Dkk1 molecule accumulates with age and inhibits formation of new neurons

As the elderly age, their ability to concentrate, reason, and recall facts tends to decline in part because their brains generate fewer new neurons than they did when they were younger.

http://www.news-medical.net/news/20130211/Dkk1-molecule-accumulates-with-age-and-inhibits-formation-of-new-neurons.aspx