The other sections of this website focus on how stem cells
are isolated, and how they can be artificially introduced as a therapy for
a variety of diseases. Those are the kinds of things you probably hear about
on the news. But there's a whole different area of research that focuses
on animals which constantly regenerate neurons throughout their life, because
those systems are the ones that help us understand how to do it ourselves.
So this section is devoted to that area of research: where and how adult neurogenesis
And it's all thanks to canaries.
Canaries? Yes, canaries. They're one of the first "higher" animals we've found to constantly regrow neural cells throughout their lifespan. Originally, scientists thought that that was impossible. For example, as recently as 1991 (11 years ago, at the time of this writing!) scientists confidently published statements like this:
...the functional specialization of the brain imposes on the neurones two great lacunae; proliferation inability and irreversibility of intraprotoplasmic differentiation. It is for this reason that, once the development was ended, the founts of growth and regeneration of the axons and dendrites dried up irrevocably. In adult centers the nerve paths are something fixed, ended, immutable. Everything may die, nothing may be regenerated. It is for the science of the future to change, if possible, this harsh decree. (Ramon y Cajal, 1991)
Needless to say, things have changed a little since then.
The first vertebrates shown to regenerate neurons throughout their lives were songbirds--canaries, to be specific. At first the only distinct part of the brain shown to regenerate cells was the ventricular/subventricular zone (referred to in a lot of literature as the SVZ). That area of the brain appears to be primarily related to song-control, which is why canaries are so imortant; they relearn songs, and sing new ones, throughout their lives. And for these kinds of birds, that flexibility is of a great deal of evolutionary value. A flexible and responsive memory is vitally necessary, because tiny details encoded in their songs communicate a great deal of information. A bird whose intonation is off just isn't as attractive as one who gets it note-perfect--but the "perfect" notes are constantly changing. It's kind of like a vocal version of the fashion industry. And if you're wearing last year's Prada, you lose your territory and your mate.
Still, no matter how much canaries like to reproduce, song control is of only limited interest to science, medical science in particular. So while people still research on canaries, those experiments have more to do with detailing the process by which adult neurogenesis occurs. Other current research focuses more on finding and understanding neurogenesis in other brain functions and other animals. The hippocampus is especially important here, because it is the site of a great deal of adult neurogenesis--and it functions in similar ways in both birds and other animals. Primarily its function appears to be to organize information into memories, although there is still a great deal left to understand here.
To help you navigate your way through the miry wilds of memory, the following sections explain how memory/learning occur, what stem cells have to do with memory, and a few other areas in which the regenerating the hippocampus may be important.
I've tried to minimize the amount of jargon you need to know to understand this page. But when it's unavoidable, terms are in italics and clicking on them will open up the glossary entry related to them.
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