Darcia Narvaez describes the affect of early stress on the infant’s developing neurobiology in her 2014 book on human morality. A new-born has few systems that are fully operational. The survival systems are in place but are further conditioned by the kind of care we receive. The many systems that contribute to the stress response still have a long way to go in terms of development. These are very reliant on the care received in order to develop. This is a sensitive period of development so early life stress can cause permanent changes in neuroendocrine and neurotransmitter systems like opiate, dopamine, serotonin and corticosteroid receptors. Intelligence, sociality and motivation will all be affected by this.
Most of the research on early life stress focuses on the extreme end of the spectrum. Developmental traumatology finds that abuse. Neglect and trauma lead to an over-reactive stress response, compromised immunity, a mis-developed endocrine system and underdeveloped neurotransmitters. There also tends to be large deficits in the emotional systems and a lack of bilateral brain integration.
In addition to this there is now increasing concern about less apparent early stress that has been called ‘toxic’. Humans are born 9-18 months too early and so this period should mimic the womb as much as possible to limit distress. The stress response much be supported so it does not overheat or collapse due to challenges the infant cannot yet handle. When a child does not experience the evolved developmental niche they experience toxic stress. When a baby does not receive what it is evolved to expect it is under-cared for leading to suboptimal development. Current epidemics of anxiety and depression suggest real problems in the laying down of the foundations of these brain systems responsible for regulation and sociality.
Postnatal relational stressors like non-responsive care may be much more detrimental that non-social stressors. This is because humans are a social species that rely on the relationships to build and sustain healthy functioning. Systems relate to the stress response are influenced by early caregiving, including the amygdala, the vagus nerve, gene expression and the LHPA axis. With poor early care the endocrine system shows increases adrenal hormone secretions. When rats are exposed to stressors as a result of poor maternal care (lack of touch) there are permanent changes in the amygdala and the ventromedial prefrontal cortex. They are more likely to become listless and hopeless in the face of challenge. It is important to note, too, that rats are not as social as humans. Chronic stress in early life increases that amygdala’s ability to learn fear associations and decreases the prefrontal cortex’s ability to control it. This creates a vicious cycle of upwards spiralling fear and anxiety creating dysregulation. Toxic stress creates abnormalities in emotion circuity. High reactivity in early life is likely to become a central part of the personality.
Michael Meaney’s work with rats has shown that gene expression of glucocorticoid receptor proteins involved in controlling anxiety is affected by early care. Meaney’s work has shown that maternal affection in the first week of life is linked to altered expression of over a thousand genes. Rats with poor nurturance have a weaker system for controlling anxiety resulting in increased stress response to unfamiliar situations throughout life. Poorly nurtured rats went on to become poor nurturers themselves showing how this downward trend becomes compounded over generations. For humans, unhappy childhoods as a result of poor nurturance are linked with methylation of mood areas of the brain related to schizophrenia and suicide. Greater stress reactivity leads to a higher resting heart rate, high blood pressure, increased appetite and systems regulating growth, reproduction, metabolism and immunity are compromised. Emotional dysregulation and poor attachment at 6 months predict diminished cognitive and social capacities later on.
Early caregiving has long-term impacts, some of which only emerges at later points as late-forming psychopathologies. When stress has gone on too long or when there is too much at a critical period, the system becomes sensitised to greater reactivity. Under excessive stress, the stress response can oscillate (like pressing the gas and accelerator at once) resulting in a freeze response, or it can ‘lock in’ or it can ‘give up’ (become unresponsive). The latter situation occurs in the case of people with antisocial personality disorder. The ‘unabomber’, Ted Kaczynski experienced severe trauma at nine months of age by being separated from his mother for several days during a hospital stay. His mother noted that this changed his personality.