Production In Songbirds Research Articles

Sex differences in myelination of the zebra finch vocal control system emerge relatively late in development.

The role of myelination in the development of motor control is widely known, but its role in the development of cognitive abilities is less understood. Here, we examined sex differences in the development of myelination of structures and tracts that support song learning and production in songbirds. We collected brains from 63 young male and female zebra finches (Taeniopygia guttata) over four stages of development that correspond to different stages of song learning. Using a myelination marker (myelin basic protein), we measured the development of myelination in three different nuclei of the vocal control system (HVC, RA, and lateral magnocellular nucleus of the anterior nidopallium [LMAN]) and two tracts (HVC-RA and lamina mesopallium ventralis [LMV]). We found that the myelination of the vocal control nuclei and tracts is sex related and male biased. In males, the patterns of myelination were age-dependent, asynchronous in rate and progression and associated with the development of song learning and production. In females, myelination of vocal control nuclei was low or absent and did not significantly change with age. Sex differences in myelination of the HVC-RA tract were large and emerged late in development well after sex differences in the size of vocal control brain regions are established. Myelination of this tract in males coincides with the age of song crystallization. Overall, the changes in myelination in the vocal control areas and tracts measured are region-, age-, and sex-specific and are consistent with sex differences in song development.

Nicotinic acetylcholine receptors in a songbird brain.

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that mediate fast synaptic transmission and cell signaling, which contribute to learning, memory, and the execution of motor skills. Birdsong is a complex learned motor skill in songbirds. Although the existence of 15 nAChR subunits has been predicted in the avian genome, their expression patterns and potential contributions to song learning and production have not been comprehensively investigated. Here, we cloned all the 15 nAChR subunits (ChrnA1-10, B2-4, D, and G) from the zebra finch brain and investigated the mRNA expression patterns in the neural pathways responsible for the learning and production of birdsong during a critical period of song learning. Although there were no detectable hybridization signals for ChrnA1, A6, A9, and A10, the other 11 nAChR subunits were uniquely expressed in one or more major subdivisions in the song nuclei of the songbird brain. Of these 11 subunits, ChrnA3-5, A7, and B2 were differentially regulated in the song nuclei compared with the surrounding anatomically related regions. ChrnA5 was upregulated during the critical period of song learning in the lateral magnocellular nucleus of the anterior nidopallium. Furthermore, single-cell RNA sequencing revealed ChrnA7 and B2 to be the major subunits expressed in neurons of the vocal motor nuclei HVC and robust nucleus of the arcopallium, indicating the potential existence of ChrnA7-homomeric and ChrnB2-heteromeric nAChRs in limited cell populations. These results suggest that relatively limited types of nAChR subunits provide functional contributions to song learning and production in songbirds.

The hummingbird syrinx morphome: a detailed three-dimensional description of the black jacobin\u2019s vocal organ

BackgroundThe ability to imitate sounds depends on a process called vocal production learning, a rare evolutionary trait. In addition to the few mammalian groups that possess this ability, vocal production learning has evolved independently in three avian clades: songbirds, parrots, and hummingbirds. Although the anatomy and mechanisms of sound production in songbirds are well understood, little is known about the hummingbird’s vocal anatomy.ResultsWe use high-resolution micro-computed tomography (μCT) and microdissection to reveal the three-dimensional structure of the syrinx, the vocal organ of the black jacobin (Florisuga fusca), a phylogenetically basal hummingbird species. We identify three features of the black jacobin’s syrinx: (i) a shift in the position of the syrinx to the outside of the thoracic cavity and the related loss of the sterno-tracheal muscle, (ii) complex intrinsic musculature, oriented dorso-ventrally, and (iii) ossicles embedded in the medial vibratory membranes.ConclusionsThe extra-thoracic placement of the black jacobin’s syrinx and the dorso-ventrally oriented musculature likely aid to uncoupling syrinx movements from extensive flight-related thorax constraints. The syrinx morphology further allows for vibratory decoupling, precise control of complex acoustic parameters, and a large motor redundancy that may be key biomechanical factors leading to acoustic complexity and thus facilitating the occurrence of vocal production learning.

