S100B and depressive symptom measurement: Although S100β has been investigated as a biomarker (in serum and CSF) in studies of head injury, depression, and neurodegenerative diseases such as Alzheimer's disease (Chaves et al., 2010, Peskind et al., 2001, Polyakova et al., 2015), the neurostructural correlates of S100β and its longitudinal trajectories in nonpathological aging are underinvestigated.