Abstract
Attachment between mothers and infants is the most primitive and primary form of human social relationship. Recently, it has
been reported that the anterior prefrontal cortex (APFC) of infants younger than 3 years old may play an important function in
forming attachments to their mothers. However, little is known about how the neural correlates of attachment develop after 3
years of age. Bowlby argued that there is a critical period, between birth and 2.5 years (0–30 months), for attachments to form
and if it does not form in this time then it is not possible to develop thereafter. The current study investigated the role of the APFC
in the attachment of 5 year olds to their mothers. Subjects included 18 young children (5.0 ± 0.4 years), whose mothers’ smiles
were video recorded. By means of near-infrared spectroscopy (NIRS), we measured APFC activation in the children while viewing
their mother smiling, and compared the activation with that resulting from an unfamiliar mother smiling. We found significant
increases in right APFC activation in these 5 year olds in response to their mother’s smile. Furthermore, the APFC response to
mothers’ smiles did not change as a function of age between 4 and 5 years old. These results suggest that the right APFC is still
involved in young childrens’ attachment to their mothers until at least 5 years of age.
