geophysics; Yale University; New Haven Connecticut
| | - Matthew W. Colbert
- Jackson School of Geosciences; The University of Texas at Austin; Austin Texas
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Manger P, Hemingway J, Haagensen M, Gilissen E. Cross-sectional area of the elephant corpus callosum: comparison to other eutherian mammals. Neuroscience 2010; 167:815-24. [DOI: 10.1016/j.neuroscience.2010.02.066] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2010] [Revised: 02/22/2010] [Accepted: 02/23/2010] [Indexed: 10/19/2022]
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Ridgway S, Keogh M, Carder D, Finneran J, Kamolnick T, Todd M, Goldblatt A. Dolphins maintain cognitive performance during 72 to 120 hours of continuous auditory vigilance. J Exp Biol 2009; 212:1519-27. [DOI: 10.1242/jeb.027896] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYThe present study reports the first use of a choice visual–vocal response time cognitive task, during 72 or 120 h of continuous auditory vigilance. Two adult bottlenose dolphins (Tursiops truncatus), NAY(male) and SAY (female), maintained a very high detection rate(91.1–98.7%) of random 1.5 s goal tones infrequently substituted in a background of frequent 0.5 s equal-amplitude tones over continuous 72 or 120 h sessions. In addition, a choice visual–vocal response time task (CVVRT)tested cognitive performance during night time sessions, when the dolphins would have ordinarily been resting or asleep as we had observed in previous studies. NAY and SAY detected a single-bar, posterior, vertical, green (S1g)or 3-bar, anterior, horizontal, red (S2r) LED light stimulus presented randomly to each eye. They responded with a different vocalization (whistle or pulse burst) to each stimulus (S1g or S2r) presented randomly to left and right eyes. The animals maintained high levels of goal tone detection without signs of sleep deprivation as indicated by behavior, blood indices or marked sleep rebound during 24 h of continuous post-experiment observation. Acoustic goal tone response time (AGTRT) overall did not change during the 72 h(F=0.528, P=0.655) or 120 h (F=0.384, P=0.816) sessions. Nor did CVVRT slow or degrade over the 72 h(F=4.188, P=0.104) or 120 h (F=2.298, P=0.119) AGTRT sessions.
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Affiliation(s)
- Sam Ridgway
- US Navy Marine Mammal Program, SSC Pacific, Code 715, 53560 Hull Street, San Diego, CA 92152, USA
- Department of Pathology, School of Medicine, University of California, San Diego, CA 92093, USA
| | - Mandy Keogh
- Department of Biology, San Diego State University, San Diego, CA 92182,USA
| | - Don Carder
- US Navy Marine Mammal Program, SSC Pacific, Code 715, 53560 Hull Street, San Diego, CA 92152, USA
| | - James Finneran
- US Navy Marine Mammal Program, SSC Pacific, Code 715, 53560 Hull Street, San Diego, CA 92152, USA
| | | | - Mark Todd
- SAIC Biosolutions Division, San Diego, CA 92110, USA
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