“In 1981", says Jacques Balthazart, “Fernando Nottebohm published a paper entitled ‘A brain for all seasons’, which revealed this extraordinary plasticity of the brain and the underlying mechanisms. He realised that there was an underlying neurogenesis to this plasticity, which contradicted a firmly established dogma: until 1980, it was generally thought that there was no neurogenesis in the adult brain of higher vertebrates. It was thought that we were born with a given number of neurons,that this number fell as we aged and that they could never be replaced."

Furthermore, neurochemical studies showed the presence of androgen receptors (i.e. testosterone receptors) in these HVC and RA nuclei. “Which also refuted a broadly accepted myth at the time because it was generally believed that the steroid receptors were expressed almost exclusively in what is known as the limbic system and the hypothalamus. It was also a kind of revolution: we thought, ‘That's where testosterone acts to control song’. But, in fact, it’s much more complicated than that; it acts in lots of places”.

The preoptic area acts on the amount of songs produced

The new work carried out in collaboration between the team of J. Balthazart (GIGA, Neurosciences, ULg) and that of Gregory Ball (Department of Psychological and Brain Sciences, Johns Hopkins University, Baltimore), which has just been published in Proceedings of the National Academy of Sciences of the USA (1), shows that testosterone acts on different parts of the brain to control song.

Their experiment was performed on three groups of canaries (Serinus canaria), that were all castrated: one group didn’t receive any treatment; the second one received a subcutaneous implant of testosterone (in order to expose the whole body to the steroid hormone, including the song nuclei as well as the preoptic area) and, finally, the third group specifically received testosterone in the preoptic area.

Principal outcome: the presence of testosterone in the preoptic area is perfectly able to induce song, at frequencies equal to those observed when the hormone is in the general circulation. Conclusion? The motivation to sing is controlled by the preoptic area and not by the song control nuclei (HVC and RA).



Jacques Balthazart and his colleagues also observed that the structure of these songs wasn’t that of a complete songs emitted by an adult canary. The insertion of testosterone into the preoptic area stimulates the motivation to sing and the amount of song, but not the quality; i.e. the stereotypy of the phrases, the vocal energy, etc. In fact, the song produced resembles that of a young bird practising and learning. However, the birds with systemic testosterone had a perfectly normal adult, crystallised song. Hence, this means that the testosterone must also act elsewhere to induce a complex song structure. There are several possible candidates, including the nucleus HVC.

Another important observation is that the context in which these animals sang wasn't controlled as it would be in a normal animal. Hence, when these canaries were kept in isolation, they sang at very high frequencies, like birds with systemic testosterone. But as soon as they were given a female, they no longer made any vocalisations in response to the female's presence. Therefore, the social context wasn’t optimally controlled by the testosterone implant in the preoptic area. In other words, the testosterone controlled the motivation to sing but it didn’t control either the structure of the song, or the social context in which song appears.

(1) Beau A. Alward, Jacques Balthazart, and Gregory F. Ball, Differential effects of global versus local testosterone on singing behavior and its underlying neural substrate, PNAS Early Edition, Nov. 2013, www.pnas.org/cgi/ doi/10.1073/pnas.1311371110