Tutor Song Research Articles

A mesocortical dopamine circuit enables the cultural transmission of vocal behaviour.

The cultural transmission of behavior depends on a pupil’s ability to identify and emulate an appropriate tutor1–4. How the pupil’s brain detects a suitable tutor and encodes the tutor’s behavior is largely unknown. Juvenile zebra finches readily copy songs of adult tutors they interact with, but not songs they listen to passively through a speaker5,6, indicating that social cues generated by the tutor facilitate song imitation. Here we show that neurons in the midbrain periaqueductal gray (PAG) of juvenile finches are selectively excited by a singing tutor and, by releasing dopamine (DA) in a sensorimotor cortical analogue (HVC), help encode tutor song representations used for vocal copying. Blocking DA signaling in the pupil’s HVC during tutoring blocked copying, whereas pairing stimulation of PAG terminals in HVC with song played through a speaker was sufficient to drive copying. Exposure to a singing tutor triggered the rapid emergence of responses to the tutor song in the pupil’s HVC and a rapid increase in the pupil’s song complexity, an early signature of song copying7,8. These findings reveal that a dopaminergic mesocortical circuit detects a tutor’s presence and helps encode the tutor’s performance, facilitating the cultural transmission of vocal behavior.

Acoustic adaptation to city noise through vocal learning by a songbird.

Anthropogenic noise imposes novel selection pressures, especially on species that communicate acoustically. Many animals—including insects, frogs, whales and birds—produce sounds at higher frequencies in areas with low-frequency noise pollution. Although there is support for animals changing their vocalizations in real time in response to noise (i.e. immediate flexibility), other evolutionary mechanisms for animals that learn their vocalizations remain largely unexplored. We hypothesize that cultural selection for signal structures less masked by noise is a mechanism of acoustic adaptation to anthropogenic noise. We test this hypothesis by presenting nestling white-crowned sparrows (Zonotrichia leucophyrs) with less-masked (higher-frequency) and more-masked (lower-frequency) tutor songs either during playback of anthropogenic noise (noise-tutored treatment) or at a different time from noise playback (control treatment). As predicted, we find that noise-tutored males learn less-masked songs significantly more often, whereas control males show no copying preference, providing strong experimental support for cultural selection in response to anthropogenic noise. Further, noise-tutored males reproduce songs at higher frequencies than their tutor, indicating a distinct mechanism to increase signal transmission in a noisy environment. Notably, noise-tutored males achieve lower performance songs than their tutors, suggesting potential costs in a sexual selection framework.

The songs of male pied flycatchers: exploring the legacy of the fathers.

Singing is a key element of songbirds’ behavioral repertoire, particularly for males, which sing during the breeding season to defend resources against other males and to attract females. Different song traits may convey honest information about males’ qualities or conditions, which may be used by females to select their mates. Traits under strong sexual selection have an important component of additive genetic variation (i.e., the main genetic inheritance from parents), and so relatively high heritability; therefore, it can be expected that song traits also do. Although the act of singing is an innate behavior, and thus, genetically determined, songbirds need to learn their songs and therefore the genetic contribution to song traits may be reduced by the effect of environmental factors. We tested this hypothesis in seven song traits recorded in the long-distance migratory bird, the pied flycatcher (Ficedula hypoleuca). From a 23-year database (1992–2015), we obtained songs for 28 father–son pairs, and for each song trait we applied parent–offspring regressions to estimate heritability. The type of syllables sung are learned from tutors, and here we also determined the cultural contribution of fathers to the song repertoires of their sons, by quantifying the percentage of syllables that sons shared with their fathers, and compared this with what sons shared with other males in the population (e.g., neighbors). The heritabilities of song traits were highly variable (ranging from −0.22 to 0.56), but most of these were around zero and none of them were significant. These results indicate that the seven song traits are most likely determined by environmental factors. Sons shared more syllables with their fathers than with neighbors (21% vs. 3%), suggesting that fathers are important song tutors during the nestling period. We conclude that there is a cultural inheritance from fathers to their sons’ syllable repertoires, but there is no strong evidence for a genetic contribution of fathers to the seven song traits studied.

