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Brain Studies

Brain Studies



Acoustic Studies | Captivity Studies | Field Studies | Toxin Studies

Dolphins can maintain vigilant behavior through echolocation for 15 days without interruption or cognitive impairment. Branstetter B, Finneran J, Fletcher E, Weisman B, Ridgway S (2012).

Dolphin social intelligence: complex alliance relationships in bottlenose dolphins and a consideration of selective environments for extreme brain size evolution in mammals. Connor, Richard (2007).

The social and cultural roots of whale and dolphin brains. Fox, Kieran C. R., et al. (2017)

Large brains and lengthened life history periods in odontocetes. Lefebvre, L, et al. (2006).

Cetacean sleep: An unusual form of mammalian sleep. Lyamina, Oleg I., et al (2008).

Towards a New Paradigm of Non-Captive Research on Cetacean Cognition. Marino, Lori, Toni Frohoff (2011).

A claim in search of evidence: reply to Manger's thermogenesis hypothesis of cetacean brain structure. Marino, Lori et al. (2008).

Cetaceans Have Complex Brains for Complex Cognition. Marino, Lori et al. (2007).

Neuroanatomy of the killer whale (Orcinus orca) from magnetic resonance images. Marino, Lori et al. (2004).

Anatomy and three-dimensional reconstructions of the brain of a bottlenose dolphin (Tursiops truncatus) from magnetic resonance images. Marino, Lori et al. (2001).

The evolutionary history of cetacean brain and body size. Montgomery, S. H. et al. (2013).

Precocious development of self-awareness in dolphins. Morrison R, Diana Reiss. (2018).

Neuroanatomy of the killer whale (Orcinus orca): a magnetic resonance imaging investigation of structure with insights on function and evolution.. Wright A, et al. (2016).

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Branstetter B, Finneran J, Fletcher E, Weisman B, Ridgway S (2012). Dolphins can maintain vigilant behavior through echolocation for 15 days without interruption or cognitive impairment. PLoS One 7(10):e47478

ABSTRACT

In dolphins, natural selection has developed unihemispheric sleep where alternating hemispheres of their brain stay awake. This allows dolphins to maintain consciousness in response to respiratory demands of the ocean. Unihemispheric sleep may also allow dolphins to maintain vigilant states over long periods of time. Because of the relatively poor visibility in the ocean, dolphins use echolocation to interrogate their environment. During echolocation, dolphin produce clicks and listen to returning echoes to determine the location and identity of objects. The extent to which individual dolphins are able to maintain continuous vigilance through this active sense is unknown. Here we show that dolphins may continuously echolocate and accurately report the presence of targets for at least 15 days without interruption. During a total of three sessions, each lasting five days, two dolphins maintained echolocation behaviors while successfully detecting and reporting targets. Overall performance was between 75 to 86% correct for one dolphin and 97 to 99% correct for a second dolphin. Both animals demonstrated diel patterns in echolocation behavior. A 15-day testing session with one dolphin resulted in near perfect performance with no significant decrement over time. Our results demonstrate that dolphins can continuously monitor their environment and maintain long-term vigilant behavior through echolocation

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Connor, Richard (2007). Dolphin social intelligence: complex alliance relationships in bottlenose dolphins and a consideration of selective environments for extreme brain size evolution in mammals. Phil. Trans. R. Soc. B doi:10.1098/rstb.2006.1997.

ABSTRACT

Bottlenose dolphins in Shark Bay, Australia, live in a large, unbounded society with a fission-fusion grouping pattern. Potential cognitive demands include the need to develop social strategies involving the recognition of a large number of individuals and their relationships with others. Patterns of alliance affiliation among males may be more complex than are currently known for any non-human, with individuals participating in 2-3 levels of shifting alliances. Males mediate alliance relationships with gentle contact behaviours such as petting, but synchrony also plays an important role in affiliative interactions. In general, selection for social intelligence in the context of shifting alliances will depend on the extent to which there are strategic options and risk. Extreme brain size evolution may have occurred more than once in the toothed whales, reaching peaks in the dolphin family and the sperm whale. All three 'peaks' of large brain size evolution in mammals (odontocetes, humans and elephants) shared a common selective environment: extreme mutual dependence based on external threats from predators or conspecific groups. In this context, social competition, and consequently selection for greater cognitive abilities and large brain size, was intense.

