Brain lesions that impair vocal imitation in adult budgerigars

Defining the multidimensional phenotype: New opportunities to integrate the behavioral ecology and behavioral neuroscience of vocal learning

Vocal learning has evolved independently in several lineages. This complex cognitive trait is commonly treated as binary: species either possess or lack it. This view has been a useful starting place to examine the origins of vocal learning, but is also incomplete and potentially misleading, as specific components of the vocal learning program - such as the timing, extent and nature of what is learned - vary widely among species. In our review we revive an idea first proposed by Beecher and Brenowitz (2005) by describing six dimensions of vocal learning: (1) which vocalizations are learned, (2) how much is learned, (3) when it is learned, (4) who it is learned from, (5) what is the extent of the internal template, and (6) how is the template integrated with social learning and innovation. We then highlight key examples of functional and mechanistic work on each dimension, largely from avian taxa, and discuss how a multi-dimensional framework can accelerate our understanding of why vocal learning has evolved, and how brains became capable of this important behaviour.

Memory-specific correlated neuronal activity in higher-order auditory regions of a parrot

Male budgerigars (Melopsittacus undulatus) are open-ended learners that can learn to produce new vocalisations as adults. We investigated neuronal activation in male budgerigars using the expression of the protein products of the immediate early genes zenk and c-fos in response to exposure to conspecific contact calls (CCs: that of the mate or an unfamiliar female) in three subregions (CMM, dNCM and vNCM) of the caudomedial pallium, a higher order auditory region. Significant positive correlations of Zenk expression were found between these subregions after exposure to mate CCs. In contrast, exposure to CCs of unfamiliar females produced no such correlations. These results suggest the presence of a CC-specific association among the subregions involved in auditory memory. The caudomedial pallium of the male budgerigar may have functional subdivisions that cooperate in the neuronal representation of auditory memory.

Comparative mitogenomic analyses of Amazona parrots and Psittaciformes

Amazon parrots are long-lived birds with highly developed cognitive skills, including vocal learning. Several parrot mitogenomes have been sequenced, but important aspects of their organization and evolution are not fully understood or have limited experimental support. The main aim of the present study was to describe the mitogenome of the blue-fronted Amazon, Amazona aestiva, and compare it to other mitogenomes from the genus Amazona and the order Psittaciformes. We observed that mitogenomes are highly conserved among Amazon parrots, and a detailed analysis of their duplicated control regions revealed conserved blocks. Population level analyses indicated that the specimen analyzed here seems to be close to A. aestiva individuals from Bahia state. Evolutionary relationships of 41 Psittaciformes species and three outgroups were inferred by BEAST. All relationships were retrieved with high support.

Cognition, personality, and stress in budgerigars, Melopsittacus undulatus

To study the fitness effects of individual variation in cognitive traits, it is paramount to understand whether traits such as personality and physiological stress influence cognitive performance. We first tested whether budgerigars showed both consistent personalities and cognitive performance across time and tasks. We tested object and food neophobia, and exploratory behavior. We measured cognitive performance in habituation, ability to solve foraging problems, spatial memory, and seed discrimination tasks. Budgerigars showed consistency in their neophobic tendencies and these tendencies were associated with their exploratory behavior. Birds were also consistent in how they performed in most of the cognitive tasks (temporal consistency), but were not consistent in their performance across tasks (context consistency). Neither corticosterone levels (baseline and stress-induced) showed a significant relationship with either cognitive or personality measures. Neophobic and exploratory tendencies determined the willingness of birds to engage only in the seed discrimination task. Such tendencies also had a significant effect on problem-solving ability. Our results suggest that consistent individual differences in cognitive performance along with consistent differences in personality could determine response to environmental change and therefore have important fitness consequences.