Dynamical model for the neural activity of singing Serinus canaria.

Vocal production in songbirds is a key topic regarding the motor control of a complex, learned behavior. Birdsong is the result of the interaction between the activity of an intricate set of neural nuclei specifically dedicated to song production and learning (known as the "song system"), the respiratory system and the vocal organ. These systems interact and give rise to precise biomechanical motor gestures which result in song production. Telencephalic neural nuclei play a key role in the production of motor commands that drive the periphery, and while several attempts have been made to understand their coding strategy, difficulties arise when trying to understand neural activity in the frame of the song system as a whole. In this work, we report neural additive models embedded in an architecture compatible with the song system to provide a tool to reduce the dimensionality of the problem by considering the global activity of the units in each neural nucleus. This model is capable of generating outputs compatible with measurements of air sac pressure during song production in canaries (Serinus canaria). In this work, we show that the activity in a telencephalic nucleus required by the model to reproduce the observed respiratory gestures is compatible with electrophysiological recordings of single neuron activity in freely behaving animals.

Manipulations of sensory experiences during development reveal mechanisms underlying vocal learning biases in zebra finches.

Biological predispositions in learning can bias and constrain the cultural evolution of social and communicative behaviors (e.g., speech and birdsong), and lead to the emergence of behavioral and cultural "universals." For example, surveys of laboratory and wild populations of zebra finches (Taeniopygia guttata) document consistent patterning of vocal elements ("syllables") with respect to their acoustic properties (e.g., duration, mean frequency). Furthermore, such universal patterns are also produced by birds that are experimentally tutored with songs containing randomly sequenced syllables ("tutored birds"). Despite extensive demonstrations of learning biases, much remains to be uncovered about the nature of biological predispositions that bias song learning and production in songbirds. Here, we examined the degree to which "innate" auditory templates and/or biases in vocal motor production contribute to vocal learning biases and production in zebra finches. Such contributions can be revealed by examining acoustic patterns in the songs of birds raised without sensory exposure to song ("untutored birds") or of birds that are unable to hear from early in development ("early-deafened birds"). We observed that untutored zebra finches and early-deafened zebra finches produce songs with positional variation in some acoustic features (e.g., mean frequency) that resemble universal patterns observed in tutored birds. Similar to tutored birds, early-deafened birds also produced song motifs with alternation in acoustic features across adjacent syllables. That universal acoustic patterns are observed in the songs of both untutored and early-deafened birds highlights the contribution motor production biases to the emergence of universals in culturally transmitted behaviors.

Genomics studies on musical aptitude, music perception, and practice.

When searching for genetic markers inherited together with musical aptitude, genes affecting inner ear development and brain function were identified. The alpha-synuclein gene (SNCA), located in the most significant linkage region of musical aptitude, was overexpressed when listening and performing music. The GATA-binding protein 2 gene (GATA2) was located in the best associated region of musical aptitude and regulates SNCA in dopaminergic neurons, thus linking DNA- and RNA-based studies of music-related traits together. In addition to SNCA, several other genes were linked to dopamine metabolism. Mutations in SNCA predispose to Lewy-body dementia and cause Parkinson disease in humans and affect song production in songbirds. Several other birdsong genes were found in transcriptome analysis, suggesting a common evolutionary background of sound perception and production in humans and songbirds. Regions of positive selection with musical aptitude contained genes affecting auditory perception, cognitive performance, memory, human language development, and song perception and production of songbirds. The data support the role of dopaminergic pathway and their link to the reward mechanism as a molecular determinant in positive selection of music. Integration of gene-level data from the literature across multiple species prioritized activity-dependent immediate early genes as candidate genes in musical aptitude and listening to and performing music.

