Altered auditory BOLD response to conspecific birdsong in zebra finches with stuttered syllables

The Direction of response selectivity between conspecific and heterospecific auditory stimuli varies with response metric

Species recognition is an essential behavioral outcome of social discrimination, flocking, mobbing, mating, and/or parental care. In songbirds, auditory species recognition cues are processed through specialized forebrain circuits dedicated to acoustic discrimination. Here we addressed the direction of behavioral and neural metrics of zebra finches' (Taeniopygia guttata) responses to acoustic cues of unfamiliar conspecifics vs. heterospecifics. Behaviorally, vocal response rates were greater for conspecific male zebra finch songs over heterospecific Pin-tailed Whydah (Vidua macroura) songs, which paralleled greater multiunit spike rates in the auditory forebrain in response to the same type of conspecific over heterospecific auditory stimuli. In contrast, forebrain activation levels were reversed to species-specific song playbacks during two functional magnetic resonance imaging experiments: we detected consistently greater responses to whydah songs over finch songs and did so independently of whether subjects had been co-housed or not with heterospecifics. These results imply that the directionality of behavioral and neural response selectivity metrics are not always consistent and appear to be experience-independent in this set of stimulus-and-subject experimental paradigms.

Rapid changes in auditory processing in songbirds following acute aromatase inhibition as assessed by fMRI

Contribution to Special Issue on Fast effects of steroids. This review introduces functional MRI (fMRI) as an outstanding tool to assess rapid effects of sex steroids on auditory processing in seasonal songbirds. We emphasize specific advantages of this method as compared to other more conventional and invasive methods used for this purpose and summarize an exemplary auditory fMRI study performed on male starlings exposed to different types of starling song before and immediately after the inhibition of aromatase activity by an i.p. injection of Vorozole™. We describe how most challenges that relate to the necessity to anesthetize subjects and minimize image- and sound-artifacts can be overcome in order to obtain a voxel-based 3D-representation of changes in auditory brain activity to various sound stimuli before and immediately after a pharmacologically-induced depletion of endogenous estrogens. Analysis of the fMRI data by assumption-free statistical methods identified fast specific changes in activity in the auditory brain regions that were stimulus-specific, varying over different seasons, and in several instances lateralized to the left side of the brain. This set of results illustrates the unique features of fMRI that provides opportunities to localize and quantify the brain responses to rapid changes in hormonal status. fMRI offers a new image-guided research strategy in which the spatio-temporal profile of fast neuromodulations can be identified and linked to specific behavioral inputs or outputs. This approach can also be combined with more localized invasive methods to investigate the mechanisms underlying the observed neural changes.

Shared neural substrates for song discrimination in parental and parasitic songbirds

In many social animals, early exposure to conspecific stimuli is critical for the development of accurate species recognition. Obligate brood parasitic songbirds, however, forego parental care and young are raised by heterospecific hosts in the absence of conspecific stimuli. Having evolved from non-parasitic, parental ancestors, how brood parasites recognize their own species remains unclear. In parental songbirds (e.g. zebra finch Taeniopygia guttata), the primary and secondary auditory forebrain areas are known to be critical in the differential processing of conspecific vs. heterospecific songs. Here we demonstrate that the same auditory brain regions underlie song discrimination in adult brood parasitic pin-tailed whydahs (Vidua macroura), a close relative of the zebra finch lineage. Similar to zebra finches, whydahs showed stronger behavioral responses during conspecific vs. heterospecific song and tone pips as well as increased neural responses within the auditory forebrain, as measured by both functional magnetic resonance imaging (fMRI) and immediate early gene (IEG) expression. Given parallel behavioral and neuroanatomical patterns of song discrimination, our results suggest that the evolutionary transition to brood parasitism from parental songbirds likely involved an "evolutionary tinkering" of existing proximate mechanisms, rather than the wholesale reworking of the neural substrates of species recognition.

Auditory functional magnetic resonance imaging in dogs--normalization and group analysis and the processing of pitch in the canine auditory pathways

Background

Functional magnetic resonance imaging (fMRI) is an advanced and frequently used technique for studying brain functions in humans and increasingly so in animals. A key element of analyzing fMRI data is group analysis, for which valid spatial normalization is a prerequisite. In the current study we applied normalization and group analysis to a dataset from an auditory functional MRI experiment in anesthetized beagles. The stimulation paradigm used in the experiment was composed of simple Gaussian noise and regular interval sounds (RIS), which included a periodicity pitch as an additional sound feature. The results from the performed group analysis were compared with those from single animal analysis. In addition to this, the data were examined for brain regions showing an increased activation associated with the perception of pitch.

