Zebra Finch Song Research Articles

A segmentation algorithm for zebra finch song at the note level

Songbirds have been widely used as a model for studying neuronal circuits that relate to vocal learning and production. An important component of this research relies on quantitative methods for characterizing song acoustics. Song in zebra finches—the most commonly studied songbird species—consists of a sequence of notes, defined as acoustically distinct segments in the song spectrogram. Here, we present an algorithm that exploits the correspondence between note boundaries and rapid changes in overall sound energy to perform an initial automated segmentation of song. The algorithm uses linear fits to short segments of the amplitude envelope to detect sudden changes in song signal amplitude. A variable detection threshold based on average power greatly improves the performance of the algorithm. Automated boundaries and those picked by human observers agree to within 8 ms for >83% of boundaries.

Temporal Structure in Zebra Finch Song: Implications for Motor Coding

Adult zebra finch songs consist of stereotyped sequences of syllables. Although some behavioral and physiological data suggest that songs are structured hierarchically, there is also evidence that they are driven by nonhierarchical, clock-like bursting in the premotor nucleus HVC (used as a proper name). In this study, we developed a semiautomated template-matching algorithm to identify repeated sequences of syllables and a modified dynamic time-warping algorithm to make fine-grained measurements of the temporal structure of song. We find that changes in song length are expressed across the song as a whole rather than resulting from an accumulation of independent variance during singing. Song length changes systematically over the course of a day and is related to the general level of bird activity as well as the presence of a female. The data also show patterns of variability that suggest distinct mechanisms underlying syllable and gap lengths: as tempo varies, syllables stretch and compress proportionally less than gaps, whereas syllable-syllable and gap-gap correlations are significantly stronger than syllable-gap correlations. There is also increased temporal variability at motif boundaries and especially strong positive correlations between the same syllables sung in different motifs. Finally, we find evidence that syllable onsets may have a special role in aligning syllables with global song structure. Generally, the timing data support a hierarchical view in which song is composed of smaller syllable-based units and provide a rich set of constraints for interpreting the results of physiological recordings.

Song Perception During the Sensitive Period of Song Learning in Zebra Finches (Taeniopygia guttata).

The sensitive period is a special time for auditory learning in songbirds. However, little is known about perception and discrimination of song during this period of development. The authors used a go/no-go operant task to compare discrimination of conspecific song from reversed song in juvenile and adult zebra finches (Taeniopygia guttata), and to test for possible developmental changes in perception of syllable structure and syllable syntax. In Experiment 1, there were no age or sex differences in the ability to learn the discrimination, and the birds discriminated the forward from reversed song primarily on the basis of local syllable structure. Similar results were found in Experiment 2 with juvenile birds reared in isolation from song. Experiment 3 found that juvenile zebra finches could discriminate songs on the basis of syllable order alone, although this discrimination was more difficult than one based on syllable structure. The results reveal well-developed song discrimination and song perception in juvenile zebra finches, even in birds with little experience with song.

HVC microlesions do not destabilize the vocal patterns of adult male zebra finches with prior ablation of LMAN

The songs of adult male zebra finches (Taeniopygia guttata) arise by an integration of activity from two neural pathways that emanate from the telencephalic nucleus HVC (proper name). One pathway descends directly from HVC to the vocal premotor nucleus RA (the robust nucleus of the arcopallium) whereas a second pathway descends from HVC into a basal ganglia circuit (the anterior forebrain pathway, AFP) that also terminates in RA. Although HVC neurons that project directly to RA outnumber those that contribute to the AFP, both populations are distributed throughout HVC. Thus, partial ablation (microlesion) of HVC should damage both pathways in a proportional manner. We report here that bilateral HVC microlesions in adult male zebra finches produce an immediate loss of song stereotypy from which birds recover, in some cases within 3 days. The contribution of the AFP to the onset of song destabilization was tested by ablating the output nucleus of this circuit (LMAN, the lateral magnocellular nucleus of the anterior nidopallium) prior to bilateral HVC microlesions. Song stereotypy was largely unaffected. Together, our findings suggest that adult vocal production involves nonproportional integration of two streams of neural activity with opposing effects on song—HVC's direct projection to RA underlies production of stereotyped song whereas the AFP seems to facilitate vocal variation. However, the rapid recovery of song in birds with HVC microlesions alone suggests the presence of dynamic corrective mechanisms that favor vocal stereotypy. © 2006 Wiley Periodicals, Inc. Develop Neurobiol 67: 205–218, 2007.

