The capacity for intersubjectivity begins to be laid down in the prenatal period during the mutually regulating relationship between the physiology of the mother and the infant across the placenta (Schore, 2021). During the last trimester of pregnancy these transactions are programming the stress-regulating hypothalamic-pituitary-adrenal axis. At this time the central and medial regulatory functions of the amygdala, which is deeply connected with the autonomic nervous system, begin to come online. Schore refers to the work of Porges, who describes how the ANS, what has been called ‘the physiological bottom of the mind’, comes into a critical period of growth in the foetal brain. The oldest and early-forming unmyelinated dorsal vagus, the later developing sympathetic nervous system and the newest parasympathetic myelinated ventral vagus system are operating in the last trimester. Porges says that the aspects of the ANS that supports social engagement begin to the develop in the final trimester. The ventral vagus continues to mature well into the first year. In primordial nonverbal communications, the mother regulates the infant’s autonomic arousal creating an emerging sense of autonomic balance and safety which manifests in the infant’s state of quiet alertness.
The neurobiology of prenatal experience: The birth of intersubjectivity and the development of the nervous system in the womb
