Song Learning In Zebra Finches Research Articles

Developmental pattern of CB1 cannabinoid receptor immunoreactivity in brain regions important to zebra finch (Taeniopygia guttata) song learning and control

Zebra finches learn song during distinct developmental stages, making them an important species for studying mechanisms underlying vocal development. Distinct interconnected forebrain regions have been identified as important to specific features of zebra finch vocal learning and production. Because prior experiments have demonstrated that late postnatal exposure to cannabinoid agonists alters zebra finch song learning, we have sought to identify brain regions likely involved in it. By using an affinity-purified polyclonal antibody directed against the zebra finch CB(1) cannabinoid receptor, we have studied staining patterns in groups of males at 25, 50, 75, and >100 days of age (adults). A general waxing and waning of staining intensity were observed over this developmental period. Distinct staining of song-related brain regions was also noted. Early establishment of staining patterns within rostral telencephalic song regions [area X and lateral magnocellular nucleus of the anterior nidopallium (lMAN)] suggests a role in auditory learning. Later establishment and maintenance in adulthood of small somata and neuropil staining within regions of rostral telencephalon [HVC and robust nucleus of the arcopallium (RA)] are consistent with a vocal motor role for cannabinoid signaling. Our results provide insight into brain regions likely responsible for cannabinoid-altered vocal learning and add to accumulating evidence supporting an important role for cannabinoid signaling in CNS development.

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.

Silent Synapses in a Thalamo-Cortical Circuit Necessary for Song Learning in Zebra Finches

Developmental changes in synaptic properties may act to limit neural and behavioral plasticity associated with sensitive periods. This study characterized synaptic maturation in a glutamatergic thalamo-cortical pathway that is necessary for vocal learning in songbirds. Lesions of the projection from medial dorsolateral nucleus of the thalamus (DLM) to the cortical nucleus lateral magnocellular nucleus of the anterior nidopallium (LMAN) greatly disrupt song behavior in juvenile birds during early stages of vocal learning. However, such lesions lose the ability to disrupt vocal behavior in normal birds at 60-70 days of age, around the time that selective auditory tuning for each bird's own song (BOS) emerges in LMAN neurons. This pattern has suggested that LMAN is involved in processing song-related information and evaluating the degree to which vocal motor output matches the tutor song to be learned. Analysis of reversed excitatory postsynaptic currents at DLM-->LMAN synapses in in vitro slice preparations revealed a pronounced N-methyl-D-aspartate receptor (NMDAR)-mediated component in both juvenile and adult cells with no developmental decrease in the relative contribution of NMDARs to synaptic transmission. However, the synaptic failure rate at DLM-->LMAN synapses in juvenile males during the sensitive period for song learning was significantly lower at depolarized potentials than at hyperpolarized potentials. In contrast, the failure rate at DLM-->LMAN synapses did not differ at hyper- versus depolarized holding potentials in adult males that had completed the acquisition of a stereotyped song. This pattern indicates that juvenile cells have a higher incidence of silent (NMDAR-only) synapses, which are postsynaptically silent at hyperpolarized potentials due to the voltage-dependent gating of NMDARs. Thus the decreased involvement of the LMAN pathway in vocal behavior is mirrored by a decline in the incidence of silent synapses but not by changes in the relative number of NMDA and AMPA receptors at DLM-->LMAN synapses. These findings suggest that a developmental decrease in silent synapses within LMAN may represent a neural correlate of behavioral plasticity during song learning.

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.

Developmental patterns of NMDAR expression within the song system do not recur during adult vocal plasticity in zebra finches.

All songbirds learn to sing during postnatal development but then display species differences in the capacity to learn song in adulthood. While the mechanisms that regulate avian vocal plasticity are not well characterized, one contributing factor may be the composition of N-methyl-D-aspartate receptors (NMDAR). Previous studies of an anterior forebrain pathway implicated in vocal plasticity revealed significant regulation of NMDAR subunit expression during the developmental sensitive period for song learning. Much less is known about the developmental regulation of NMDAR subunit expression in regions that participate more directly in motor aspects of song behavior. We show here that an increase in NR2A subunit mRNA and a decrease in NR2B subunit mRNA within the vocal motor pathway accompany song learning in zebra finches; however, manipulations that can alter the timing of song learning did not alter the course of these developmental changes. We also tested whether adult deafening, a treatment that provokes vocal change in songbirds that normally sing a stable song throughout adulthood, would render NMDAR subunit expression more similar to that observed developmentally. We report that NR2A and NR2B mRNA levels did not change within the anterior forebrain or vocal motor pathways after adult deafening, even after substantial changes in song structure. These results indicate that vocal plasticity does not require "juvenile patterns" of NMDAR gene expression in the avian song system.

