Tải bản đầy đủ - 0 (trang)
3 Development of a Neurophysiological System that Responds to “External Coping” by the Caregiver

3 Development of a Neurophysiological System that Responds to “External Coping” by the Caregiver

Tải bản đầy đủ - 0trang

5.3 Development of a Neurophysiological System that Responds …



109



neurophysiological system that responds to social interactions emerges from the

PNS, specifically, from the vagal system. They call this the social engagement

system:

A face–heart connection evolved in mammals as source nuclei of vagal pathways shifted

ventrally from the phylogenetically older dorsal motor nucleus (e.g. unmyelinated vagal

pathways) to the NA [nucleus ambiguus] (e.g. myelinated vagal pathways). This resulted in

an anatomical and neurophysiological linkage between neural regulation of the heart via the

myelinated vagus and the special visceral efferent pathways that regulate the striated

muscles of the face, head, and neck. Together this linkage, between brainstem motor

systems responsible for cardiovascular functions and those necessary for regulating the

face, head, and neck, forms an integrated ‘Social Engagement System.’…

Specifically, the Social Engagement System includes the regulation of the eyelids through

the orbicularis oculi (e.g. social gaze and gesture), muscles of facial expression (e.g.

emotional expression), middle ear muscles (e.g. extracting human voice from background

sounds), muscles of mastication (e.g. ingestion, sucking), laryngeal and pharyngeal muscles

(e.g. vocalizing, swallowing, breathing), and muscles of head turning and tilting (e.g. social

gesture and orientation). Collectively, these muscles act as filters for social stimuli (i.e.

observing others’ facial expressions and detecting prosody in human voice), and they allow

the expression of motor behaviours necessary for engagement with the social environment.

Based on the Polyvagal Theory, the development of the mammalian myelinated vagus is

critical in the development of the face–heart connection, which links social behaviour and

autonomic regulation. Thus, with more optimal vagal regulation, features of more adaptive

social behaviour emerge. Without a functioning myelinated vagus, social behaviour would

be compromised, and more primitive defensive strategies, such as fight-flight mobilization

and tantrums (mediated by the sympathetic nervous system) and shutdown behaviours

(mediated by the unmyelinated vagal system) would be more frequently expressed.

Clinically, the status of vagal myelination becomes critical for the newborn and the young

infant as they attempt to engage and disengage the caregiver and to explore social

reciprocity as a mechanism to regulate physiology and behaviour. (p. 113)



Capacity to benefit from coping efforts of social partners. The capacity to be

soothed and calmed by social interactions is both neurophysiological and psychological, in that during these early months (as long as they are characterized by

sensitive responding and external coping), the neonate’s stress reactivity systems are

both prevented from “going off” and are smoothly down-regulated by the caregiver’s

actions. Through neurocortical learning processes, these experiences lead to the

emergence of additional corticolimbic pathways that eventually allow these

buffering and calming functions to be served more distally by the caregiver’s voice,

smell, sight, and other markers of a caregiver’s presence (Porges and Furman 2011).

As explained by Hostinar et al. (2014) in their review of research that supports

the notion of social buffering of the HPA axis,

there are likely developmental changes in the types of cues triggering the social buffering of

stress and by inference also in the neurobiology involved. During early development,

sensory cues and homeostatic regulators (e.g., feeding, warmth, tactile stimulation) seem to

play an important role in buffering the HPA axis in both human infants and rodents. With

brain development and the maturation of the PFC, the simple presence of caregivers or

peers seems to be enough in many instances for both human and nonhuman animals. In

humans, there is increased complexity with cognitive development, as social partners can



110



5 Development of “Coping” in Newborns …



provide coping assistance, coach the cognitive reappraisal of stressors, and support the

development of self-esteem. Furthermore, experiencing the stress-relieving effects of

caregivers early on may teach the organism to seek social partners and may entrain certain

neural activation patterns that promote affiliative behaviors across development, thus

serving as positive feedback signals in the process of becoming disposed to exhibit a

buffering of stress by social stimuli. (pp. 272–273)



The infant’s capacity to benefit from the participation of caregivers and other social

partners in dealing with stress is another ingredient essential to the healthy development of coping—both during this early period of development and during later

periods as well—since all the more advanced forms of coping (including especially

interpersonal strategies such as seeking comfort, help, advice, and information) are

facilitated by this interpersonal matrix.