Spatial unmasking of birdsong in human listeners: Energetic and informational factors

Spatial unmasking describes the improvement in the detection or identification of a target sound afforded by separating it spatially from simultaneous masking sounds. This effect has been studied extensively for speech intelligibility in the presence of interfering sounds. In the current study, listeners identified zebra finch song, which shares many acoustic properties with speech but lacks semantic and linguistic content. Three maskers with the same long-term spectral content but different short-term statistics were used: (1) chorus (combinations of unfamiliar zebra finch songs), (2) song-shaped noise (broadband noise with the average spectrum of chorus), and (3) chorus-modulated noise (song-shaped noise multiplied by the broadband envelope from a chorus masker). The amount of masking and spatial unmasking depended on the masker and there was evidence of release from both energetic and informational masking. Spatial unmasking was greatest for the statistically similar chorus masker. For the two noise maskers, there was less spatial unmasking and it was wholly accounted for by the relative target and masker levels at the acoustically better ear. The results share many features with analogous results using speech targets, suggesting that spatial separation aids in the segregation of complex natural sounds through mechanisms that are not specific to speech.

Tuning for spectro-temporal modulations as a mechanism for auditory discrimination of natural sounds

Vocal communicators discriminate conspecific vocalizations from other sounds and recognize the vocalizations of individuals. To identify neural mechanisms for the discrimination of such natural sounds, we compared the linear spectro-temporal tuning properties of auditory midbrain and forebrain neurons in zebra finches with the statistics of natural sounds, including song. Here, we demonstrate that ensembles of auditory neurons are tuned to auditory features that enhance the acoustic differences between classes of natural sounds, and among the songs of individual birds. Tuning specifically avoids the spectro-temporal modulations that are redundant across natural sounds and therefore provide little information; rather, it overlaps with the temporal modulations that differ most across sounds. By comparing the real tuning and a less selective model of spectro-temporal tuning, we found that the real modulation tuning increases the neural discrimination of different sounds. Additionally, auditory neurons discriminate among zebra finch song segments better than among synthetic sound segments.

FOS and ZENK responses in 45-day-old zebra finches vary with auditory stimulus and brain region, but not sex

Male zebra finches ( Taeniopygia guttata) begin to sing around 45 days posthatch (d45) and tune their songs to match learned templates. Females never develop song, but they use male conspecific vocalizations for mate choice. While auditory perception is critical for both sexes, the responses of the immediate early genes (IEGs) ZENK and FOS differ in auditory brain areas of d30 males and females. The present study examined expression of these IEGs in the caudomedial nidopallium (NCM), caudomedial mesopallium (CMM; formerly cHV), and the hippocampus (HP) in both sexes at d45 in response to conspecific, heterospecific, or no songs. Overall, zebra finch song presentations resulted in the highest density of ZENK and FOS cells in each region analyzed, but expression varied across brain areas. Contrary to d30 birds, the IEG response patterns did not differ between the sexes. ZENK-immunoreactivity was significantly increased following exposure to conspecific songs compared to no songs, and zebra finch song presentations produced more FOS-immunoreactive nuclei than both heterospecific and no songs. While the pattern was consistent, significant effects of stimulus type were seen only in the NCM when the brain regions were analyzed separately. Furthermore, levels of FOS- and ZENK-immunoreactive neurons were higher in the lateral than medial NCM in both sexes. Along with previous work from our lab and others, these data suggest that at d45 neuronal responses within perceptual regions are still maturing on some levels, but IEG expression has acquired a number of adult characteristics.

