It is now widely accepted that new neurons are in fact generated in adult brain. What is not understood is how those newborn brain cells, once they emerge from neural stem cells, muscle their way into networks already established by more mature nerve cells.
In a study published in Nature Neuroscience, Fred H. Gage, professor in the Laboratory of Genetics, showed that the newcomers jump right into the fray and aren't shy about reaching out to the mature nerve cells, or neurons, that have already established complex brain circuits.
Knowing how young neurons integrate into mature circuits is critical if neural stem cells are ever to be used to replace damaged neurons in neurodegenerative conditions such as Alzheimer's or Parkinson's disease.
To follow the social dynamics of young neurons, Gage and postdoctoral fellow Nicolas Toni labeled neural stem cells in adult mouse brain with a fluorescent dye so they could literally watch how they behaved on the brain playground as they developed into full-fledged neurons.
Neurons contact each other at junctions called synapses. Typical neurons sport about 7,000 synapses through which they touch roughly 1,000 other cells. The researchers found that immature neurons assertively put out tiny feelers at synaptic "cliques" consisting of more mature cells.
The investigators found that in time many of those feelers actually started to monopolize synaptic connections. Interestingly, in mice living in bare cages, only about half successfully integrated into those networks.
But in mice living in enriched environments filled with running wheels or colored tunnels, the number of young neurons successfully hooking up with existing networks rose to 80 percent.
For neuroscientists, these studies demonstrate how newborn mouse neurons insinuate themselves into pre-existing brain networks. However, for the rest of us, these observations suggest that using one's brain cells is the best way to maximize the brain's regenerative capacity.