The studies cited above all involve infants and young children for whom attachment did occur. This article is about the correlation between brain development and the quality of the attachment. The capacity to attach appears to be genetic, and given the opportunity to attach, an infant will attach to an abusive caregiver as readily as to a nurturing caregiver.   

There have been some studies done on Rumanian orphans (more info in the "This American Life" podcast linked in an earlier post), some of whom never had the opportunity to attach at all in infancy or early childhood. These children were also deprived of many stimulation experiences over a period of a number of years. Those not left at the orphanages near their time of birth probably experienced other forms of deprivation, including nutritional, before ever arriving at the orphanage. It is therefore not possible to conclude that brain abnormalities noted in many of these children are the direct result of lack of attachment. Be that as it may, brain scans on a number of these children showed significant areas of brain atrophy and/or failure of parts of the brain to develop.