Here’s some great motivation to keep up with your running program: John Medina is a developmental molecular biologist who posits that exercise is like fertilizer for the brain. From his book Brain Rules: 12 Principles for Surviving and Thriving at Work, Home, and School:

At the molecular level, early studies indicate that exercise stimulates one of the brain’s most powerful growth factors, BDNF. That stands for Brain Derived Neurotrophic Factor and it aids in the development of healthy tissue. BDNF exerts a fertilizer-like growth effect on certain neurons in the brain. The protein keeps existing neurons young and healthy, rendering them much more willing to connect with one another. It also encourages neurogenesis, the formation of new cells in the brain. The cells most sensitive to this are in the hippocampus, inside the very regions deeply involved in human cognition. Exercise increases the level of usable BDNF inside those cells.