Article summary with Early life stress and brain function: Activity and connectivity associated with processing emotion and reward by Herzberg & Gunnar - 2020

What is early life stress?

Early life stress (ELS) is the result of adversities that produce frequent or chronic activation of stress-responsive physiological systems. These adversities deprive infants and children of the social and physical care that they need, cause homeostasis, provoke fear and anxiety, and dysregulate the function of the stress system itself. The most common forms of ELS are characterized by an accumulation of adversity. For example, poverty is a chronic, multi-dimensional stressor, and maltreated children typically experience multiple types of abuse.

What is the effect of early life stress on emotion processing?

Research shows differences in emotion processing after experiencing early life stress. There are interesting results with regards to brain function. Increased amygdala activation to emotional contexts appears to be beneficial following early life stress. And activation in prefrontal and striatal regions differ based on the type of adversity experienced.

What is the effect of early life stress on reward processing?

Differences in reward sensitivity have been observed following early life stress. There are differences between the type of ELS experienced and neural activation in the context of reward. In rewarding contexts neural activation is more consistent in maltreated and post-institutionalized individuals, while impoverished individuals show different patterns of activity. It is as of yet unclear whether altered reward sensitivity is protective and reduces the likelihood of risky behavior, or if it is a risk and leading individuals to seek larger rewards.

What is functional connectivity?

Functional connectivity refers to the connectivity between brain regions that share functional properties. In ELS literature, two main approaches have been used to investigate functional connectivity:

• Psychophysiological interaction (PPI) is used to understand the functional relationship between two regions in the context of a task. It examines the functional connectivity between two regions of interest whose activity has been convolved with task-related timing information.
• Seed-based resting-state functional connectivity (rsFC) looks at functional coherence between two regions of interest when the individual is not engaged in a task, the individual´s resting-state. In rsFC, a single region of interest is chosen as the “seed”. Then the time course of the seed´s functional activity is correlated with a set of regions or all other regions of the brain. Correlations with greater magnitude are interpreted as being more functionally connected.

What are the main findings from investigations of ELS and functional connectivity in the emotion processing system?

The main findings can be organized by ELS type:

• Poverty. Lower income-to-needs ratio is associated with diminished amygdala-prefrontal cortex connectivity. Individuals with lower family income during childhood show different patterns of frontolimbic connectivity when viewing aversive images or emotional faces, possibly causing altered emotion processing.
• Maltreatment. Maltreated individuals display lower amygdala- and hippocampus-prefrontal cortex connectivity, and lower amygdala-prefrontal cortex connectivity. These connectivity patterns are associated with poorer context memory and conflict regulation. Stronger amygdala-prefrontal cortex connectivity predicts more adaptive functioning regardless of maltreatment history. This means that high functioning individuals with a history of ELS may exhibit a compensatory neural phenotype that aids in adaptive functioning later in life, supporting the notion that adaptation may occur during the transition from adolescence into adulthood.
• Institutional care. Previously institutionalized children show more mature negative amygdala-mPFC coupling during emotion-matching, and they show significant amygdala- and hippocampus-PFC connectivity during aversive learning. The relationship between striatum-mPFC connectivity and social problems was moderated by age, in the way that functional connectivity was more likely to predict social problems in adolescents compared to children, highlighting the importance of investigating developmental trajectories after ELS.