Adult brain
Animal studies
ECS involvement
In adult mice, voluntary exercise induces hippocampal progenitor cell proliferation in a CB1-dependent way (Hill et al., 2010).

Plant cannabinoids
In adult mice, the effect of THC-rich (41.2%) or CBD-rich (38.8%) diet on spatial learning and adult neurogenesis was tested. CBD did not impair learning but increased adult neurogenesis, whereas THC reduced learning without affecting adult neurogenesis. The neurogenic effect of CBD was dependent on the CB1 receptor, which is expressed over the whole dentate gyrus. Similarly, the neurogenic effect of environmental enrichment and voluntary wheel running depends on the presence of the CB1 receptor. In the absence of CB1 receptors, cell proliferation was increased and neuronal differentiation reduced (Wolf et al., 2010).

Human studies
Plant cannabinoids
In a longitudinal psychological and MRI study of heavy cannabis users (mean age 21 years, range 18-24 years smoking on average 5 days/week) and 23 matched non-cannabis using healthy controls, heavy cannabis use did not affect hippocampal neuroanatomical changes in early adulthood. This contrasts with prior evidence on alterations in this region in samples of older adult cannabis users. In young adults using cannabis at this level, cannabis use may not be heavy enough to affect hippocampal neuroanatomy (Koenders et al., 2017).

Literature:
Hill, M.N., Titterness, A.K., Morrish, A.C., Carrier, E.J., Lee, T.T.-Y., Gil-Mohapel, J., Gorzalka, B.B., Hillard, C.J., and Christie, B.R. (2010). Endogenous cannabinoid signaling is required for voluntary exercise-induced enhancement of progenitor cell proliferation in the hippocampus. Hippocampus 20, 513–523.
Koenders, L., Lorenzetti, V., de Haan, L., Suo, C., Vingerhoets, W., van den Brink, W., Wiers, R.W., Meijer, C.J., Machielsen, M., Goudriaan, A.E., et al. (2017). Longitudinal study of hippocampal volumes in heavy cannabis users. J. Psychopharmacol. Oxf. Engl. 269881117718380.
Wolf, S.A., Bick-Sander, A., Fabel, K., Leal-Galicia, P., Tauber, S., Ramirez-Rodriguez, G., Müller, A., Melnik, A., Waltinger, T.P., Ullrich, O., et al. (2010). cannabinoid receptor CB1 mediates baseline and activity-induced survival of new neurons in adult hippocampal neurogenesis. Cell Commun. Signal. CCS 8, 12.