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Fox, Kieran C. R., Michael Muthukrishna and Susanne Shultz The social and cultural roots of whale and dolphin brains. Nature Ecology & Evolution 1, 1699–1705 (2017); doi :10.1038/s41559-017-0336-y. (2017)

ABSTRACT

Encephalization, or brain expansion, underpins humans’ sophisticated social cognition, including language, joint attention, shared goals, teaching, consensus decision-making and empathy. These abilities promote and stabilize cooperative social interactions, and have allowed us to create a ‘cognitive’ or ‘cultural’ niche and colonize almost every terrestrial ecosystem. Cetaceans (whales and dolphins) also have exceptionally large and anatomically sophisticated brains. Here, by evaluating a comprehensive database of brain size, social structures and cultural behaviours across cetacean species, we ask whether cetacean brains are similarly associated with a marine cultural niche. We show that cetacean encephalization is predicted by both social structure and by a quadratic relationship with group size. Moreover, brain size predicts the breadth of social and cultural behaviours, as well as ecological factors (diversity of prey types and to a lesser extent latitudinal range). The apparent coevolution of brains, social structure and behavioural richness of marine mammals provides a unique and striking parallel to the large brains and hyper-sociality of humans and other primates. Our results suggest that cetacean social cognition might similarly have arisen to provide the capacity to learn and use a diverse set of behavioural strategies in response to the challenges of social living. Full paper.

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Lefebvre, L, Marino, L., Sol, D, Lemieux S, Arshad, S. (2006). Large brains and lengthened life history periods in odontocetes. Brain Behavior and Evolution. 268: 218-228.

ABSTRACT

Previous work on primates and birds suggests that large brains require longer periods of juvenile growth, leading to reproductive constraints due to delayed maturation. We examined the relationship between brain size and life history periods in cetaceans, a large-brained mammalian order that has been largely ignored. We looked at males and females of twenty-five species of odontocetes, using independent contrasts and multiple regressions to disentangle possible phylogenetic effects and inter-correlations among life history traits. We corrected all variables for body size allometry and separated life span into adult and juvenile periods. For females and both sexes combined, gestation, time to sexual maturity, time as an adult and life span were all positively associated with residual brain size in simple regressions; in multiple regressions maximum life span and time as an adult were the best predictors of brain size. Males showed few significant trends. Our results suggest that brain size has co-evolved with extended life history periods in odontocetes, as it has in primates and birds, and that a lengthened adult period could have been an important component of encephalization in cetaceans. Full paper.

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Lyamina, Oleg I., Paul R. Manger,, Sam H. Ridgway, Lev M. Mukhametov and Jerome M. Siegel (2008). Cetacean sleep: An unusual form of mammalian sleep. Neuroscience & Biobehavioral Reviews Volume 32, Issue 8, October 2008, Pages 1451-1484.

ABSTRACT
Our knowledge of the form of lateralized sleep behavior, known as unihemispheric slow wave sleep (USWS), seen in all members of the order Cetacea examined to date, is described. We trace the discovery of this phenotypically unusual form of mammalian sleep and highlight specific aspects that are different from sleep in terrestrial mammals. We find that for cetaceans sleep is characterized by USWS, a negligible amount or complete absence of rapid eye movement (REM) sleep, and a varying degree of movement during sleep associated with body size, and an asymmetrical eye state. We then compare the anatomy of the mammalian somnogenic system with what is known in cetaceans, highlighting areas where additional knowledge is needed to understand cetacean sleep. Three suggested functions of USWS (facilitation of movement, more efficient sensory processing and control of breathing) are discussed. Lastly, the possible selection pressures leading to this form of sleep are examined, leading us to the suggestion that the selection pressure necessitating the evolution of cetacean sleep was most likely the need to offset heat loss to the water from birth and throughout life. Aspects such as sentinel functions and breathing are likely to be proximate evolutionary phenomenon of this form of sleep.

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Marino, Lori, Toni Frohoff (2011). Towards a New Paradigm of Non-Captive Research on Cetacean Cognition. PLoS ONE 6(9): e24121. doi:10.1371/journal.pone.0024121.

ABSTRACT

Contemporary knowledge of impressive neurophysiology and behavior in cetaceans, combined with increasing opportunities for studying free-ranging cetaceans who initiate sociable interaction with humans, are converging to highlight serious ethical considerations and emerging opportunities for a new era of progressive and less-invasive cetacean research. Most research on cetacean cognition has taken place in controlled captive settings, e.g., research labs, marine parks. While these environments afford a certain amount of experimental rigor and logistical control they are fraught with limitations in external validity, impose tremendous stress on the part of the captive animals, and place burdens on populations from which they are often captured. Alternatively, over the past three decades, some researchers have sought to focus their attention on the presence of free-ranging cetacean individuals and groups who have initiated, or chosen to participate in, sociable interactions with humans in the wild. This new approach, defined as Interspecies Collaborative Research between cetacean and human, involves developing novel ways to address research questions under natural conditions and respecting the individual cetacean's autonomy. It also offers a range of potential direct benefits to the cetaceans studied, as well as allowing for unprecedented cognitive and psychological research on sociable mysticetes. Yet stringent precautions are warranted so as to not increase their vulnerability to human activities or pathogens. When conducted in its best and most responsible form, collaborative research with free-ranging cetaceans can deliver methodological innovation and invaluable new insights while not necessitating the ethical and scientific compromises that characterize research in captivity. Further, it is representative of a new epoch in science in which research is designed so that the participating cetaceans are the direct recipients of the benefits.

