Summary: A new study finds that the preference for using one hand over the other is already established by the 18th week of pregnancy.
Source: SISSA
Are people born right- or left-handed, or do they become so? Researchers led by Valentina Parma of the International School for Advanced Studies (SISSA) in Trieste and Professor Umberto Castiello of the University of Padua report in Scientific Reports that hand preference is already evident by the 18th week of gestation.
By analysing specific fetal hand movements captured with 4D ultrasound, the research team was able to predict the later manual dominance of the same children at age nine with high accuracy. This kinematic approach not only reveals advanced prenatal motor specialization but also suggests potential clinical applications for early detection of conditions associated with atypical brain asymmetry.
Infants take weeks to begin grasping objects and several years to develop drawing and writing skills that reveal a hand preference. However, this study demonstrates that the foundations of handedness form well before birth and that the motor system in utero is more refined than previously assumed.
The study followed 29 fetuses whose arm and hand movements were recorded during short 20-minute 4D ultrasound sessions at approximately the 14th, 18th, and 22nd weeks of gestation. Researchers examined three kinds of reaches: two precision-targeted movements aimed toward the eyes and the mouth, and one reaching toward the uterine wall used as a control. The analysis focused on movement time and deceleration patterns.
Results show that from the 18th week of gestation, fetuses performed precision reaches faster with the hand that later became their preferred hand. Using either movement time or deceleration metrics, the researchers could classify fetal handedness with an accuracy ranging from 89% to 100%, depending on the parameter and gestational age. Postnatal follow-up at age nine confirmed the prenatal predictions, with population proportions of right- and left-handedness similar to expected norms (about 86% right-handed in this sample).
The study was a collaboration among SISSA, the Integrated University Hospital of Trieste (ASUITs), Ab.Acus (Milan), the University of Padua, and the Lincean Centre Beniamino Segre (Rome). Its findings highlight the early emergence of lateralized motor control and suggest that routine ultrasonography—when combined with quantitative kinematic analysis—could become a noninvasive tool to investigate prenatal brain development.
Because handedness is linked to the relative dominance of one cerebral hemisphere, alterations in this asymmetry have been associated with several neurodevelopmental and psychiatric conditions, including autism spectrum disorders, schizophrenia, and depression. Identifying reliable prenatal markers of lateralization could therefore open avenues for earlier monitoring and intervention strategies aimed at mitigating developmental risks.
Source: Chiara Saviane – SISSA
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is in the public domain.
Original Research: “The origin of human handedness and its role in pre-birth motor control” by Valentina Parma, Romain Brasselet, Stefania Zoia, Maria Bulgheroni & Umberto Castiello. Scientific Reports. Published online December 1, 2017. DOI: 10.1038/s41598-017-16827-y.
SISSA. “Right or Left Handed? Handedness Is Determined During Gestation.” NeuroscienceNews. December 4, 2017.
Abstract
The origin of human handedness and its role in pre-birth motor control
Most humans are right-handed, yet the timing and mechanisms by which this bias develops remain unclear. This study proposes a fetal kinematic approach that links prenatal motor behavior to postnatal handedness, accurately predicting manual dominance from the 18th gestational week. Researchers recorded different fetal arm movements during 4D ultrasonography and later classified the same children’s hand dominance at age nine. Both fetuses who became right-handed and those who became left-handed reached precision targets (eyes and mouth) more quickly with the hand that eventually proved dominant. Classification based on movement times or deceleration measures yielded accuracy between 89% and 100% from gestational week 18 onward. These findings demonstrate that lateralized motor control is present prenatally and indicate that standard ultrasonography, combined with quantitative analysis, has untapped potential for advancing our understanding of early human development and identifying markers of atypical brain lateralization.
“The origin of human handedness and its role in pre-birth motor control” by Valentina Parma, Romain Brasselet, Stefania Zoia, Maria Bulgheroni & Umberto Castiello. Scientific Reports. Published online December 1, 2017. DOI: 10.1038/s41598-017-16827-y.