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ABSTRACTBackgroundThe hypothalamus receives ingested nutrient information via ascending gut-related projections and plays a significant role in the regulation of food intake. Human neuroimaging studies have observed changes in the activity or connectivity of the hypothalamus in response to nutrient ingestion. However, previous neuroimaging studies have not yet assessed differences in temporal changes of hypothalamic responses to various nutrients in humans. Thus a repeated measures functional magnetic resonance imaging (fMRI) study using 30-min scans was designed to examine differences in hypothalamic responses to various nutrients.MethodsIn this study, 18 healthy adults (mean age, 22.4 years; standard deviation, 4.8; age range, 19–39 years; 11 males and seven females) underwent fMRI sessions. On the day of each session, one of the four solutions (200 ml of monosodium glutamate, glucose, safflower oil emulsion, or saline) was administered to participants while fMRI scanning.ResultsInfused amino acid and glucose, but not lipid emulsion, increased lateral hypothalamic responses as compared to a saline infusion ([x, y, z] = [4, −4, −10], z = 2.96). In addition, only hypothalamic responses to saline, but not those to the infusion of other nutrients, elicited a subjective sensation of hunger.ConclusionThese findings suggest that lateral hypothalamic responses to ingested nutrients may mediate homeostatic sensations in humans.

Human infants acquire motor patterns for speech during the first several years of their lives. Sequential vocalizations such as human speech are complex behaviors, and the ability to learn new vocalizations is limited to only a few animal species. Vocalizations are generated through the coordination of three types of organs: namely, vocal, respiratory, and articulatory organs. Moreover, sophisticated temporal respiratory control might be necessary for sequential vocalization involving human speech. However, it remains unknown how coordination develops in human infants and if this developmental process is shared with other vocal learners. To answer these questions, we analyzed temporal parameters of sequential vocalizations during the first year in human infants and compared these developmental changes to song development in the Bengalese finch, another vocal learner. In human infants, early cry was also analyzed as an innate sequential vocalization. The following three temporal parameters of sequential vocalizations were measured: note duration (ND), inter-onset interval, and inter-note interval (INI). The results showed that both human infants and Bengalese finches had longer INIs than ND in the early phase. Gradually, the INI and ND converged to a similar range throughout development. While ND increased until 6 months of age in infants, the INI decreased up to 60 days posthatching in finches. Regarding infant cry, ND and INI were within similar ranges, but the INI was more stable in length than ND. In sequential vocalizations, temporal parameters developed early with subsequent articulatory stabilization in both vocal learners. However, this developmental change was accomplished in a species-specific manner. These findings could provide important insights into our understanding of the evolution of vocal learning.

ABSTRACTBengalese finches learn and produce sequential vocalizations with a complex song syntax. Various models for the song syntax have been proposed, each of which focuses on several different characteristics of the syntax. However, methods to model these multiple characteristics in a single framework have not been well studied. Here, we propose a model that explains three prominent characteristics of the song syntax in Bengalese finches in a single unified framework. First, the generation of a vocal element depends on multiple preceding elements. Second, a song often contains repetitions of a single element type. Third, a song often begins with a special sequence called an introductory sequence. In this study, an effective way was sought to model these three characteristics in the framework of a conditional probability in symbol sequences. The model takes a distributed representation of a preceding sequence as an input, which is defined by a set of decaying values activated when the vocal elements are generated. The proposed model is shown to outperform conventional syntax models in predicting sequences in novel songs. The results suggest that the song syntax of the bird’s brain might also be represented by decaying activities of populations of neurons.

The functional overlap of language and arithmetic is debatable. Although some studies have reported independent representations of arithmetic and language in the brain, other studies have reported shared activity of the two cognitive domains in the inferior frontal gyrus. Although most previous studies have evaluated right-handed individuals, variability of hemispheric dominance in non-right-handed individuals should provide important information on the functional collateralization of these two cognitive domains. The present study evaluated the cortical lateralization patterns of the two cognitive domains using functional magnetic resonance imaging in 30 non-right-handed participants who performed language and arithmetic tasks. We found that language and arithmetic tasks demonstrated shared activity in the bilateral inferior frontal gyrus (IFG). Furthermore, the lateralization patterns of language and arithmetic tasks were correlated with each other. Most participants with language dominance in the left hemisphere also exhibited dominance of arithmetic tasks in the left hemisphere; similarly, most participants with language dominance in the right hemisphere exhibited dominance of arithmetic tasks in the right hemisphere. Among all the brain regions, the precentral gyrus, which is located slightly posterior to the IFG, exhibited the highest correlation coefficient between laterality indices of language and arithmetic tasks. These results suggest a shared functional property between language and arithmetic in the brain.