Age and Sex Differences in Mitotic Activity within the Zebra Finch Telencephalon

Brain regions associated with song learning in zebra finches are larger and contain more neurons in males than females. Differences in cell proliferation, migration, survival, and specification may all contribute to the divergent development of the song-control system in developing birds. This study quantified levels of cell proliferation within the telencephalic ventricular zone (VZ) of juvenile and adult birds to look for both age and sex differences in mitotic activity that might contribute to the construction of song-control circuits. A single pulse of [3H]thymidine was administered to juveniles and adults of both sexes, and animals were killed 2 hr later. Analysis of thymidine labeling within the telencephalic VZ at the levels of area X, the anterior commissure, and high vocal center (HVC) revealed two major findings: (1) levels of mitotic activity decreased as a function of age in both males and females because of a reduction in the number of dividing cells within the VZ, and (2) sex differences in thymidine labeling occurred in restricted, localized segments of the VZ at the levels of area X and the anterior commissure in juveniles but not adults. Thus, overall proliferative activity decreases as birds mature, and the incidence of cell division in all regions of the VZ becomes equivalent in both sexes, such that no regions of sexually dimorphic proliferation are evident by adulthood. These data suggest that regions of sexually dimorphic proliferation within the VZ may contain precursor cells that give rise to song-control neurons, such that higher rates of mitotic activity in juvenile males could contribute to the growth of song-control nuclei such as HVC and area X.

Developmental and hormonal regulation of NR2A mRNA in forebrain regions controlling avian vocal learning.

Developmental changes in the composition of NMDA receptors can alter receptor physiology as well as intracellular signal transduction cascades, potentially shifting thresholds for neural and behavioral plasticity. During song learning in zebra finches, NMDAR currents become faster, and transcripts for the modulatory NR2B subunit of this receptor decrease in lMAN, a region in which NMDAR activation is critical for vocal learning. Using in situ hybridization, we found that NR2A transcripts change reciprocally, increasing significantly in both lMAN (59%) and in another song region, Area X (38%), between posthatch day (PHD) 20 and 40, but not changing further at PHD60 or 80. In adjacent areas not associated with song learning, NR2A mRNA did not change between PHD20-80. Although early song deprivation (which extends the sensitive period for song learning) delays changes in NR2B gene expression and NMDAR physiology within the lMAN, it did not alter NR2A mRNA levels measured at PHD40, 45, or 60. Early testosterone (T) treatment, which disrupts vocal development and accelerates the maturation of both NR2B levels and NMDAR physiology in lMAN, also significantly increased NR2A transcripts measured at PHD35 in lMAN. In Area X, a similar effect of T approached significance. Together with our previous studies, these results show that in a pathway critical for vocal plasticity, the ratio of NR2A:NR2B mRNA rises abruptly early during the sensitive period for song learning. Furthermore, androgen regulation of NMDAR gene expression may alter thresholds for experience-dependent synaptic change.

Development of Individual Axon Arbors in a Thalamocortical Circuit Necessary for Song Learning in Zebra Finches

Individual axon arbors within developing neural circuits are remodeled during restricted sensitive periods, leading to the emergence of precise patterns of connectivity and specialized adaptive behaviors. In male zebra finches, the circuit connecting the medial dorsolateral nucleus of the thalamus (DLM) and its cortical target, the lateral magnocellular nucleus of the anterior neostriatum (lMAN), is crucial for the acquisition of a normal vocal pattern during the sensitive period for song learning. The shell subregion of lMAN as well as the entire terminal field of DLM axons within lMAN undergo a striking increase in overall volume during early stages of vocal learning followed by an equally substantial decrease by adulthood, by which time birds have acquired stable song patterns. Because the total number of DLM neurons remains stable throughout this period, the dramatic changes within the overall DLM-->lMAN circuit are presumably attributable to dynamic rearrangements at the level of individual DLM axon arbors over the course of vocal learning. To study such rearrangements directly, we reconstructed individual DLM axon arbors in three dimensions at different stages during vocal learning. Unlike axon arbors in other model systems, in which the number of branches increases during development, DLM arbors are unusual in that they have the greatest number of branches at the onset of vocal learning and undergo large-scale retraction during the sensitive period for song learning. Decreases in the degree of overlap between DLM arbors apparently contribute to the increased overall volume of the DLM-->lMAN circuit during vocal learning. These developmental changes in DLM axon arbors occur at the height of the sensitive period for vocal learning, and hence may represent either a morphological correlate of song learning or a necessary prerequisite for acquisition of song.

Slow NMDA-EPSCs at synapses critical for song development are not required for song learning in zebra finches.

