Figure 2. Frame of reference and measurement unit
used to refer the examined body position
Here is another cool article from PLoS ONE - this one is on the ontogeny of social interaction in humans. We are wired from the very beginning to be socially interactive beings. In fact, as the sad cases of feral children have demonstrated, once a certain window of development has closed, if there has not been adequate social interaction, development will generally be irreversibly stunted.
To my knowledge, there have been few (if any) studies on social interaction in utero, but how better to do so than with twins? Very cool.
(2010) Wired to be social: The ontogeny of human interaction. PLoS ONE; 5(10): e13199. doi:10.1371/journal.pone.0013199
Approaching this as a twin study seems unique to me for some reason - so I want to offer the introduction to the article to maybe whet your appetite a little for this article - interesting stuff for sure.
Newborns come into the world wired to socially interact. Is a propensity to socially oriented action already present before birth? Twin pregnancies provide a unique opportunity to investigate the social pre-wiring hypothesis. Although various types of inter-twins contact have been demonstrated starting from the 11th week of gestation, no study has so far investigated the critical question whether intra-pair contact is the result of motor planning rather then the accidental outcome of spatial proximity.
Kinematic profiles of movements in five pairs of twin foetuses were studied by using four-dimensional ultrasonography during two separate recording sessions carried out at the 14th and 18th week of gestation. We demonstrate that by the 14th week of gestation twin foetuses do not only display movements directed towards the uterine wall and self-directed movements, but also movements specifically aimed at the co-twin, the proportion of which increases between the 14th and 18th gestational week. Kinematic analysis revealed that movement duration was longer and deceleration time was prolonged for other-directed movements compared to movements directed towards the uterine wall. Similar kinematic profiles were observed for movements directed towards the co-twin and self-directed movements aimed at the eye-region, i.e. the most delicate region of the body.
We conclude that performance of movements towards the co-twin is not accidental: already starting from the 14th week of gestation twin foetuses execute movements specifically aimed at the co-twin.
You can read the whole article online or download the PDF - loving the open access.
One-to-one interactions are the cradle of social cognition. Infants do not develop social understanding by merely watching other people at a distance. Rather, they learn by engaging in reciprocal exchanges with others –. Even hours after birth, newborns have been found to show preparedness for social interaction that, among other things, is expressed in their imitation of facial gestures , . Altogether such evidence indicates that newborns come into the world wired to socially interact. But, is a propensity to interact with others demonstrable before birth?
Twin pregnancies provide a unique opportunity to investigate the social pre-wiring hypothesis. Unlike ordinary siblings, twins share a most important environment – the uterus. If a predisposition towards social interaction is present before birth, one may expect twin foetuses to engage in some form of interaction. Although inter-twin contact has been demonstrated starting from the 11th week of gestation , no study has so far investigated the critical question of whether twin foetuses plan and execute movements directed towards each other. Put differently, whether intra-pair contact is the result of motor planning rather then the accidental outcome of spatial proximity. Whilst twins are initially too distant and their movements too weak to reach one another, with advancing gestational age contact between them becomes possible and soon almost inevitable. From the 11th week onwards, different patterns of inter-twin contact such as head to head, head to arm and arm to head contact are observed . It is, however, between the 15th and 22nd week that intra-pair contact becomes a constant and increasing feature of all twin pregnancies –.
Whereas inter-twin contact is well established, little is known about the organization of movements bringing twins in touch. The motor behaviour of foetuses has traditionally been described in terms of reflexes rather than actions . Although reflexes serve important functions, they are stereotyped, elicited and once launched run their predetermined course. This signifies, for instance, that reflexes are not goal directed, are not subject to learning and do not adjust to future states in a prospective fashion . In contrast with the idea that foetuses only display reflexes, Zoia and colleagues  recently demonstrated kinematic adaptation to the somatosensory properties of the target in 22-week-old single foetuses. Three types of hand movements were isolated and subsequently analyzed: movements ending at contact of fingers with the mouth, movements ending at contact of fingers with the eye, and movements directed away from the body, towards the uterine wall. The results showed that the spatial and temporal characteristics of foetal movements were by no means uncoordinated, but depended on the goal of the different motor acts, suggesting a surprisingly advanced level of motor planning.
Along these lines it might be advanced that, if foetuses plan movements towards the co-twin, then a specific kinematic pattern related to the social end goal of the movement might be expected. Social actions differ from those used in negotiating the physical environment in many important aspects. The fact that one's own actions affect the behaviour of the person towards whom they are directed creates new action problems, which are not encountered when the actions are directed towards objects , . In adults, indeed, specific kinematic profiles have been shown to differentiate social actions from actions performed in isolation –. In particular, kinematics for arm-actions aimed at a social target have shown to be different from those of similar movements ending on a physical object . If inter-twin contact reflects motor planning, then differences in kinematics might be expected between movements directed towards the co-twin and movements directed towards one's own body or the uterine wall. Here we tested this hypothesis by investigating the kinematics of movement in five pairs of twin foetuses. Arm movements were studied using four-dimensional ultrasonography (4D-US) during two separate recording sessions carried out at the 14th and 18th week of gestation. Foetuses were videotaped for 20 minutes in each session and the video recordings were then digitized with purposely-developed software for off-line kinematic analysis. Three main categories of arm movements were isolated and subsequently analyzed: i) self-directed movements, including hand to mouth and hand to eye movements; ii) non-targeted movements, encompassing movements directed towards the uterine wall; and iii) other-directed movements, including hand to the back and hand to the head of the co-twin. We employed three analyses in order to explore whether the organization of foetal movements differed depending on the nature of the executed movement. The first analysis compared the incidence of each type of movement at the two gestational periods. The trend in the incidence of motor activities is considered to directly reflect developmental and maturational processes of the foetal central nervous system –. If specific movement patterns underlie other-directed movements, the trend in the incidence of other-directed movements might be expected to be dissociated from that of movements directed towards one's own body or outer-directed movements. The second analysis compared the kinematic profiles of the different categories of movements. Based on the social pre-wiring hypothesis, we predicted that the kinematic pattern of other-directed movements would be different from the kinematic pattern of those movements directed towards one's own body or outer-directed movements. Finally, the third analysis employed a comparison of self-directed movements towards the mouth and the eye region, and movements directed towards the sibling. Kinematic adaptation to the properties of the target has been reported in single foetuses by the 22nd week of gestation . Because the presence of a co-twin may facilitate or prime an anticipated propensity to act, signs of kinematic differentiation between hand to mouth and hand to eye movements might be expected to appear earlier in twin foetuses.