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World experiences involve multisensory stimulation that arises simultaneously from multiple sources. Yet, we experience a coherent and unified world. Many studies have focused on how sensory information from distinct modalities are integrated and showed that numerous behavioural and cognitive benefits are provided by multisensory processes. Much work has been done with mammalian models but research on avian species also expands our knowledge on multisensory processes. Avian species exhibit a great diversity of behaviours and these species have provided evidence that multisensory processes benefit by the learning that occurs in natural situations. Cross-modal influences on the control of sensorimotor processes occur in circumstances of sensory loss. Also, studies suggest pervasive multisensory influences throughout the avian brain. This review summarizes research done on the imprinting behaviour of precocial bird species, on the ability of barn owls to detect prey and on the vocal communication of songbirds.

The plasticity of nervous systems allows animals to quickly adapt to a changing environment. In particular, seasonal plasticity of brain structure and behavior is often critical to survival or mating in seasonal climates. Songbirds provide striking examples of seasonal changes in neural circuits and vocal behavior and have emerged as a leading model for adult brain plasticity. While seasonal plasticity and the well-characterized process of juvenile song learning may share common neural mechanisms, the extent of their similarity remains unclear. Especially, it is unknown whether the basal ganglia (BG)–forebrain loop which implements song learning in juveniles by driving vocal exploration participates in seasonal plasticity. To address this issue, we performed bilateral lesions of the output structure of the song-related BG–forebrain circuit (the magnocellular nucleus of the anterior nidopallium) in canaries during the breeding season, when song is most stereotyped, and just after resuming singing in early fall, when canaries sing their most variable songs and may produce new syllable types. Lesions drastically reduced song acoustic variability, increased song and phrase duration, and decreased syntax variability in early fall, reverting at least partially seasonal changes observed between the breeding season and early fall. On the contrary, lesions did not affect singing behavior during the breeding season. Our results therefore indicate that the BG–forebrain pathway introduces acoustic and syntactic variability in song when canaries resume singing in early fall. We propose that BG–forebrain circuits actively participate in seasonal plasticity by injecting variability in behavior during non-breeding season. Significance Statement The study of seasonal plasticity in temperate songbirds has provided important insights into the mechanisms of structural and functional plasticity in the central nervous system. The precise function and mechanisms of seasonal song plasticity however remain poorly understood. We show here that a basal ganglia–forebrain circuit involved in the acquisition and maintenance of birdsong is actively inducing song variability outside the breeding season, when singing is most variable, while having little effect on the stereotyped singing during the breeding season. Our results suggest that seasonal plasticity reflects an active song-maintenance process akin to juvenile learning, and that basal ganglia–forebrain circuits can drive plasticity in a learned vocal behavior during the non–injury-induced degeneration and reconstruction of the neural circuit underlying its production.

International audience; Learning by imitation involves not only perceiving another individual’s action to copy it, but also the formation of a memory trace in order to gradually establish a correspondence between the sensory and motor codes, which represent this action through sensorimotor experience. Memory and sensorimotor processes are closely intertwined. Mirror neurons, which fire both when the same action is performed or perceived, have received considerable attention in the context of imitation. An influential view of memory processes considers that the consolidation of newly acquired information or skills involves an active offline reprocessing of memories during sleep within the neuronal networks that were initially used for encoding. Here, we review the recent advances in the field of mirror neurons and offline processes in the songbird. We further propose a theoretical framework that could establish the neurobiological foundations of sensorimotor learning by imitation. We propose that the reactivation of neuronal assemblies during offline periods contributes to the integration of sensory feedback information and the establishment of sensorimotor mirroring activity at the neuronal level.

International audience; The neuronal selectivity observed in the avian song system for the Bird's Own Song progressively emerged as an extraordinary fruitful model to investigate the neural code underlying the recognition of complex stimuli and the occurrence of learned behaviors. In adult zebra finch, neurons from the HVC (used as a proper name) show very selective auditory responses, firing more to presentation of the Bird's Own Song (BOS) than to reverse BOS or other conspecific songs. However, as adult zebra finches always produce the same stereotyped song, the presence of such highly selective neurons in birds with larger repertoire still remains an open question. Data presented here show that neurons selective for the BOS can be found in adult canary, a seasonal breeding bird which display a large repertoire. More precisely, we found that a large proportion of neurons (29/36) exhibits higher responses to presentation of the forward than to the reverse BOS, and that 22% of the cells were identified as selective on the basis of the d' value. For a cell that was extensively studied, we evaluated to what extent temporal stimulus-related structure predicts the acoustic stimulus using linear or non-linear artificial neural networks (ANN). These analyses indicated that the temporal structure contained in spike trains characterizes more accurately the stimulus than the firing rate. The limitations of applying ANN analyses to electrophysiological data are discussed and potential solutions to increase the confidence in these analysis are proposed.

