Population dependent rearing modifies sleep and decision-making ability with the involvement of noradrenaline: A study conducted using zebrafish as a model.

Sleep is an instinct phenomenon, which affects cognitive processes including learning, memory and decision-making. Its quality, quantity and pattern vary in species through evolution. Living in groups (compared to living individually) with an increased population (as a family and a society) is an important contributing factor influencing the evolution of many behaviours. We hypothesized that rearing (upbringing) among many individuals (as compared to in isolation) and socialization might have influenced the quality, quantity and pattern of optimum sleep (a fundamental behaviour), which in turn affected animal behaviour(s) including learning and decision-making. To confirm, using zebrafish (which expresses shoaling) as a model we evaluated their sleep pattern as well as decision-making ability when reared post-birth under isolated (individually) or populated conditions. We observed that zebrafish reared under isolation affected sleep and compromised their decision-making ability when exposed to predator, which otherwise threatens their survivability. Also, the adverse effects of isolation were improved when the zebrafish were either reared in shoal or, by α1-adrenoceptor antagonist, prazosin, suggesting the role of noradrenaline in mediating the responses. Based on our findings we propose that one of the physiological benefits of living in a society is better (optimum) sleep health, which in turn helps with quality living.