Dopamine D3 receptors modulate the rate of neuronal recovery, cell recruitment in Area X, and song tempo after neurotoxic damage in songbirds

Songbirds, like humans, learn vocalizations and their striatum recruits new neurons in adulthood. Injury in striatal vocal nucleus Area X, involved in song learning and production in songbirds, is followed by massive regeneration. The newborn neurons arise from the subventricular zone (SVZ) rich in dopamine D3 receptors (D3Rs). The aim of this study was to investigate whether the D3Rs affect the rate of neuronal recovery in Area X. Male zebra finches (Taeniopygia guttata) received bilateral neurotoxic lesion of Area X and were implanted with osmotic minipumps containing D3R agonist 7-OH-DPAT, antagonist U99194, or saline. Treatment with 7-OH-DPAT but not U99194 led to significant reduction of lesion size and increased numbers of migrating neuroblasts and newborn cells in the Area X. These cells were detected in the lesion border as well as the lesion center. Lesion also led to increased mRNA expression of the D3Rs in the neurogenic SVZ and in the nucleus robustus arcopallialis (RA) involved in song production. Moreover, lesion alone prolonged the song duration and this may be facilitated by D3Rs in RA. Parallel lesion and stimulation of D3Rs prolonged it even more, while blocking of D3Rs abolished the lesion-induced effect. These data suggest that D3R stimulation after striatal injury accelerates the striatal recovery and can cause behavioral alterations.

A circular model for song motor control in Serinus canaria.

Song production in songbirds is controlled by a network of nuclei distributed across several brain regions, which drives respiratory and vocal motor systems to generate sound. We built a model for birdsong production, whose variables are the average activities of different neural populations within these nuclei of the song system. We focus on the predictions of respiratory patterns of song, because these can be easily measured and therefore provide a validation for the model. We test the hypothesis that it is possible to construct a model in which (1) the activity of an expiratory related (ER) neural population fits the observed pressure patterns used by canaries during singing, and (2) a higher forebrain neural population, HVC, is sparsely active, simultaneously with significant motor instances of the pressure patterns. We show that in order to achieve these two requirements, the ER neural population needs to receive two inputs: a direct one, and its copy after being processed by other areas of the song system. The model is capable of reproducing the measured respiratory patterns and makes specific predictions on the timing of HVC activity during their production. These results suggest that vocal production is controlled by a circular network rather than by a simple top-down architecture.

The effect of music performance on the transcriptome of professional musicians.

Music performance by professional musicians involves a wide-spectrum of cognitive and multi-sensory motor skills, whose biological basis is unknown. Several neuroscientific studies have demonstrated that the brains of professional musicians and non-musicians differ structurally and functionally and that musical training enhances cognition. However, the molecules and molecular mechanisms involved in music performance remain largely unexplored. Here, we investigated the effect of music performance on the genome-wide peripheral blood transcriptome of professional musicians by analyzing the transcriptional responses after a 2-hr concert performance and after a ‘music-free' control session. The up-regulated genes were found to affect dopaminergic neurotransmission, motor behavior, neuronal plasticity, and neurocognitive functions including learning and memory. Particularly, candidate genes such as SNCA, FOS and DUSP1 that are involved in song perception and production in songbirds, were identified, suggesting an evolutionary conservation in biological processes related to sound perception/production. Additionally, modulation of genes related to calcium ion homeostasis, iron ion homeostasis, glutathione metabolism, and several neuropsychiatric and neurodegenerative diseases implied that music performance may affect the biological pathways that are otherwise essential for the proper maintenance of neuronal function and survival. For the first time, this study provides evidence for the candidate genes and molecular mechanisms underlying music performance.

The effect of listening to music on human transcriptome.

Although brain imaging studies have demonstrated that listening to music alters human brain structure and function, the molecular mechanisms mediating those effects remain unknown. With the advent of genomics and bioinformatics approaches, these effects of music can now be studied in a more detailed fashion. To verify whether listening to classical music has any effect on human transcriptome, we performed genome-wide transcriptional profiling from the peripheral blood of participants after listening to classical music (n = 48), and after a control study without music exposure (n = 15). As musical experience is known to influence the responses to music, we compared the transcriptional responses of musically experienced and inexperienced participants separately with those of the controls. Comparisons were made based on two subphenotypes of musical experience: musical aptitude and music education. In musically experiencd participants, we observed the differential expression of 45 genes (27 up- and 18 down-regulated) and 97 genes (75 up- and 22 down-regulated) respectively based on subphenotype comparisons (rank product non-parametric statistics, pfp 0.05, >1.2-fold change over time across conditions). Gene ontological overrepresentation analysis (hypergeometric test, FDR < 0.05) revealed that the up-regulated genes are primarily known to be involved in the secretion and transport of dopamine, neuron projection, protein sumoylation, long-term potentiation and dephosphorylation. Down-regulated genes are known to be involved in ATP synthase-coupled proton transport, cytolysis, and positive regulation of caspase, peptidase and endopeptidase activities. One of the most up-regulated genes, alpha-synuclein (SNCA), is located in the best linkage region of musical aptitude on chromosome 4q22.1 and is regulated by GATA2, which is known to be associated with musical aptitude. Several genes reported to regulate song perception and production in songbirds displayed altered activities, suggesting a possible evolutionary conservation of sound perception between species. We observed no significant findings in musically inexperienced participants.