Metacognition is defined as cognition about one's own cognitive state; it enables us to estimate our own performance during goal-directed actions and to select a suitable strategy based on that estimation. Identifying the neural mechanisms that underlie this process will contribute to our understanding of how we realize adaptive self-control in daily life. Here, we focused on the neural substrates that allow us to voluntarily utilize prospective metacognition to carry out such action selection. Participants were asked to bet on their recall of sound stimuli presented at an earlier time in a delayed match-to-sample task of rapidly changing sound stimuli. During the task, brain activity was measured using functional magnetic resonance imaging. We found that the brain network composed of the ventral and dorsal parts of the medial prefrontal cortex and the medial precuneus regulated the strategic selection of risk/return profiles based on metacognition. In particular, increments in functional connectivity between the ventral and dorsal medial prefrontal cortices during high-risk/return bets correlated with the adaptiveness of the bet (as measured by the correspondence between choosing high risk/return bets and high accuracy of task performance). This index is considered to reflect the degree of voluntary use of metacognition to bet. These findings suggest that the strong connectivity within the network involving the ventral and dorsal medial prefrontal cortices enables us to utilize metacognition to select actions for achieving a goal efficiently.

Turn-taking is a common feature in human speech, and is also seen in the communication of other primate species. However, evidence of turn-taking in vocal exchanges within a short time frame is still scarce in nonhuman primates. This study investigated whether dynamic adjustment during turn-taking in short calls exists in Japanese macaques Macaca fuscata.We observed exchanges of short calls such as grunts, girneys, and short, low coos during social interactions in a free-ranging group of Japanese macaques. We found that the median gap between the turns of two callers was 250 ms. Call intervals varied among individuals, suggesting that call intervals were not fixed among individuals. Solo call intervals were shorter than call intervals interrupted by responses from partners (i.e., exchanges) and longer than those between the partner's reply and the reply to that call, indicating that the monkeys did not just repeat calls at certain intervals irrespective of the social situation. The differences in call intervals during exchanged and solo call sequences were explained by the response interval of the partner, suggesting an adjustment of call timing according to the tempo of the partner's call utterance. These findings suggest that monkeys display dynamic temporal adjustment in a short time window, which is comparable with turn-taking in human speech.

Absolute pitch (AP) is the ability to label the pitch of tones without any reference tones. Previous studies have shown that the anatomical and functional basis of AP exists in the superior temporal gyrus (STG), although the associated neurotransmitters remain unknown. We used proton magnetic resonance spectroscopy to quantify the concentration of γ-aminobutyric acid (GABA), an inhibitory neurotransmitter, in the bilateral STG of adult AP possessor and non-AP possessors. We found a significant negative correlation between AP scores and GABA concentration in the left STG. Furthermore, mean GABA concentration was significantly reduced in the AP possessors group compared to the non-AP possessors group. Our results suggest that less inhibition in the bilateral STG may enable AP possessors to associate categorical labels with tones.

Dopaminergic neurons (DANs) drive associative learning to update the value of sensory cues, but their contribution to the assessment of sensory values outside the context of association remains largely unexplored. Here, we show in Drosophilathat DANs in the mushroom body encode the innate value of odors and constantly update the current value by inducing plasticity during olfactory maneuver. Our connectome-based network model linking all the way from the olfactory neurons to DANs reproduces the characteristics of DAN responses, proposing a concrete circuit mechanism for computation. Downstream of DANs, odors alone induce value- and dopamine-dependent changes in the activity of mushroom body output neurons, which store the current value of odors. Consistent with this neural plasticity, specific sets of DANs bidirectionally modulate flies’ steering in a virtual olfactory environment. Thus, the DAN circuit known for discrete, associative learning also continuously updates odor values in a nonassociative manner.

Emotional communication involves transmitting information on affective states. Rat 50- and 22-kHz ultrasonic vocalizations (USVs) are emotional communication signals that reflect positive or negative states, respectively. In general, emotional communication signals that elicit changes in event-related potentials (ERPs), suggesting a specific mechanism for processing these signals. As this is observed in several communication systems including humans, we hypothesized that rat USVs can also trigger such changes. In this study, we measured rat local field potentials and used them to calculate ERPs from the anterior cingulate cortex (ACC), an area related to motor production of USVs. In Experiment 1, we measured ERPs to pure tones with peak frequencies around 50 or 22 kHz to examine whether the ACC is involved in auditory sensory processing related to pitch. The results showed that pure tones around 50 kHz elicited large amplitude ERPs, whereas those around 22 kHz resulted in smaller ERPs. In Experiment 2, we compared ERPs in response to rat USVs (emotional stimuli) with ERPs to pure tones modeled after USVs (neutral stimuli). The peak frequencies were the same between USVs and neutral sounds, but USVs showed more frequency modulation than neutral sounds. USVs elicited larger changes in the amplitude of ERP components than neutral stimuli did. These experiments suggest that the rat ACC is sensitive to frequencies around 50 and 22 kHz, and is especially tuned to frequency modulation around these frequencies. Taken together, the rat ACC may process the emotional content of communication signals on the basis of pitch and frequency modulation.

