AKT1 and major depressive disorder: Most importantly, Reif et al. found that the neural stem cell proliferation required for adult neurogenesis is reduced in schizophrenia, but not in major depression.61 The PI3K/Akt pathway is involved in schizophrenia and mediates the effects of stress, hormones and growth factors on SY plasticity and adult neurogenesis (that is, on neuronal and SY repair)34, 35 (see Figure 2).