BDNF and insomnia: BDNF mRNA pre- and post-ratio was also assessed, as it might reflect the dynamics of changes better than simple difference between relative mRNA expression level, taking into account variability in BDNF expression levels among individuals, additionally modified by physical activity, circadian rhythm, sex, etc. The discussed parameter was correlated negatively with poor sleep quality and severity of insomnia symptoms, but positively with sleep efficiency.