A particular feature of the inferior frontal gyrus (IFG), which is considered a central region for language processing, is leftward functional/anatomical asymmetry. However, previous studies have not clearly shown lateralization of neurotransmitters in the cortical regions. Using proton magnetic resonance spectroscopy, we measured γ-aminobutyric acid (GABA) concentrations in the bilateral IFG. To evaluate individual variability in linguistic performance, we further used a verbal fluency test. Although GABA+/creatine (Cr) values were not different between the left and the right IFG, we found a significant correlation between category fluency scores and GABA+/Cr values in the left IFG. No correlation was found between letter fluency scores and GABA+/Cr values. We also confirmed that the result was independent of the references used (Cr and H2O). Our results show a new physiological basis of linguistic performance as well as leftward asymmetry of the IFG.

Music is an essential communication tool that can convey emotional information. Segmentation of a sound stream of music at event boundaries is necessary for identification and extraction of musical context and features. To investigate recognition of music termination structure, or cadence, we composed music sequences with two types of dominant–tonic termination structures and presented them to participants and analyzed their segment recognition and brain activities using EEG. The results revealed that a sense of termination was caused by listening to a tonic chord. Frontal area positivity at 380–480 ms was elicited by a dominant chord in cadence type I with a stronger sense of termination. These activities possibly reflected the expectation of the next tonic chord in the cadence.

Birdsong is an excellent research model for sound sequences consisting of complex structures. Neural and behavioral experiments have shown that auditory feedback is necessary for songbirds, especially Bengalese finches, to maintain the quality of the songs and that the nucleus HVC (used as proper name) and the anterior forebrain pathway (AFP) in the nervous system play key roles in this maintenance process. Neurons in the HVC and AFP exhibit higher spike rate to the bird’s own song (BOS) than to other sound stimuli, such as temporally reversed song. To systematically evaluate what aspects of the BOS are captured by the different types of neural activities, both average spike rate and trial-to-trial spike timing variability in the BOS-selective neurons in the HVC and Area X (used as proper name), a gateway to the AFP from the HVC, were investigated following the presentation of auditory stimuli consisting of the BOS with systematic temporal inversion. Within-subjects analysis of the average spike rate and spike timing revealed that neural activity in the HVC and Area X is more sensitive to the local sound modulation of songs than to the global amplitude modulation. In addition, neurons in the HVC exhibit greater consistency of spike timing than neurons in Area X.

Models of birdsong are useful in the study of developmental and evolutional mechanisms of vocal learning behaviour. Knowledge of these mechanisms is important for understanding the evolutionary adaptation strategies of organisms. The Bengalese finch sings a complex song believed to have evolved by domestication because the song of its wild ancestor, the white-backed munia, was very simple. There is evidence that the song complexity is used as an indicator of male quality during mate selection. Because songbirds learn their song as juveniles, development of the song system is affected by developmental stress. Therefore, song traits may reflect developmental conditions and that may be honest sexually selected signals. We compared the level of the stress hormone corticosterone between Bengalese finches and white-backed munias. Results showed that Bengalese finches had lower circulating corticosterone levels than white-backed munias. Relaxation from natural selection pressures and the addition of artificial selection due to domestication may have decreased the corticosterone levels and allowed for the evolution of the complex song in the Bengalese finch. Two subtypes of corticosterone receptors, the glucocorticoid receptor and mineralocorticoid receptor, showed expression in song nuclei of the Bengalese finch brain. Thus, these results suggest the possibility that song development is regulated by corticosterone via binding to the corticoid receptors. Song-nuclei-related expression of corticoid receptors might have had an increasing developmental condition-dependent influence on song traits. Thus, our results suggest that decreased stress hormone levels secondary to domestication might account for one reason why songs became complex in Bengalese finches.

Node-perturbation learning is a type of statistical gradient descent algorithm that can be applied to problems where the objective function is not explicitly formulated, including reinforcement learning. Node-perturbation learning with $M$ linear perceptrons has previously been analyzed using the methods of statistical mechanics. It was shown that cross-talk noise, which originates from the error of the other outputs, increases the generalization error as the number of outputs increases. On the other hand, a nonlinear perceptron has several advantages over a linear perceptron, such as the ability to use nonlinear outputs, learnability, storage capacity, and so forth. However, node-perturbation for a nonlinear perceptron has yet to be analyzed theoretically. In this paper, we derive a learning rule of node-perturbation learning for a nonlinear perceptron within the framework of REINFORCE learning and analyze the learning behavior by using statistical mechanical methods. From the results, we found that the signal and cross-talk terms of the order parameter $Q$ have different forms for a nonlinear perceptron. Moreover, the increase in the generalization error with increasing number of outputs is less than for a linear perceptron.