Recurrent development of song idiosyncrasy without auditory inputs in the canary, an open-ended vocal learner

Complex learned behaviors, like bird song and human speech, develop under the influence of both genetic and environmental factors. Accordingly, learned behaviors comprise species specificity and individual variability. Auditory information plays a critical role in vocal learning by songbirds, both to memorize tutor songs and to monitor own vocalizations. Nevertheless, audition-deprived songbirds develop structured, species-specific song patterns. It remains to be elucidated how the auditory input contributes to the development of individual variability of song characteristics. Here we show that an open-ended vocal learner, the canary, annually recapitulates individually unique songs without audition. Although the total number of syllable types was reduced by auditory deprivation, other vocal phenotypes examined in the syllable, phrase, and syntax of songs were conserved between the 1st and 2nd years, both in deafened and intact birds. In deafened canaries, approximately 60% of the syllables were yearly reproduced with consistent acoustic features, whereas the remaining syllables were replaced with new ones in an annual cycle of song development. These results indicate that the open-ended vocal learning of canaries involves an audition-independent mechanism for the development of recurrent song idiosyncrasy.

Epigenetic regulation of transcriptional plasticity associated with developmental song learning.

Ethologists discovered over 100 years ago that some lifelong behavioural patterns were acquired exclusively during restricted developmental phases called critical periods (CPs). Developmental song learning in zebra finches is one of the most striking examples of a CP for complex learned behaviour. After post-hatch day 65, whether or not a juvenile male can memorize the song of a 'tutor' depends on his experiences in the month prior. If he experienced a tutor, he can no longer learn, but if he has been isolated from hearing a tutor the learning period is extended. We aimed to identify how tutor experience alters the brain and controls the ability to learn. Epigenetic landscapes are modulated by experience and are able to regulate the transcription of sets of genes, thereby affecting cellular function. Thus, we hypothesized that tutor experiences determine the epigenetic landscape in the auditory forebrain, a region required for tutor song memorization. Using ChIPseq, RNAseq and molecular biology, we provide evidence that naturalistic experiences associated with the ability to learn can induce epigenetic changes, and propose transcriptional plasticity as a mediator of CP learning potential.

Early life conditions that impact song learning in male zebra finches also impact neural and behavioral responses to song in females.

Early life stressors can impair song in songbirds by negatively impacting brain development and subsequent learning. Even in species in which only males sing, early life stressors might also impact female behavior and its underlying neural mechanisms, but fewer studies have examined this possibility. We manipulated brood size in zebra finches to simultaneously examine the effects of developmental stress on male song learning and female behavioral and neural response to song. Although adult male HVC volume was unaffected, we found that males from larger broods imitated tutor song less accurately. In females, early condition did not affect the direction of song preference: all females preferred tutor song over unfamiliar song in an operant test. However, treatment did affect the magnitude of behavioral response to song: females from larger broods responded less during song preference trials. This difference in activity level did not reflect boldness per se, as a separate measure of this trait did not differ with brood size. Additionally, in females we found a treatment effect on expression of the immediate early gene ZENK in response to tutor song in brain regions involved in song perception (dNCM) and social motivation (LSc.vl, BSTm, TnA), but not in a region implicated in song memory (CMM). These results are consistent with the hypothesis that developmental stressors that impair song learning in male zebra finches also influence perceptual and/or motivational processes in females. However, our results suggest that the learning of tutor song by females is robust to disturbance by developmental stress. © 2018 Wiley Periodicals, Inc. Develop Neurobiol, 2018.