Characterization of respiratory neurons in the rostral ventrolateral medulla, an area critical for vocal production in songbirds

Much is known about the neuronal cell types and circuitry of the mammalian respiratory brainstem and its role in normal, quiet breathing. Our understanding of the role of respiration in the context of vocal production, however, is very limited. Songbirds contain a well-defined neural circuit, known as the song system, which is necessary for song production and is strongly coupled to the respiratory system. A major target of this system is nucleus parambigualis (PAm) in the ventrolateral medulla, a structure that controls inspiration by way of its bulbospinal projections but is also an integral part of the song-pattern generation circuit by way of its "thalamocortical" projections to song-control nuclei in the telencephalon. We have mapped out PAm to characterize the cell types and its functional organization. Extracellular single units were obtained in anesthetized adult male zebra finches while measuring air sac pressure to monitor respiration. Single units were characterized by their discharge patterns and the phase of the activity in the respiratory cycle. Several classes of neurons were identified and were analogous to those reported for mammalian medullary respiratory neurons. The majority of the neurons in PAm was classified as inspiratory augmenting or preinspiratory, although other basic discharge patterns were observed as well. The well-characterized connectivity of PAm within the vocal motor circuit and the similarity of its neural firing patterns to the rostral ventral respiratory group and pre-Bötzinger complex of mammals make it an ideal system for investigating the integration of breathing and vocalization.

The acoustic effect of vocal tract adjustments in zebra finches

Vocal production in songbirds requires the control of the respiratory system, the syrinx as sound source and the vocal tract as acoustic filter. Vocal tract movements consist of beak, tongue and hyoid movements, which change the volume of the oropharyngeal-esophageal cavity (OEC), glottal movements and tracheal length changes. The respective contributions of each movement to filter properties are not completely understood, but the effects of this filtering are thought to be very important for acoustic communication in birds. One of the most striking movements of the upper vocal tract during vocal behavior in songbirds involves the OEC. This study measured the acoustic effect of OEC adjustments in zebra finches by comparing resonance acoustics between an utterance with OEC expansion (calls) and a similar utterance without OEC expansion (respiratory sounds induced by a bilateral syringeal denervation). X-ray cineradiography confirmed the presence of an OEC motor pattern during song and call production, and a custom-built Hall-effect collar system confirmed that OEC expansion movements were not present during respiratory sounds. The spectral emphasis during zebra finch call production ranging between 2.5 and 5 kHz was not present during respiratory sounds, indicating strongly that it can be attributed to the OEC expansion.

Characterization of respiratory neurons in the ventrolateral medulla, an area critical for vocal production in songbirds

Characterization of respiratory neurons in the ventrolateral medulla, an area critical for vocal production in songbirds

Interaction Between Telencephalic Signals and Respiratory Dynamics in Songbirds

Song production in songbirds requires the action and coordination of several motor systems, like the respiratory muscles, the syrinx and the upper vocal tract. In particular, the main temporal features of the song are determined by the respiratory patterns, which are complex and diverse. It is not known how vocal motor control is integrated into the respiratory network. One model proposes that all temporal scales of song emerge from telencephalic nucleus (HVC) of the song system. Alternatively, the generation of respiratory patterns for song could be the result of an interaction between the neural instructions from the song control centers and the respiratory system, such that simple telencephalic signals might drive the nonlinear respiratory network and thus give rise to diverse respiratory patterns of song. We tested the basic assumption of the latter model by electrically stimulating telencephalic song control areas and monitored the temporal structure of the respiratory pattern. We found a strong interaction between the induced activation of song centers and the intrinsic respiratory rhythm. The evoked respiratory patterns are consistent with a nonlinear interaction as proposed by the alternative model. Supported by NIH.