An object that includes occluded parts is sometimes perceived as a complete image and this phenomenon is known as amodal or visual completion. A sign stimulus is a minimum set of information that elicits a behavior, but this notion raises questions about whether animals ever engage in the behavior when they cannot see the occluded sign stimulus, but they can visually complete it. Male Bengalese finches engage in courtship behavior toward video images of female finches. We conducted three experiments with Bengalese finches to show both sign stimuli and visual completion function in an ecological context. We used three types of visual images recorded from female finches as stimuli: the head, the body, and the whole. Results showed that male Bengalese finches showed courtship behavior toward the head-occluded stimuli whereas they did not toward the headless body image. The results imply that the males completed this occluded sign stimulus through the process of visual completion. Exposure to a sign stimulus combined with the process of visual completion may operate cooperatively to facilitate adaptive responses under conditions of limited information.

There are two kinds of musical emotions: perceived emotion (expressed by musical pieces) and felt emotion (induced in listeners). In this study, we hypothesized that the emotion perceived by people listening to dissonant music and music in a minor key would not necessarily correspond to the one they felt. Twenty-four participants listened to 21 newly composed musical stimuli and rated the intensities of two kinds of emotions by using a two-dimensional evaluation: valence (pleasant/unpleasant) and arousal (active/passive). ANOVA results showed that the perceived emotion did not always coincide with the felt emotion. Participants with music training listened to minor-key, dissonant, and high-note-density music and rated the felt emotion as less unpleasant or more pleasant than the perceived emotion. This finding may lead to a better understanding of why people sometimes like or otherwise enjoy sad music.

The ‘uncanny valley’ response is a phenomenon involving the elicitation of a negative feeling and subsequent avoidant behaviour in human adults and infants as a result of viewing very realistic human-like robots or computer avatars. It is hypothesized that this uncanny feeling occurs because the realistic synthetic characters elicit the concept of ‘human’ but fail to satisfy it. Such violations of our normal expectations regarding social signals generate a feeling of unease. This conflict-induced uncanny valley between mutually exclusive categories (human and synthetic agent) raises a new question: could an uncanny feeling be elicited by other mutually exclusive categories, such as familiarity and novelty? Given that infants prefer both familiarity and novelty in social objects, we address this question as well as the associated developmental profile. Using the morphing technique and a preferential-looking paradigm, we demonstrated uncanny valley responses of infants to faces of mothers (i.e. familiarity) and strangers (i.e. novelty). Furthermore, this effect strengthened with the infant's age. We excluded the possibility that infants detect and avoid traces of morphing. This conclusion follows from our finding that the infants equally preferred strangers’ faces and the morphed faces of two strangers. These results indicate that an uncanny valley between familiarity and novelty may accentuate the categorical perception of familiar and novel objects.

In adult songbirds, the degree of dependency on audition for maintenance of stable song structure varies from species to species. To date, studies suggest that song deterioration after deafening may be related to the song complexity of the species. Bengalese finches sing songs that are composed of complex note-to-note transitions, and their songs are critically dependent on auditory feedback. Song deterioration occurs within five days of auditory deprivation surgery, much faster than in other species. In contrast, white-rumped munias, a wild strain of Bengalese finches, sing simple songs. To test the hypothesis that the degree of dependency on auditory feedback for the maintenance of song structure is related to song complexity, we deafened two adult white-rumped munias by cochlear removal. Songs of white-rumped munias changed in syntax within five days of surgery, a similar trend observed in Bengalese finches. We suggest that real-time auditory feedback is important in white-rumped munias, despite the simplicity of their song structure. The time course of song alteration by deafened adult birds not determined solely by song complexity. [ABSTRACT FROM AUTHOR]

Mice produce ultrasonic vocalizations (USVs) in several behavioural contexts. In particular, male mice articulate a long series of various sounds to females during courtship behaviour. To determine the relationships between this kind of vocal behaviour and emotion, we examined the lesion effects of the amygdala, an important neural module in emotional behaviour, on USVs. We recorded USVs from mice in the lesion and the control (sham operation) groups upon presentation of females and compared USVs before and after surgery. We found that the mean syllable duration of the USVs shortened and the appearance rate of longer syllables decreased after the surgery. The main reasons for these alterations could be explained by the altered courtship behaviour. As reported previously, the mounting behaviour of the lesion group after surgery was markedly less than that of the control group. Therefore, the appearance rate of those longer syllables would decrease logically because longer syllables primarily appear during mounting and intromission. However, we can hypothesize another scenario for the alterations to vocal behaviour: effects on the direct amygdala-periaqueductal grey (PAG) projection might be involved in the increase in the appearance rate of shorter syllables owing to lesion-induced loss of emotions, such as vigilance. Overall, the results suggested two possible mechanisms of the amygdala lesions on the alteration of the vocal behaviour.