Results

With the group analysis, significant activations matching the position of the right superior olivary nucleus, lateral lemniscus and internal capsule were identified, which could not be detected in the single animal analysis. In addition, a large cluster of activated voxels in the auditory cortex was found. The contrast of the RIS condition (including pitch) with Gaussian noise (no pitch) showed a significant effect in a region matching the location of the left medial geniculate nucleus.

Conclusion

By using group analysis additional activated areas along the canine auditory pathways could be identified in comparison to single animal analysis. It was possible to demonstrate a pitch-specific effect, indicating that group analysis is a suitable method for improving the results of auditory fMRI studies in dogs and extending our knowledge of canine neuroanatomy.

An Adapting Auditory-motor Feedback Loop Can Contribute to Generating Vocal Repetition

Consecutive repetition of actions is common in behavioral sequences. Although integration of sensory feedback with internal motor programs is important for sequence generation, if and how feedback contributes to repetitive actions is poorly understood. Here we study how auditory feedback contributes to generating repetitive syllable sequences in songbirds. We propose that auditory signals provide positive feedback to ongoing motor commands, but this influence decays as feedback weakens from response adaptation during syllable repetitions. Computational models show that this mechanism explains repeat distributions observed in Bengalese finch song. We experimentally confirmed two predictions of this mechanism in Bengalese finches: removal of auditory feedback by deafening reduces syllable repetitions; and neural responses to auditory playback of repeated syllable sequences gradually adapt in sensory-motor nucleus HVC. Together, our results implicate a positive auditory-feedback loop with adaptation in generating repetitive vocalizations, and suggest sensory adaptation is important for feedback control of motor sequences.

Repetitions are common in animal vocalizations. Songs of many songbirds contain syllables that repeat a variable number of times, with non-Markovian distributions of repeat counts. The neural mechanism underlying such syllable repetitions is unknown. In this work, we show that auditory feedback plays an important role in sustaining syllable repetitions in the Bengalese finch. Deafening reduces syllable repetitions and skews the repeat number distribution towards short repeats. These effects are explained with our computational model, which suggests that syllable repeats are initially sustained by auditory feedback to the neural networks that drive the syllable production. The feedback strength weakens as the syllable repeats, increasing the likelihood that the syllable repetition stops. Neural recordings confirm such adaptation of auditory feedback to the auditory-motor circuit in the Bengalese finch. Our results suggests that sensory feedback can directly impact repetitions in motor sequences, and may provide insights into neural mechanisms of speech disorders such as stuttering.

Arrhythmic song exposure increases ZENK expression in auditory cortical areas and nucleus taeniae of the adult zebra Finch

Rhythm is important in the production of motor sequences such as speech and song. Deficits in rhythm processing have been implicated in human disorders that affect speech and language processing, including stuttering, autism, and dyslexia. Songbirds provide a tractable model for studying the neural underpinnings of rhythm processing due to parallels with humans in neural structures and vocal learning patterns. In this study, adult zebra finches were exposed to naturally rhythmic conspecific song or arrhythmic song. Immunohistochemistry for the immediate early gene ZENK was used to detect neural activation in response to these two types of stimuli. ZENK was increased in response to arrhythmic song in the auditory association cortex homologs, caudomedial nidopallium (NCM) and caudomedial mesopallium (CMM), and the avian amygdala, nucleus taeniae (Tn). CMM also had greater ZENK labeling in females than males. The increased neural activity in NCM and CMM during perception of arrhythmic stimuli parallels increased activity in the human auditory cortex following exposure to unexpected, or perturbed, auditory stimuli. These auditory areas may be detecting errors in arrhythmic song when comparing it to a stored template of how conspecific song is expected to sound. CMM may also be important for females in evaluating songs of potential mates. In the context of other research in songbirds, we suggest that the increased activity in Tn may be related to the value of song for assessing mate choice and bonding or it may be related to perception of arrhythmic song as aversive.

