Song Learning in Birds

Birds sing to communicate. Male birds use song to advertise their territories and attract females. Each bird species has a unique song or set of songs. Song conveys both species and individual identity. In most species, young birds learn some features of adult song. Song develops gradually from amorphous to fixed patterns of vocalization as if crystals form out of liquid. Learning of a song proceeds in two steps; birds commit the song to memory in the first stage and then they vocally reproduce it in the second stage. The two stages overlap each other in some species, while they are separated by several months in other species. The ability of a bird to commit a song to memory is restricted to a period known as the sensitive phase. Vocal reproduction of the memorized song requires auditory feedback. Birds deafened before the second stage cannot reproduce the memorized song. Birds change vocal output until it matches with the memorized song, which thus serves as a template. Birds use a built-in template when a tutor model is not available. Exposure to a tutor model modifies this innate template

Vocal learning promotes patterned inhibitory connectivity.

Skill learning is instantiated by changes to functional connectivity within premotor circuits, but whether the specificity of learning depends on structured changes to inhibitory circuitry remains unclear. We used slice electrophysiology to measure connectivity changes associated with song learning in the avian analog of primary motor cortex (robust nucleus of the arcopallium, RA) in Bengalese Finches. Before song learning, fast-spiking interneurons (FSIs) densely innervated glutamatergic projection neurons (PNs) with apparently random connectivity. After learning, there was a profound reduction in the overall strength and number of inhibitory connections, but this was accompanied by a more than two-fold enrichment in reciprocal FSI-PN connections. Moreover, in singing birds, we found that pharmacological manipulations of RA's inhibitory circuitry drove large shifts in learned vocal features, such as pitch and amplitude, without grossly disrupting the song. Our results indicate that skill learning establishes nonrandom inhibitory connectivity, and implicates this patterning in encoding specific features of learned movements

The Role of Nestling Acoustic Experience in Song Discrimination in a Sparrow

Oscine songbirds are an ideal system for investigating how early experience affects vocal behavior. Young songbirds face a challenging task: how to recognize and selectively learn only their own species’ song, often during a time-limited window. Because birds are capable of hearing birdsong very early in life, early exposure to song could plausibly affect recognition of appropriate models; however, this idea conflicts with the traditional view that song learning occurs only after a bird leaves the nest. Thus, it remains unknown whether natural variation in acoustic exposure prior to song learning affects the template for recognition. In a population where sister species, golden-crowned and white-crowned sparrows, breed syntopically, we found that nestlings discriminate between heterospecific and conspecific song playbacks prior to the onset of song memorization. We then asked whether natural exposure to more frequent or louder heterospecific song explained any variation in golden-crowned nestling response to heterospecific song playbacks. We characterized the amount of each species’ song audible in golden-crowned sparrow nests and showed that even in a relatively small area, the ratio of heterospecific to conspecific song exposure varies from 0 to 20%. However, although many songbirds hear and respond to acoustic signals before fledging, golden-crowned sparrow nestlings that heard different amounts of heterospecific song did not behave differently in response to heterospecific playbacks. This study provides the first evidence that song discrimination at the onset of song learning is robust to the presence of closely related heterospecifics in nature, which may be an important adaptation in sympatry between potentially interbreeding taxa

Of mice, birds, and men: the mouse ultrasonic song system has some features similar to humans and song-learning birds.

Humans and song-learning birds communicate acoustically using learned vocalizations. The characteristic features of this social communication behavior include vocal control by forebrain motor areas, a direct cortical projection to brainstem vocal motor neurons, and dependence on auditory feedback to develop and maintain learned vocalizations. These features have so far not been found in closely related primate and avian species that do not learn vocalizations. Male mice produce courtship ultrasonic vocalizations with acoustic features similar to songs of song-learning birds. However, it is assumed that mice lack a forebrain system for vocal modification and that their ultrasonic vocalizations are innate. Here we investigated the mouse song system and discovered that it includes a motor cortex region active during singing, that projects directly to brainstem vocal motor neurons and is necessary for keeping song more stereotyped and on pitch. We also discovered that male mice depend on auditory feedback to maintain some ultrasonic song features, and that sub-strains with differences in their songs can match each other's pitch when cross-housed under competitive social conditions. We conclude that male mice have some limited vocal modification abilities with at least some neuroanatomical features thought to be unique to humans and song-learning birds. To explain our findings, we propose a continuum hypothesis of vocal learning

A sensorimotor area (NIf) is required for the production of learned vocalizations

Sensory feedback is essential for the acquisition of complex motor behaviors, including birdsong. In zebra finches, auditory feedback is relayed to the descending motor pathway primarily through the nucleus interfacialis nidopalii (NIf). NIf projects to HVC - a premotor region essential for song, which projects to RA, a motor cortex analogue brain area that drives muscle activity required for vocalizations. NIf is also essential for ‘sleep replay’, a recapitulation of song-related neural dynamics in the motor pathway during sleep. Despite being one of the major inputs to the song control pathway, there is no known role for NIf in the production of zebra finch song. To address this, we reversibly inactivated NIf using TTX or Muscimol in 13 birds. We compared songs before and during inactivation and found large effects of NIf inactivation on song structure. Vocalizations after NIf inactivation resembled subsong, highly variable utterances typical of the very early phases of song learning. Subsong is driven by LMAN, the output nucleus of an avian basal ganglia circuit that projects to RA. To verify that NIf inactivations indeed switched song control from HVC to LMAN, we inactivated LMAN in conjunction with NIf in four birds. As with LMAN inactivations after HVC lesions, this manipulation led to a complete cessation of singing. We also lesioned NIf using ibotenic acid and saw the song recover within a day, consistent with previous studies. Our results show that NIf input to HVC is acutely necessary for generating learned vocal behavior in songbirds, and that in its absence vocal production reverts to subsong driven by LMAN. Absent NIf input, the song circuit reorganizes and recovers its ability to produce pre-lesion song over the course of 1-2 days, suggesting a redundant role for NIf that can be assumed by other parts of the song circuit

