Many diseases of the central nervous system involve the death of neurons—so, theoretically, the replacement of dead cells should improve symptoms of degenerative disorders such as Parkinson's, Huntington's, amyotrophic lateral sclerosis (ALS) and Alzheimer's, as well as stroke and brain tumors. Stem cell therapy may do just that even though evidence of its effectiveness is mixed.

In any cell transplant procedure, the host organ—in this case, the brain—may reject its new additions. Further, it is unclear whether grafted cells can truly integrate into complex neural circuitry. Finally, current procedures require invasive surgical implantation, which can be expensive and risky. The surgery can cause neural inflammation, and the implanted cells may quickly die.

Intranasal administration may address at least some of these issues. Most important, it eliminates the need for surgery. Further, some research suggests that stem cells delivered intranasally are “smart”—they do not spread through the brain indiscriminately but instead target damaged cells.

Although it is difficult to predict when medical practice will adopt stem cell therapy for the brain, animal studies have produced some promising results. In a rat model of Parkinson's, for example, treatment with intranasal stem cells appeared to improve motor function and slow the neurological deterioration associated with the disease.