International audience; In songbirds, anatomical attributes of song nuclei exhibit sexual and seasonal differences. To extend these data to physiological correlates, neurons ( n= 374) were recorded in the HVc of male and female canaries during and outside the breeding period. Surprisingly, a particular type of action potential waveforms was observed more frequently in breeding than in non-breeding birds and in males than in females. These neurons showed both a shorter action potential duration (< 0.4 ms) and a higher firing rate (2.5 1.4 spikes/s) than the other neurons. Such characteristics are usually associated with interneurons in the songbird HVc as well as in the mammalian neocortex. Thus, these results provide the first electrophysiological evidence for an alteration of the neuronal network of HVc across sexes and seasons.

Based on neuronal recordings in the HVc, this study investigated differences between reproductively active male and sexually receptive female canaries. It is the first study to describe auditory responses and cell characteristics of HVc neurons in female songbirds and to compare them with the responses and characteristics obtained in males. Extracellular single unit recordings showed that in males HVc cells exhibited two types of auditory responses to conspecific and heterospecific song playbacks: tonic and phasic responses. The major finding of the present study is the absence of tonic responses in females. Neurons in the HVc of females only responded phasically to song playbacks. In both sexes, neurons exhibiting auditory responses had thinner action potentials than the others. As all the tonic cells recorded in males were thin spike cells (action potential < or = 0.6 ms) [corrected] and had high firing rates (6 Hz in average), they are potentially interneurons. In both sexes, two categories of nonresponsive cells were found: neurons that did not fire at song onset and had the lowest spontaneous firing rate; and neurons that did not exhibit changes in activity in response to song playbacks. Analyses of physiological characteristics of HVc neurons revealed that the rate of spontaneous activity was higher in males than in females. This study is a first step towards identifying [corrected] the cellular bases of the sexual dimorphism in HVc function and highlights the pivotal role of interneurons in HVc auditory processing.

International audience; Songbirds constitute a powerful model system for the investigation of how complex vocal communication sounds are represented and generated, offering a neural system in which the brain areas involved in auditory, motor and auditory-motor integration are well known. One brain area of considerable interest is the nucleus HVC. Neurons in the HVC respond vigorously to the presentation of the bird's own song and display song-related motor activity. In the present paper, we present a synthesis of neurophysiological studies performed in the HVC of one songbird species, the canary (Serinus canaria). These studies, by taking advantage of the singing behavior and song characteristics of the canary, have examined the neuronal representation of the bird's own song in the HVC. They suggest that breeding cues influence the degree of auditory selectivity of HVC neurons for the bird's own song over its time-reversed version, without affecting the contribution of spike timing to the information carried by these two song stimuli. Also, while HVC neurons are collectively more responsive to forward playback of the bird's own song than to its temporally or spectrally modified versions, some are more broadly tuned, with an auditory responsiveness that extends beyond the bird's own song. Lastly, because the HVC is also involved in song production, we discuss the peripheral control of song production, and suggest that interspecific variations in song production mechanisms could be exploited to improve our understanding of the functional role of the HVC in respiratory-vocal coordination.

International audience; In songbirds, experience of social and environmental cues during a discrete period after birth may dramatically influence song learning. In the canary, the ability to learn new songs is assumed to persist throughout life. The aim of the present study was to investigate whether social context could guide changes in adult song. Three groups of canaries were kept in different social and temporal conditions. Results showed that the multiple hierarchical levels of the canary song structure were affected by social environment: songs of males housed together for 2 years were more similar than those of males that spent the same time in individual cages in regard to acoustic parameters, syllable repertoire and repertoire of sequences of two-syllable types. However, social housing did not result in the emergence of a group-specific vocal signature within songs. In conclusion, these results suggested that under the influence of social factors, a copying process could allow adult canaries to adjust, at least in part, their songs to those of other individuals.

In songbirds, auditory neurons of the nucleus HVC respond selectively to a particular complex sound, the bird's own song (BOS). In the canary, this song selectivity did not exclude responses to conspecific songs. Here, we recorded single units in nucleus HVC of adult canaries to assess to what extent repertoire sharing among birds contributed to auditory responsiveness to birds' songs other than the BOS. Results indicated that song phrases driving auditory responses could differ from bird's own phrases suggesting that a subset of neurons were not strictly tuned to acoustic features of self-generated song components. In the canary, auditory representation of the BOSs might be more complex than that which has been described for birds with a small repertoire.

Through variations in features, both within and between individuals, songs of male passerines provide information on the identity of the singer. In domesticated canaries (Serinus canaria), these variations remain, for a large part, to be investigated. This led us to question whether individual identity might be coded at one or more hierarchical levels of song organization, i.e. in acoustic parameters, in the syllable repertoire and in the delivery order of syllables. A song as a whole had numerous individual distinctive acoustic features. However, the structure of its individual signature appeared to be complex. A repertoire combined syllables never sung by other individuals with those shared by other birds. But, most of the individual-specific syllables that accounted for 16% of a repertoire did not recur frequently. Variation in sequences of multiple syllable types appeared to reflect the individual identity of a male canary. Nearly all sequences larger than three syllable types were specific to the individual that produced them. Some of these occurred recurrently in songs and differed in their acoustic structure between individuals. Focusing upon recurrent sequences might allow vocal recognition of an individual without requiring the knowledge of its full repertoire. However, acoustic parameters and repertoire composition might also serve as additional cues to limit confusion between individuals.