Functional magnetic resonance imaging of the ascending stages of the auditory system in dogs

Background

Functional magnetic resonance imaging (fMRI) is a technique able to localize neural activity in the brain by detecting associated changes in blood flow. It is an essential tool for studying human functional neuroanatomy including the auditory system. There are only a few studies, however, using fMRI to study canine brain functions. In the current study ten anesthetized dogs were scanned during auditory stimulation. Two functional sequences, each in combination with a suitable stimulation paradigm, were used in each subject. Sequence 1 provided periods of silence during which acoustic stimuli could be presented unmasked by scanner noise (sparse temporal sampling) whereas in sequence 2 the scanner noise was present throughout the entire session (continuous imaging). The results obtained with the two different functional sequences were compared.

Results

This study shows that with the proper experimental setup it is possible to detect neural activity in the auditory system of dogs. In contrast to human fMRI studies the strongest activity was found in the subcortical parts of the auditory pathways. Especially sequence 1 showed a high reliability in detecting activated voxels in brain regions associated with the auditory system.

Conclusion

These results indicate that fMRI is applicable for studying the canine auditory system and could become an additional method for the clinical evaluation of the auditory function of dogs. Additionally, fMRI is an interesting technique for future studies concerned with canine functional neuroanatomy.

Investigation of musicality in birdsong

Songbirds spend much of their time learning, producing, and listening to complex vocal sequences we call songs. Songs are learned via cultural transmission, and singing, usually by males, has a strong impact on the behavioral state of the listeners, often promoting affiliation, pair bonding, or aggression. What is it in the acoustic structure of birdsong that makes it such a potent stimulus? We suggest that birdsong potency might be driven by principles similar to those that make music so effective in inducing emotional responses in humans: a combination of rhythms and pitches-and the transitions between acoustic states-affecting emotions through creating expectations, anticipations, tension, tension release, or surprise. Here we propose a framework for investigating how birdsong, like human music, employs the above "musical" features to affect the emotions of avian listeners. First we analyze songs of thrush nightingales (Luscinia luscinia) by examining their trajectories in terms of transitions in rhythm and pitch. These transitions show gradual escalations and graceful modifications, which are comparable to some aspects of human musicality. We then explore the feasibility of stripping such putative musical features from the songs and testing how this might affect patterns of auditory responses, focusing on fMRI data in songbirds that demonstrate the feasibility of such approaches. Finally, we explore ideas for investigating whether musical features of birdsong activate avian brains and affect avian behavior in manners comparable to music's effects on humans. In conclusion, we suggest that birdsong research would benefit from current advances in music theory by attempting to identify structures that are designed to elicit listeners' emotions and then testing for such effects experimentally. Birdsong research that takes into account the striking complexity of song structure in light of its more immediate function - to affect behavioral state in listeners - could provide a useful animal model for studying basic principles of music neuroscience in a system that is very accessible for investigation, and where developmental auditory and social experience can be tightly controlled.

Noninvasive diffusive optical imaging of the auditory response to birdsong in the zebra finch

Songbirds communicate by learned vocalizations with concomitant changes in neurophysiological and genomic activities in discrete parts of the brain. Here, we tested a novel implementation of diffusive optical imaging (also known as diffuse optical imaging, DOI) for monitoring brain physiology associated with vocal signal perception. DOI noninvasively measures brain activity using red and near-infrared light delivered through optic fibers (optodes) resting on the scalp. DOI does not harm subjects, so it raises the possibility of repeatedly measuring brain activity and the effects of accumulated experience in the same subject over an entire life span, all while leaving tissue intact for further study. We developed a custom-made apparatus for interfacing optodes to the zebra finch (Taeniopygia guttata) head using 3D modeling software and rapid prototyping technology, and applied it to record responses to presentations of birdsong in isoflurane-anesthetized zebra finches. We discovered a subtle but significant difference between the hemoglobin spectra of zebra finches and mammals which has a major impact in how hemodynamic responses are interpreted in the zebra finch. Our measured responses to birdsong playback were robust, highly repeatable, and readily observed in single trials. Responses were complex in shape and closely paralleled responses described in mammals. They were localized to the caudal medial portion of the brain, consistent with response localization from prior gene expression, electrophysiological, and functional magnetic resonance imaging studies. These results define an approach for collecting neurophysiological data from songbirds that should be applicable to diverse species and adaptable for studies in awake behaving animals.