Social interaction with a tutor modulates responsiveness of specific auditory neurons in juvenile zebra finches

Behavioral states of animals, such as observing the behavior of a conspecific, modify signal perception and/or sensations that influence state-dependent higher cognitive behavior, such as learning. Recent studies have shown that neuronal responsiveness to sensory signals is modified when animals are engaged in social interactions with others or in locomotor activities. However, how these changes produce state-dependent differences in higher cognitive function is still largely unknown. Zebra finches, which have served as the premier songbird model, learn to sing from early auditory experiences with tutors. They also learn from playback of recorded songs however, learning can be greatly improved when song models are provided through social communication with tutors (Eales, 1989; Chen et al., 2016). Recently we found a subset of neurons in the higher-level auditory cortex of juvenile zebra finches that exhibit highly selective auditory responses to the tutor song after song learning, suggesting an auditory memory trace of the tutor song (Yanagihara and Yazaki-Sugiyama, 2016). Here we show that auditory responses of these selective neurons became greater when juveniles were paired with their tutors, while responses of non-selective neurons did not change. These results suggest that social interaction modulates cortical activity and might function in state-dependent song learning.

Early social experience alters transcriptomic responses to species-specific song stimuli in female songbirds

Amongst an array of stimuli from countless species, animals must recognize salient signals, including those of their own species. In songbirds, behavioral tests have demonstrated that preferences for conspecific male songs are determined by both preexisting biases and social experience with a male ‘tutor’ during the sensitive period for learning. Although immediate early gene expression (e.g. ZENK) and electrophysiological experiments generally find greater neural responses for conspecific songs, it remains unclear whether distinct mechanisms, such as sensory gating, are engaged to filter out irrelevant heterospecific songs. Here we compare the transcriptomic profiles, via RNA-seq, of non-singing females of a songbird, the zebra finch (Taeniopygia guttata), by focusing on the auditory forebrain, a region known to be critical in the processing of conspecific vs. heterospecific songs. Gene expression profiles demonstrate that different neural mechanisms are involved in the processing of conspecific versus heterospecific Bengalese finch (Lonchura striata) songs. In particular, one gene known to mediate sensory gating, the alpha 3 subunit member of nicotinic cholinergic receptors (CHRNA3), was significantly downregulated in response to hearing Bengalese finch song, but not when young females were tutored by a Bengalese male during early development. Overall, our results confirm previous behavioral and physiological studies, such that heterospecific-tutored individuals processed both conspecific and tutor songs similarly. Using transcriptomic profiling of peripheral blood samples, we also demonstrate the methodological potential of non-terminal sampling to identify transcriptomic biomarkers for conspecific auditory recognition. These results show how experience and inherited preferences facilitate the neural processing of salient songs by female songbirds.

A common neural circuit mechanism for internally guided and externally reinforced forms of motor learning

The complex skills underlying verbal and musical expression can be learned without external punishment or reward, indicating their learning is internally guided. The neural mechanisms that mediate internally guided learning are poorly understood, but a circuit comprising dopamine-releasing neurons in the midbrain ventral tegmental area (VTA) and their targets in the basal ganglia are important to externally reinforced learning. Juvenile zebra finches copy a tutor song in a process that is internally guided and, in adulthood, can learn to modify the fundamental frequency (pitch) of a target syllable in response to external reinforcement with white noise. Here we combined intersectional genetic ablation of VTA neurons, reversible blockade of dopamine receptors in the basal ganglia, and singing-triggered optogenetic stimulation of VTA terminals to establish that a common VTA–basal ganglia circuit enables internally guided song copying and externally reinforced syllable pitch learning.

MiR-9 regulates basal ganglia-dependent developmental vocal learning and adult vocal performance in songbirds.

miR-9 is an evolutionarily conserved miRNA that is abundantly expressed in Area X, a basal ganglia nucleus required for vocal learning in songbirds. Here, we report that overexpression of miR-9 in Area X of juvenile zebra finches impairs developmental vocal learning, resulting in a song with syllable omission, reduced similarity to the tutor song, and altered acoustic features. miR-9 overexpression in juveniles also leads to more variable song performance in adulthood, and abolishes social context-dependent modulation of song variability. We further show that these behavioral deficits are accompanied by downregulation of FoxP1 and FoxP2, genes that are known to be associated with language impairments, as well as by disruption of dopamine signaling and widespread changes in the expression of genes that are important in circuit development and functions. These findings demonstrate a vital role for miR-9 in basal ganglia function and vocal communication, suggesting that dysregulation of miR-9 in humans may contribute to language impairments and related neurodevelopmental disorders.