Altered Auditory BOLD Response to Conspecific Birdsong in Zebra Finches with Stuttered Syllables

How well a songbird learns a song appears to depend on the formation of a robust auditory template of its tutor's song. Using functional magnetic resonance neuroimaging we examine auditory responses in two groups of zebra finches that differ in the type of song they sing after being tutored by birds producing stuttering-like syllable repetitions in their songs. We find that birds that learn to produce the stuttered syntax show attenuated blood oxygenation level-dependent (BOLD) responses to tutor's song, and more pronounced responses to conspecific song primarily in the auditory area field L of the avian forebrain, when compared to birds that produce normal song. These findings are consistent with the presence of a sensory song template critical for song learning in auditory areas of the zebra finch forebrain. In addition, they suggest a relationship between an altered response related to familiarity and/or saliency of song stimuli and the production of variant songs with stuttered syllables

Own Song Selectivity in the Songbird Auditory Pathway: Suppression by Norepinephrine

Like human speech, birdsong is a learned behavior that supports species and individual recognition. Norepinephrine is a catecholamine suspected to play a role in song learning. The goal of this study was to investigate the role of norepinephrine in bird's own song selectivity, a property thought to be important for auditory feedback processes required for song learning and maintenance.Using functional magnetic resonance imaging, we show that injection of DSP-4, a specific noradrenergic toxin, unmasks own song selectivity in the dorsal part of NCM, a secondary auditory region.The level of norepinephrine throughout the telencephalon is known to be high in alert birds and low in sleeping birds. Our results suggest that norepinephrine activity can be further decreased, giving rise to a strong own song selective signal in dorsal NCM. This latent own song selective signal, which is only revealed under conditions of very low noradrenergic activity, might play a role in the auditory feedback and/or the integration of this feedback with the motor circuitry for vocal learning and maintenance

ACUTE ESTROGEN SYNTHESIS AND ACTION IN THE AUDITORY CORTEX OF DEVELOPING MALE ZEBRA FINCHES (TAENIOPYGIA GUTTATA)

Birdsong, as with human speech, is learned during an age- and experience-dependent sensitive period early in life. Songbirds must first memorize their parents’ song during a sensory phase, then refine their own burgeoning vocalizations to match the auditory memory of their parents’ song during a sensorimotor phase. While the error-correction aspect of the sensorimotor phase of song learning is comparatively well understood, it is largely unknown how auditory memories are formed and how auditory processing may change across development to facilitate song memorization. The songbird caudomedial nidopallium (NCM) is a brain region that encodes complex communication signals like song and is rich in aromatase (enzyme necessary for converting precursor androgens to estrogens) and estrogen receptors. In adults, acute estrogen signaling enhances auditory encoding, suggesting that one role for 17β-estradiol (E2) in NCM during development may be to enhance auditory processing and facilitate auditory memorization. Moreover, in the hippocampus of rodents, birds, and nonhuman primates, local E2 acts to enhance post-training memory consolidation. As such, I set out to determine whether this role for E2 in auditory processing and memorization occurs within the auditory cortex of juvenile songbirds. I tested this hypothesis across several experiments: I first tested how local E2 administration in NCM modulated auditory processing in developing songbirds. Next, I explored how changes in developing neural architecture and aromatase expression are aligned with distinct song learning phases. I then tested how global and local aromatase inhibition following song learning sessions impacted motor production, vocal learning, and neurophysiology in developing songbirds. Finally, using a stimulus-specific adaptation paradigm, I determined whether findings in juvenile songbirds extended to adults. Specifically, I locally blocked local E2 synthesis in NCM immediately following song exposure and subsequently measured neural recognition of the exposed song. My results showed that sensory coding is substantially enhanced in the NCM of sensory-aged birds compared to song-producing (sensorimotor-aged) juvenile birds, and that E2 exerts an age- and hemisphere-dependent effect on modulation of auditory processing. I also found that cell density in NCM peaks in sensory-aged birds, and is overall higher in dorsal vs. ventral NCM, but that aromatase and parvalbumin expression remain high and constant across development; no hemispheric differences for cell density or expression were found. Further, I found that neither circulating nor locally-derived E2 are required for tutor song memorization in development and adulthood; however, estrogen synthesis blockade can impair song production in developing birds and can also transform the lasting neural representations of autogenous and tutor song in adulthood. Taken together, this dissertation provides new insights into the pleiotropic effects of rapid steroid signaling and synthesis within the auditory cortex of developing male songbirds with implications for communication processing and sensorimotor learning

THE EFFECTS OF EARLY NUTRITIONAL STRESS ON PHYSIOLOGY, COGNITON AND SONG PRODUCTION IN EUROPEAN STARLINGS (STURNUS VULGARIS)

Song is a phenotypic expression of male quality. According to the developmental stress hypothesis, birds subjected to stressful environments while their song system is developing should advertise this with a more simple song. The first aim of this study was to investigate whether song learning was reflective of learning abilities in general. The second aim was to determine what underlying physiological systems could be affected by stress early in development that may be responsible for altered song learning. A nutritional stressor was enforced in developing European starlings (Sturnus vulgaris) and song learning was measure in addition to learning in general. Physiological measures comprising growth rates, stress response and metabolic rates were taken. Results from this study suggest stress does negatively affect song and certain aspects of cognition. The onset at which stress is applied and sex are important factors in physiological changes in response to developmental stress