Presentation Abstract

Program#/Poster#: 446.08/MM12
Presentation Title: Complex brains for complex cognition - neuronal scaling rules for bird brains
Location: WCC Hall A-C
Presentation time: Monday, Nov 17, 2014, 4:00 PM - 5:00 PM
Presenter at Poster: Mon, Nov. 17, 2014, 4:00 PM - 5:00 PM
Topic: ++D.19.a. Comparative anatomy and Evolution
Authors: *S. OLKOWICZ1, M. KOCOUREK1, R. LUCAN1, M. PORTES1, S. HERCULANO-HOUZEL2, P. NEMEC1;
1Dept. of Zoology, Charles Univ. in Prague, Prague, Czech Republic; 2Inst. de Ciências Biomédicas, Univ. Federal do Rio de Janeiro, Rio de Janeiro, Brazil
Abstract: Many birds show remarkable cognitive abilities rivaling those observed in apes, the closest human relatives. Because absolute size of avian brains is rather small, it remains unclear how birds can accomplish this level of behavioral sophistication. Using the isotropic fractionator we determine directly the numbers of neuronal and nonneuronal cells in a total of 74 brains of adult specimens of 11 species of parrots, 14 species of songbirds and 4 selected model species representing other bird groups. We show that in parrots and songbirds the total brain mass as well as telencephalic mass scales approximately linearly with the total number of neurons, i.e. neuronal density does not change significantly as brains get larger. The neuronal densities in the telencephalon exceed those observed in the cerebral cortex of primates by a factor of 2-8. As a result, the numbers of telencephalic neurons in the brains of the largest birds examined (raven, kea and macaw) equal or exceed those observed in the cerebral cortex of many species of monkeys. The avian cerebellum features neuronal densities similar or higher than those found in primates. In contrast to primates, however, both the relative size of the cerebellum and the percentage of total brain neurons found in the cerebellum decrease in birds with increasing brain mass, from 12% to 7% and from around 50% to 20%, respectively. In the macaw brain, for instance, almost 80% of all brain neurons are contained in the telencephalon, while only 20% reside in the cerebellum, a condition reversed to what is found in mammals. By contrast, the densities of nonneuronal cells remain fairly constant regardless of brain size and brain region. These findings are congruent with data from all mammals analyzed so far, and indicate that while neuronal scaling rules for the avian brain differ from those that apply to mammalian brains, nonneuronal scaling rules are shared between the two animal classes. Finally, our findings of comparable numbers of neurons in the cerebral cortex of medium-sized primates and in the telencephalon of large parrots and songbirds (particularly corvids) strongly suggest that large numbers of forebrain neurons, and hence a large computational capacity, underpin the behavioral and cognitive complexity reported for parrots and songbirds, despite their small brain size.
Disclosures:  S. Olkowicz: None. M. Kocourek: None. R. Lucan: None. M. Portes: None. S. Herculano-Houzel: None. P. Nemec: None.
Keyword (s): EVOLUTION
ALLOMETRY
PASSERINE
Support: Czech Science Foundation Grant 14-21758S to PN
Grant Agency of Charles University Grant 851613 to MK
ECOP, ESF and State budget to SO