You'll recall that stem cells transplanted into the heart spur regeneration of damage, such as that caused by a stroke, through releasing growth factors and other signaling chemicals. Researchers have now demonstrated that a similar process can be made to happen in the brain:
Mice genetically engineered to have Alzheimer's performed markedly better on memory tests a month after mouse neural stem cells were injected into their brains. The stem cells secreted a protein that created more neural connections, improving cognitive function.
the stem cells were found to have secreted a protein called brain-derived neurotrophic factor, or BDNF. This caused existing tissue to sprout new neurites, strengthening and increasing the number of connections between neurons. When the team selectively reduced BDNF from the stem cells, the benefit was lost, providing strong evidence that BDNF is critical to the effect of stem cells on memory and neuronal function.
"If you look at Alzheimer's, it's not the plaques and tangles that correlate best with dementia; it's the loss of synapses - connections between neurons," Blurton-Jones said. "The neural stem cells were helping the brain form new synapses and nursing the injured neurons back to health."
This work is, obviously, performed in the context of trying to do something about Alzheimer's - if only by spurring the body to greater feats of ongoing repair rather than by altering the conditions that are causing damage - but I'm sure you can see the potential for more general application. Memory declines in everyone with age, and some fraction of that process is caused by damage to the same synaptic connections as are devastated by Alzheimer's. The memories are still encoded in there somewhere, but the brain has lost the connections needed to retrieve them, and in its default state of operation will not fix this situation.
If we can spur regeneration in a worn heart, then why not in a worn brain?
Those folk interested in human enhancement should also be pondering this research with some interest. What beneficial effects could be gained for memory and other aspects of the brain's performance in healthy people through accelerated growth of neural connections?