5.4



Social Tuning of the Neurophysiological Stress

Reactivity and Recovery System



The emergence of the integrated social engagement system, which subserves the

functioning of the attachment system, also allows caregiver behaviors, along with

other environmental conditions encountered by infants, to “tune” or “program”

neonates’ developing neurophysiological stress reactivity and regulatory systems—

both the actual structures (e.g., the number of molecular receptors) and their

interrelated functioning. Research suggests that the development of each of these

neurophysiological subsystems (i.e., the HPA axis, amygdala, hippocampus, and

sympathetic and parasympathetic nervous systems) is “experience expectant,” in

that their healthy development requires the participation of a sensitive caregiver

(Hostinar et al. 2014; Lupien et al. 2009; Tottenham 2012).

All these neurobiological systems are plastic. They are open and ready to be

calibrated according to the environmental conditions they encounter prenatally and

during the first months of life, such as the levels of threat and danger the newborn

experiences (e.g., the amount of stress hormones present during gestation or the

degree of attunement experienced postnatally). In fact, by birth, stress reactivity

systems have already been shaped and tuned, not only by genetics but also by

epigenetics, based on the prenatal environment (Lupien et al. 2009).

Social buffering of stress reactivity. A special feature of these neurophysiological systems is that they are all highly responsive to contextual conditions and

social interactions, in that they can be activated and deactivated to some extent by

caregivers and other external factors. As a result, interactions with caregivers play a

decisive role in how each subsystem functions and how their joint functioning is

coordinated over time. When neonates experience sensitive caregiving and develop

within a secure attachment relationship, their stress reactivity systems become

“tuned” to a safe and trustworthy environment (Gunnar and Donzella 2002;

Hostinar et al. 2014; Spangler and Grossmann 1993; Spangler et al. 1994).



5.4 Social Tuning of the Neurophysiological Stress Reactivity …



111



For example, if the infant experiences a sensitive caregiving environment, in

which needs are reliably met and expressions of emotions and distress are

responded to dependably, the HPA axis goes into a period of hyporesponsivity by

about 3 months of age (Gunnar and Quevedo 2007), as described in the previous

chapter. In a similar vein, in sensitive responsive contexts, the amygdala exhibits

suppressed reactivity, including delayed engagement with dangerous and stressful

aspects of the environment, and protracted development of its integration with

prefrontal circuitry (Gee et al. 2013). In these same social conditions, the PNS

develops a high resting vagal tone, accompanied by the capacity to quickly remove

the vagal brake to allow the SAM to provide resources when they are needed to deal

with demanding encounters, and then reinstate it to allow speedy recovery of the

SAM when demands are over (Propper and Holochwost 2013; Tottenham 2012).

When encouraged to operate in concert with their expected social partners, these

integrated neurophysiological systems appear to show a normative trajectory over

the first three to six months, in which, over time and with experience, each of these

stress reactivity subsystems starts to slowly ramp down its responsivity—raising the

threshold for the levels of stress needed to trigger the release of its many stress

mediators, “turning down the volume” of its levels of activation, and augmenting

the speed of its down-regulation after a stressor has safely passed. It is as if stress

reactivity systems have learned that the infant is in a safe environment, and will not

need the high vigilance and quick responding with which it negotiated the first

weeks of life. This emerging hyporesponsivity is sometimes considered part of a

larger evolutionary process of “biological sensitivity to context” (Boyce and Ellis

2005), in which it is adaptive for individual stress reactivity systems to develop the

kinds of functioning that are called for by the contexts they actually encounter

prenatally and postnatally.

Sensitive periods or continuity of caregiving. At this point in the research, it is

unclear whether the last months of gestation and first months of life represent a

“sensitive period” for the development of the stress reactivity system, in which,

after three to six months, the developmental window “shuts” and infants who have

experienced loving and contingent caregiving enjoy the benefits of a permanently

resilient stress reactivity system that is hyporesponsive at least until adolescence

(Hostinar et al. 2014; Gee et al. 2014; Lupien et al. 2009). Alternatively, it seems

possible that it is the continuity of caregiving, in which caregivers repeatedly and

reliably provide comfort and care when their offspring are distressed, that

dynamically maintains the high threshold, low responsivity, and quick recovery of

the neurophysiological stress reactivity system that is so helpful as a platform for

the development of constructive coping.



112



5.5



5 Development of “Coping” in Newborns …



The Emergence of a Hierarchy of Reactivity,

Regulatory, and Coping Processes



By the end of the first three months, if infants develop within the “average

expectable environment” of sensitive caregiving and a secure attachment, they

reach three important milestones. First, they are able to establish the regular biorhythms that allow them to devote their energy to activities and interactions

involving focused attention, novelty, and exploration. Second, many of the reactive

and recovery systems for dealing with stress that were once run by automatic

processes have begun to be shifted over to the social engagement system and so are

regulated interpersonally. Third, the “hyporesponsivity” of their stress reactivity

systems seems to result in a decoupling of these systems from the actions they once

controlled. At this point, infants continue to show behavioral expressions of distress

to stressful stimuli (such as inoculations), but these occur in the absence of the

previously coupled neurobiological stress reactions (Nachmias et al. 1996). This

allows infants to exercise adaptive actions without the biological costs with which

they were previously fused. These three milestones seem to allow the rudimentary

action regulation systems of neonates, as long as they continue to develop with the

support of a sensitive and responsive caregiver, to have the opportunity to practice

and expand their regulatory capacities.