In many species, neurons with highly selective stimulus-response properties characterize higher order sensory areas and/or sensory motor areas of the CNS. In the songbird nuclei, the responses of HVC (used as a proper name) neurons during playback of the bird's own song (BOS) are probably one of the most striking examples of selectivity for natural stimuli. We examined here to what extent spike-timing carries information about natural and time-reversed versions of the BOS. From a heterogenous population of 107 HVC neurons recorded in long-day or short-day conditions, a standard indicator of stimulus preference based on spike-count (the d' index) indicates that a limited proportion of cells can be classified as selective for the BOS (20% with a |d'| > 1). In contrast, quantifying the information conveyed by spike trains with the metric-space of J.D. Victor & K.P Purpura [(1996) J. Neurophysiol., 76, 1310-1326] indicates that 62% of the cells display significant amounts of transmitted information, among which 77% are 'temporal cells'. 'Temporal cells' correspond to cells transmitting significant amounts of information when spike-timing is considered, whereas no information, or lower amounts of transmitted information, is obtained when only spike-count is considered. Computing a correlation index between spike trains [S. Schreiber et al. (2003) Neurocomputing, 52-54,925-931] revealed that spike-timing reliability is higher for the forward than for the reverse BOS, whatever the day length and the cell type are. Cells classified as selective in terms of spike-counts (d' index) had greater amounts of transmitted information, but cells classified as non-selective (d' < 0.5) can also transmit significant amounts of information. Thus, information theory methods demonstrate that a much larger proportion of neurons than expected based on spike-count only participate in the discrimination between stimuli.

Among songbird species, the canary, Serinus canaria, is considered to be an ‘open-ended’ song learner because adults continue to change their syllable repertoire throughout their lives. However, it remains unclear whether the capacity to alter the syllable repertoire allows birds to acquire new song material to correct abnormal song characteristics that result from auditory isolation during development. To address this question, we reared males without any experience of typical adult conspecific song models from fledging to sexual maturity. They were then placed for at least 2 years in an aviary that included adult conspecific males. Discriminant function analyses on songs indicated that features describing the fine structure of syllables showed significant differences between isolation-reared and control birds. Analysis of syllable repertoires attributed differences to a higher proportion of multiple-element syllables in songs of isolation-reared males than in songs of control males. Isolation-reared birds were able to modify their syllable repertoire throughout their lives. However, the proportion of multiple-element syllables, instead of decreasing during the years spent in the aviary, continued to form a large part of the songs. The ability of isolation-reared canaries to change their repertoires failed to rectify, at least in large part, the syllable abnormalities caused by the lack of a song model during their first year of life. Therefore, new and previously acquired syllables might result from similar underlying processes that would set limits to the kinds of syllables produced in adulthood.

To what extent seasonal factors modify the neuronal functional properties within the nuclei of the avian song system remains an open question. In adult songbirds, neurons of the song premotor nucleus HVC (used as a proper name) exhibit selective responses for the bird's own song (BOS). Here we examine whether, outside the breeding season, when songs are less stereotyped, HVC neurons of male canaries still respond selectively to the BOS produced during this period. In an initial experiment, single-unit recordings (n= 114) revealed that the neuronal selectivity for the current BOS was attenuated in males exposed to a short-day photoperiod (typical of the nonbreeding season) compared with that found in males exposed to a long-day photoperiod. In long-day conditions, 35% of the cells responded to the BOS, whereas only 12% did in short-day conditions; there were four times more selective cells (d′ > 1) in long-day than in short-day conditions.To determine whether these effects were the consequence of differences in acoustic features between breeding and nonbreeding songs, neurons (n= 72) recorded in short-day conditions were tested with both a short-day BOS and a long-day BOS. A low percentage of neurons exhibited responses to short-day or to long-day BOS (11% for each song). Responses of putative interneurons (spike duration

An ethological procedure, based on the study of the sexual responsiveness of female canaries (Serinus canaria) to song playbacks was used to investigate the function of central noradrenergic inputs in the processing of auditory information. The effects of a noradrenergic denervation on sexual responses was analyzed in females exposed to playbacks of biological relevant auditory stimuli, i.e. sexually stimulating songs, presented alone or masked by auditory distractors. A decrease in behavioral responsiveness was observed as a function of the amount of masking distractors indicating that female canaries have the perceptual ability to discriminate and selectively attend to biologically relevant songs. After the systemic administration of DSP-4, a specific noradrenergic neurotoxin, females exhibited an overall decrease in sexual responsiveness to songs masked or not by distractors. No effect of DSP-4 were detected on the motor activity nor on reproductive behaviors. These results indicate that central noradrenergic inputs modulate the sexual behavior of female canaries by affecting the auditory processing of relevant information contained in sexually stimulating songs.