Sex differences in behavioural and neural responsiveness to mate calls in a parrot

Vocalisation in songbirds and parrots has become a prominent model system for speech and language in humans. We investigated possible sex differences in behavioural and neural responsiveness to mate calls in the budgerigar, a vocally-learning parrot. Males and females were paired for 5 weeks and then separated, after which we measured vocal responsiveness to playback calls (a call of their mate versus a call of an unfamiliar conspecific). Both sexes learned to recognise mate calls during the pairing period. In males, but not females, mate calls evoked significantly fewer vocal responses than unfamiliar calls at one month after separation. Furthermore, in females, there was significantly greater molecular neuronal activation in response to mate calls compared to silence in the caudomedial mesopallium (CMM), a higher-order auditory region, in both brain hemispheres. In males, we found right-sided dominance of molecular neuronal activation in response to mate calls in the CMM. This is the first evidence suggesting sex differences in functional asymmetry of brain regions related to recognition of learned vocalisation in birds. Thus, sex differences related to recognition of learned vocalisations may be found at the behavioural and neural levels in avian vocal learners as it is in humans.

Bird brains and tool use: beyond instrumental conditioning

Few displays of complex cognition are as intriguing as nonhuman tool use. Long thought to be unique to humans, evidence for tool use and manufacture has now been gathered in chimpanzees, dolphins, and elephants. Outside of mammals, tool use is most common in birds, especially in corvids and parrots. The present paper reviews the evidence for avian tool use, both in the wild and in laboratory settings. It also places this behavioral evidence in the context of longstanding debates about the kinds of mental processes nonhumans can perform. Descartes argued that animals are unable to think because they are soulless machines, incapable of flexible behavior. Later, as human machines became more sophisticated and psychologists discovered classical and instrumental conditioning, skepticism about animal thinking decreased. However, behaviors that involve more than simple conditioning continued to elicit skepticism, especially among behaviorists. Nonetheless, as reviewed here, strong behavioral data now indicate that tool use in some birds cannot be explained as resulting entirely from instrumental conditioning. The neural substrates of tool use in birds remain unclear, but the available data point mainly to the caudolateral nidopallium, which shares both functional and structural features with the mammalian prefrontal cortex. As more data on the neural mechanisms of complex cognition in birds accrue, skepticism about those mental capacities should continue to wane.

Morphometric analysis of telencephalic structure in a variety of neognath and paleognath bird species reveals regional differences associated with specific behavioral traits

Birds exhibit a huge array of behavior, ecology and physiology, and occupy nearly every environment on earth, ranging from the desert outback of Australia to the tropical rain forests of Panama. Some birds have adopted a fully nocturnal lifestyle, such as the barn owl and kiwi, while others, such as the albatross, spend nearly their entire life flying over the ocean. Each species has evolved unique adaptations over millions of years to function in their respective niche. In order to increase processing power or network efficiency, many of these adaptations require enlargements and/or specializations of the brain as a whole or of specific brain regions. In this study, we examine the relative size and morphology of 9 telencephalic regions in a number of Paleognath and Neognath birds and relate the findings to differences in behavior and sensory ecology. We pay particular attention to those species that have undergone a relative enlargement of the telencephalon to determine whether this relative increase in telencephalic size is homogeneous across different brain regions or whether particular regions have become differentially enlarged. The analysis indicates that changes in the relative size of telencephalic regions are not homogeneous, with every species showing hypertrophy or hypotrophy of at least one of them. The three-dimensional structure of these regions in different species was also variable, in particular that of the mesopallium in kiwi. The findings from this study provide further evidence that the changes in relative brain size in birds reflect a process of mosaic evolution.

Localized brain activation related to the strength of auditory learning in a parrot

Parrots and songbirds learn their vocalizations from a conspecific tutor, much like human infants acquire spoken language. Parrots can learn human words and it has been suggested that they can use them to communicate with humans. The caudomedial pallium in the parrot brain is homologous with that of songbirds, and analogous to the human auditory association cortex, involved in speech processing. Here we investigated neuronal activation, measured as expression of the protein product of the immediate early gene ZENK, in relation to auditory learning in the budgerigar (Melopsittacus undulatus), a parrot. Budgerigar males successfully learned to discriminate two Japanese words spoken by another male conspecific. Re-exposure to the two discriminanda led to increased neuronal activation in the caudomedial pallium, but not in the hippocampus, compared to untrained birds that were exposed to the same words, or were not exposed to words. Neuronal activation in the caudomedial pallium of the experimental birds was correlated significantly and positively with the percentage of correct responses in the discrimination task. These results suggest that in a parrot, the caudomedial pallium is involved in auditory learning. Thus, in parrots, songbirds and humans, analogous brain regions may contain the neural substrate for auditory learning and memory.