Birdsong, like human speech, is learned via auditory experience during a developmentally restricted sensitive period. Within projection neurons of two avian forebrain nuclei, NMDA receptor-mediated EPSCs (NMDA-EPSCs) become fast during song development, a transition posited to limit learning. To discover whether slow NMDA-EPSCs at these synapses are required for learning, we delayed song learning beyond its normal endpoint, post-hatch day (PHD) 65, by raising zebra finches in isolation from song tutors. At PHD45, before learning, isolation delayed NMDA-EPSC maturation, but only transiently. By PHD65, NMDA-EPSCs in isolates were fast and adult-like, yet isolates presented with tutors readily learned song. Thus song learning did not require slow NMDA-EPSCs at synapses critical for song development.

Song learning with audiovisual compound stimuli in zebra finches

We investigated the effects of audiovisual compound training on song learning in zebra finches,Taeniopygia guttata . In the first experiment, presentation of a stuffed adult zebra finch male was found to be reinforcing to zebra finch males in an operant task. In a separate experiment, zebra finch males were reared without their father from day 7 after hatching onwards. Between 35 and 76 days, they were placed in isolation and exposed to taped songs of a zebra finch male, according to a random schedule (20 presentations/h). For half of the birds, presentation of the song coincided with presentation of a stuffed zebra finch male. For the remaining birds, each presentation of the song was followed by presentation of a stuffed male. The birds were subsequently isolated until day 142, when their own songs were recorded and analysed. Birds in both groups shared significantly more song elements with their tutor songs than with an unfamiliar song. There was no significant difference in song learning between the groups. These results confirm that zebra finches can learn part of their songs from taped tutor songs. Furthermore, simultaneous presentation of the tutor song and a relevant, salient visual stimulus is not superior to sequential presentation.

Correction for Solis et al., Anterior Forebrain Neurons Develop Selectively by an Intermediate Stage of Song Learning in Zebra Finches

Correction: In the article, “Anterior Forebrain Neurons Develop Selectively by an Intermediate Stage of Song Learning in Zebra Finches,” by M. M. Solis and Allison J. Doupe, which appeared on pages 6447–6462 of the August 15, 1997 issue, the formula for d ′ on page 6449 of Materials and

Do Contingencies with Tutor Behaviour Influence Song Learning in Zebra Finches?

AbstractSocial interaction with a song tutor is often found to be important for the song learning process in songbirds, but the mechanism is still unclear. The main aim of this study is to find indications for contingencies between singing and interactive behaviours, between and within tutors and tutees, which might influence the song learning process of zebra finches (Taeniopygia guttata). To this end we observed the interactions of eleven juvenile zebra finch males with their fathers (the tutors) and their mothers during the sensitive phase for song learning, and examined four different types of possible contingencies. The evidence for these contingencies was not very strong: (1) We found some weak indications that a tutee can anticipate tutor song by preceding tutor behaviour. There were no indications that (2) tutor song is contingent upon subsequent behaviour of the tutor, that (3) juvenile males can control singing of their tutor by preceding operant social behaviour, or that (4) social behaviour of the tutor reinforces singing of the tutee. We found some indications that the juvenile males attend actively to the tutor song. Furthermore, we found that the juvenile males maintained more mutual interactions with their father than with their mother. In general, we did not find any clear relationship between aspects of social interaction and song copying in zebra finches.

Early isolation from conspecific song does not affect the normal developmental decline of N‐methyl‐D‐aspartate receptor binding in an avian song nucleus

Early effects of experience on synaptic reorganization and behavior often involve activation of N-methyl-D-aspartate (NMDA) receptors. We have begun to explore the role of this glutamate-receptor subtype in the development of learned birdsong. Song learning in zebra finches occurs during a restricted period that coincides with extensive synaptic reorganization within neural regions controlling song behavior. In one brain region necessary for song learning, the lateral magnocellular nucleus of the anterior neostriatum (IMAN), NMDA receptor binding is twice as high at the onset of song learning as in adulthood. In the present study, we used quantitative autoradiography with the noncompetitive NMDA antagonist [3H]MK-801 to examine more closely the developmental decline in NMDA receptor binding within IMAN and found that it occurred gradually over the period of song learning and was not associated with a particular stage of the learning process. In addition, early isolation from conspecific song did not affect [3H]MK-801 binding in IMAN at 30, 60, or 80 days. Since behavioral studies confirmed that our isolate rearing conditions extended the sensitive period for song learning, we conclude that the normal developmental decline in overall NMDA receptor binding within IMAN does not terminate the capacity for song learning. Finally, early deafening, which prevents both stages of song learning, also did not affect [3H]MK-801 binding in IMAN at 80 days, indicating that the decline in NMDA receptor binding occurs in the absence of auditory experiences associated with song development.

