Researchers at the University of Toronto, using two groups of mice, places both groups in a stressful situation and returned them to housing either with or with out a running wheel. When both groups returned to the familiar stressful environment at one day and one week, both exhibited fear. The running group however, lost the fear memory of the environment after two weeks while the sedentary group remained fearful.
While neurogenesis from running is a plus among other body changes, the researchers also spawned neurogenesis with drugs and noted the same loss of memory. When neurogenesis was inhibited in exercising mice and infant mice, where neurogenesis is abundant naturally, it was noted both remembered better. So does this mean runner are forgetful? Absolutely not! Neurogenesis is important in adults for learning new things and letting go of information not needed, such as what was in the fridge a month ago versus whether you have apples for the kids lunch tomorrow.