Comparative gene expression analysis among vocal learners (bengalese finch and budgerigar) and non-learners (quail and ring dove) reveals variable cadherin expressions in the vocal system

Birds use various vocalizations to communicate with one another, and some are acquired through learning. So far, three families of birds (songbirds, parrots, and hummingbirds) have been identified as having vocal learning ability. Previously, we found that cadherins, a large family of cell-adhesion molecules, show vocal control-area-related expression in a songbird, the Bengalese finch. To investigate the molecular basis of evolution in avian species, we conducted comparative analysis of cadherin expressions in the vocal and other neural systems among vocal learners (Bengalese finch and budgerigar) and a non-learner (quail and ring dove). The gene expression analysis revealed that cadherin expressions were more variable in vocal and auditory areas compared to vocally unrelated areas such as the visual areas among these species. Thus, it appears that such diverse cadherin expressions might have been related to generating species diversity in vocal behavior during the evolution of avian vocal learning.

Feeding and contact call stimulation both induce zenk and cfos expression in a higher order telencephalic area necessary for vocal learning in budgerigars

Stimulation with natural contact calls and feeding were used to assess zenk and fos protein expression in budgerigars (Melopsittacus undulatus), a vocal learning parrot species in which feeding and physical contact often occur in conjunction with vocalization. Although only calls induced gene expression in Field L, the primary telencephalic auditory area, both calls and feeding induced gene expression in the frontal lateral nidopallium (NFl), a brain area in receipt of input from Field L which projects to areas afferent to vocal control nuclei and which is necessary for new call learning. NFl thus appears poised to provide both non-auditory as well as auditory feedback to the vocal system.

The evolution of cerebrotypes in birds

Multivariate analyses of brain composition in mammals, amphibians and fish have revealed the evolution of 'cerebrotypes' that reflect specific niches and/or clades. Here, we present the first demonstration of similar cerebrotypes in birds. Using principal component analysis and hierarchical clustering methods to analyze a data set of 67 species, we demonstrate that five main cerebrotypes can be recognized. One type is dominated by galliforms and pigeons, among other species, that all share relatively large brainstems, but can be further differentiated by the proportional size of the cerebellum and telencephalic regions. The second cerebrotype contains a range of species that all share relatively large cerebellar and small nidopallial volumes. A third type is composed of two species, the tawny frogmouth (Podargus strigoides) and an owl, both of which share extremely large Wulst volumes. Parrots and passerines, the principal members of the fourth group, possess much larger nidopallial, mesopallial and striatopallidal proportions than the other groups. The fifth cerebrotype contains species such as raptors and waterfowl that are not found at the extremes for any of the brain regions and could therefore be classified as 'generalist' brains. Overall, the clustering of species does not directly reflect the phylogenetic relationships among species, but there is a tendency for species within an order to clump together. There may also be a weak relationship between cerebrotype and developmental differences, but two of the main clusters contained species with both altricial and precocial developmental patterns. As a whole, the groupings do agree with behavioral and ecological similarities among species. Most notably, species that share similarities in locomotor behavior, mode of prey capture or cognitive ability are clustered together. The relationship between cerebrotype and behavior/ecology in birds suggests that future comparative studies of brain-behavior relationships will benefit from adopting a multivariate approach.

Sexual dimorphism of vocal control nuclei in budgerigars (Melopsittacus undulatus) revealed with Nissl and NADPH-d staining

Nissl staining and nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry were used to explore the existence of sexual dimorphism in vocal control nuclei of adult budgerigars (Melopsittacus undulatus), a parrot species capable of lifelong vocal learning. Behavioral studies indicate that adult males possess larger vocal repertoires than adult females and learn new calls more quickly. The results of the present study show that the volumes of all vocal nuclei, as measured using both Nissl-stained and NADPH-d-stained material, as well as the total numbers of NADPH-d neurons, were 35-110% greater in males. Furthermore, all vocal nuclei exhibit conspicuous NADPH-d staining compared to surrounding fields in both adult males and females. Nevertheless, there were no significant gender differences in either the intensity of neuropil staining or the densities of NADPH-d neurons in vocal nuclei. Moreover NADPH-d neuron somal shapes were similar in males and females. Diameters of NADPH-d neurons in vocal nuclei were 8.5-32% larger in males than in females. Greater size of NADPH-d neuronal somata in males may be a general property of this cell type in budgerigars because a similar gender difference was found in a visual nucleus, the entopallium, which is not directly associated with the vocal control system and does not exhibit sexual dimorphism in total volume or total NADPH-d neuron numbers. Taken together, the results of the present study favor the hypothesis that superior lifelong vocal learning ability in male budgerigars rests largely on larger volumes of vocal control nuclei in males rather than on sexual dimorphism in the internal composition of vocal nuclei.

