association between the brain laterality, gender and birth season

objective: in recent years different hypotheses with respect to the formation of cerebral laterality were proposed. some of the researchers claim that cerebral dominance and laterality are determined by genetic factors, just as the case with eye color and blood type. however, another group states that in addition to genetic factors, environmental factors, too, have a remarkable role in hemispheric dominance and lateral dominance. hence, the present research was designed to study the relationship between 1- lateral dominance and birth season 2- lateral dominance and gender. method: 1355(girls and boys) fifth graders from the 19 educational regions of tehran were selected using multi stage cluster sampling in the 2003-2004 school year. coren lateral preference and personal information questionnaire were applied. results: the following results were obtained at the level of ل=0.05 and probability of 95%. there were significant association between lateral dominance and birth season, between lateral dominance and gender, between ambidexterity and birth season, between non-genetic sinistrality and birth season, between dexterality and gender, between ambidexterity and gender, between genetic sinistrality and gender. there were no significant associations between dexterality and birth season, genetic sinistrality and birth season, between non-genetic sinistrality and gender. conclusion: the gestational environmental factors can have significant effect on the formation of lateral dominance and cerebral laterality.