BDNF and depressive disorder: Lower thickness and volume could be a consequence of depression episodes and be related to other disturbances also seen in depression, such as inflammation (Byrne et al., 2016), lower brain-derived neurotrophic factor (BDNF) levels (Polyakova et al., 2020), or increased activity of HPA-axis related processes (Frodl and O’Keane, 2013).