Songs of songbirds, such as speech in humans, requires fine recognition of emitted acoustic signals. But bird's song isn’t only a succession of sound elements, called syllables. The order of syllables follows rules, and, from a behavioral point of view, birds can discriminate songs according to this order. Moreover, since they have a set of specialized brain regions in the perception, production and learning of singing, they are a major model for studying neural mechanisms involved in the processing of temporal order of acoustic signals. During this thesis, the focus was on two studies based on electrophysiological recordings (extracellular) of neurons activity during the song diffusion.The first study focused on the treatment of order in an analog area of the mammalian secondary auditory cortex, the caudomedial nidopallium (NCM), in one species, the zebra finch (Taeniopygia guttata), able to discriminate songs according to syllables order. NCM neurons responses decrease during iterations of a stimulus and increase if a new song is presented. Based on this adaptation property, we have shown that it's not necessary to change the song, a change in the order of syllables is sufficient to re-establish responses. Changing the order changes the acoustic context of the syllable (what comes before is different), so the NCM neurons would be sensitive to this context. To go further, we used as stimuli a short sequence composed of 2 different syllables, A and B, organized according to ABAB or AABB grammatical structures. The results show that the neurons detect this difference in structure, providing an additional argument to the hypothesis of a treatment depending on how the syllables follow each other in a song.The second study focused on the treatment of the order of syllables in a sensorimotor area, the HVC (proper noum), in the canary (Serinus canaria). HVC neurons have already been identified as sensitive to syllable order in the bird's own song (BOS). The canary produces complex songs composed of successive phrases, themselves containing repetitions of the same syllable. The arrangement of the phrases in the songs depends on transition probabilities and leads to the formation of stereotyped and recurrent sequences, called chunks. In addition, the position of sentences varies from one sentence to another. The activity of the HVC neurons was recorded during the diffusion of one of the BOS composed of 3 chunks and variants: BOS in which only the order of the phrases in a chunk or only the order of the chunks, is changed. The results show a stronger impact on the neuronal responses, of changes in the order of the chunks than in the order of sentences in the chunks. At the contrary to a study of another species of bird, our results don’t provide any arguments in favor of the idea that order sensitivity is based on a treatment of transition probabilities between phrases. They suggest that the sensitivity of neurons extends over several phrases, beyond the structure of the chunks themselves and depends on chunks order in the song.These studies show that responses of neurons to a given syllable or phrase depend on what precedes it, whether at the level of a sensorimotor area or a high-level auditory area. At the HVC level, this sensitivity to context can extend over several phrases, and therefore several seconds, to consider how the order of words of human language could be treated at the neuronal level.; Le chant des oiseaux, comme le langage oral chez les humains, nécessite une reconnaissance fine des signaux acoustiques émis. Mais un chant d’oiseau n’est pas qu’une simple succession d’éléments sonores, appelés syllabes. L’agencement des syllabes suit des règles, et, d’un point de vue comportemental, les oiseaux peuvent discriminer les chants en fonction de cet agencement. Comme ils possèdent, de plus, un ensemble de régions cérébrales spécialisées dans la perception, la production et l’apprentissage du chant, ils sont un très bon modèle d’étude des mécanismes neuronaux impliqués dans le traitement de l’ordre temporel des signaux acoustiques. Au cours de cette thèse, cette question a été le cœur de deux études basées sur des enregistrements électrophysiologiques (extracellulaires) de l’activité des neurones lors de la diffusion de chants.La première étude a porté sur le traitement de l’ordre au niveau d’une aire analogue du cortex auditif secondaire des mammifères, le nidopallium caudo-médian (NCM), chez une espèce, le diamant mandarin (Taeniopygia guttata), capable de discriminer des chants suivant l’agencement des syllabes. Les neurones du NCM ont la particularité d’avoir des réponses qui diminuent lors des répétitions d’un stimulus et qui augmentent si un nouveau chant est présenté. En se basant sur cette propriété d’adaptation, nous avons montré qu’il n’est pas nécessaire de changer de chant, un changement de l’ordre des syllabes suffit à réinstaller des réponses. Changer l’ordre modifie le contexte acoustique dans lequel se trouve une syllabe (ce qui précède est différent), les neurones du NCM seraient donc sensibles à ce contexte. Pour aller plus loin, nous avons utilisé comme stimuli de courtes séquences composées de 2 syllabes différentes, A et B, organisées selon les structures grammaticales ABAB ou AABB. Les résultats montrent que les neurones détectent cette différence de structure, apportant un argument supplémentaire à l’hypothèse d’un traitement de la façon dont les syllabes se succèdent dans un chant.La deuxième étude a porté sur le traitement de l’ordre des syllabes dans une aire sensori-motrice, le HVC, chez le canari (Serinus canaria). Les neurones du HVC ont déjà été identifiés comme sensibles à l’ordre des syllabes dans le propre chant de l’oiseau (bird’s own song ou BOS). Le canari produit des chants complexes composés de phrases successives, elles-mêmes contenant des répétitions d’une même syllabe. L’agencement des phrases dans les chants est régi par des probabilités de transition et conduit à former des séquences stéréotypées et récurrentes dans les chants, les chunks. De plus, la position des phrases varie d’une phrase à l’autre. L’activité des neurones du HVC a été enregistrée lors de la diffusion d’un des BOS de l’oiseau composé de 3 chunks et de variantes : le BOS dans lequel seul l’ordre des phrases dans un chunk ou seul l’ordre des chunks est modifié. Les résultats montrent un impact plus fort des modifications de l’ordre des chunks que de l’ordre des phrases dans les chunks, sur les réponses neuronales. Contrairement à une étude chez une autre espèce d’oiseau, nos résultats n’apportent pas d’arguments en faveur de l’idée que la sensibilité à l’ordre repose sur un traitement des probabilités de transition entre les phrases. Ils suggèrent que la sensibilité des neurones s’étend sur plusieurs phrases, au-delà de la structure des chunks eux-mêmes et dépend de l’ordre des chunks dans le chant.Ces études montrent que les réponses des neurones à une syllabe ou à une phrase donnée dépendent de ce qui la précède, que ce soit au niveau d’une aire sensorimotrice ou d’une aire auditive de haut niveau. Au niveau du HVC, cette sensibilité au contexte peut s’étendre sur plusieurs phrases, et donc plusieurs secondes, permettant d’envisager comment l’ordre des mots du langage humain pourrait être traité au niveau neuronal.