Processing of Modulated Sounds in the Zebra Finch Auditory Midbrain: Responses to Noise, Frequency Sweeps, and Sinusoidal Amplitude Modulations

The avian auditory midbrain nucleus, the mesencephalicus lateralis, dorsalis (MLd), is the first auditory processing stage in which multiple parallel inputs converge, and it provides the input to the auditory thalamus. We studied the responses of single MLd neurons to four types of modulated sounds: 1) white noise; 2) band-limited noise; 3) frequency modulated (FM) sweeps, and 4) sinusoidally amplitude-modulated tones (SAM) in adult male zebra finches. Responses were compared with the responses of the same neurons to pure tones in terms of temporal response patterns, thresholds, characteristic frequencies, frequency tuning bandwidths, tuning sharpness, and spike rate/intensity relationships. Most neurons responded well to noise. More than one-half of the neurons responded selectively to particular portions of the noise, suggesting that, unlike forebrain neurons, many MLd neurons can encode specific acoustic components of highly modulated sounds such as noise. Selectivity for FM sweep direction was found in only 13% of cells that responded to sweeps. Those cells also showed asymmetric tuning curves, suggesting that asymmetric inhibition plays a role in FM directional selectivity. Responses to SAM showed that MLd neurons code temporal modulation rates using both spike rate and synchronization. Nearly all cells showed low-pass or band-pass filtering properties for SAM. Best modulation frequencies matched the temporal modulations in zebra finch song. Results suggest that auditory midbrain neurons are well suited for encoding a wide range of complex sounds with a high degree of temporal accuracy rather than selectively responding to only some sounds.

Vocal Experimentation in the Juvenile Songbird Requires a Basal Ganglia Circuit

Songbirds learn their songs by trial-and-error experimentation, producing highly variable vocal output as juveniles. By comparing their own sounds to the song of a tutor, young songbirds gradually converge to a stable song that can be a remarkably good copy of the tutor song. Here we show that vocal variability in the learning songbird is induced by a basal-ganglia-related circuit, the output of which projects to the motor pathway via the lateral magnocellular nucleus of the nidopallium (LMAN). We found that pharmacological inactivation of LMAN dramatically reduced acoustic and sequence variability in the songs of juvenile zebra finches, doing so in a rapid and reversible manner. In addition, recordings from LMAN neurons projecting to the motor pathway revealed highly variable spiking activity across song renditions, showing that LMAN may act as a source of variability. Lastly, pharmacological blockade of synaptic inputs from LMAN to its target premotor area also reduced song variability. Our results establish that, in the juvenile songbird, the exploratory motor behavior required to learn a complex motor sequence is dependent on a dedicated neural circuit homologous to cortico-basal ganglia circuits in mammals.

Rhythmic Activity in a Forebrain Vocal Control NucleusIn Vitro

The learned vocalizations of songbirds constitute a rhythmic behavior that is thought to be governed by a central pattern generator and that is accompanied by highly patterned neural activity. Phasic premotor activity is observed during singing in HVC [used as a proper name following the nomenclature of Reiner et al. (2004)], a telencephalic song system nucleus that is essential for song production. Moreover, HVC neurons display phasic patterns of auditory activity in response to song stimulation. To address the cellular basis of pattern generation in HVC, we investigated its rhythm-generating abilities. We report here the induction of sustained, rhythmic activity patterns in HVC when isolated in vitro. Brief, high-frequency stimulation evoked repetitive postsynaptic potentials (PSPs) and local field potentials (LFPs) from HVC neurons recorded in a brain slice preparation made from adult male zebra finches. These rhythmic events were sustained for seconds in the absence of ongoing, phasic stimulation, and they had temporal properties similar to those of syllable occurrence within zebra finch song. Paired recordings revealed synchrony between repetitive PSP and LFP occurrence, indicating that a population of cells participates in this patterned activity. The PSPs resulted from multiple, coordinated, fast-glutamatergic, synaptic inputs. Moreover, their occurrence and timing relied on inhibitory synaptic transmission. Thus, HVC itself has rhythmic abilities that could influence the timing of neural activity over relatively long time windows. These rhythmic properties may contribute to song production or perception in vivo.

