Final Report Summary - ODMIR (The origins and development of the human mirror neuron system.)
The project deals with an issue, that of the development of mirror mechanisms in humans, that is a timely and up-to-date scientific topic. Despite the growing body of evidence detailing the existence of a mirror neuron system in the adult brain, the question of how this system emerges during development remains almost unsolved. Yet, a better understanding of the development of the mirror mechanisms would be of considerable theoretical and clinical importance and of particular relevance in relation to the comprehension of how the capacity to understand the other minds emerges. This project provides the first neurophysiological evidence that the infant’s motor system is recruited and selectively modulated during the observation of goal-directed actions performed by other individuals. Specifically, we demonstrated that the motor system of 6-month-old infants but not 3-month-old infants dynamically replicates the observed actions, as if the latter are executed by the infant him/herself. Also, to directly investigate the early development of the understanding of emotions expressed by other individuals, we measured facial mimicry reactions to static images of female faces and bodies expressing happiness, anger, fear, and neutral emotional states in 3-year-old children. Results demonstrated that observing others' happy faces lead to increased activation of the muscle involved in the expression of happiness, along with decreased activation of the muscle used to express fear. Observing angry faces elicited the opposite pattern of activation. The current project is the first to use EMG recordings with infants and 3-year-old children.
Obtained evidence also shows that newborns discriminate between a hand movement of their own motor repertoire, and a similar movement which violates the constrains of human anatomy. Newborns looked longer at an impossible than at a possible hand movement. Also, their preference for the hand movement never experienced before suggests that the possible movement was recognized as familiar. This indicates that mechanisms linking motor representations of movements, which are part of the newborn’s motor repertoire, and their visual representations are in place already at birth. Moreover, 9-month-old infants’ motor grasping experience acquired during post-natal life modulates infants’ visual preferences, driving a preferential response toward the novel unexperienced impossible pincer grip hand movement. We also investigated infants’ ERP responses triggered by visually presented human gestures and human action sounds. Results demonstrated that 6-month-olds rely on biomechanical properties of human hand movements to orient attention in their visual environment, and 7-month-olds process human action sounds as a distinct category of sounds compared to human vocalizations, environmental and mechanical sounds. Finally, we explored the developmental origins of visuo-tactile mirroring mechanisms, by investigating the developmental origins of the ability to visually recognize touching gestures involving others. Three-month-olds, but not newborns, could differentiate between the touching vs no-touching gesture. These results highlight the importance of sensorimotor and visual experience in infants' ability to process the visual information associated with touch.
Obtained evidence also shows that newborns discriminate between a hand movement of their own motor repertoire, and a similar movement which violates the constrains of human anatomy. Newborns looked longer at an impossible than at a possible hand movement. Also, their preference for the hand movement never experienced before suggests that the possible movement was recognized as familiar. This indicates that mechanisms linking motor representations of movements, which are part of the newborn’s motor repertoire, and their visual representations are in place already at birth. Moreover, 9-month-old infants’ motor grasping experience acquired during post-natal life modulates infants’ visual preferences, driving a preferential response toward the novel unexperienced impossible pincer grip hand movement. We also investigated infants’ ERP responses triggered by visually presented human gestures and human action sounds. Results demonstrated that 6-month-olds rely on biomechanical properties of human hand movements to orient attention in their visual environment, and 7-month-olds process human action sounds as a distinct category of sounds compared to human vocalizations, environmental and mechanical sounds. Finally, we explored the developmental origins of visuo-tactile mirroring mechanisms, by investigating the developmental origins of the ability to visually recognize touching gestures involving others. Three-month-olds, but not newborns, could differentiate between the touching vs no-touching gesture. These results highlight the importance of sensorimotor and visual experience in infants' ability to process the visual information associated with touch.