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Marino, Lori, Camilla Butti, Richard C. Connor, R. Ewan Fordyce, Louis M. Herman, Patrick R. Hof, Louis Lefebvre, David Lusseau, Brenda McCowan, Esther A. Nimchinsky, Adam A. Pack, Joy S. Reidenberg, Diana Reiss, Luke Rendell, Mark D. Uhen, Estelle Van der Gucht, and Hal Whitehead (2008). A claim in search of evidence: reply to Manger's thermogenesis hypothesis of cetacean brain structure. Biological Reviews doi:10.1111/j.1469-185X.2008.00049.x.

ABSTRACT

In a recent publication in Biological Reviews, Manger (2006) made the controversial claim that the large brains of cetaceans evolved to generate heat during oceanic cooling in the Oligocene epoch and not, as is the currently accepted view, as a basis for an increase in cognitive or information-processing capabilities in response to ecological or social pressures. Manger further argued that dolphins and other cetaceans are considerably less intelligent than generally thought. In this review we challenge Manger's arguments and provide abundant evidence that modern cetacean brains are large in order to support complex cognitive abilities driven by social and ecological forces. FULL PAPER HERE.

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Marino, Lori; Richard C. Connor, R. Ewan Fordyce, Louis M. Herman, Patrick R. Hof, Louis Lefebvre, David Lusseau, Brenda McCowan, Esther A. Nimchinsky, Adam A. Pack, Luke Rendell, Joy S. Reidenberg, Diana Reiss, Mark D. Uhen, Estel Van der Gucht, Hal Whitehead. Cetaceans Have Complex Brains for Complex Cognition. PLos Biol 5(5): e139 doi:10.1371/journal.pbio.0050139. 2007.

ABSTRACT

The brain of a sperm whale is about 60% larger in absolute mass than that of an elephant. Furthermore, the brains of toothed whales and dolphins are significantly larger than those of any nonhuman primates and are second only to human brains when measured with respect to body size [1]. How and why did such large brains evolve in these modern cetaceans? One current view of the evolution of dolphin brains is that their large size was primarily a response to social forces-the requirements for effective functioning within a complex society characterized by communication and collaboration as well as competition among group members [2-4]. In such a society, individuals can benefit from the recognition of others and knowledge of their relationships and from flexibility in adapting to or implementing new behaviors as social or ecological context shifts. Other views focus on the cognitive demands associated with the use of echolocation [5-7].

Recently, Manger [8] made the controversial claim that cetacean brains are large because they contain an unusually large number of thermogenic glial cells whose numbers increased greatly to counteract heat loss during a decrease in ocean temperatures in the Eocene-Oligocene transition. Therefore, he argues, cetacean brain size could have evolved independently of any cognitive demands and, further, that there is neither neuronal evidence nor behavioral evidence of complex cognition in cetaceans. These claims have garnered considerable attention in the popular press, because they challenge prevailing knowledge and understanding of cetacean brain evolution, cognition, and behavior.

We believe that the time is ripe to present an integrated view of cetacean brains, behavior, and evolution based on the wealth of accumulated and recent data on these topics. Our conclusions support the more generally accepted view that the large brain of cetaceans evolved to support complex cognitive abilities.

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Marino, Lori; Chet C. Sherwood, Bradley N. Delman, Cheuk Y. Tang, Thomas P. Naidich, Patrick R. Hof. Neuroanatomy of the killer whale (Orcinus orca) from magnetic resonance images. Anat Rec 281A, 2:1256-1263 264:397-414, 2004.

ABSTRACT

This article presents the first series of MRI-based anatomically labeled sectioned images of the brain of the killer whale (Orcinus orca). Magnetic resonance images of the brain of an adult killer whale were acquired in the coronal and axial planes. The gross morphology of the killer whale brain is comparable in some respects to that of other odontocete brains, including the unusual spatial arrangement of midbrain structures. There are also intriguing differences. Cerebral hemispheres appear extremely convoluted and, in contrast to smaller cetacean species, the killer whale brain possesses an exceptional degree of cortical elaboration in the insular cortex, temporal operculum, and the cortical limbic lobe. The functional and evolutionary implications of these features are discussed.
Full paper HERE.

