Of note, an association between the PSS and BDNF was only observed in subjects with no insomnia (rp = −0.511, p = 0.013) compared to subjects with sub threshold (rp = 0.069, p = 0.814) or clinical insomnia (rp = 0.199, p = 0.608) (Fig. 2). Here, BDNF is linked to insomnia.