The neural response of female zebra finches (Taeniopygia guttata) to conspecific, heterospecific, and isolate song depends on early-life song exposure

The auditory forebrain regions caudo-medial nidopallium (NCM) and caudo-medial mesopallium (CMM) of songbirds exhibit differential expression of the immediate-early gene ZENK in response to playback of different song stimuli, and dependent on early-life auditory experience. Similarly, song preferences depend both on auditory experience and unlearned biases for particular song features. We explored the contributions of early-life auditory experience and the type of song stimuli on the Zenk response in the auditory forebrain of female zebra finches. Females were raised in three different early tutoring conditions: conspecific tutors that sang isolate song, heterospecific tutors, or conspecific tutors that sang wild-type song. At maturity, these females were exposed to one of five different playback conditions: wild-type song, isolate song, tutor song, heterospecific song, or white noise. Subsequently, the number of cells immunoreactive for ZENK in CMM and NCM was measured. We predicted that birds exposed to conspecific song early in life, and during the song playback in adulthood, would have the highest neural response. Instead, we found that the Zenk response varied across playback conditions with the highest response to conspecific wild-type and conspecific isolate song. In addition, we found a main effect of tutoring, with the lowest overall Zenk response in females tutored by males singing isolate song. Most importantly, there was a significant interaction in that females tutored by wild-type conspecific or heterospecific songs showed a similar increased response to zebra finch songs (wild-type or isolate), but females tutored by isolate song showed no differential response to conspecific song and only showed elevated Zenk response to the particular songs they were tutored with. Combined, our results indicate that unlearned response biases to conspecific song elements depend on previous auditory experience. That is, early experience appears to modulate the expression of innate biases.

Neural activity in cortico-basal ganglia circuits of juvenile songbirds encodes performance during goal-directed learning.

Cortico-basal ganglia circuits are thought to mediate goal-directed learning by a process of outcome evaluation to gradually select appropriate motor actions. We investigated spiking activity in core and shell subregions of the cortical nucleus LMAN during development as juvenile zebra finches are actively engaged in evaluating feedback of self-generated behavior in relation to their memorized tutor song (the goal). Spiking patterns of single neurons in both core and shell subregions during singing correlated with acoustic similarity to tutor syllables, suggesting a process of outcome evaluation. Both core and shell neurons encoded tutor similarity via either increases or decreases in firing rate, although only shell neurons showed a significant association at the population level. Tutor similarity predicted firing rates most strongly during early stages of learning, and shell but not core neurons showed decreases in response variability across development, suggesting that the activity of shell neurons reflects the progression of learning.

A neuronal signature of accurate imitative learning in wild-caught songbirds (swamp sparrows, Melospiza georgiana)

In humans and other animals, behavioural variation in learning has been associated with variation in neural features like morphology and myelination. By contrast, it is essentially unknown whether cognitive performance scales with electrophysiological properties of individual neurons. Birdsong learning offers a rich system to investigate this topic as song acquisition is similar to human language learning. Here, we address the interface between behavioural learning and neurophysiology in a cohort of wild-caught, hand-reared songbirds (swamp sparrows, Melospiza georgiana). We report the discovery in the forebrain HVC of sensorimotor ‘bridge’ neurons that simultaneously and selectively represent two critical learning-related schemas: the bird’s own song, and the specific tutor model from which that song was copied. Furthermore, the prevalence and response properties of bridge neurons correlate with learning ability – males that copied tutor songs more accurately had more bridge neurons. Our results are consistent with the hypothesis that accurate imitative learning depends on a successful bridge, within single cortical neurons, between the representation of learning models and their sensorimotor copies. Whether such bridge neurons are a necessary mechanism for accurate learning or an outcome of learning accuracy is unknown at this stage, but can now be addressed in future developmental studies.