Male Bengalese finches have a complex song-sequence pattern containing multiple elements. Learning and producing songs require memorization of the phonology and the sequence of elements. We tested the auditory memory of male finches for their own songs to determine whether the auditory memory included the sequence of elements. An immediate early gene ZENKis induced by auditory processing in the secondary auditory area of the caudomedial nidopallium (NCM) and the caudomedial mesopallium (CMM) in response to song presentations. Repeated presentations of the same song result in a decrease in ZENKexpression in these areas, reflecting habituation to auditory processing. We examined sequential differences in auditory processing using the habituation–dishabituation method. After repeatedly presenting the male finches’ own song stimulus, we changed the stimulus to a shuffled sequence of songs. If the shuffled songs induced ZENKexpression, it indicated that the auditory areas had been dishabituated by the sequential differences. The shuffled songs caused intermediate ZENKexpression in the NCM when compared with the expression by a conspecific new song and that by the same song. The tendency toward intermediate expression was similar in the CMM; however, a significant difference was observed between the conspecific song and shuffled songs. These results suggest that the sequential difference caused a partial dishabituation in the NCM. Thus, the auditory areas processed not only the phonology but also the sequence of songs.

Tactile sensation, which is one of the earliest developing sensory systems, is very important in the perception of an individual’s body and the surrounding physical environment, especially in newborns. However, currently, only little is known about the response of a newborn’s brain to tactile sensation. The objective of the present study was to determine the response of a newborn’s brain to tactile sensation and to compare the brain responses to various sensory stimuli. Ten healthy newborns, 2–9 days after birth, were enrolled. A multichannel near-infrared spectroscopy system was used to measure brain responses. The probe array covered broad cortical areas, including the parietal, temporal, and occipital areas. We measured cortical hemodynamic changes in response to three different types of stimuli: tactile, auditory, and visual. Activated areas were analyzed by t-tests, and the number of activated channels among the three different stimuli was compared by 2-tests. The results showed that when the brain responded to each type of stimulation, the corresponding primary sensory area was activated, and tactile stimuli induced broader areas of brain activation than the other two types of stimuli (auditory or visual). Thus, broad brain areas, including the temporal and parietal areas, were activated by tactile stimuli in early newborn periods. These results suggest that there are differences in newborns’ reactions to various types of sensory stimuli, which may reflect the importance of tactile sensation in the early newborn period.

There are remarkable behavioral, neural, and genetic similarities between song learning in songbirds and speech acquisition in human infants. Previously, we have argued that this parallel cannot be extended to the level of sentence syntax. Although birdsong can indeed have a complex structure, it lacks the combinatorial complexity of human language syntax. Recently, this conclusion has been challenged by a report purporting to show that songbirds can learn so-called context-free syntactic rules and then use them to discriminate particular syllable patterns. Here, we demonstrate that the design of this study is inadequate to draw such a conclusion, and offer alternative explanations for the experimental results that do not require the acquisition and use of context-free grammar rules or a grammar of any kind, only the simpler hypothesis of acoustic similarity matching. We conclude that the evolution of vocal learning involves both neural homologies and behavioral convergence, and that human language reflects a unique cognitive capacity.

Cadherins, cell adhesion molecules widely expressed in the nervous system, are thought to be involved in synapse formation and function. To explore the role of cadherins in neuronal activity, we performed electrophysiological and morphological analyses of rat hippocampal cultured neurons overexpressing type-II cadherins, such as cadherin-6B and cadherin-7. We found that cadherin-6B increased but cadherin-7 decreased the number of protrusions of dendritic spines, and affected the frequency of miniature excitatory postsynaptic currents. Our results suggest that type-II cadherins may modulate neural activity by regulating neuronal morphology.

In reward-based learning, reward is typically given with some delay after a behavior that causes the reward. In machine learning literature, the framework of the eligibility trace has been used as one of the solutions to handle the delayed reward in reinforcement learning. In recent studies, the eligibility trace is implied to be important for difficult neuroscience problem known as the “distal reward problem”. Node perturbation is one of the stochastic gradient methods from among many kinds of reinforcement learning implementations, and it searches the approximate gradient by introducing perturbation to a network. Since the stochastic gradient method does not require a objective function differential, it is expected to be able to account for the learning mechanism of a complex system, like a brain. We study the node perturbation with the eligibility trace as a specific example of delayed reward-based learning, and analyzed it using a statistical mechanics approach. As a result, we show the optimal time constant of the eligibility trace respect to the reward delay and the existence of unlearnable parameter configurations.