Interspecific Allometry of the Brain and Brain Regions in Parrots (Psittaciformes): Comparisons with Other Birds and Primates

Despite significant progress in understanding the evolution of the mammalian brain, relatively little is known of the patterns of evolutionary change in the avian brain. In particular, statements regarding which avian taxa have relatively larger brains and brain regions are based on small sample sizes and statistical analyses are generally lacking. We tested whether psittaciforms (parrots, cockatoos and lorikeets) have larger brains and forebrains than other birds using both conventional and phylogenetically based methods. In addition, we compared the psittaciforms to primates to determine if cognitive similarities between the two groups were reflected by similarities in brain and telencephalic volumes. Overall, psittaciforms have relatively larger brains and telencephala than most other non-passerine orders. No significant difference in relative brain or telencephalic volume was detected between psittaciforms and passerines. Comparisons of other brain region sizes between psittaciforms and other birds, however, exhibited conflicting results depending upon whether body mass or a brain volume remainder (total brain volume - brain region volume) was used as a scaling variable. When compared to primates, psittaciforms possessed similar relative brain and telencephalic volumes. The only exception to this was that in some analyses psittaciforms had significantly larger telencephala than primates of similar brain volume. The results therefore provide empirical evidence for previous claims that psittaciforms possess relatively large brains and telencephala. Despite the variability in the results, it is clear that psittaciforms tend to possess large brains and telencephala relative to non-passerines and are similar to primates in this regard. Although it could be suggested that this reflects the advanced cognitive abilities of psittaciforms, similar studies performed in corvids and other avian taxa will be required before this claim can be made with any certainty.

Learned birdsong and the neurobiology of human language

Vocal learning, the substrate for human language, is a rare trait found to date in only three distantly related groups of mammals (humans, bats, and cetaceans) and three distantly related groups of birds (parrots, hummingbirds, and songbirds). Brain pathways for vocal learning have been studied in the three bird groups and in humans. Here I present a hypothesis on the relationships and evolution of brain pathways for vocal learning among birds and humans. The three vocal learning bird groups each appear to have seven similar but not identical cerebral vocal nuclei distributed into two vocal pathways, one posterior and one anterior. Humans also appear to have a posterior vocal pathway, which includes projections from the face motor cortex to brainstem vocal lower motor neurons, and an anterior vocal pathway, which includes a strip of premotor cortex, the anterior basal ganglia, and the anterior thalamus. These vocal pathways are not found in vocal non-learning birds or mammals, but are similar to brain pathways used for other types of learning. Thus, I argue that if vocal learning evolved independently among birds and humans, then it did so under strong genetic constraints of a pre-existing basic neural network of the vertebrate brain.

Neuronal activation in female budgerigars is localized and related to male song complexity

Females of several songbird species have been shown to respond preferentially to a more complex song. The male budgerigar (Melopsittacus undulatus) sings complex songs consisting of discrete components, known as syllables. We exposed female budgerigars to either standard male song, complex song, or simple song, the iteration of only one syllable (either frequency-modulated or unmodulated). Using immunocytochemistry, we analysed the expression of the protein product of the immediate early gene ZENK in a number of forebrain regions. The level of Zenk protein expression caused by song stimuli varied among each of the brain regions. Expression was highest in the caudomedial neostriatum (NCM), lower in the caudomedial hyperstriatum ventrale (CMHV), and lowest in the hippocampus. There was a significant effect of song complexity on the number of Zenk-immunoreactive cells in the NCM, but not in the hippocampus. Zenk protein expression correlated significantly and positively with the number of different syllables to which the females were exposed in the NCM and to a lesser extent in the CMHV, but not in the hippocampus. For the NCM this correlation was also significant within the group exposed to natural song. These results suggest that the NCM is involved in the perception of song complexity in female budgerigars.