Testosterone implants alter the frequency range of zebra finch songs

To investigate whether changes in testosterone alter the frequency range in which a zebra finch produces song, we assigned male zebra finches to two groups, one of which received testosterone implants and the other empty silastic capsule implants. We then recorded songs up to 52 weeks after the surgery and measured frequency changes in the fundamental frequencies of arbitrarily chosen harmonic stacks in the songs of birds in either group. We found statistically significant decreases after 5 weeks in the songs of the testosterone-treated birds. No changes were found in the fundamental frequencies of the control group. The frequency change remained after the apparent effects of the testosterone implants ended. These data show that high levels of testosterone can lower the frequencies of elements in zebra finch songs.

Ensemble Coding of Vocal Control in Birdsong

Zebra finch song is represented in the high-level motor control nucleus high vocal center (HVC) (Reiner et al., 2004) as a sparse sequence of spike bursts. In contrast, the vocal organ is driven continuously by smoothly varying muscle control signals. To investigate how the sparse HVC code is transformed into continuous vocal patterns, we recorded in the singing zebra finch from populations of neurons in the robust nucleus of arcopallium (RA), a premotor area intermediate between HVC and the motor neurons. We found that highly similar song elements are typically produced by different RA ensembles. Furthermore, although the song is modulated on a wide range of time scales (10-100 ms), patterns of neural activity in RA change only on a short time scale (5-10 ms). We suggest that song is driven by a dynamic circuit that operates on a single underlying clock, and that the large convergence of RA neurons to vocal control muscles results in a many-to-one mapping of RA activity to song structure. This permits rapidly changing RA ensembles to drive both fast and slow acoustic modulations, thereby transforming the sparse HVC code into a continuous vocal pattern.

Neuronal activation related to auditory perception in the brain of a non-songbird, the ring dove

In songbirds, parrots, and hummingbirds, which need to learn their songs, exposure to conspecific song leads to increased expression of the immediate early gene (IEG) ZENK in a number of forebrain regions, including the caudomedial nidopallium (NCM) and the caudomedial mesopallium (CMM). Here we investigated the pattern of IEG expression in response to auditory stimulation in the brain of the ring dove (Streptopelia risoria), a non-songbird that does not need to learn its vocalizations. Ring dove males were exposed to conspecific vocalizations (coos), to heterospecific vocalizations (zebra finch song) or they were kept in silence. IEG expression was investigated by means of immunocytochemical analysis of the distribution of the ZENK protein product Zenk. In all three groups there was Zenk expression in several forebrain regions including the NCM and the CMM, similar to earlier findings in song-learning species. Quantitative analysis of the NCM, the CMM, and the hippocampus revealed significantly greater Zenk expression in birds exposed to conspecific vocalizations than in birds kept in silence, in the CMM only. These results show that there is substantial Zenk expression in the forebrain of a non-song-learning bird, comparable to that in avian song-learning taxa. These findings suggest that there is IEG expression specific to conspecific auditory stimulation in the CMM in both songbirds and non-songbirds.

Dissociation between extension of the sensitive period for avian vocal learning and dendritic spine loss in the song nucleus lMAN

Several instances of early learning coincide with significant rearrangements of neural connections in regions contributing to these behaviors. In fact developmentally restricted learning may be constrained temporally by the opportunity for experience to selectively maintain appropriate synapses amidst the elimination of exuberant connections. Consistent with this notion, during the normal sensitive period for vocal learning in zebra finches ( Taenopygia guttata), there is a decline in the density of dendritic spines within a region essential for song development, the lateral magnocellular nucleus of the anterior nidopallium (lMAN). Moreover, in birds isolated from conspecific song shortly after hatching, both the closure of the sensitive period for vocal learning and the pruning of spines from lMAN neurons is delayed. Here, we employed a more subtle form of deprivation to delay the close of the sensitive period for song learning, and found that late song learning occurred without obvious alterations in the pruning of dendritic spines on lMAN neurons. At posthatch day (PHD) 65 (beyond the end of the normal sensitive period for song memorization in zebra finches), birds isolated from song beginning on PHD30 did not differ from normally reared birds in measures of dendritic spine density on Golgi-Cox stained lMAN neurons. Moreover, tutor exposure from PHD65 to 90 did not increase spine elimination in these isolates (who memorized new song material) relative to controls (who did not). Thus, we conclude that the extent of normally occurring lMAN spine loss is not sufficient to account for the timing of the sensitive period for zebra finch song learning.

