BDNF transcripts containing Bdnf exon-IV and -VI are particularly interesting as their translation is directly or indirectly regulated by changes in neuronal activity (Hong et al., 2008; West et al., 2014; Tuvikene et al., 2016) and their dysregulation is linked to various brain pathologies related to sleep, loss of fear memory (Hill et al., 2016), and depression (Marosi and Mattson, 2014). Here, BDNF is linked to depressive disorder.