Songs of songbirds, such as speech in humans, requires fine recognition of emitted acoustic signals. But bird's song isn’t only a succession of sound elements, called syllables. The order of syllables follows rules, and, from a behavioral point of view, birds can discriminate songs according to this order. Moreover, since they have a set of specialized brain regions in the perception, production and learning of singing, they are a major model for studying neural mechanisms involved in the processing of temporal order of acoustic signals. During this thesis, the focus was on two studies based on electrophysiological recordings (extracellular) of neurons activity during the song diffusion.The first study focused on the treatment of order in an analog area of the mammalian secondary auditory cortex, the caudomedial nidopallium (NCM), in one species, the zebra finch (Taeniopygia guttata), able to discriminate songs according to syllables order. NCM neurons responses decrease during iterations of a stimulus and increase if a new song is presented. Based on this adaptation property, we have shown that it's not necessary to change the song, a change in the order of syllables is sufficient to re-establish responses. Changing the order changes the acoustic context of the syllable (what comes before is different), so the NCM neurons would be sensitive to this context. To go further, we used as stimuli a short sequence composed of 2 different syllables, A and B, organized according to ABAB or AABB grammatical structures. The results show that the neurons detect this difference in structure, providing an additional argument to the hypothesis of a treatment depending on how the syllables follow each other in a song.The second study focused on the treatment of the order of syllables in a sensorimotor area, the HVC (proper noum), in the canary (Serinus canaria). HVC neurons have already been identified as sensitive to syllable order in the bird's own song (BOS). The canary produces complex songs composed of successive phrases, themselves containing repetitions of the same syllable. The arrangement of the phrases in the songs depends on transition probabilities and leads to the formation of stereotyped and recurrent sequences, called chunks. In addition, the position of sentences varies from one sentence to another. The activity of the HVC neurons was recorded during the diffusion of one of the BOS composed of 3 chunks and variants: BOS in which only the order of the phrases in a chunk or only the order of the chunks, is changed. The results show a stronger impact on the neuronal responses, of changes in the order of the chunks than in the order of sentences in the chunks. At the contrary to a study of another species of bird, our results don’t provide any arguments in favor of the idea that order sensitivity is based on a treatment of transition probabilities between phrases. They suggest that the sensitivity of neurons extends over several phrases, beyond the structure of the chunks themselves and depends on chunks order in the song.These studies show that responses of neurons to a given syllable or phrase depend on what precedes it, whether at the level of a sensorimotor area or a high-level auditory area. At the HVC level, this sensitivity to context can extend over several phrases, and therefore several seconds, to consider how the order of words of human language could be treated at the neuronal level., Le chant des oiseaux, comme le langage oral chez les humains, nécessite une reconnaissance fine des signaux acoustiques émis. Mais un chant d’oiseau n’est pas qu’une simple succession d’éléments sonores, appelés syllabes. L’agencement des syllabes suit des règles, et, d’un point de vue comportemental, les oiseaux peuvent discriminer les chants en fonction de cet agencement. Comme ils possèdent, de plus, un ensemble de régions cérébrales spécialisées dans la perception, la production et l’apprentissage du chant, ils sont un très bon modèle d’étude des mécanismes neuronaux impliqués dans le traitement de l’ordre temporel des signaux acoustiques. Au cours de cette thèse, cette question a été le cœur de deux études basées sur des enregistrements électrophysiologiques (extracellulaires) de l’activité des neurones lors de la diffusion de chants.La première étude a porté sur le traitement de l’ordre au niveau d’une aire analogue du cortex auditif secondaire des mammifères, le nidopallium caudo-médian (NCM), chez une espèce, le diamant mandarin (Taeniopygia guttata), capable de discriminer des chants suivant l’agencement des syllabes. Les neurones du NCM ont la particularité d’avoir des réponses qui diminuent lors des répétitions d’un stimulus et qui augmentent si un nouveau chant est présenté. En se basant sur cette propriété d’adaptation, nous avons montré qu’il n’est pas nécessaire de changer de chant, un changement de l’ordre des syllabes suffit à réinstaller des réponses. Changer l’ordre modifie le contexte acoustique dans lequel se trouve une syllabe (ce qui précède est différent), les neurones du NCM seraient donc sensibles à ce contexte. Pour aller plus loin, nous avons utilisé comme stimuli de courtes séquences composées de 2 syllabes différentes, A et B, organisées selon les structures grammaticales ABAB ou AABB. Les résultats montrent que les neurones détectent cette différence de structure, apportant un argument supplémentaire à l’hypothèse d’un traitement de la façon dont les syllabes se succèdent dans un chant.La deuxième étude a porté sur le traitement de l’ordre des syllabes dans une aire sensori-motrice, le HVC, chez le canari (Serinus canaria). Les neurones du HVC ont déjà été identifiés comme sensibles à l’ordre des syllabes dans le propre chant de l’oiseau (bird’s own song ou BOS). Le canari produit des chants complexes composés de phrases successives, elles-mêmes contenant des répétitions d’une même syllabe. L’agencement des phrases dans les chants est régi par des probabilités de transition et conduit à former des séquences stéréotypées et récurrentes dans les chants, les chunks. De plus, la position des phrases varie d’une phrase à l’autre. L’activité des neurones du HVC a été enregistrée lors de la diffusion d’un des BOS de l’oiseau composé de 3 chunks et de variantes : le BOS dans lequel seul l’ordre des phrases dans un chunk ou seul l’ordre des chunks est modifié. Les résultats montrent un impact plus fort des modifications de l’ordre des chunks que de l’ordre des phrases dans les chunks, sur les réponses neuronales. Contrairement à une étude chez une autre espèce d’oiseau, nos résultats n’apportent pas d’arguments en faveur de l’idée que la sensibilité à l’ordre repose sur un traitement des probabilités de transition entre les phrases. Ils suggèrent que la sensibilité des neurones s’étend sur plusieurs phrases, au-delà de la structure des chunks eux-mêmes et dépend de l’ordre des chunks dans le chant.Ces études montrent que les réponses des neurones à une syllabe ou à une phrase donnée dépendent de ce qui la précède, que ce soit au niveau d’une aire sensorimotrice ou d’une aire auditive de haut niveau. Au niveau du HVC, cette sensibilité au contexte peut s’étendre sur plusieurs phrases, et donc plusieurs secondes, permettant d’envisager comment l’ordre des mots du langage humain pourrait être traité au niveau neuronal.

