New research suggests that extremely unsettled babies have a much higher risk of mental health problems in childhood. The question is now what we do with this, and I have a few ideas.
The dismissal of the importance of a rise in cortisol on the developing brain is very popular with extinction sleep training apologists. Although we do not know the exact influences, there are reasons to be cautious of this dismissal, which ignores key evolutionary and biological information.
The premise behind extinction sleep training is that infants (and toddlers) are being taught to "self-soothe"; however, this ignores key points of what self-soothing abilities can be expected from children and how distressed they are at the time of separation. Instead of focusing on these extinction methods, gentler methods that respect where the child is developmentally should be considered.