Taken together, these developments normatively result in a set of reorganizations

during the first months of life. Newborns start with a biobehavioral system, run by

reflexes and the “neurosymphony of stress”, that can be thought of as relatively

“flat” in the diffuse and undifferentiated expressions of distress it generates. By the

end of the first months of life, this system is hierarchical and has added several

additional first lines of defense, both neurophysiological and social. This more

flexible new system builds on the autonomic nervous system, which incorporates

two phylogenetically older neurophysiological systems (described in previous

chapters), namely, the vegetative vagal system, which subserves “freeze” reactions,

and the SNS, which subserves fight/flight reactions. Reflecting a phylogenetically

more recent adaptation of the mammalian nervous system, the social engagement

system represents a third circuit—a social circuit—for helping the neonate regulate

its physiology and behavior during both stressful and playful interactions with the

environment. As explained by Porges and Furman (2011),

In this phylogenetically organized hierarchy, the newest circuit associated with social

communication is used first. If that circuit fails to provide safety, then the older

survival-oriented circuits are recruited sequentially. From a developmental perspective, the

oldest circuits develop first, and the newest circuit develops last, leaving it the most vulnerable to neural insult and the most sensitive to postpartum experience. The newest circuit

becomes only partially available during the last trimester and is expressed at term as the

brainstem reflexes that enable the coordination of sucking, swallowing, and breathing. By

six months postpartum, these brainstem reflexes, which become coordinated with cortical

processes, provide a biobehavioural pathway through which reciprocal social engagement

behaviour can calm and soothe physiological state in both participants of a social dyad (e.g.

mother–infant interactions). (p. 109)



5.5 The Emergence of a Hierarchy of Reactivity, Regulatory…



113



This kind of differentiation and hierarchical integration is a familiar pattern

characteristic of development in many domains (Raeff 2011; Werner 1957). In the

development of coping, at this early period, it seems that the first neurophysiological subsystems charged with stress reactivity already during prenatal development are initially fused with regulatory actions in the form of reflexes. However,

starting at birth, through the regulatory participation of caregivers, the newborn’s

actions gradually become decoupled or differentiated from the direct control of

neurophysiological subsystems and are turned over to social partners for interpersonal stress reactivity and regulation postnatally. The neurophysiological systems

are, in turn, buffered by these social relationships, and space for “coping” is created,

even if the first forms of coping are almost completely external, carried out by the

soothing and comforting actions of the caregiver, and only guided or informed by

the expressive actions of the newborn.

This process adds to the hierarchy of reactivity and regulatory systems that, like

the development of the autonomic nervous system, prioritizes the most recently

emergent forms of regulation as the first line of defense. At this age, these are

interpersonal coping systems, which are still integrated with infants’ neurophysiology through the sensitive attunement of the caregiver to the authentic cues of the

infant. If this system is effective in establishing homeostatic functions, it can help

maintain the infant in a state of alert readiness to interact with the social and

physical context, smoothly utilizing the developing parasympathetic vagal system

to up-regulate resources for energy and attention when demands increase, and to

down-regulate arousal when demands subside. If these integrated systems are not

effective in dealing with stress, infants can fall back on their more primitive (and

energetically expensive) SAM and HPA systems for orchestrating stress responses.

In a securely attached dyad, the kinds of infant distress responses that these older

systems generate, which may be initially low in volume but can be amplified as

needed, also result in greater attention and participation by the caregiver to help

comfort and care for the infant.



5.6



Summary of Transformations of the Coping System

during the Neonatal Period



By the end of the first three months of life, infants’ coping equipment, which started

as a diffuse set of undirected expressions of distress and reflexive reactions fused to

a vigilant and reactive neurophysiological system, has become an integrated stress

reactivity and regulatory system that is tuned to safety and thus hyporesponsive—

capable of both supporting homeostatic functions and dispatching energetic

resources for responding to external demands. A scaffold for the progressive

reorganization of these systems is the development of a secure attachment relationship, in which caregivers respond to infants’ initially undifferentiated expressions of distress, protest, and other negative emotion, using increasingly more



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

3 Development of a Neurophysiological System that Responds to “External Coping” by the Caregiver

Tải bản đầy đủ ngay(0 tr)

×