Comparative Morphology of the Avian Cerebellum: I. Degree of Foliation

Iwaniuk, Andrew N.; Hurd, Peter L.; Wylie, Douglas R.

doi:10.1159/000093530

Cited by 63 publications

(105 citation statements)

References 115 publications

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“…Considering only primates (35) or a smaller but diverse set of mammals (36), both absolute and relative brain sizes contribute to gyrification. In birds, "foliation," or the amount of folding in the cerebellum, is similarly related to both the absolute size of the cerebellum and its relative size compared with the medulla (40).…”

Section: Discussionmentioning

confidence: 99%

A conserved pattern of brain scaling from sharks to primates

Yopak

Lisney

Darlington

et al. 2010

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

162

211

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Several patterns of brain allometry previously observed in mammals have been found to hold for sharks and related taxa (chondrichthyans) as well. In each clade, the relative size of brain parts, with the notable exception of the olfactory bulbs, is highly predictable from the total brain size. Compared with total brain mass, each part scales with a characteristic slope, which is highest for the telencephalon and cerebellum. In addition, cerebellar foliation reflects both absolute and relative cerebellar size, in a manner analogous to mammalian cortical gyrification. This conserved pattern of brain scaling suggests that the fundamental brain plan that evolved in early vertebrates permits appropriate scaling in response to a range of factors, including phylogeny and ecology, where neural mass may be added and subtracted without compromising basic function.T he allometric relationship of brain parts to overall brain size has been studied and debated extensively (1-7). At the core of the debate lies the question of whether the brain is best characterized as a collection of independently varying structures/devices evolved for particular behavioral requirements or niches or as a single coordinated processing structure/device in which adaptation for species-specific behavioral capacities occurs without the production of delineable modules (8, 9). Many methodological issues have arisen as well, including what about a brain should be quantified [cells or volumes (10)], what should be compared and how, and how to take into account the statistical dependence of both structural and species relationships (11).Until recently, a single data corpus comprising primates, bats, and insectivorous mammals was the sole source for comparison (2), leaving the question of whether these mammals represented all vertebrates, or even all other mammals, unresolved. The addition of carnivorous mammals (including marine mammals), ungulates, xenarthrans, and the manatee demonstrated that the original conclusions drawn from primates, bats, and insectivores could be extended to this larger data set (8, 12). These studies revealed that mammalian brain structure exhibits a pattern of variation containing two principal components. The first component, accounting for ≈96% of the total variance of related brain parts to total brain size, loads most highly on neocortex and cerebellum. The second component loads most highly on the olfactory bulb and associated limbic structures and accounts for ≈3% of the original variance. Each brain part also has a characteristic slope with respect to absolute brain size, such that every large mammalian brain is composed disproportionately of neocortex and cerebellum. The remaining 1% of the variance must subsume all remaining sources, including niche, sex and individual differences, and measurement error. This 1% contribution is large in one sense: In two species with the same brain size, a single structure might differ by a factor of 2.5. The total range of structure sizes may differ by a factor of 100,000 or more b...

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Section: Discussionmentioning

confidence: 99%

A conserved pattern of brain scaling from sharks to primates

Yopak

Lisney

Darlington

et al. 2010

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

162

211

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“…Many other species have more foliated cerebella (e.g., fig. 3 D, I, K, L), but these are generally larger birds, as the degree of foliation is correlated with cerebellar volume, brain volume and body mass [Iwaniuk et al, 2006c]. This is best demonstrated within the Corvida ( fig.…”

Section: Phylogenetic Effectsmentioning

confidence: 91%

“…Larsell [1967] defined individual folia and their subdivisions based upon cerebellar development in chickens (Gallus domesticus) and ducks (Anas platyrhynchos) and extrapolated this to other species. This is problematic, however, because there are species differences in how the cerebellum develops [Larsell 1967] and the pattern of cerebellar development is unknown for For further details regarding the sources of these specimens, see Iwaniuk et al [2006c].…”

