Starting from a stem cell and maturing over three weeks into a fully functional neuron that begins to link with other neurons, neurogenesis offsets neuropathic losses caused by age, illness, or injury. The process continues throughout life, but ebbs and flows, depending on several factors.
Neurogenesis requires just-right challenges both to cognitive capacity and to aerobic capacity, within the context of good control of stress. Neurogenesis is occurring constantly, even now as you read this. The ebb and flow of neurogenesis changes throughout the day and continues as you sleep.
Because of the positive effect of aerobic activity on both stress and neurogenesis, I encourage my clients and students to integrate high-demand learning activities with aerobic activities. My wife Mary and I do that ourselves. For example, I often listen to podcast lectures on interesting but challenging subjects while I ride my bicycle on the Katy Trail. Mary reads while on the treadmill. When studying for important examinations, I encourage my students to audio record study guides and listen to them while walking. Rather than sitting and studying, walking and reading or listening is certainly more effective.
An excellent popular press treatment of this topic and its importance in education is Spark: The Revolutionary New Science of Exercise and the Brain (2008) by John J. Ratey and Eric Hagerman. The authors describe an educational program in Illinois that integrates physical education with demanding academic education. High school students are encouraged to participate in aerobic activities in zero-period and take difficult courses like calculus or physics or chemistry in the first half of the morning. The results are impressive, presented by the authors with adequate research references.