Male Bengalese finches sing complex song sequences during courtship. To examine the female perception of sequence complexity, we tested female auditory processing with respect to sequential differences in the caudomedial nidopallium and caudomedial mesopallium. Repeated song presentations caused lower expression of the immediate early gene ZENK; however, consecutive presentation of a new song reinduced full ZENK expression. We presented a sequence-shuffled version of the father's song after repeated presentation of the original (unmodified) father's song. The shuffled songs caused lower ZENK expression in both the caudomedial nidopallium and caudomedial mesopallium. Although phonological differences caused full ZENK expression, sequential differences in song elements did not induce ZENK expression. Thus, it appears that female song perception is based on phonological, rather than sequential, information.

The song control system of songbirds consists mainly of the ‘motor pathway’ and ‘anterior forebrain pathway’. The medial magnocellular nucleus of anterior nidopallium (mMAN) projects to the song control nucleus HVC, which is the point of divergence of the two pathways. We made simultaneous multiunit electrophysiological recordings from the mMAN and HVC in anesthetized Bengalese finches. We confirmed that the mMAN neurons showed song-selective auditory responses, and found temporal correlations between song-related activities of the mMAN and HVC neurons. The temporal relationship between the neural activation of the HVC and mMAN suggests that these nuclei are parts of a closed loop, which could provide internal feedback to the HVC for sequential syllable control.

Male Bengalese finches sing directed songs in response to video images of females projected onto a thin-film transistor monitor. We used this experimental paradigm to elucidate which properties of visual stimuli are important for eliciting singing. When video recordings of female Bengalese or zebra finches were used as visual stimuli, only images of conspecific females elicited singing from male Bengalese finches. When images of female Bengalese finches were rotated by 0°, 90°, or 180°, only the upright images elicited singing. Finally, temporally normal (forward playback) images were more effective than time-reversed images and still images for eliciting singing. These results suggest that both the spatial and temporal arrangements of visual stimuli affect the singing behavior of male finches.

Auditory neurons in the songbird forebrain nucleus high vocal center HVC) show high selectivity to the temporal structure of bird's own song but the relationship between the degree of song complexity and neural selectivity is not known. We investigated the song temporal selectivity of HVC neurons by multi-unit recordings in seven male Bengalese finches with different song complexity. Results showed that HVC multi-units of the individuals with more complex songs responded strongly to each of the self-generated song elements but were relatively insensitive to the element order, while those with stereotyped songs responded only to the song elements ordered exactly as in the self-produced songs. Data suggest that the individually learned song syntax correlates with individualized temporal combination selectivity in HVC neurons.

Male Bengalese finches rely heavily on hearing to maintain adult songs and deafening a bird changes its song syntax immediately. Eight adult male Bengalese finches were placed in a helium atmosphere, which changes the resonance of the vocal tract. Undirected songs were recorded before, during and after this procedure, and the changes in song structure were analyzed. A helium environment increases the amplitude of higher harmonics, as in other bird species. Furthermore, note-to-note transition patterns that were never recorded when singing in normal air appeared in the songs sung in helium air. Therefore, helium can be used to cause reversible syntactical re-organization of songs in Bengalese finches, which can be used to study the neural mechanisms of auditory feedback.

Estrildid finches have two song types directed (courtship) and undirected (solo). These are acoustically identical and differ only in social context. Recent studies have shown that undirected singing is accompanied by strong activation of the basal ganglia pathway, whereas directed singing is not, which suggests a different degree of feedback control between the two. We examined whether the magnitude of the Lombard effect, i.e., vocal amplitude regulation in response to environmental noise, differed based on the song context. Our results indicate that Bengalese finches change the amplitude of undirected song based on background noise levels, but do not do so for directed song. This is the first behavioral evidence suggesting that feedback control of song output vary by social context.

Male Bengalese finches are left-side dominant for the motor control of song in the sensorimotor nucleus (the high vocal center, or HVc) of the telencephalon. We examined whether perceptual discrimination of songs might also be lateralized in this species. Twelve male Bengalese finches were trained by operant conditioning to discriminate between a Bengalese finch song and a zebra finch song. Before training, the left HVc was lesioned in four birds and the right HVc was lesioned in four other birds. The remaining four birds were used as controls without surgery. Birds with a left HVc lesion required significantly more time to learn to discriminate between the two songs than did birds with a right HVc lesion or intact control birds. These results suggest that the left HVc is not only dominant for the motor control of song, but also for the perceptual discrimination of song.

The avian song system consists of two main parts the descending motor pathway and the anterior forebrain (AF) pathway. The former directly controls the motor act of singing, but the role of the AF pathway in real-time song production is not understood; lesioning a nucleus in the AF pathway in adult zebra finches did not cause any notable effects. Here we show that in a related species of songbirds, the Bengalese finch, a partial lesion located in Area X, a nucleus of the avian basal ganglia that is part of the AF pathway, causes a transient but substantial song motor deficit. This is the first demonstration that the AF pathway is involved in real-time song production in adulthood.

