It is unclear why infants in the Arm
It is unclear why infants in the Arm condition showed suppression over the left arm area, while infants in the Leg condition showed suppression over the right arm area. One possible explanation could be that infants in the Leg condition were predominantly left-handed while infants in the Arm condition where predominantly right-handed. However, there were no significant differences in handedness between the two groups, X2 (1, N=20)=1.485, p=.223, as assessed by the proportion of left-handed vs. right-handed reaches during the execution phase of the study. Alternatively, the difference in lateralisation between the Arm and Leg condition could be due to difference in the proportion of left- and right-effector actions that was observed. Indeed, even though left-ward and right-ward stimuli were presented randomly, by chance more trials with leftward movements (performed by the right leg) were included in the Leg condition, and more trials with rightward actions (performed by the left arm) where included in the Arm condition, F(1,25)=3.892, p=.060. This interpretation is consistent with previous studies that suggest that when actions are observed from a third-person perspective, there is more activation over the ipsilateral motor cortex, i.e. observing a right-handed action increases activity in the right hemisphere (e.g. Shmuelof and Zohary, 2008; Vingerhoets et al., 2012).
Conclusions This study demonstrated that 12-month-old infants, like adults, show somatotopically organised sensorimotor Neuronal Signaling Library activation during action execution. Adults also showed somatotopically-organised activation when they observed goal-directed arm and leg actions. In contrast, infants did not show somatotopically organised activation during action observation, but instead activated the arm areas when observing both arm and leg actions. These findings suggest that infants might have activated the motor programme of the effector that they more commonly use to displace objects (i.e. the arm area) during the observation of the kicking actions. Thus, although the somatotopic arrangement of the sensorimotor cortex for action execution seems to be in place in the first year of life, the somatotopic organisation of sensorimotor cortex activation during action observation may depend on infants’ understanding of the action goal and their expectations about how this goal will be achieved. Future studies are needed to investigate whether infants indeed flexibly employ their motor system during action observation to generate predictions about how the action will unfold.
Conflict of interest
Acknowledgements We are very grateful to all the infants and parents who participated in this study. This work has been supported by EC grant MC-ITN-264301 (TRACKDEV) to C. de Klerk and a Wellcome Trust Research Career Development Fellowship (088427/Z/09/Z) awarded to V. Southgate. M.H. Johnson is supported by a UK Medical Research Council Programme Grant (MR/K021389/1). We would like to thank E. Parise, L. Filippin, & G. Csibra for creating the analysis software.
Adolescence is a time of dramatic changes in brain, behavioral, and psychological functioning. A key change during this phase of development is a steep rise in risk taking. Compared with younger children, adolescents tend to engage in a variety of risky behaviors, such as reckless driving, substance use, and unprotected sexual activity (), resulting in significant increases in morbidity and mortality rates in an otherwise healthy developmental period (e.g., ). It is therefore crucial to identify protective factors that can prevent these upward trajectories of risk-taking behavior. Given the important role of family relationships in adolescents’ adjustment (), the current study aimed to examine how changes in family relationships during the teen years influence trajectories of adolescent risk taking through changes in neural reactivity.