Section: Measurementsmentioning

confidence: 99%

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Comparative Morphology of the Avian Cerebellum: II. Size of Folia

Iwaniuk

Hurd²,

Wylie³

2006

Brain Behav Evol

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Despite the highly conserved circuitry of the cerebellum, its overall shape varies significantly among and within vertebrate classes. In birds, one of the most prominent differences among orders is the relative size of the cerebellar folia. The enlargement/reduction of individual folia is thought to relate to specific behavioral differences among taxa, but this has not been adequately tested. Here, we survey variation in cerebellar folia size among 96 species of birds and test for phylogenetic effects and correlations with behavior using a combination of conventional and phylogeny-based statistics. Overall, we found that phylogenetic history accounts for a significant amount of variation in the relative size of individual folia. Order membership, in particular, accounted for more than half of the interspecific variation in folia size. There are also complex relationships among folia such that the expansion of one folium is often accompanied by a reduction in other folia. With respect to behavioral correlates: (1) we did not find any significant correlations between folia size and reliance on trigeminal input; (2) there was some evidence supporting a correlation between strong hindlimbs and an expansion of the anterior lobe; and (3) there were significant reductions in folia I–III and expansions in folia VI and VII in species classified as strong fliers. This expansion likely reflects increased visual processing requirements in species with rapid and/or agile flight. It therefore appears that folium size is a product of both phylogenetic history and behavior in birds.

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“…Based on a previously devised visual grading schema on a scale of 1-5 , the folding of the corpus has been visually quantified in the deep-sea sharks and holocephalans in this study, and the foliation index gradings were found to range from 1 to 2 ( table 1 ). Foliation of the cerebellum has been studied in a number of other vertebrate groups, including birds [Senglaub, 1963;Larsell, 1967;Pearson and Pearson, 1976;Iwaniuk et al, 2006Iwaniuk et al, , 2007 and mammals [Zilles et al, 1989;Striedter, 2005], and has been correlated with behavioral specializations and cognitive capabilities across these clades [Butler and Hodos, 1996]. Low foliation levels in these deep-sea fishes have been linked to lower activity levels and a close association to the substrate [Northcutt, 1989;Yopak and Frank, 2007;, in addition to less active predation strategies in a 2-dimensional environment [Yopak and Frank, 2007;.…”

Section: Brain Organizationmentioning

confidence: 99%

Brain Organization and Specialization in Deep-Sea Chondrichthyans

Yopak

Montgomery²

2008

Brain Behav Evol

125

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Chondrichthyans occupy a basal place in vertebrate evolution and offer a relatively unexplored opportunity to study the evolution of vertebrate brains. This study examines the brain morphology of 22 species of deep-sea sharks and holocephalans, in relation to both phylogeny and ecology. Both relative brain size (expressed as residuals) and the relative development of the five major brain areas (telencephalon, diencephalon, mesencephalon, cerebellum, and medulla) were assessed. The cerebellar-like structures, which receive projections from the electroreceptive and lateral line organs, were also examined as a discrete part of the medulla. Although the species examined spanned three major chondrichthyan groupings (Squalomorphii, Galeomorphii, Holocephali), brain size and the relative development of the major brain areas did not track phylogenetic groupings. Rather, a hierarchical cluster analysis performed on the deep-sea sharks and holocephalans shows that these species all share the common characteristics of a relatively reduced telencephalon and smooth cerebellar corpus, as well as extreme relative enlargement of the medulla, specifically the cerebellar-like lobes. Although this study was not a functional analysis, it provides evidence that brain variation in deep-sea chondichthyans shows adaptive patterns in addition to underlying phylogenetic patterns, and that particular brain patterns might be interpreted as ‘cerebrotypes’.

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Comparative Morphology of the Avian Cerebellum: I. Degree of Foliation

Cited by 63 publications

References 115 publications

A conserved pattern of brain scaling from sharks to primates

A conserved pattern of brain scaling from sharks to primates

Comparative Morphology of the Avian Cerebellum: II. Size of Folia

Brain Organization and Specialization in Deep-Sea Chondrichthyans

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