Although various studies have suggested that learning increases neurogenesis in the adult dentate gyrus (Gould et al., 1999b; Leuner et al., 2004; 2006; Epp et al., 2010), when learning is difficult or stressful, it can have a negative impact on cell proliferation (Aztiria et al., 2007). Stress related to using novel testing paradigms decreases cell proliferation even though learning occurs (Ehninger & Kempermann, 2006). Step-wise increases in task difficulty do not change cell proliferation, but decrease survival of new neurons in the adult rat dentate gyrus (Epp et al., 2010).
