Abstrakti

The known bias in human hand usage is fascinating, but the origins of handedness remain largely unknown, with about 10% of people being left-handed. Studies however point to early development in handedness formation. As a developmental approach, we asked whether perinatal covariates have an association with left-handedness. Such associations have been reported, although not without controversies: Prenatal ultrasound associated with increased proportion of left-handedness or twins having an increased proportion of left-handedness. Study I of the thesis addressed the ultrasound hypothesis. Studies II and III investigated twins and triplets with perinatal correlates other than ultrasound: twin status, birthweight, gestational age, Apgar scores, birth order and some others. Among triplets, we tested the motor control development of the left- vs right-handed. A dataset of singletons (N=4150) was used for showing that ultrasound was not associated with left-handedness. Twins (N=8786) and singletons (N=5892) were compared in study II. Based on earlier findings on very-low-birthweight singletons we expected birthweight to be a correlate. Many of our correlates were twin-specific (birthweight smaller than in singletons etc). Using them we tried to address risks of multiple births. Twins eventually were slightly more often left-handed than singletons in Study II, and the difference was explained by twin-specific correlates. After Study II we proceeded to investigate triplets in Study III. We had two datasets: Dutch (N=947 triplet individuals) and Japanese (N=1305 triplet individuals). These were used exclusively, without comparing to singletons and birthweight was used as continuous (in kg). The two triplet datasets consistently showed that left-handedness was associated with lower birthweight (Japanese OR = 0.50, 95% CI 0.31 to 0.78, p <0.01; Dutch OR = 0.62, 95% CI 0.43 to 0.90, p = 0.01). The left-handed triplets showed delayed motoric development in comparison to the right-handed, with this delay being totally explained in models by the lower birthweight of the left-handed. Some handedness theories have tried to explain excess left-handedness by perinatal mechanisms so far unconfirmed. Future research of mechanisms will thus be challenging with the small associations found herein. The mystery of handedness formation mostly remains, but we could demonstrate an involvement of developmental factors in handedness formation.
Alkuperäiskielienglanti
JulkaisupaikkaHelsinki
Kustantaja
Painoksen ISBN978-951-51-6177-2
Sähköinen ISBN978-951-51-6178-9
TilaJulkaistu - 2020
OKM-julkaisutyyppiG5 Tohtorinväitöskirja (artikkeli)

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