How sensory signals are encoded in the brain and whether their behavioural relevance affects their encoding are central questions in sensory neuroscience. Studies have consistently shown that behavioural relevance can change the neural representation of sounds in the auditory system, but what occurs in the context of natural acoustic communication where significance could be acquired through social interaction remains to be explored. The zebra finch, a highly social songbird species that forms lifelong pair bonds and uses a vocalization, the distance call, to identify its mate offers an opportunity to address this issue. One auditory area in the songbird telencephalon, the caudo-medial nidopallium (NCM) that is considered as being analogous to the secondary mammalian auditory cortex, has recently emerged as part of the neural substrate for sensory representation of species-specific vocalizations: the activation of NCM neurons is greatest when birds are exposed to conspecific song, as compared to heterospecific song or artificial stimuli. This led us to investigate whether, in the zebra finch, NCM neurons could contribute to the discrimination among vocalizations that differ in their degree of familiarity: calls produced by the mate, by familiar individuals (males or females), or by unfamiliar individuals (males or females). In females, behaviourally relevant calls, i.e. the mate’s call and familiar calls, evoked responses of greater magnitude than unfamiliar calls. This distinction between responses was seen both in multiunit recordings from awake freely moving mated females (using a telemetric system) and in single unit recordings from anesthetized mated females. In contrast, control females that had not heard them previously displayed response of similar magnitude to call stimuli. In addition, more cells showed highly selective responses in mated than in control females suggesting that experience-dependent plasticity in call-evoked responses resulted in enhanced discrimination of auditory stimuli. In males, as in females, call playback evoked robust auditory responses. However, neurons in males did not appear capable of categorizing the calls of individuals (males or females) as ‘‘familiar’’ or ‘‘unfamiliar’’. Then, we investigated how calls are represented in the NCM of zebra finches by assessing whether certain call-specific acoustic cues drove NCM neurons to a greater degree than others. Behavioural studies had previously identified call-specific acoustic cues that are necessary to elicit a vocal response from male and female zebra finches. Single-unit recordings indicated that NCM neurons in females were particularly sensitive to call modifications in the spectral domain: suppressing the fundamental frequency of call stimuli or modifying the relative energy levels of harmonics in call caused a marked decrease in response magnitude of NCM neurons. In males, NCM neurons also appear to be sensitive to call modifications in the spectral domain, however changes in magnitude of responses (increase or decrease) depended on the acoustic cue that had been modified.Our results provide evidence that the NCM is a telencephalic auditory region that contributes to the processing of the distance call, in females as well in males. However, how the distance call is processed and represented in the NCM appears to differ between males and females. In females, the NCM could be involved in dicrimination between call stimuli whereas, in males, its functional role in call-processing remains to be determined. Our results also suggest that, in females, social experience with the call of individuals, by affecting the degree to which neurons discriminated between these calls, may shape the functional properties of neurons in a telencephalic auditory area. The functional properties of auditory neurons may therefore change continuously to adapt to the social environment.; A l’heure