Modulation power and phase spectrum of natural sounds enhance neural encoding performed by single auditory neurons.

We examined the neural encoding of synthetic and natural sounds by single neurons in the auditory system of male zebra finches by estimating the mutual information in the time-varying mean firing rate of the neuronal response. Using a novel parametric method for estimating mutual information with limited data, we tested the hypothesis that song and song-like synthetic sounds would be preferentially encoded relative to other complex, but non-song-like synthetic sounds. To test this hypothesis, we designed two synthetic stimuli: synthetic songs that matched the power of spectral-temporal modulations but lacked the modulation phase structure of zebra finch song and noise with uniform band-limited spectral-temporal modulations. By defining neural selectivity as relative mutual information, we found that the auditory system of songbirds showed selectivity for song-like sounds. This selectivity increased in a hierarchical manner along ascending processing stages in the auditory system. Midbrain neurons responded with highest information rates and efficiency to synthetic songs and thus were selective for the spectral-temporal modulations of song. Primary forebrain neurons showed increased information to zebra finch song and synthetic song equally over noise stimuli. Secondary forebrain neurons responded with the highest information to zebra finch song relative to other stimuli and thus were selective for its specific modulation phase relationships. We also assessed the relative contribution of three response properties to this selectivity: (1) spiking reliability, (2) rate distribution entropy, and (3) bandwidth. We found that rate distribution and bandwidth but not reliability were responsible for the higher average information rates found for song-like sounds.

Distinct periods of cannabinoid sensitivity during zebra finch vocal development

Zebra finch song is a form of vocal communication learned during at least two distinct stages of late postnatal development. During the first of these stages, termed auditory learning, nestlings memorize the song pattern of an adult male tutor, usually the father. During the second stage, sensory-motor learning, these song patterns are practiced and refined until a good copy is produced by adulthood. Vocal learning has made zebra finches a useful model for studying drug effects during vocal development. Prior work has shown that daily exposure to a modest dosage of the cannabinoid agonist WIN55212-2 (WIN) alters sensory-motor learning by reducing stereotypy scores and numbers of note types learned. Here we report that these two effects are produced independently during subperiods of the sensory-motor learning stage. Additional temporally distinct WIN effects during sensory-motor learning include differential incorporation of tutor-derived and improvised note types. We have also evaluated acute and chronic effects of WIN exposure on ability to encode a tutor's song during auditory learning, finding significant effects on stereotypy and distinct effects on note duration and internote intervals. Taken together, these results demonstrate the presence of distinct subperiods of cannabinoid sensitivity during zebra finch auditory and sensory-motor vocal development.

Limits on reacquisition of song in adult zebra finches exposed to white noise.

Zebra finches (Taeniopygia guttata) learn a specific song pattern during a sensitive period of development, after which song changes little or not at all. However, recent studies have demonstrated substantial behavioral plasticity in song behavior during adulthood under a range of conditions. The current experiment examined song behavior of adult zebra finches temporarily deprived of auditory feedback by chronic exposure to loud white noise (WN). Long-term exposure to continuous WN resulted in disruption of song similar to that observed after deafening. When auditory feedback was restored by discontinuing WN, birds were either tutored using tape-recorded playback or housed with adult conspecific tutors. No evidence of learning new tutor syllables was observed, and recovery of pre-WN song patterns was very limited after restoration of hearing. However, many birds did reacquire some aspects of their pretreatment song, suggesting an adult form of learning that may retain some of the initial aspects of sensorimotor acquisition of song in which vocalizations are shaped to match a stored template representation. The failure to learn novel song elements and the modest degree of recovery observed overall suggest a limit on plasticity in adult birds that have acquired species-typical song patterns and may reflect an important species difference between zebra finches and Bengalese finches.

