No abstract

Handedness is the most prominent manifestation of behavioural lateralization in the human population. However, little is known about its ontogeny. This study examined the prenatal development of behavioural lateralization by observing, longitudinally, the occurrence of left- and right-arm movements in 17 human fetuses at 3-week intervals from 12 to 27 weeks gestational age. Fetuses exhibited significantly more right-arm movements than left-arm movements at every gestational age. Throughout all periods of observation, 83.3% of fetuses showed more right-arm than left-arm movements. The number of arm movements observed peaked at 15 to 18 weeks' gestation and declined rapidly in mid-gestation. The occurrence of laterality in early gestation indicates that asymmetric behaviour is probably under muscular or spinal, rather than cortical, control and points to a 'genetic' origin for such behaviour. The presence of lateralized motor behaviour in early gestation suggests it may have a potential causative role for subsequent lateralized behaviour and asymmetric brain development.

No abstract

Handedness is the most prominent manifestation of behavioural lateralization in the human population. However, little is known about its ontogeny. This study examined the prenatal development of behavioural lateralization by observing, longitudinally, the occurrence of left-and right-arm movements in 17 human fetuses at 3-week intervals from 12 to 27 weeks gestational age. Fetuses exhibited significantly more right-arm movements than leftarm movements at every gestational age. Throughout all periods of observation, 83.3% of fetuses showed more rightarm than left-arm movements. The number of arm movements observed peaked at 15 to 18 weeks' gestation and declined rapidly in mid-gestation. The occurrence of laterality in early gestation indicates that asymmetric behaviour is probably under muscular or spinal, rather than cortical, control and points to a 'genetic' origin for such behaviour. The presence of lateralized motor behaviour in early gestation suggests it may have a potential causative role for subsequent lateralized behaviour and asymmetric brain development.Lateralized behaviour is a prominent feature of human experience. One of the most obvious manifestations of lateralized behaviour is the bias toward right-handedness found in the human population.

Purpose:  The behavior of the human fetus consists of complex dynamic relationships. To date, previous methods of measuring fetal behavior have failed to capture the complexity of behavior. However, as behavior is a reflection of neural functioning it is only when quantitative assessment of this complexity has been undertaken that underlying neural organization can be elucidated. In order to reveal fundamental features of neurobehavioral organization and development, the present study provided a quantitative description of the complex spatial (sequential) and temporal (synchronous and asynchronous) patterning of behavior in the human fetus in early pregnancy. Methods:  Twenty fetuses from normal singleton pregnancies were scanned at two weekly intervals for a period of 1 h from 9 to 17 weeks' gestation. An ethogram of the timing and sequencing of right and left arm and leg movements was constructed from each videotaped session. A description of sequential and synchronous relationships between limb movements was determined using stochastic modeling. The temporal patterning of activity in arm, leg and all limb movements was examined by quantitatively determining bout criterion using survivor analysis. Results:  Fetuses exhibited within and between limb synchronous, sequential and temporal patterning from the appearance of single limb movements indicating that initial patterning may be genetically hard‐wired. Self‐organization of behavior was apparent in increasing synchronous, sequential and temporal patterning with advancing gestation. These changes coincided with rapid increases in neurulation, synaptogenesis and myelinization in early pregnancy. Different sequential, synchronous and temporal organization was found in arm and leg movements indicating differential neural control of co‐ordination in these limbs. Furthermore, lateralization and gender differences were found to be important features of behavioral organization. Conclusions:  The present study has revealed that quantitative assessment can define and measure behavioral complexity and this can elucidate fundamental neurobehavioral organization in early pregnancy.