Neuronal Intrinsic Physiology Changes During Development of a Learned Behavior.

Juvenile male zebra finches learn their songs over distinct auditory and sensorimotor stages, the former requiring exposure to an adult tutor song pattern. The cortical premotor nucleus HVC (acronym is name) plays a necessary role in both learning stages, as well as the production of adult song. Consistent with neural network models where synaptic plasticity mediates developmental forms of learning, exposure to tutor song drives changes in the turnover, density, and morphology of HVC synapses during vocal development. A network's output, however, is also influenced by the intrinsic properties (e.g., ion channels) of the component neurons, which could change over development. Here, we use patch clamp recordings to show cell-type-specific changes in the intrinsic physiology of HVC projection neurons as a function of vocal development. Developmental changes in HVC neurons that project to the basal ganglia include an increased voltage sag response to hyperpolarizing currents and an increased rebound depolarization following hyperpolarization. Developmental changes in HVC neurons that project to vocal-motor cortex include a decreased resting membrane potential and an increased spike amplitude. HVC interneurons, however, show a relatively stable range of intrinsic features across vocal development. We used mathematical models to deduce possible changes in ionic currents that underlie the physiological changes and to show that the magnitude of the observed changes could alter HVC circuit function. The results demonstrate developmental plasticity in the intrinsic physiology of HVC projection neurons and suggest that intrinsic plasticity may have a role in the process of song learning.

Early life manipulations of vasopressin-family peptides alter vocal learning.

Vocal learning from social partners is crucial for the successful development of communication in a wide range of species. Social interactions organize attention and enhance motivation to learn species-typical behaviour. However, the neurobiological mechanisms connecting social motivation and vocal learning are unknown. Using zebra finches (Taeniopygia guttata), a ubiquitous model for vocal learning, we show that manipulations of nonapeptide hormones in the vasopressin family (arginine vasotocin, AVT) early in development can promote or disrupt both song and social motivation. Young male zebra finches, like human infants, are socially gregarious and require interactive feedback from adult tutors to learn mature vocal forms. To investigate the role of social motivational mechanisms in song learning, in two studies, we injected hatchling males with AVT or Manning compound (MC, a nonapeptide receptor antagonist) on days 2-8 post-hatching and recorded song at maturity. In both studies, MC males produced a worse match to tutor song than controls. In study 2, which experimentally controlled for tutor and genetic factors, AVT males also learned song significantly better compared with controls. Furthermore, song similarity correlated with several measures of social motivation throughout development. These findings provide the first evidence that nonapeptides are critical to the development of vocal learning.

Bilateral neurotoxic lesions in NCM before tutoring onset do not prevent successful tutor song learning

Sensorimotor learning crucially depends on the ability to acquire a sensory memory for shaping motor commands. Such learning is conveniently studied in young songbirds when they memorize the song of an adult singer and gradually transform their own vocalizations toward the memorized target song. Here we study the involvement of the Caudal Medial Nidopallium (NCM), a higher auditory cortical area, in acquisition of a song memory. NCM has previously been shown to be involved in tutor song memorization. To study the necessity of NCM in this process, we perform large irreversible NCM lesions using ibotenic acid injections in about 40-days old juvenile zebra finches, before their first exposure to tutor song. Surprisingly, NCM-lesioned juveniles successfully copied the tutor song at least as well as untreated control animals, showing that a fully intact NCM is not required for tutor song memory formation and normal song development.

Overproduction and attrition: the fates of songs memorized during song learning in songbirds

Most songbirds learn their songs through imitation. However, what a male sings as an adult is not necessarily a complete inventory of what he memorized at some earlier point in time: songbirds commonly memorize more material than they eventually sing as adults. Work with swamp sparrows, Melospiza georgiana, first confirmed that males rehearse many of the song models to which they are exposed during the sensory phase of song acquisition but subsequently include only a subset of those rehearsed songs in their adult repertoire. This process of overproduction and selective attrition has since been demonstrated in other species as well. More recently, the persistent memory of tutor songs rehearsed but not included in the adult repertoire has been demonstrated at the neural level. Furthermore, memories of song models heard during the sensory phase of acquisition but never detected during rehearsal in the sensorimotor phase also may persist into adulthood. Here we review behavioural and neural studies of overproduction and attrition in song learning. We discuss factors that may trigger the persistence of some models and the rejection of others in an individual's repertoire and possible functional consequences of this phenomenon. Data from human speech research indicates that humans also may unconsciously retain memories of features of languages heard early in life but never spoken.

