European Journal of Neuroscience, Trends in Neurosciences, The Journal of Neuroscience: the work resulting from the collaboration of Professor Jacques Balthazart’s team from the University of Liège (GIGA-Neurosciences) and the group of researchers led by Professor Annemie Van der Linden (Bio-Imaging Lab at the University of Antwerp), was in the spotlight three times in one year. It relates to the strange plasticity of the songbird’s brain. This peculiar phenomenon is helping neurobiologists in their quest to elucidate the neural bases of complex behaviours.

When we hear sparrows, chaffinches or canaries singing, we have no idea of the strange way their brain behaves all year round. Throughout the seasons, the size of the cerebral nuclei that control the vocalisations of passerines (1) changes, sometimes significantly. Examined from the angle of neurobiology, the study of this spectacular phenomenon is favourable to the development of models that allow us to better determine how a complex behaviour (song in this case) is based on the “dynamics” of the living, involving close relations between a neuroanatomical substrate (neural structures) and neuroendocrine and neurochemical mechanisms.

The presence of an intense periodical neurogenesis within certain song nuclei in several species of passerines has not escaped the researchers. Understanding the laws that govern the emergence of new neurons in these regions of the brain, falls under the scope of fundamental research, while also marking a way that could one day lead to man and form the outlines of new therapeutic pathways for the treatment of degenerative diseases of the central nervous system.

Learning to sing

It was Peter Marler, an English ethologist working at the University of Cambridge some fifty years ago, who sparked the sustained interest scientists have had in songbirds ever since. First of all, he confirmed what ornithologists had sensed: passerines learn their vocalisations from the environment in which they live. We know today that psittacines (parrots, budgerigars, cockatoos) and certain hummingbirds share the same characteristic, but that other birds have vocalisations that can be qualified as innate. Thus, a cockerel placed in total isolation from birth, will nevertheless develop its crow.

Marler’s essential contribution was to demonstrate the song-learning mechanism in passerines. Let us take the case of the chaffinch, in which he took particular interest. “In the beginning (from September to December), the animal is happy to listen to its fellow birds and store their songs in its memory”, explains Professor Jacques Balthazart of GIGA-Neurosciences (previously known as the Centre de Recherche en Neurobiologie Cellulaire et Moléculaire or CNCM). “Then, in January and February, it practises, producing rather disorganised vocalisations – or subsong – which it compares with the examples it has memorised. In short, it proceeds by trial and error. This phase is followed by the third step: crystallisation, which takes place in March, during which the bird selects the vocalisations from those it has emitted that correspond to the songs inscribed in its memory. The chaffinch produces a stable song, the adult song.” In some species, like the zebra finch, an Australian passerine, there is nevertheless a partial overlap between the auditory phase and the active production phase. As for the starling, it learns new vocalisations all its life.

(1) Passerines are a category of bird to which three-fifths of all the living species belong.