The Goal of New Neurons in an Old Brain
It used to be the common wisdom that adult brains never generated new neurons - that you had what you started with, and it was irreversibly downhill from there. Fortunately this turned out to be far from the case. The thinking now is that since mechanisms exist to generate new neurons, we should find out whether these mechanisms be enhanced and manipulated to regenerate at least some of the damage of aging - exactly the same model that drives stem cell researchers focused on other organs. But this is all some years behind other branches of regenerative medicine, and likely a much more challenging goal than repair of a heart or a liver. Researchers are still mapping out the basics with the new tools of modern biotechnology:
One of the most remarkable, and unexpected, discoveries in brain science over the past two decades was that, contrary to a century of neuroscience dogma, the brain can generate new neurons throughout adulthood. Not only can, but does, and prolifically: thousands of new neurons are created each day in several regions of the brain....
But it is not enough for such neurons merely to be formed. To play their part in memory storage, they must send out processes - dendrites to receive information, and axons to pass it along - to other brain regions, and become integrated into pre-existing neuronal circuitry. A new study by Sebastian Jessberger et al. shows that a protein called cdk5 plays a pivotal role in this integration.
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Whatever the precise mechanism, the discovery of cdk5's role in guiding new neurons to their proper place improves the understanding of neurogenesis in the adult hippocampus, a process that is believed to be aberrant in cognitive aging, Alzheimer disease, and some forms of epilepsy and depression. In addition, it may suggest ways to improve prospects for neural transplantation for neurodegenerative diseases such as Parkinson disease.
The clinical benefits of experimental transplants have been inconsistent and largely disappointing to date, with most transplanted neurons unable to integrate into existing brain circuits. A better understanding of what neurons need to find their way and fit into their new surroundings may increase the chances of success for this treatment.
Progess continues, slow and steady.
Forgive my ignorance, but how does this kind of thing fit in with SENS proposed timeframe for success of 20-30 years in humans? Won't these issues have to be worked out before we can effectively adress the problem of aging in a meaningful way? How can we reasonably speculate about such a timetable when we still seem to know so little about brain regeneration?
The SENS approach is to sidestep much of our ignorance. We know the brain works just fine in our 30s, therefore we identify the biochemical differences between a young and old brain and work to remove them. Those differences seem to involve more intracellular and extracellular aggregates in the brain than in other organs - or perhaps its just more sensitive to the presence of different types of aggregates than other tissues.
You're right in that there's a lot of work left to do, but the list of root causes of aging put forward in SENS applies just as much to the brain as to other organs.