These two effects lead to a net increase and stabilization in spine density that would possibly allow for an increased cognitive vigilance (and thus possibly also for resilience to further neuronal insults), making it seem plausible that lowered BDNF levels induce a state of increased vulnerability to stress and stress-related disorders such as MDD, given the assessed importance of BDNF in relation to psychiatric disorders47. Here, BDNF is linked to major depressive disorder.