Rapid and reliable sedation induced by diazepam and antagonized by flumazenil in zebra finches (Taeniopygia guttata)

Songbirds have emerged as attractive model systems in many areas of biological research. Notably, songbirds are used in studies of the neurobiological and neuroendocrine mechanisms that shape vocal communication, and zebra finches (Taeniopygia guttata) are the most commonly studied species. In these studies, some form of chemical restraint is often needed to facilitate procedures and to minimize the risk of injury during handling. To determine the minimum dose of the benzodiazepine diazepam that is adequate to achieve deep sedation across individual birds, a low dose (5 mg/kg) and a high dose (10 mg/kg) was administered intramuscularly to 20 zebra finches. Results showed that a 10 mg/kg dose of diazepam resulted in deep sedation, defined by dorsal recumbency, which was achieved in minutes and lasted for several hours. Sedation was induced without complication, because no birds displayed signs of distress during sedation or lethargy after recovery, and was adequate to permit minimally invasive surgical procedures. In addition, the duration of sedation was dose dependent, which provides additional information for researchers who seek to match the depth of sedation to their experimental requirements. Finally, complete recovery from the deeply sedated state was induced by a 0.3 mg/kg dose of the antagonist flumazenil, which enabled birds to more rapidly resume homeostatic behaviors to promote well-being and survival. Together, these results indicate that diazepam is a safe and reliable sedative for use in zebra finches and support specific recommendations to achieve rapid and reliable sedation and recovery.

Current state-of-the-art of auditory functional MRI (fMRI) on zebra finches: technique and scientific achievements

Songbirds provide an excellent model system exhibiting vocal learning associated with an extreme brain plasticity linked to quantifiable behavioral changes. This animal model has thus far been intensively studied using electrophysiological, histological and molecular mapping techniques. However, these approaches do not provide a global view of the brain and/or do not allow repeated measures, which are necessary to establish correlations between alterations in neural substrate and behavior. In contrast, functional Magnetic Resonance Imaging (fMRI) is a non-invasive in vivo technique which allows one (i) to study brain function in the same subject over time, and (ii) to address the entire brain at once. During the last decades, fMRI has become one of the most popular neuroimaging techniques in cognitive neuroscience for the study of brain activity during various tasks ranging from simple sensory-motor to highly cognitive tasks. By alternating various stimulation periods with resting periods during scanning, resting and task-specific regional brain activity can be determined with this technique. Despite its obvious benefits, fMRI has, until now, only been sparsely used to study cognition in non-human species such as songbirds. The Bio-Imaging Lab (University of Antwerp, Belgium) was the first to implement Blood Oxygen Level Dependent (BOLD) fMRI in songbirds - and in particular zebra finches - for the visualization of sound perception and processing in auditory and song control brain regions. The present article provides an overview of the establishment and optimization of this technique in our laboratory and of the resulting scientific findings. The introduction of fMRI in songbirds has opened new research avenues that permit experimental analysis of complex sensorimotor and cognitive processes underlying vocal communication in this animal model.

A hierarchical neuronal model for generation and online recognition of birdsongs

The neuronal system underlying learning, generation and recognition of song in birds is one of the best-studied systems in the neurosciences. Here, we use these experimental findings to derive a neurobiologically plausible, dynamic, hierarchical model of birdsong generation and transform it into a functional model of birdsong recognition. The generation model consists of neuronal rate models and includes critical anatomical components like the premotor song-control nucleus HVC (proper name), the premotor nucleus RA (robust nucleus of the arcopallium), and a model of the syringeal and respiratory organs. We use Bayesian inference of this dynamical system to derive a possible mechanism for how birds can efficiently and robustly recognize the songs of their conspecifics in an online fashion. Our results indicate that the specific way birdsong is generated enables a listening bird to robustly and rapidly perceive embedded information at multiple time scales of a song. The resulting mechanism can be useful for investigating the functional roles of auditory recognition areas and providing predictions for future birdsong experiments.

How do birds communicate via their songs? Investigating this question may not only lead to a better understanding of communication via birdsong, but many believe that the answer will also give us hints about how humans decode speech from complex sound wave modulations. In birds, the output and neuronal responses of the song generation system can be measured precisely and this has resulted in a considerable body of experimental findings. We used these findings to assemble a complete model of birdsong generation and use it as the basis for constructing a potentially neurobiologically plausible, artificial recognition system based on state-of-the-art Bayesian inference techniques. Our artificial system resembles the real birdsong system when performing recognition tasks and may be used as a functional model to explain and predict experimental findings in song recognition.