Children's initial sleep-associated changes in motor skill are unrelated to long-term skill levels.

Sleep is considered to support the formation of skill memory. In juvenile but not adult song birds learning a tutor's song, a stronger initial deterioration of song performance over night-sleep predicts better song performance in the long run. This and similar observations have stimulated the view of sleep supporting skill formation during development in an unsupervised off-line learning process that, in the absence of external feedback, can initially also enhance inaccuracies in skill performance. Here we explored whether in children learning a motor sequence task, as in song-learning juvenile birds, changes across sleep after initial practice predict performance levels achieved in the long run. The task was a serial reaction time task (SRTT) where subjects had to press buttons which were lighted up in a repeating eight-element sequence as fast as possible. Twenty-five children (8-12years) practised the task in the evening before nocturnal sleep which was recorded polysomnographically. Retrieval was tested on the following morning and again 1week later after daily training on the SRTT. As expected, changes in response speed over the initial night of sleep were negatively correlated with final performance speed after the 1-week training. However, unlike in song birds, this correlation was driven by the baseline speed level achieved before sleep. Baseline-corrected changes in speed or variability over the initial sleep period did not predict final performance on the trained SRTT sequence, or on different sequences introduced to assess generalization of the trained behaviour. The lack of correlation between initial sleep-dependent changes and long-term performance might reflect that the children were too experienced for the simple SRTT, possibly also favouring ceiling effects in performance. A consistent association found between sleep spindle activity and explicit sequence knowledge alternatively suggests that the expected correlation was masked by explicit memory systems interacting with skill memory formation.

Familial bias and auditory feedback regulation of vocal babbling patterns during early song development.

Learned vocalizations are a crucial acoustic biosignal conveying individual traits in many species. Songbirds learn song patterns by listening to a tutor song and performing vocal practice during a sensitive developmental period. However, when and how individual differences in song patterns develop remain unknown. Here, we report that individual differences in vocal output exist even at the earliest song development stage, called subsong. Experiments involving the manipulation of both breeding pairs and song tutoring conditions revealed that the parental pair combination contributes to generating familial differences in syllable duration and variability in the subsong of offspring. Furthermore, after deafening, juveniles immediately changed their subsong by shortening the syllable durations but maintained the individual variability of their subsong temporal patterns, suggesting both auditory-sensitive modification and independent intrinsic regulation of vocal output. These results indicate that the temporal patterns of subsong are not merely disordered vocalization but are regulated by familial bias with sensitivity to auditory feedback, thus generating individual variability at the initiation of vocal development.

Auditory experience-dependent cortical circuit shaping for memory formation in bird song learning.

As in human speech acquisition, songbird vocal learning depends on early auditory experience. During development, juvenile songbirds listen to and form auditory memories of adult tutor songs, which they use to shape their own vocalizations in later sensorimotor learning. The higher-level auditory cortex, called the caudomedial nidopallium (NCM), is a potential storage site for tutor song memory, but no direct electrophysiological evidence of tutor song memory has been found. Here, we identify the neuronal substrate for tutor song memory by recording single-neuron activity in the NCM of behaving juvenile zebra finches. After tutor song experience, a small subset of NCM neurons exhibit highly selective auditory responses to the tutor song. Moreover, blockade of GABAergic inhibition, and sleep decrease their selectivity. Taken together, these results suggest that experience-dependent recruitment of GABA-mediated inhibition shapes auditory cortical circuits, leading to sparse representation of tutor song memory in auditory cortical neurons.