Brain expression and song regulation of the cholecystokinin gene in the zebra finch (Taeniopygia guttata)

The gene encoding cholecystokinin (Cck) is abundantly expressed in the mammalian brain and has been associated with such functions as feeding termination and satiety, locomotion and self-stimulation, the modulation of anxiety-like behaviors, and learning and memory. Here we describe the brain expression and song regulation of Cck in the brain of the adult male zebra finch (Taeniopygia guttata), a songbird species. Using in situ hybridization we demonstrate that Cck is highly expressed in several discrete brain regions, most prominently the caudalmost portion of the hippocampal formation, the caudodorsal nidopallial shelf and the caudomedial nidopallium (NCM), the core or shell regions of dorsal thalamic nuclei, dopaminergic cell groups in the mesencephalon and pons, the principal nucleus of the trigeminal nerve, and the dorsal raphe. Cck was largely absent in song control system, a group of nuclei required for vocal learning and song production in songbirds, although sparse labeling was detected throughout the striatum, including song nucleus area X. We also show that levels of Cck mRNA and the number of labeled cells increase in the NCM of males and females following auditory stimulation with conspecific song. Double labeling further reveals that the majority of Cck cells, excluding those in the reticular nucleus of the thalamus, are non-GABAergic. Together, these data provide the first comprehensive characterization of Cck expression in a songbird, and suggest a possible involvement of Cck regulation in important aspects of birdsong biology, such as perceptual processing, auditory memorization, and/or vocal-motor control of song production.

Peripheral mechanisms for vocal production in birds – differences and similarities to human speech and singing

Song production in songbirds is a model system for studying learned vocal behavior. As in humans, bird phonation involves three main motor systems (respiration, vocal organ and vocal tract). The avian respiratory mechanism uses pressure regulation in air sacs to ventilate a rigid lung. In songbirds sound is generated with two independently controlled sound sources, which reside in a uniquely avian vocal organ, the syrinx. However, the physical sound generation mechanism in the syrinx shows strong analogies to that in the human larynx, such that both can be characterized as myoelastic-aerodynamic sound sources. Similarities include active adduction and abduction, oscillating tissue masses which modulate flow rate through the organ and a layered structure of the oscillating tissue masses giving rise to complex viscoelastic properties. Differences in the functional morphology of the sound producing system between birds and humans require specific motor control patterns. The songbird vocal apparatus is adapted for high speed, suggesting that temporal patterns and fast modulation of sound features are important in acoustic communication. Rapid respiratory patterns determine the coarse temporal structure of song and maintain gas exchange even during very long songs. The respiratory system also contributes to the fine control of airflow. Muscular control of the vocal organ regulates airflow and acoustic features. The upper vocal tract of birds filters the sounds generated in the syrinx, and filter properties are actively adjusted. Nonlinear source-filter interactions may also play a role. The unique morphology and biomechanical system for sound production in birds presents an interesting model for exploring parallels in control mechanisms that give rise to highly convergent physical patterns of sound generation. More comparative work should provide a rich source for our understanding of the evolution of complex sound producing systems.

Social Context Rapidly Modulates the Influence of Auditory Feedback on Avian Vocal Motor Control

