Now researchers at Penn State may have found a way to boost the brain's regenerative abilities, using certain molecules to convert neighboring cells into new neurons. The technique could eventually lead to pills that treat brain injuries, stroke or Alzheimer's disease.

Most cells in the body can patch up damage by dividing to create new versions of themselves. But neurons lack this ability, so once they're damaged through illness or injury, there's not much that can be done. Worse still, in an overzealous attempt to protect the injured site, glial cells form scar tissue around damaged brain regions, which can reduce what little neuron growth there might be and prevent neurons from effectively communicating with each other.