actuelle, il reste largement à étudier comment le codage sensoriel des signaux vocaux de communication contribue à leur détection et à leur reconnaissance. Peu d’études se sont, en effet, penchées sur le codage des vocalisations au niveau des régions auditives en fonction de l’individu qui les produit et du degré de familiarité avec cet individu. Dans ce cadre, les oiseaux chanteurs sont un bon modèle parce qu’ils utilisent des vocalisations pour interagir et reconnaître leurs congénères et qu’ils possèdent, de plus, un ensemble de régions auditives. Parmi ces régions, le nidopallium caudomedian (NCM), une aire auditive analogue du cortex auditif secondaire chez les mammifères, est actuellement considérée comme une région spécialisée dans le traitement des vocalisations (chants et cris) de l’espèce : les neurones du NCM répondent plus fortement aux vocalisations de l’espèce qu’à celles d’une autre espèce. À partir de là, parce que chez le diamant mandarin, le cri de distance permet aux individus, mâles ou femelles, de reconnaître leur partenaire sexuel, nous avons cherché à savoir si, chez les femelles comme chez les mâles, les neurones du NCM montraient une discrimination dans leurs réponses auditives entre le cri d’individus connus (parmi lesquels figurait le partenaire sexuel) et ceux d’individus inconnus et si ces réponses reflétaient le degré de familiarité de ces vocalisations. Les enregistrements de l’activité des neurones du NCM, chez des diamants mandarins vigiles (grâce à un système de télémétrie) ou anesthésiés, lors de la présentation de cris de distance, ont révélé, chez les femelles vivant en couple et ayant été familiarisées avec un autre couple de diamants mandarins, une plus forte augmentation de l’activité lors de la diffusion des cris d’individus connus, mâles ou femelles, qu’aux cris d’individus inconnus. Une telle augmentation n’a pas été, en outre, observée chez des femelles contrôles qui n’avaient jamais entendu ces mêmes cris auparavant. De plus, ils ont indiqué que le nombre de neurones montrant un fort degré de sélectivité ainsi que la quantité d’information portée par les trains de potentiels d’action étaient plus importants chez les femelles vivant en couple que chez les femelles contrôles. En revanche, chez les mâles, bien que la plupart des neurones montrait des réponses lors de la diffusion des cris, aucune différence n’a été mise en évidence entre les cris d’individus connus et ceux d’inconnus. Nous avons alors cherché à savoir comment, d’un point de vue acoustique, les cris de distance étaient représentés au sein du NCM. En se basant sur une étude comportementale ayant déterminé quelles étaient les caractéristiques acoustiques qui contribuaient à la reconnaissance de ces cris, nous avons cherché à savoir si les neurones du NCM étaient sensibles à ces mêmes caractéristiques acoustiques. Les résultats ont montré que, chez les femelles, la suppression de la fréquence fondamentale et la modification du timbre du cri du partenaire sexuel ou du propre cri de l’oiseau provoquaient une forte diminution des réponses au sein du NCM alors que, chez les mâles, les réponses variaient selon le paramètre modifié et le type de cri présenté. Nos résultats suggèrent donc que, chez le diamant mandarin, le NCM est impliqué dans le codage du cri de distance. Cependant, ils mettent en évidence des différences dans ce codage entre les mâles et les femelles. Chez les femelles, ce codage permet de discriminer entre les cris d’individus connus et ceux d’individus inconnus alors que chez les mâles, son rôle reste à être déterminé. Chez les femelles, l’expérience sociale au travers de la mémorisation des signaux de communication des individus peut donc façonner les propriétés fonctionnelles des neurones d’une aire auditive secondaire. Ces propriétés pourraient donc continuellement subir des changements pour s'adapter à l’environnement social de l’individu.