Males of territorial songbird species have to remember a large number of conspecific songs to defend their territories, while non-territorial songbirds do not need to. A study of a territorial species suggested seemingly unlimited auditory memory size. We measured auditory memory in Bengalese finches, a non-territorial songbird species, to examine whether the auditory memory size for conspecific songs depends on the ecological requirements for song use. Five birds were trained by operant techniques to classify song stimuli into two arbitrary categories. The learning curve reached an asymptote within ∼100 sessions in all five birds and only eight songs were concurrently remembered on average. Results suggest that ecological requirements for song use are correlated with the auditory song memory capacity.

Studies in zebra finches failed to demonstrate the involvement of the NIf, a higher-order song nucleus afferent to the HVc, in the production of learned song. The song of the Bengalese finch, a related species, has a higher level of temporal organization; multiple song phrases are organized into a song. We hypothesized that the Nlf might control this complexity. To test this, we bilaterally lesioned the Nlf in adult male Bengalese finches. The songs of birds with multi-phrase organization changed into simpler, mono-phrase songs. This is the first demonstration of the Nlf's involvement in the production of birdsong. Zebra finch songs are syntactically simple and deterministic, and this might have caused the difficulty in demonstrating the function of the Nlf in zebra finches.

We trained two budgerigars (Melopsittacus undulatus) with operant techniques in a delayed matching-to-sample task using pairs of acoustic stimuli. These stimuli included simple pure tones, complex, species-specific vocalizations, and tone-vocalization combinations. The birds were then tested with different retention intervals. The budgerigars’ short-term memory was similar for complex, species-specific vocalizations and for simple pure tones. By contrast, they showed significantly better short-term memory when tested with two sounds drawn from different acoustic categories.

Abstract: Adult Bengalcse finches emit sexually dimorphic distance calls which are used to locate each other when visually separated. Distance calls of adult females are amplitude modulated while those of adult males are not. We studied the ontogeny of sexual differentiation in these calls. Before 50 days of age, both males and females emitted amplitude modulated, female-type distance calls. After day 55, juvenile males began to emit adult-male type distance calls which were not amplitude modulated, whereas females continued to emit amplitude modulated distance calls. In males, the transitional period coincided with the onset of subsongs. These results suggest that the sexual dimorphism of the distance calls in Bengalese finches involves hormonal and developmental processes.

Abstract: Standard operant conditioning techniques have been successfully applied to the problem of call discrimination in small birds. Budgerigars (Melopsittacus undulatus) and canaries (Serinus canarius) were trained with a GO/NOGO procedure using positive reinforcement to discriminate between both conspecific contact calls and contact calls of the other species. Budgerigars showed equal facility at each task. By contrast, canaries learned the task involving conspecific contact calls but failed, as a group, to discriminate between budgerigar contact calls. These results show that conditioning techniques can be used to study perceptual learning of species typical calls in small birds.

Abstract: Species-specific distance calls (DCs) were recorded from Zebra finches (Taeniopygia guttata castanotis) obtained from three different breeding stocks: Japanese breeders that use Bengalese finches as fostering parents, and Japanese and American breeders that let natural parents rear Zebra finches. These calls were analyzed for five acoustic parameters that were shown to be sexually dimorphic in wild Zebra finches. Male Zebra finches had DCs that were variable among breeding stocks and among individuals. Female DCs recorded from Bengalese-fostered birds were generally longer in duration and higher in pitch than those recorded from Zebra-finch-reared birds, males and females in each breeding stock differed in at least one acoustic parameter, but that parameter was unique in each of the breeding stocks. These results suggest that although sexual dimorphism in Zebra finch DCs has gradually disappeared during the process of domestication, at least one acoustic attribute which allows discrimination between the calls of the sexes has been preserved.

Songbirds develop their songs by imitating songs of adults. For song learning to proceed normally, the bird's hearing must remain intact throughout the song development process. In many species, song learning takes place during one period early in life, and no more new song elements are learned thereafter. In these so-called close-ended learners, it has long been assumed that once song development is complete, audition is no longer necessary to maintain the motor patterns of full song. However, many of these close-ended learners maintain plasticity in overall song organization; the number and the sequence of song elements included in a song of an individual vary from one utterance to another, although no new song elements are added or lost in adulthood. It is conceivable that these species rely on continued auditory feedback to produce normal song syntax. The Bengalese finch is a close-ended learner that produces considerably variable songs as an adult. In the present study, we found that Bengalese finches require real-time auditory feedback for motor control even after song learning is complete; deafening adult finches resulted in development of abnormal song syntax in as little as 5 days. We also found that there was considerable individual variation in the degree of song deterioration after deafening. The neural mechanisms underlying adult song production in different species of songbirds may be more diverse than has been traditionally considered. © 1997 John Wiley & Sons, Inc. J Neurobiol 33: 343–356, 1997

Perception of song syllables by female song sparrows (Melospiza melodia) and swamp sparrows (Melospiza georgiana) was examined using operant conditioning techniques. Similarity matrices among song syllables were constructed from response latencies to detect changes in a repeating background of syllables. Multidimensional scaling (MDS) of these similarity matrices described the perceived relations among the syllable types for each bird. Both species distinguished in a similar way between song- and swamp-sparrow syllables extracted from natural songs. However, when selected features of the syllables were modified, song sparrows and swamp sparrows showed different patterns of perceptual confusion. These results illustrate the utility of MDS techniques for investigating the perception of complex vocal signals, as they demonstrate species differences in the perceptual significance of equivalent physical changes in such complex sounds. The findings also support the notion that swamp sparrows are more selective than song sparrows in the perception of species-specific song syllables.

