What happens in a baby’s brain when they see themselves in the mirror?

How do we learn, from such an early age, to imitate expressions and recognise emotions? Long before they can speak, babies are already immersed in a world of faces, where every smile or frown can contribute to the development of social life. A recent study investigated whether exposure to one’s own reflection influences the development of facial imitation – a process associated with empathy and emotional recognition. The research is based on the hypothesis that the associations between “seeing” and “doing” may not be entirely innate but are also shaped by sensorimotor experience throughout development.

To test this hypothesis, fifty-two babies, around four months old, took part in a study led by Carina de Klerk at the University of Essex. Over two weeks, one group had daily contact with a small mirror incorporated into a toy, while the other group used the same object but without access to the mirror. Before and after this period, the babies watched videos of other babies displaying facial expressions, while researchers simultaneously recorded brain activity using electroencephalography (EEG) and facial muscle activity using electromyography (EMG), allowing neural and behavioural responses to be assessed separately.

The results showed that mirror experience had an impact at the neural level. Babies exposed to their own reflection showed changes in brain activity: when observing the faces of other babies, there was greater activation in sensorimotor regions involved in linking perception and action. This effect was particularly evident in the right hemisphere, in an area associated with face representation, suggesting that the experience of observing one’s own movements may strengthen neural circuits involved in perceiving others’ actions.

However, these changes did not translate into behavioural differences. The researchers found no evidence of increased facial imitation, measured via EMG, in the babies who had contact with the mirror. Thus, although the brain showed signs of modulation, the babies did not become more likely to reproduce the expressions they observed. This result suggests that neural changes may precede behavioural manifestations, or that the exposure period (two weeks) may not have been sufficient to produce measurable effects at the behavioural level.

Taken together, the study suggests that simple experiences, such as seeing one’s own reflection, can influence the social brain at an early stage. Still, important questions remain: how long is needed for these changes to translate into behaviour? And what role do other interactions, such as imitation by caregivers, play? These findings reinforce the idea that the infant brain is highly sensitive to experience from very early on, helping to clarify how the foundations of social interaction emerge. This study is part of project 134/20 - Copy me, copy you: Investigating the development of facial mimicry, supported by Fundação Bial, and was published in the journal Developmental Science in the article Two Weeks of Mirror Exposure Enhances Sensorimotor Cortex Activation but not Facial Mimicry in 4-Month-old Infants.

ABSTRACT

This study aimed to test the causal role of sensorimotor experience in the development of facial mimicry. We systematically manipulated 4-month-old infants’ experience with their own facial actions, and measured the effect on their sensorimotor cortex activation and facial mimicry when they observed others’ facial actions. Infants in the mirror condition received two weeks of daily sensorimotor experience with their own facial actions via a toy mirror, while infants in the control condition played with the same toy without the mirror for the same amount of time. Before and after this experience, we measured infants’ facial mimicry using electromyography (EMG) and their sensorimotor cortex activation using electroencephalography (EEG) while they observed videos of other infants’ facial actions. As predicted, infants in the mirror condition showed a greater increase in sensorimotor cortex activation during the observation of other infants’ facial actions than infants in the control condition. However, this greater neural activation did not translate into a greater increase in facial mimicry in the mirror group. These findings suggest that although the neural processing of others’ facial actions was enhanced as a result of the sensorimotor training, longer training periods may be necessary for this to lead to greater facial mimicry.