Sensory feedback is important for the learning and control of a variety of behaviors. Vocal motor production in songbirds is a powerful model system to study sensory influences on behavior because the learning, maintenance, and control of song are critically dependent on auditory feedback. Based on previous behavioral and neural experiments, it has been hypothesized that songs produced in isolation [undirected (UD) song] represent a form of vocal practice, whereas songs produced to females during courtship interactions [female-directed (FD) song] represent a form of vocal performance. According to this "practice versus performance" framework, auditory feedback should be more influential when birds engage in vocal practice than when they engage in vocal performance. To directly test this hypothesis, we used a computerized system to perturb auditory feedback at precise locations during the songs of Bengalese finches and compared the degree to which feedback perturbations caused song interruptions as well as changes to the sequencing and timing of syllables between interleaved renditions of UD and FD song. We found that feedback perturbation caused fewer song interruptions and smaller changes to syllable timing during FD song than during UD song. These data show that changes in the social context in which song is produced rapidly modulate the influence of auditory feedback on song control in a manner consistent with the practice versus performance framework. More generally, they indicate that, for song, as for other motor skills including human speech, the influence of sensory feedback on activity within vocal premotor circuitry can be dynamically modulated.

Superfast vocal muscles control song production in songbirds

Birdsong is a widely used model for vocal learning and human speech, which exhibits high temporal and acoustic diversity. Rapid acoustic modulations are thought to arise from the vocal organ, the syrinx, by passive interactions between the two independent sound generators or intrinsic nonlinear dynamics of sound generating structures. Additionally, direct neuromuscular control could produce such rapid and precisely timed acoustic features if syringeal muscles exhibit rare superfast muscle contractile kinetics. However, no direct evidence exists that avian vocal muscles can produce modulations at such high rates. Here, we show that 1) syringeal muscles are active in phase with sound modulations during song over 200 Hz, 2) direct stimulation of the muscles in situ produces sound modulations at the frequency observed during singing, and that 3) syringeal muscles produce mechanical work at the required frequencies and up to 250 Hz in vitro. The twitch kinematics of these so-called superfast muscles are the fastest measured in any vertebrate muscle. Superfast vocal muscles enable birds to directly control the generation of many observed rapid acoustic changes and to actuate the millisecond precision of neural activity into precise temporal vocal control. Furthermore, birds now join the list of vertebrate classes in which superfast muscle kinetics evolved independently for acoustic communication.

Differential effects of testosterone on neuronal populations and their connections in a sensorimotor brain nucleus controlling song production in songbirds: a manganese enhanced-magnetic resonance imaging study

Nucleus HVC (formerly called high vocal center) of songbirds contains two types of projecting neurons connecting HVC respectively to the nucleus robustus archistriatalis, RA, or to area X. These two neuron classes exhibit multiple neurochemical differences and are differentially replaced by new neurons during adult life: high rates of neuronal replacement are observed in RA-projecting neurons only. The activity of these two types of neurons may also be modulated differentially by steroids. We analyzed by magnetic resonance imaging the effect of testosterone on the volume of RA and area X and on the dynamics of Mn 2+ accumulation in RA and area X of female starlings that had been injected with MnCl 2 through a permanent cannula implanted in HVC. Repeated visualization 6 weeks apart (before and after testosterone treatment) identified a volume increase of both nuclei in testosterone-treated birds associated with a concomitant decrease in controls. Following testosterone treatment, the total amount of Mn 2+ transported to RA and area X increased but the dynamics of accumulation, reflecting in part the activity of HVC neurons, was specifically altered in area X but not in RA. These data indicate that testosterone differentially affects the RA- and area X-projecting neurons in HVC. Manganese-enhanced magnetic resonance imaging (ME-MRI) thus provides repeated measures of connected brain areas and demonstrates testosterone-dependent regionally specific changes in brain activity and functional connectivity. The slow time scales investigated by this technique (compared to functional MRI) appear ideally suited for characterizing slow processes such as those involved in brain plasticity and learning.

Beaks, Adaptation, and Vocal Evolution in Darwin's Finches

Abstract Darwin's finches are well known for their remarkable diversity in beak form and function. Field studies have shown that beaks evolve by natural selection in response to variation in local ecological conditions. We posit a new hypothesis: As a consequence of beak evolution, there have been changes in the structure of finch vocal signals. We base this hypothesis on the discovery that beaks play a functional role in song production in songbirds. Recent field studies provide support for a link between beak morphology and song structure in Darwin's finches, although much remains to be learned. Because song plays a significant role in finch mating dynamics, we suggest that the functional link between beaks and song may have contributed to the process of speciation and adaptive radiation in these birds.