Article summary of Growing a social brain by Atzil - Chapter

In what sense are humans a social species?

Humans are a social species. Sociality is evolutionarily related to allostasis. Allostasis refers to the ongoing adjustment of an individual’s internal milieu that is necessary for survival, growth and reproduction. Social animals gradually learn to regulate their own and others’ allostasis using social communication. The literature indicates that across different species, higher allostatic demands are associated with more complex sociality. A caregiver’s allostatic support is rewarding, which makes social interactions a strong reinforcement for youngsters. With repeated care, the infant gradually builds an internal model of the caregiver. As the experience with the caregiver is repeatedly associated with a vigorous reward, it is hypothesized that the internal model of the caregiver is acquired as rewarding, which promotes infant attachment and motivation towards social interactions. 

It is proposed that neural systems that support human social behaviours overlap with those supporting allostasis. The neural circuitry that is needed for social affiliation is not evident in newborns, and develops throughout childhood. It is proposed that this potentiates a child's susceptibility to environmental input. Brain development and social development may be two manifestations of the same phenomenon: namely that of becoming social experts.

What do we mean when we talk about 'the social brain'?

The salience and default mode networks of the brain together make up an integrated network for implementing allostasis. The core intrinsic networks and hubs, specifically those in the default mode and salience networks, have been repeatedly demonstrated to participate in social brain processing. Examples of processes that can be described as social brain processing are maternal bonding, social cognition and social network size. These brain processes impaired in patients with social deficits such as in autistic spectrum disorder (ASD). Evidence from human neuroimaging studies suggests that there is an overlap between the neural system that supports social behaviours and the one that supports allostasis.

How does the brain develop throughout the life course of humans?

Human brain development is a protracted process that starts in utero and lasts for up to 25 years postnatal. The myelination of the long-distance axon tracts that allow for the fast, efficient information transfer throughout the networks of the brain, develops for the most part after birth. In general, sensory and motor-control networks become synchronized early in life and even during the prenatal period. However, major nodes of the default mode network continue to develop until young adulthood.

Research has established that provision of early life care shapes brain anatomy. Early social care also appears to determine the behavioural phenotype of the off-spring. Variation in maternal behaviour impacts children’s social development. It is hypothesised that infants will show facilitated network development when their allostatic needs are sensitively regulated. This hypothesis is supported by literature demonstrating that child development is optimized and even accelerated where provision of parental care is sensitively attuned to the infant needs.

What alternative framework for the social development of children is proposed?

A key feature of the predictive coding model is the interaction between the forward and backward flow of information: The backward flow delivers predictions while the forward flow computes the residual errors between prediction and sensory inputs. In early life as infants’ sensory pathways become intact, without sufficient sensory experience to form valid predictive models, most sensory input is considered ‘prediction error’, simply because the brain cannot predict it. Of special importance for the development of sociality is neural prediction within the interoceptive system, which is the sensory consequence of allostasis. A recent comparative study supports the importance of maternal care predictability by demonstrating that when infants can predict maternal sensory input, they can develop optimally.

With development, it is hypothesised that as top-down predictive models gradually govern infants’ experience, infants’ allostasis and allostatic independence will exponentially increase. This process might involve a gradual decrease in the salience of interoceptive prediction errors. It is also hypothesised that infants’ experience mostly includes bottom-up information, or prediction errors.

The amygdala, nucleus accumbens and hypothalamus are considered key regions in social processing. They also have a key role in allostasis regulation and are thought to compute prediction error and motivate behaviour. It is hypothesized that these regions’ involvement in social processing reflects an underlying process of preparing the organism for upcoming changes in allostasis.

In what way is the brain a conceptual processing system?

The mental representations of categories in the brain are referred to as concepts. It has been proposed that when the brain assembles populations of predictions, it is constructing concepts. Every event of new learning is categorised into a concept.

The first step in social development is acquisition of rudimentary social concepts. During early infancy, the infant gains experience interacting with the caretaker, and most interactions will be implicitly or explicitly aimed towards allostasis regulation. Through social regulation of allostasis, a child experientially acquires not only social concepts but also social competencies. One of the basic social competencies infants gain is synchrony. Bio-behavioural synchrony is an important aspect of mother–infant attachment, and has been shown to be important for shaping optimal developmental outcomes of physiological regulation, executive functions and social aptitude. Starting from gestation, a mother controls her foetus’s allostasis via mother–foetus physiological synchronization processes, such as synchronising heart rates and body temperature. 

In what way does culture influence social development?

Infants learn conceptual knowledge by synchronizing their attention with others. It is hypothesised that stimuli with a higher predictive value for allostasis will be learned quicker than stimuli with lower impact on allostasis. During development, infants learn social concepts and skills to prepare for allostatic needs, as caretakers introduce all the culturally relevant concepts using language. In addition to social learning, allostasis-driven learning can also shape other human features such as cognition, emotion and culture. Emotion and social concepts are environmentally constructed in each culture, and transferred between generations in social dyads during early life social training.

How does neural development of the social brain take place?

The neural trajectories of social development are not yet well-understood in neurological research. Of specific interest to social cognition is the temporal contingency between the developmental trajectories of the default mode network and of cognitive abilities such as conceptualization. The default mode network is believed to construct mental representations of concepts, including complex representations about other people’s minds. most of the core nodes of the default mode network become synchronized by six months of age. The grey matter volumes as well as functional and structural connectivity in the default mode network continue to develop during childhood, reaching full maturity in late adolescence.

Social care controls social and cognitive development via maturation of whole-brain neural networks. Parental care, which is consistently reinforced by allostasis, is necessary for the infant to build and refine a multisensory mental representation of concepts. Early life is a critical window for social learning due to the acute nature of the social dependency. The potentially crucial role of social experience during infancy in shaping brain and social development suggests that social animals do not necessarily rely on a predetermined specialized brain system to support affiliation. Instead, domain-general neural systems implement a conceptual system to regulate allostasis, and that underlies social behaviour.

Through social interactions, humans learn to link those abstract concepts to their allostasis to survive and prosper in their culture. This can potentially explain how beyond the immediate dyadic bond with the caregiver, extended social effects, including social class or economic status, may carry powerful effects on child development and even brain development.