Nicotine-mediated plasticity in robust nucleus of the archistriatum of the adult zebra finch

Activation of neuronal nicotinic acetylcholine receptors (nAChRs) modulates the induction of long-term potentiation (LTP), a possible cellular mechanism for learning. This study was undertaken to determine the effects of activation of nAChRs by nicotine on long-term plasticity in the songbird zebra finch, which is a valuable model to study synaptic plasticity and its implications to behavioral learning. Electrophysiological recordings in the robust nucleus of the archistriatum (RA) in adult zebra finch brain slices reveal that tetanic stimulation alone does not produce LTP. However, LTP is induced by such stimulation in the presence of nicotine. The nicotine-mediated LTP is blocked by dihydro-β-erythroidine (DHβE, 1 μM), an antagonist having a greater effect against nAChRs containing the alpha 4 subunit. In the presence of methyllcaconitine (MLA, 10 nM), an antagonist of nAChRs containing the alpha 7 subunit, a long-term depression (LTD) is unmasked, implicating a bi-directional type of plasticity in the zebra finch RA, which is modulated by differential activation of nAChR subtypes. Intracellular recordings from single neurons show a depression of the afterhyperpolarization (AHP) and an increase in frequency of evoked and spontaneous action potentials in the presence of nicotine. These results suggest that nicotinic cholinergic mechanisms may play a critical role in synaptic plasticity in the zebra finch song system and thereby influence song learning and plasticity.

Peripheral motor dynamics of song production in the zebra finch.

Singing behavior in songbirds is a model system for motor control of learned behavior. The target organs of its central motor programs are the various muscle systems involved in sound generation. Investigation of these peripheral motor mechanisms of song production is the first step toward an understanding of how different motor systems are coordinated. Here we review physiological studies of all major motor systems that are involved in song production and modification in the zebra finch (Taeniopygia guttata). Acoustic syllables of zebra finch song are produced by a characteristic air sac pressure pattern. Electromyographic (EMG) and sonomicrometric recording of expiratory muscle activity reveals that respiratory motor control is tightly coordinated with syringeal gating of airflow. Recordings of bronchial airflow demonstrate that most of the song syllables are composed of simultaneous independent contributions from the two sides of the syrinx. Sounds generated in the syrinx can be modified by the resonance properties of the upper vocal tract. Tracheal length affects resonance, but dynamic changes of tracheal length are unlikely to make a substantial contribution to sound modification. However, beak movements during song contribute to sound modification and, possibly, affect the vibratory behavior of the labia. Rapid beak aperture changes were associated with nonlinear transitions in the acoustic structure of individual syllables. The synergy between respiratory and syringeal motor systems, and the unique bilateral, simultaneous, and independent sound production, combined with dynamic modification of the acoustic structure of song, make the zebra finch an excellent model system for exploring mechanisms of sensorimotor integration underlying a complex learned behavior.

Sexual differentiation of the zebra finch song system.

The song system of zebra finches (Taeniopygia gutatta) is highly sexually dimorphic. Only males sing, and the brain regions and muscles controlling song are much larger in males than in females. Development of the song system is highly sensitive to steroid hormones. However, unlike similar sexually dimorphic systems in other animal models, masculinization of song system structure and function is most likely not induced by testosterone secreted from the testes. Instead, sex-specific development of the neural song system appears to be regulated by factors intrinsic to the brain, probably by the expression of sex chromosome gene(s) that influence the levels of estradiol synthesized in the brain and/or the responses of brain tissue to estradiol. However, the existing data are complex and in some cases contradictory. More work is required to identify the critical genes and their relationships with steroid hormones.