ABSTRACTTwo zebra finches and two budgerigars were trained, by operant conditioning, to detect autogenous (self-generated) distance calls in the presence of masking noise. For both species, there were no differences in detection thresholds for normal calls compared to time- reversed calls. Thresholds for autogenous calls were also compared with thresholds of the other species of birds listening to the same call. When detecting a zebra finch call, budgerigars had slightly lower thresholds than that of the zebra finch. On the other hand, when detecting a budgerigar call, zebra finches showed significantly higher thresholds than the budgerigar. From these results, and from what is known about basic hearing capabilities in these species, we conclude that these birds are not using a mechanism which utilizes “matched” or cross-correlational filtering. It is more likely that they are using “frequency-based” filtering in detecting calls in noise.

Discrimination of synthetic speech sounds from the bilabial, alveolar,and velar voice onset time (VOT) series was studied in 5 budgerigars. The birds were trained, using operant conditioning procedures, to detect changes in a repeating background of sound consisting of a synthetic speech token. Response latencies for detection were measured and were used to construct similarity matrices. Multidimensional scaling procedures were then used to produce spatial maps of these speech sounds, in which perceptual similarity was represented by spatial proximity. The results of these experiments suggest that budgerigars discriminate among synthetic speech sounds from these three VOT continua, especially between those from the bilabial and alveolar series, in a categorical fashion. [ABSTRACT FROM AUTHOR]

Understanding the structure and function of neural circuits underlying speech and language is a vital step toward better treatments for diseases of these systems. Songbirds, among the few animal orders that share with humans the ability to learn vocalizations from a conspecific, have provided many insights into the neural mechanisms of vocal development. However, research into vocal learning circuits has been hindered by a lack of tools for rapid genetic targeting of specific neuron populations to meet the quick pace of developmental learning. Here, we present a viral tool that enables fast and efficient retrograde access to projection neuron populations. In zebra finches, Bengalese finches, canaries, and mice, we demonstrate fast retrograde labeling of cortical or dopaminergic neurons. We further demonstrate the suitability of our construct for detailed morphological analysis, for in vivoimaging of calcium activity, and for multi-color brainbow labeling.

Without Abstract:

Operant conditioning and a psychophysical tracking procedure were used to measure auditory thresholds for pure tones in quiet and in noise for a European starling. The audibility curve for the starling is similar to the auditory sensitivity reported earlier for this species using a heart-rate conditioning procedure. Masked auditory thresholds for the starling were measured at a number of test frequencies throughout the bird’s hearing range. Critical ratios (signal-to-noise ratio at masked threshold) were calculated from these pure tone thresholds. Critical ratios increase throughout the starling’s hearing range at a rate of about 3 dB per octave. This pattern is similar to that observed for most other vertebrates. These results suggest that the starling shares a common mechanism of spectral analysis with many other vertebrates, including the human.

Three zebra finches were trained with operant techniques to respond to pure tones. Absolute thresholds were obtained for nine durations of a 3‐kHz tone and five durations of a 1‐kHz tone. The temporal integration functions finches were described using the negative exponential function proposed by Plomp and Bouman [J. Acoust. Soc. Am. 31, 749–758 (1959)]. The time constants obtained for zebra finches are about 250 ms, which are similar to those reported for a number of species, including humans and other bird species.

Unlike simple biological rhythms, the rhythm of the oscine bird song is a learned time series of diverse sounds that change dynamically during vocal ontogeny. How to quantify rhythm development is one of the most important challenges in behavioural biology. Here, we propose a simple method, called ‘rhythm landscape’, to visualize and quantify how rhythm structure, which is measured as durational patterns of sounds and silences, emerges and changes over development. Applying this method to the development of Bengalese finch songs, we show that the rhythm structure begins with a broadband rhythm that develops into diverse rhythms largely through branching from precursors. Furthermore, an information-theoretic measure, the Jensen–Shannon divergence, was used to characterize the crystallization process of birdsong rhythm, which started with a high rate of rhythm change and progressed to a stage of slow refinement. This simple method provides a useful description of rhythm development, thereby helping to reveal key temporal constraints on complex biological rhythms.