Hugo Cousillas

Direct social contacts override auditory information in the song-learning process in starlings (Sturnus vulgaris).

Social influence on song acquisition was studied in 3 groups of young European starlings raised under different social conditions but with the same auditory experience of adult song. Attentional focusing on preferred partners appears the most likely explanation for differences found in song acquisition in relation to experience, sex, and song categories. Thus, pair-isolated birds learned from each other and not from broadcast live songs, females did not learn from the adult male tutors, and sharing occurred more between socially associated peers. On the contrary, single-isolated birds clearly copied the adult songs that may have been the only source of attention stimulation. Therefore, social preference appears as both a motor for song learning and a potential obstacle for acquisition from nonpreferred partners, including adults.

Experience-dependent neuronal specialization and functional organization in the central auditory area of a songbird

The effect of early experience on brain development was investigated in the central auditory area of a songbird, the fieldu2003L complex, which is analogous to the mammalian auditory cortex. Multi‐unit recordings of auditory responses in the fieldu2003L complex of adult starlings raised without any experience of adult song during development provide strong evidence of developmental plasticity both in the neuronal responses and in the functional organization of this area. Across the entire area, experimental birds, separated from adults from the age of 1u2003week old until they were 2u2003years old, had a much larger number of neurons that responded to all the stimuli than did control birds. The well‐known tonotopy demonstrated in adult wild birds using the same procedure was altered. This study is the first to bring evidence of developmental plasticity in the organization of the central auditory areas in songbirds. These results are discussed in relation to other reports on effects of early experience on brain development.

Categorization in birdsong: from behavioural to neuronal responses

This paper reviews some aspects on the perceptual processes involved in the categorization of natural sounds, especially in birdsong. Different models have been proposed to account for the simple filtering observed at the peripheral level to the recognition processes, revealed through behavioural responses. Some studies have shown that neurons in some of the motor nuclei (high vocal center) in the brain are specialized towards precise species-specific characteristics, even the birds own song. These results indicate a high level of integration, but little is known about intermediate levels. Studies of the perception of natural songs by starlings show that many neurons in field L are selective towards particular features of the songs. Neighbouring neurons tend to show complementary or similar selectivities, determining areas of response. Such studies emphasize the importance of combining ethology and neurophysiology, and of the use of natural sounds to test neuronal selectivity.

Functional organization of the forebrain auditory centres of the European starling: A study based on natural sounds

The field L complex is thought to be the highest auditory centre and the input in the song vocal nuclei. Different anatomical and functional subdivisions have been described in field L. Auditory neurons of field L are well activated by natural sounds and especially by species-specific sounds. A complex sound coding appears to exist in field L. However, until now, the spatial organization of the different functional subdivisions has been described only using artificial sounds. Here, we investigated the spatial distribution of neuronal responses in field L to species-specific songs. Starlings seemed to be a very appropriate species for this investigation, both because of their complex vocal behaviour that implies different levels of categorization and their neuronal responses towards complex song elements. Multi-unit recordings were performed in wild starlings that were awake. The method of backward correlation was used to visualize the functional organization and we represented the neuronal responses as both activity maps and correlation maps. The use of natural sounds allowed us to define several functional sub-areas with different neuronal processing. These results show that field L is involved in a more complex task than simple frequency processing.

Linking social and vocal brains: could social segregation prevent a proper development of a central auditory area in a female songbird?

Direct social contact and social interaction affect speech development in human infants and are required in order to maintain perceptual abilities; however the processes involved are still poorly known. In the present study, we tested the hypothesis that social segregation during development would prevent the proper development of a central auditory area, using a “classical” animal model of vocal development, a songbird. Based on our knowledge of European starling, we raised young female starlings with peers and only adult male tutors. This ensured that female would show neither social bond with nor vocal copying from males. Electrophysiological recordings performed when these females were adult revealed perceptual abnormalities: they presented a larger auditory area, a lower proportion of specialized neurons and a larger proportion of generalist sites than wild-caught females, whereas these characteristics were similar to those observed in socially deprived (physically separated) females. These results confirmed and added to earlier results for males, suggesting that the degree of perceptual deficiency reflects the degree of social separation. To our knowledge, this report constitutes the first evidence that social segregation can, as much as physical separation, alter the development of a central auditory area.

New insights into the auditory processing of communicative signals in the HVC of awake songbirds.

