 using real - time gene expression imaging and behavioral analysis , we found that perinatal photoperiod has lasting effects on the circadian rhythms expressed by clock neurons as well as on mouse behavior , and sets the responsiveness of the biological clock to subsequent changes in photoperiod . 
 these developmental gene x environment interactions tune circadian clock responses to subsequent seasonal photoperiods and may contribute to the influence of season on neurobehavioral disorders in humans . 
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