Do adult brains learn by neurogenesis?

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Andrea Gawrylewski from "The Scientist" has written a nice blog post describing new research that addresses whether adult brains learn by neurogenesis (the birth of new neurons).

In the blog she writes:

While researchers agree that the birth of new neurons plays an important role in the adult brain, they have long debated to which aspects of learning, memory and behavior the process contributes. A new study published today (January 30) in Nature has used a gene knockout approach to link adult neurogenesis to spatial learning. The paper showed that adult mice that were deficient for a neurogenesis-linked gene , Tlx, had diminished learning and memory capabilities compared to their wild-type counterparts.

Because Tlx is linked to diseases like microencephaly, retinal dystrophy, blindness and aggression, research like this is important for its potential to help scientists better understand the disease pathology and possibly develop new treatments.

Log on to The Scientist to read the rest of her blog post or click here for the full press release.

Image of neurons taken from here.

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I haven't seen your blog before, but I'll be back if you keep up interesting snippets like this one! Thanks.

Dear Ian,

Thank you for your comment. I certainly hope you visit the site again and tell other people about it.

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Take care.
Karen

Hey Karen,
I don't have time to read your links but this sounds fascinating. I know I have seen research before on the density of neurons in the brains of mice from 2 categories. One was sensory starved and the others grew up in enriched environments. The autopsies showed a much denser packing of neurons in the same sized skulls from the enriched groups.
I don't know if your links went into this or not. The genesis of more neurons seems like it would always be a good thing! I don't know if your links was trying to say that you had to grow new cells to learn more or not, but it seems logical that if you grew more cells you would have more room for new thoughts, memories and capabilities!
Thanks again and have a great weekend!
Dave Briggs :~)

Hi Dave,
I agree with your logic. It follows that neurogenesis would be expected to improve our capacity for "new thoughts, memories and capabilities" (as you mention above). This study, however, focused specifically on how neurogenesis affects spatial learning and memory (i.e. learning about our environment and spatial orientation). Thanks for your comment.

There is substantial evidence in the neuroscience field to show that in fact neuronal plasticity remains in the adult brains of rats/mice. Most studies have only looked at the regeneration capacity of neurons in response to acute damage (stroke, glutamate excitatory death, ect). The role of this gene should prove interesting in understanding how the brain normally learns things.

In response to the previous comments about neurogenesis always being a good thing, I would like to point out 1 instance where neurogenesis is bad. When the brain is maturing through adolecence superrfluous neurons are actually culled (systematically killed off). When we are born we have 25% more nuerons than when we reach adulthood. In a sort of streamlining process the brain determines which neurons have made essential connections (long term potentiation of synapses) for memory and learning; the rest are eliminated b/c otherwise they would be an energy drain on the body. Evolutionarilly this makes sense. The bottom line is that what really matters for brain cognition and memory is the degree of interconnectedness (how many other neurons is each cortex nueron connected to) and the precise web or map of connections between brain centers. Our brains are smaller in size and have less neurons than other higher apes and even our ancestor hominids; yet we overcome this with a higher level of complexity.

An analogy can be found in the size of the genetic code and proteome among species. While humans have approximately 20-25,000 genes the lowly plant Arabidopsis has 27,000 and some species of grass have 100,000 genes. And really only 1-2% of our genome actually codes for useful protein. But humans have a much larger proteome due to alternate splicing of the transcripts. Furthermore, our proteins do more as a result of immensely complex regulatory systems and enzymes. The same can be said about neurons.

Sorry for such a rambling response but I think it is important to qualify the previous comments. Evolution will rarely ever favor a greater number of anything when compared to a lesser number that can accomplish the same task.

Science is Life!
Thomas Roos

Hi Thomas,
Thank you for your always insightful comments and yes, "Science is Life!" :)