In the present study, using a systematic recording method and a variety of stimuli, we determined the proportion of responsive sites and their response features in the vocal control nucleus HVC of awake-restrained starlings, a species with multiple song types. Responsive sites were classified into three groups, according to the number of stimuli to which they responded. Sites in the three groups showed responses to individual-specific songs, with sites in the group that showed responses to only one stimulus responding mostly to a birds own song. In comparison, very few sites exhibited responses to universal species-specific songs and to artificial nonspecific sounds. By contrast, data obtained in the same birds under urethane anesthesia show that, although the total proportion of responsive sites was similar, numerous responses to a universal species-specific song and to an artificial nonspecific pure tone could be observed.

A new extensive approach to single unit responses using multisite recording electrodes: application to the songbird brain

One of the most challenging issues in neuroethology concerns the neural substrates for song production, perception and learning in songbirds. However, electrophysiological studies of the song system of songbirds are often fragmented and centered on a small number of selected neurons. Here, we have developed a new extensive approach to record a great number of single units in the brain of a songbird, the European starling. The aim of this approach is to formulate quantitative assumptions about the electrophysiological characteristics of the brain nucleus investigated: e.g. the proportion of auditory neurons, neuronal selectivity, etc. We applied a mapping method using multisite recording electrodes and online isolation of single-units, without preselecting neurons with a search stimulus. As an example of the application of this technique, we have mapped the responses to a variety of natural and artificial acoustic stimuli recorded systematically throughout the HVC of both awake and anaesthetized male starlings. This method appears to be powerful and allowed us to quantitatively compare responses obtained in awake and anaesthetized birds by recording over 1000 single units. We think that, in future, this will enable us to characterize and compare parts of nuclei or entire nuclei and to better understand how the song system works.

Auditory responses in the HVC of anesthetized starlings.

The present study, using a systematic recording method that we recently developed, describes the behavior of the neurons of the vocal control nucleus HVC in response to a variety of acoustic stimuli in a songbird species with multiple song types, the European starling. Most neurons did not respond to any of the stimuli that were presented, and those neurons that did respond responded to a different number of stimuli and showed distinct response features. The latter were thus classified into 3 categories, according to the number of stimuli to which they responded. Although only intracellular data could unambiguously determine to which population the neurons we recorded belonged, these 3 categories might correspond to the 3 populations of neurons that have been previously described in the HVC. Interestingly, responsive neurons of the 3 categories appeared to mainly respond to stimuli that were not the birds own song. However, most of the stimuli to which the HVC neurons responded correspond to sounds that are important in the everyday social life of the starlings. We thus discuss our results in relation to the social life of these birds, to possible species differences in the processing of communicative signals, and to methodological issues.

Anesthesia and brain sensory processing: impact on neuronal responses in a female songbird.

Whether anesthesia impacts brain sensory processing is a highly debated and important issue. There is a general agreement that anesthesia tends to diminish neuronal activity, but its potential impact on neuronal “tuning” is still an open question. Here we show, based on electrophysiological recordings in the primary auditory area of a female songbird, that anesthesia induces neuronal responses towards biologically irrelevant sounds and prevents the seasonal neuronal tuning towards functionally relevant species-specific song elements.

An Ambulatory Electroencephalography System for Freely Moving Horses: An Innovating Approach

Electroencephalography (EEG) that has been extensively studied in humans presents also a large interest for studies on animal brain processes. However, since the quality of the recordings is altered by muscular activity, most EEG recordings on animals are obtained using invasive methods with deeply implanted electrodes. This requires anesthesia and can thus only be used in laboratory or clinical settings. As EEG is a very useful tool both for detecting brain alterations due to diseases or accidents and to evaluate the arousal and attentional state of the animal, it seemed crucial to develop a tool that would make such recordings possible in the horse’s home environment, with a freely moving horse. Such a tool should neither be invasive nor cause discomforts to the horse as the usual other practice which consists, after shaving the zone, in gluing the electrodes to the skin. To fulfill these requirements, we developed a novel EEG headset adapted to the horse’s head that allows an easy and fast positioning of the electrodes and that can be used in the home environment on a freely moving horse. In this study, we show that this EEG headset allows to obtain reliable recordings, and we propose an original evaluation of an animal’s “EEG profile” that allows comparisons between individuals and situations. This EEG headset opens new possibilities of investigation on horse cognition, and it can also become a useful tool for veterinarians to evaluate cerebral disorders or check the anesthesia level during a surgery.