Can Lack of Experience Delay the End of the Sensitive Phase for Song Learning?

Some bird species will modify their songs in adulthood, whereas in others, once developed, song appears relatively fixed. However, even in some of the latter, social experience may lead birds to learn songs later than was previously thought possible. Do age-limited learners really exist or is failure to learn later in those species where it has been described a result of inadequate stimulation? If learning is normally restricted to a certain age period, is the decline in sensitivity due to age as such or to enough adequate information having been received? We discuss some of the issues involved and describe some experiments on zebra finches which we have carried out. Our results suggests that drastic changes in adulthood are rare. Birds deprived of tutors in the sensitive phase are more likely to produce elements learnt from the father before that stage, but show little evidence of learning from tutors encountered when adult (at 120 d+). Birds that are female-raised in groups and deprived of any male tutor till 120 days learn little from their tutors thereafter but have quite normal songs; these converge strongly within groups, as do the songs of all group-reared birds. Birds reared by both parents but without siblings, and then deprived of song during the sensitive phase, show learning both from the father and from the tutors encountered after 120 days. The most abnormal songs are those of birds reared by the mother alone and then kept singly till they were placed with singing adults at 120 days. The songs of these birds were more variable than those of the other groups, and they showed more evidence of learning between 120 and 240 days. These results do suggest some flexibility in the timing of song learning in zebra finches depending on experience but argue against profound change occurring once birds are adult even where their early experience has been greatly reduced.

Neural and hormonal substrates for song learning in zebra finches

Many songbirds learn vocal sounds used to communicate with other members of their species during a restricted period of development. For example, male zebra finches (Poephila guttata) need to hear their father's song until approximately 40 days of age in order to learn to produce normal vocalizations. By the time they are fully adult (100 days of age), the song pattern they produce is a faithful copy of the song heard earlier in life, and this song pattern is maintained in a highly stereotyped fashion throughout adulthood. Song learning and behavior are controlled by a discrete system of neural circuits, which undergo profound developmental changes during the time when song behavior is being learned; both song learning and its neural substrate are regulated by sex hormones.

Behaviour-contingent exposure to taped song and zebra finch song learning

Behaviour-contingent exposure to taped song and zebra finch song learning

Song learning in zebra finches: how are elements from two tutors integrated?

Song learning in zebra finches: how are elements from two tutors integrated?

Song Learning in Zebra Finches Exposed to a Series of Tutors during the Sensitive Phase

AbstractYoung male zebra finches exposed to a series of adult males during their sensitive phase for song learning tended to learn from several of them, in contrast to those exposed to two or more tutors simultaneously. There is a tendency to learn more from later tutors, either because the memory of their elements over‐writes that of earlier ones or because sensitivity is greater at this stage. No clear relation could be found between features of the song or behaviour of tutors and whether or not they were copied. In common with earlier studies, tutor song output, beyond a certain minimum was found to be unimportant.

Subspecies recognition and song learning in zebra finches

The songs of captive Taeniopygia guttata guttata from Timor, T. g. castanotis from the Australian mainland and hybrid zebra finch males were analysed sonagraphically and the response of females was measured in playback experiments. Guttata and Castanotis young were either raised normally by members of their own subspecies or cross-fostered to members of the other subspecies. Hybrid young were raised by Guttata male-Castanotis female pairs. Guttata songs were significantly longer than Castanotis songs, with more elements per phrase, and were sung at a higher frequency, irrespective of whether males had been raised normally or cross-fostered. Hybrid songs were intermediate between Guttata and Castanotis songs. The results suggest that rearing experience has little, if any, effect on these macrostructural differences between the songs of the two subspecies. Females implanted with oestradiol preferred songs of males of their foster-father subspecies, irrespective of whether these males had been cross-fostered or raised normally, indicating that females use macrostructural song features for subspecies recognition and that their song preferences are learnt. It is suggested that these macrostructural differences in song function in subspecies recognition.

Developmental changes in the cellular composition of a brain nucleus involved with song learning in zebra finches

Using a double-labeling technique to characterize projection neurons and androgen target cells, we examined ontogenetic changes in the cellular composition of IMAN, a forebrain nucleus that plays an important role in song learning during a restricted period of male zebra finch development. This nucleus undergoes a massive loss of neurons during the time of song acquisition. We report that during the period of cell loss in IMAN, neither the property of projecting to an efferent target nor the ability to concentrate androgens is able to spare neurons from ontogenetic cell death. Furthermore, we report that, at the time when IMAN ceases to influence song production, a large proportion of androgen-sensitive cells that do not make an efferent projection lose the ability to accumulate androgens.