How sensory signals are encoded in the brain and whether their behavioural relevance affects their encoding are central questions in sensory neuroscience. Studies have consistently shown that behavioural relevance can change the neural representation of sounds in the auditory system, but what occurs in the context of natural acoustic communication where significance could be acquired through social interaction remains to be explored. The zebra finch, a highly social songbird species that forms lifelong pair bonds and uses a vocalization, the distance call, to identify its mate offers an opportunity to address this issue. One auditory area in the songbird telencephalon, the caudo-medial nidopallium (NCM) that is considered as being analogous to the secondary mammalian auditory cortex, has recently emerged as part of the neural substrate for sensory representation of species-specific vocalizations: the activation of NCM neurons is greatest when birds are exposed to conspecific song, as compared to heterospecific song or artificial stimuli. This led us to investigate whether, in the zebra finch, NCM neurons could contribute to the discrimination among vocalizations that differ in their degree of familiarity: calls produced by the mate, by familiar individuals (males or females), or by unfamiliar individuals (males or females). In females, behaviourally relevant calls, i.e. the mate’s call and familiar calls, evoked responses of greater magnitude than unfamiliar calls. This distinction between responses was seen both in multiunit recordings from awake freely moving mated females (using a telemetric system) and in single unit recordings from anesthetized mated females. In contrast, control females that had not heard them previously displayed response of similar magnitude to call stimuli. In addition, more cells showed highly selective responses in mated than in control females suggesting that experience-dependent plasticity in call-evoked responses resulted in enhanced discrimination of auditory stimuli. In males, as in females, call playback evoked robust auditory responses. However, neurons in males did not appear capable of categorizing the calls of individuals (males or females) as ‘‘familiar’’ or ‘‘unfamiliar’’. Then, we investigated how calls are represented in the NCM of zebra finches by assessing whether certain call-specific acoustic cues drove NCM neurons to a greater degree than others. Behavioural studies had previously identified call-specific acoustic cues that are necessary to elicit a vocal response from male and female zebra finches. Single-unit recordings indicated that NCM neurons in females were particularly sensitive to call modifications in the spectral domain: suppressing the fundamental frequency of call stimuli or modifying the relative energy levels of harmonics in call caused a marked decrease in response magnitude of NCM neurons. In males, NCM neurons also appear to be sensitive to call modifications in the spectral domain, however changes in magnitude of responses (increase or decrease) depended on the acoustic cue that had been modified.Our results provide evidence that the NCM is a telencephalic auditory region that contributes to the processing of the distance call, in females as well in males. However, how the distance call is processed and represented in the NCM appears to differ between males and females. In females, the NCM could be involved in dicrimination between call stimuli whereas, in males, its functional role in call-processing remains to be determined. Our results also suggest that, in females, social experience with the call of individuals, by affecting the degree to which neurons discriminated between these calls, may shape the functional properties of neurons in a telencephalic auditory area. The functional properties of auditory neurons may therefore change continuously to adapt to the social environment.; A l’heure actuelle, il reste largement à étudier comment le codage sensoriel des signaux vocaux de communication contribue à leur détection et à leur reconnaissance. Peu d’études se sont, en effet, penchées sur le codage des vocalisations au niveau des régions auditives en fonction de l’individu qui les produit et du degré de familiarité avec cet individu. Dans ce cadre, les oiseaux chanteurs sont un bon modèle parce qu’ils utilisent des vocalisations pour interagir et reconnaître leurs congénères et qu’ils possèdent, de plus, un ensemble de régions auditives. Parmi ces régions, le nidopallium caudomedian (NCM), une aire auditive analogue du cortex auditif secondaire chez les mammifères, est actuellement considérée comme une région spécialisée dans le traitement des vocalisations (chants et cris) de l’espèce : les neurones du NCM répondent plus fortement aux vocalisations de l’espèce qu’à celles d’une autre espèce. À partir de là, parce que chez le diamant mandarin, le cri de distance permet aux individus, mâles ou femelles, de reconnaître leur partenaire sexuel, nous avons cherché à savoir si, chez les femelles comme chez les mâles, les neurones du NCM montraient une discrimination dans leurs réponses auditives entre le cri d’individus connus (parmi lesquels figurait le partenaire sexuel) et ceux d’individus inconnus et si ces réponses reflétaient le degré de familiarité de ces vocalisations. Les enregistrements de l’activité des neurones du NCM, chez des diamants mandarins vigiles (grâce à un système de télémétrie) ou anesthésiés, lors de la présentation de cris de distance, ont révélé, chez les femelles vivant en couple et ayant été familiarisées avec un autre couple de diamants mandarins, une plus forte augmentation de l’activité lors de la diffusion des cris d’individus connus, mâles ou femelles, qu’aux cris d’individus inconnus. Une telle augmentation n’a pas été, en outre, observée chez des femelles contrôles qui n’avaient jamais entendu ces mêmes cris auparavant. De plus, ils ont indiqué que le nombre de neurones montrant un fort degré de sélectivité ainsi que la quantité d’information portée par les trains de potentiels d’action étaient plus importants chez les femelles vivant en couple que chez les femelles contrôles. En revanche, chez les mâles, bien que la plupart des neurones montrait des réponses lors de la diffusion des cris, aucune différence n’a été mise en évidence entre les cris d’individus connus et ceux d’inconnus. Nous avons alors cherché à savoir comment, d’un point de vue acoustique, les cris de distance étaient représentés au sein du NCM. En se basant sur une étude comportementale ayant déterminé quelles étaient les caractéristiques acoustiques qui contribuaient à la reconnaissance de ces cris, nous avons cherché à savoir si les neurones du NCM étaient sensibles à ces mêmes caractéristiques acoustiques. Les résultats ont montré que, chez les femelles, la suppression de la fréquence fondamentale et la modification du timbre du cri du partenaire sexuel ou du propre cri de l’oiseau provoquaient une forte diminution des réponses au sein du NCM alors que, chez les mâles, les réponses variaient selon le paramètre modifié et le type de cri présenté. Nos résultats suggèrent donc que, chez le diamant mandarin, le NCM est impliqué dans le codage du cri de distance. Cependant, ils mettent en évidence des différences dans ce codage entre les mâles et les femelles. Chez les femelles, ce codage permet de discriminer entre les cris d’individus connus et ceux d’individus inconnus alors que chez les mâles, son rôle reste à être déterminé. Chez les femelles, l’expérience sociale au travers de la mémorisation des signaux de communication des individus peut donc façonner les propriétés fonctionnelles des neurones d’une aire auditive secondaire. Ces propriétés pourraient donc continuellement subir des changements pour s'adapter à l’environnement social de l’individu.