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From birdsong to neurodegenerative diseases
1/27/14

The key role of song in shaping the brain

A final point in this study: it has long been suspected that the fact of singing in itself induces the growth of the song control regions of the brain. Like athletes who build their leg muscles through exercise, by repeatedly executing a behaviour, the brain is sculpted and reshaped through the addition of new neurons and the increase in the complexity of their connections.

It was known that testosterone induces a growth in volume of the song nuclei – which is associated with extremely active neurogenesis- and it was assumed that this growth resulted from a direct effect on HVC and RA. The recently published paper demonstrates that putting testosterone in the preoptic area increases the frequency of song and the size of the nuclei HVC. They practically double in volume in birds with testosterone in the preoptic area, exactly like those with systemic testosterone. The researchers further showed that the number of songs produced correlated with the size of the nuclei, observed at the end of the experiment. All this proves the vital importance of the singing activity.

“These are very strong arguments showing that the actual singing increases the volume of these nuclei controlling song”, concludes the neurobiologist. The two teams were able to show that it wasn’t a direct effect of the testosterone because testosterone implanted in the preoptic area was incapable of directly reaching the song nuclei: indeed, this hormone wasn’t detectable in the general circulation. Furthermore, testosterone was implanted unilaterally in the preoptic area and the researchers did not observe any effect of the steroid in the non-implanted side of the preoptic area. Neither is there any direct nerve connection between the preoptic area and the song nuclei HVC.

We also know that singing induces the secretion of a neurotransmitter, BDNF (Brain Derived Neurotrophic Factor), a neurotrophin that controls neuroplasticity, neuronal growth, etc. And, BDNF increases the size of the song nuclei. We can therefore make the following assumption: testosterone induces the motivation to sing, song induces the synthesis of BDNF and BDNF induces the growth of the nuclei.

Sonagram

And in the brains of humans (who sing?...)

As explained earlier, this research on the canary was not taken very seriously in the beginning. Destroying a dogma is no easy matter and Fernando Nottebohm had to conduct many studies to convince scientists that there really were new neurons added to the HVC of adult canaries. “He was able to demonstrate it”, Jacques Balthazart adds, “and as a result, researchers began to investigate the phenomenon in mammals. They realised that this was also the case in the latter, though to a lesser degree, because the canary replaces more or less 1 % of its neurons a day in this area of the brain, while humans only replace 1.75 % a year in a limited region of the brain, the hippocampus! It is not the same thing, but it still occurs. And this adult neurogenesis has an important function in problems concerning memory consolidation, reaction to stress, etc. We now believe that a certain number of treatments for depression act by modulating neurogenesis and bringing new neurons to certain areas in the brain, for instance”.

Therefore, there are many reasons for studying these phenomena and the canary has become a model for biomedical research because neurogenesis in this species is extremely visible and easier to study. The hope is to be able to transpose the mechanisms observed canaries to humans. "In the very long term”, Jacques Balthazart observes, “the idea is that if we manage to create neurogenesis or encourage greater neurogenesis in the human brain, we will be able to counter, and even cure neurodegenerative diseases, or at least manage to partly repair traumatic brain damage".

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