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Marino, Lori; Keith D. Sudheimer, Timothy L. Murphy, Kristina K. Davis, D. Ann Pabst, William A. McLellan, James K. Rilling, John I. Johnson. 2001. Anatomy and three-dimensional reconstructions of the brain of a bottlenose dolphin (Tursiops truncatus) from magnetic resonance images. Anat Rec 264:397-414.

ABSTRACT

Cetacean (dolphin, whale, and porpoise) brains are among the least studied mammalian brains because of the formidability of collecting and histologically preparing such relatively rare and large specimens. Magnetic resonance imaging offers a means of observing the internal structure of the brain when traditional histological procedures are not practical. Furthermore, internal structures can be analyzed in their precise anatomic positions, which is difficult to accomplish after the spatial distortions often accompanying histological processing. In this study, images of the brain of an adult bottlenose dolphin, Tursiops truncatus, were scanned in the coronal plane at 148 antero-posterior levels. From these scans a computer-generated three-dimensional model was constructed using the programs VoxelView and VoxelMath (Vital Images, Inc.). This model, wherein details of internal and external morphology are represented in three-dimensional space, was then resectioned in orthogonal planes to produce corresponding series of virtual sections in the horizontal and sagittal planes. Sections in all three planes display the sizes and positions of major neuroanatomical features such as the arrangement of cortical lobes and subcortical structures such as the inferior and superior colliculi, and demonstrate the utility of MRI for neuroanatomical investigations of dolphin brains.

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Montgomery, Stephen H, Jonathan H. Geisler, Michael R. McGowen, Charlotte Fox, Lori Marino, John Gatesy. The evolutionary history of cetacean brain and body size. Int. Jour. of Organic Evolution, Volume 67, Issue 11 November 2013.

ABSTRACT

Cetaceans rival primates in brain size relative to body size and include species with the largest brains and biggest bodies to have ever evolved. Cetaceans are remarkably diverse, varying in both phenotypes by several orders of magnitude, with notable differences between the two extant suborders, Mysticeti and Odontoceti. We analyzed the evolutionary history of brain and body mass, and relative brain size measured by the encephalization quotient (EQ), using a data set of extinct and extant taxa to capture temporal variation in the mode and direction of evolution. Our results suggest that cetacean brain and body mass evolved under strong directional trends to increase through time, but decreases in EQ were widespread. Mysticetes have significantly lower EQs than odontocetes due to a shift in brain:body allometry following the divergence of the suborders, caused by rapid increases in body mass in Mysticeti and a period of body mass reduction in Odontoceti. The pattern in Cetacea contrasts with that in primates, which experienced strong trends to increase brain mass and relative brain size, but not body mass. We discuss what these analyses reveal about the convergent evolution of large brains, and highlight that until recently the most encephalized mammals were odontocetes, not primates.

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Morrison R, Diana Reiss. (2018). Precocious development of self-awareness in dolphins. PLOS One: 10 January 2018.

ABSTRACT

Mirror-self recognition (MSR) is a behavioral indicator of self-awareness in young children and only a few other species, including the great apes, dolphins, elephants and magpies. The emergence of self-awareness in children typically occurs during the second year and has been correlated with sensorimotor development and growing social and self-awareness. Comparative studies of MSR in chimpanzees report that the onset of this ability occurs between 2 years 4 months and 3 years 9 months of age. Studies of wild and captive bottlenose dolphins (Tursiops truncatus) have reported precocious sensorimotor and social awareness during the first weeks of life, but no comparative MSR research has been conducted with this species. We exposed two young bottlenose dolphins to an underwater mirror and analyzed video recordings of their behavioral responses over a 3-year period. Here we report that both dolphins exhibited MSR, indicated by self-directed behavior at the mirror, at ages earlier than generally reported for children and at ages much earlier than reported for chimpanzees. The early onset of MSR in young dolphins occurs in parallel with their advanced sensorimotor development, complex and reciprocal social interactions, and growing social awareness. Both dolphins passed subsequent mark tests at ages comparable with children. Thus, our findings indicate that dolphins exhibit self-awareness at a mirror at a younger age than previously reported for children or other species tested. Full paper here: https://doi.org/10.1371/journal.pone.0189813

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Wright A, Scadeng M, Stec D, Dubowitz R, Ridgway S, St. Leger J. (2016). Neuroanatomy of the killer whale (Orcinus orca): a magnetic resonance imaging investigation of structure with insights on function and evolution. Brain Structure and Function pp 1-20 First online: 27 April 2016.

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.
The publication is available online or by request (awright@ucsd.edu or alexandrakwright@gmail.com)

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