Suggested explanations for the associations between SOB and this wide array of psychological and physiological phenotypes include variations in infectious disease exposure, nutrition, temperature, maternal hormones, maternal egg quality, birth complications and photoperiod [6], [17], [29]. Photoperiod is perhaps the best explored and supported hypothesis as to why SOB bears an association with risky behaviors. It is hypothesized that variation in daylight during gestation or perinatally impacts the dopamine-melatonin balance regulating circadian and seasonal rhythms and serotonin turnover [24], [28], [30], [31]. The serotonin metabolite, 5-hydroxyindoleacetic acid (5-HIAA) and dopamine metabolite, homovanillic acid (HVA) have both been shown to vary with SOB [31]. Consistent with an effect of photoperiod on risky-behaviors, HVA increases with increasing novelty seeking and dopamine turnover reaches its extremes with the solstices [30]. A somewhat different type of risky behavior, suicide, also seems to be inter-related with SOB and 5-HIAA [30].
