Animal intelligence as encephalization

Jerison, Harry J.

doi:10.1098/rstb.1985.0007

Cited by 177 publications

(60 citation statements)

References 25 publications

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“…Thus, it appears likely that dorsal cortex in turtles plays a different role in information processing than does isocortex in mammals. It should be noted that these conclusions provide support for the idea that mammals may differ qualitatively from reptiles in some aspects of learning capacity (Hodos, 1982;Jerison, 1985;Macphail, 1982). It seems possible that mammals may be capable of some tasks requiring complex isolation processing and feature abstraction of which reptiles {or at least reptiles similar to turtles in brain organization) are incapable.…”

Section: Implications For Turtle Cortical Organization and Functionsupporting

confidence: 57%

Neurotransmitter organization and connections of turtle cortex: implications for the evolution of mammalian isocortex

Reiner

1993

Comparative Biochemistry and Physiology Part A: Physiology

117

116

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Abstract-Telencephalic cortex in turtles is a simple three layered-structure. The dorsal most part of this structure is thought to resemble the reptilian forerunner of at least parts of mammalian isocortex. This dorsal part of turtle cortex contains several functionally distinct regions that show similarity in their connections and function to specific areas in mammalian isocortex. The types of neurons found in turtle dorsal cortex (as defined by their morphology and neurotransmitter content) also show great similarity to those observed in mammals, with the major exception that turtle cortex appears to lack the types of neurons found in granular and supragranular layers of mammalian isocortex. Similar results have also been observed in other living reptiles. Thus, one major step in the evolution of reptilian cortex into mammalian cortex must have been the addition of the types of neurons found in the granular and supragranular layers of mammalian isocortex. These observations for turtles also suggest that turtle cortex in particular and reptilian telencephalic cortex in general must differ functionally from mammalian isocortex with respect to those features associated with the laminar and columnar organization of isocortex. These issues are discussed in more detail below and in Reiner (1991).

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Section: Implications For Turtle Cortical Organization and Functionsupporting

confidence: 57%

Neurotransmitter organization and connections of turtle cortex: implications for the evolution of mammalian isocortex

Reiner

1993

Comparative Biochemistry and Physiology Part A: Physiology

117

116

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“…By definition, a large brain of large EQ would be expected to have much more excess brain mass than a small brain of similarly large EQ. Interestingly, however, Jerison expected that ''when the larger-bodied species is encephalized to the same extent as the smaller one, it should have the same number of 'extra neurons' as the smaller species'' (Jerison, 1985). This expectation was based on the smaller density of neurons in larger than smaller brains (Tower and Elliott, 1952;Tower, 1954;Jerison, 1963).…”

Section: Discussionmentioning

confidence: 99%

“…Of interest, much evidence suggests that larger EQs or relative brain size endow species with improved cognitive abilities (Lefebvre et al, 2004); with behavioral flexibility, such as the ability to respond successfully to novel environments (Sol et al, 2005) or to alternate between feeding strategies (Ratcliffe et al, 2006); and even correlate with intelligence (Jerison, 1985). These findings seem to agree with the fact that humans, dolphins, and chimpanzees have the largest known EQs (Marino, 1998).…”

mentioning

confidence: 85%

Encephalization, Neuronal Excess, and Neuronal Index in Rodents

Herculano‐Houzel

2007

The Anatomical Record

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Encephalization, or brain size larger than expected from body size, has long been considered to correlate with improved cognitive abilities across species and even intelligence. However, it is still unknown what characteristics of relatively large brains underlie their improved functions. Here, it is shown that more encephalized rodent species have the number of neurons expected for their brain size, but a larger number of neurons than expected for their body size. The number of neurons in excess relative to body size might be available for improved associative functions and, thus, be responsible for the cognitive advantage observed in more encephalized animals. It is further proposed that, if such neuronal excess does provide for improved cognitive abilities, then the total number of excess neurons in each species-here dubbed the neuronal index-should be a better indicator of cognitive abilities than the encephalization quotient (EQ). Because the neuronal index is a function of both the number of neurons expected from the size of the body and the absolute number of neurons in the brain, differences in this parameter across species that share similar EQs might explain why these often have different cognitive capabilities, particularly when comparing across mammalian orders.

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“…That notion is based on the idea that an "excess brain mass," relative to the brain mass necessary to operate the body, would endow the behavior of more encephalized animals with more complexity and flexibility (11). The most encephalized species should also be the most cognitively able, and that species, finally, was our own.…”

mentioning

confidence: 99%

The remarkable, yet not extraordinary, human brain as a scaled-up primate brain and its associated cost

Herculano‐Houzel

2012

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

507

372

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Neuroscientists have become used to a number of “facts” about the human brain: It has 100 billion neurons and 10- to 50-fold more glial cells; it is the largest-than-expected for its body among primates and mammals in general, and therefore the most cognitively able; it consumes an outstanding 20% of the total body energy budget despite representing only 2% of body mass because of an increased metabolic need of its neurons; and it is endowed with an overdeveloped cerebral cortex, the largest compared with brain size. These facts led to the widespread notion that the human brain is literally extraordinary: an outlier among mammalian brains, defying evolutionary rules that apply to other species, with a uniqueness seemingly necessary to justify the superior cognitive abilities of humans over mammals with even larger brains. These facts, with deep implications for neurophysiology and evolutionary biology, are not grounded on solid evidence or sound assumptions, however. Our recent development of a method that allows rapid and reliable quantification of the numbers of cells that compose the whole brain has provided a means to verify these facts. Here, I review this recent evidence and argue that, with 86 billion neurons and just as many nonneuronal cells, the human brain is a scaled-up primate brain in its cellular composition and metabolic cost, with a relatively enlarged cerebral cortex that does not have a relatively larger number of brain neurons yet is remarkable in its cognitive abilities and metabolism simply because of its extremely large number of neurons.

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Animal intelligence as encephalization

Cited by 177 publications

References 25 publications

Neurotransmitter organization and connections of turtle cortex: implications for the evolution of mammalian isocortex

Neurotransmitter organization and connections of turtle cortex: implications for the evolution of mammalian isocortex

Encephalization, Neuronal Excess, and Neuronal Index in Rodents

The remarkable, yet not extraordinary, human brain as a scaled-up primate brain and its associated cost

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