A Relationship between the Characteristics of the Oval Nucleus of the Mesopallium and Parrot Vocal Response to Playback.

Correlations between differences in animal behavior and brain structures have been used to infer function of those structures. Brain region size has especially been suggested to be important for an animal's behavioral capability, controlled by specific brain regions. The oval nucleus of the mesopallium (MO) is part of the anterior forebrain vocal learning pathway in the parrot brain. Here, we compare brain volume and total number of neurons in MO of three parrot species (the peach-fronted conure, Eupsittula aurea, the peach-faced lovebird, Agapornis roseicollis, and the budgerigar, Melopsittacus undulatus), relating the total neuron numbers with the vocal response to playbacks of each species. We find that individuals with the highest number of neurons in MO had the shortest vocal latency. The peach-fronted conures showed the shortest vocal latency and largest number of MO neurons, the peach-faced lovebird had intermediary levels of both, and the budgerigar had the longest latency and least number of neurons. These findings indicate the MO nucleus as one candidate region that may be part of what controls the vocal capacity of parrots.

Core and Shell Song Systems Unique to the Parrot Brain.

The ability to imitate complex sounds is rare, and among birds has been found only in parrots, songbirds, and hummingbirds. Parrots exhibit the most advanced vocal mimicry among non-human animals. A few studies have noted differences in connectivity, brain position and shape in the vocal learning systems of parrots relative to songbirds and hummingbirds. However, only one parrot species, the budgerigar, has been examined and no differences in the presence of song system structures were found with other avian vocal learners. Motivated by questions of whether there are important differences in the vocal systems of parrots relative to other vocal learners, we used specialized constitutive gene expression, singing-driven gene expression, and neural connectivity tracing experiments to further characterize the song system of budgerigars and/or other parrots. We found that the parrot brain uniquely contains a song system within a song system. The parrot "core" song system is similar to the song systems of songbirds and hummingbirds, whereas the "shell" song system is unique to parrots. The core with only rudimentary shell regions were found in the New Zealand kea, representing one of the only living species at a basal divergence with all other parrots, implying that parrots evolved vocal learning systems at least 29 million years ago. Relative size differences in the core and shell regions occur among species, which we suggest could be related to species differences in vocal and cognitive abilities.

Stereological estimation of total cell numbers in the human cerebral and cerebellar cortex.

Our knowledge of the relationship between brain structure and cognitive function is still limited. Human brains and individual cortical areas vary considerably in size and shape. Studies of brain cell numbers have historically been based on biased methods, which did not always result in correct estimates and were often very time-consuming. Within the last 20-30 years, it has become possible to rely on more advanced and unbiased methods. These methods have provided us with information about fetal brain development, differences in cell numbers between men and women, the effect of age on selected brain cell populations, and disease-related changes associated with a loss of function. In that this article concerns normal brain rather than brain disorders, it focuses on normal brain development in humans and age related changes in terms of cell numbers. For comparative purposes a few examples of neocortical neuron number in other mammals are also presented.

Stereological estimate of the total number of neurons in spinal segment D9 of the red-eared turtle.

The red-eared turtle is an important animal model for investigating the neural activity in the spinal circuit that generates motor behavior. However, basic anatomical features, including the number of neurons in the spinal segments involved, are unknown. In the present study, we estimate the total number of neurons in segment D9 of the spinal cord in the red-eared turtle (Trachemys scripta elegans) using stereological cell counting methods. In transverse spinal cord sections stained with modified Giemsa, motoneurons (MNs), interneurons (INs), and non-neuronal cells were distinguished according to location and morphology. Each cell type was then counted separately using an optical disector with the cell nucleus as counting item. The number of cells in segment D9 was as follows (mean ± SE): MNs, 2049 ± 74; INs, 16,135 ± 316; non-neuronal cells, 47,504 ± 478 (n = 6). These results provide the first estimate of the total number of neurons in a spinal segment in a terrestrial vertebrate based on unbiased stereological methods and an upper bound on the number of neurons involved in segmental sensorimotor activity. These findings also form a crucial quantitative foundation for integrating electrophysiological data into mathematical circuit models.

A neurological comparative study of the harp seal (Pagophilus groenlandicus) and harbor porpoise (Phocoena phocoena) brain.

The cetacean brain is well studied. However, few comparisons have been done with other marine mammals. In this study, we compared the harp seal (Pagophilus groenlandicus) and the harbor porpoise brain (Phocoena phocoena). Stereological methods were applied to compare three areas of interest: the entire neocortex and two subdivisions of the neocortex, the auditory and visual cortices. The total number of neurons and glial cells in the three regions was estimated. The main results showed that the harbor porpoise have an estimated 14.9 × 10(9) neocortical neurons and 34.8 × 10(9) neocortical glial cells, whereas the harp seal have 6.1 × 10(9) neocortical neurons and 17.5 × 10(9) neocortical glial cells. The harbor porpoise have significantly more neurons and glial cells in the auditory cortex than in the visual cortex, whereas the pattern was opposite for the harp seal. These results are the first to provide estimates of the number of neurons and glial cells in the neocortex of the harp seal and harbor porpoise brain and offer new data to the comparative field of mammalian brain evolution.