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From the Field: Neuroscience experiments
Brief summaries of several key experiments revealing some of the hidden links between childhood experiences of abuse and neglect and brain function.
To improve our understanding of children, neuroscientists across the world have been looking at the brain in tightly controlled experiments. These experiments address very specific questions and are designed to be as fun and stress-free as possible for young volunteers. Each one helps shed a little more light on a complex puzzle.
Threat System
HEIGHTENED NEURAL REACTIVITY TO THREAT IN CHILD VICTIMS OF FAMILY VIOLENCE
Children in this study decided if a series of neutral, sad or angry faces presented on a screen inside an MRI scanner were male or female. They weren’t asked to focus on the emotional expression. Compared to a group of peers who had not experienced childhood trauma, the group of children who had been exposed to domestic violence / physical abuse showed a pattern of increased neural reactivity in the amygdala and insula while viewing angry faces. This pattern is similar to that observed in soldiers before and after they were exposed to combat, suggesting this is an adaptive pattern of hypervigilance and heighted sensitivity to potential danger following maltreatment. A follow-up study (McCrory et al., 2013) found that this heightened response in the amygdala was observed even when children were presented with angry faces subliminally – that is, for less than two hundredths of a second. This suggested that increased hypervigilance to danger following abuse and neglect may even occur outside a child’s conscious awareness and control.
HEIGHTENED AMYGDALA REACTIVITY AND INCREASED STRESS GENERATION PREDICT INTERNALIZING SYMPTOMS IN ADULTS FOLLOWING CHILDHOOD MALTREATMENT
In this study a large sample of young adults self-reported experiences of childhood abuse and neglect. Two closely matched groups were identified. As expected, those with high levels of childhood trauma showed higher brain activation in the amygdala to threat cues compared to those with no such history. This partly mediated the level of anxiety and depression symptoms one year later. That is, greater amygdala reactivity associated with abuse and neglect was a vulnerability factor for future mental health problems. This study also showed that those young adults with childhood trauma experienced more stressful life events than their peers, even when baseline levels of mental health symptoms were taken into account. The greater the number of these stressful events, the greater level of mental health symptoms one year later. This study provides compelling evidence for stress generation – that experiencing childhood trauma increases propensity to experience stressful life events that in turn increases the risk of future mental health symptoms.
EARLY DEVELOPMENTAL EMERGENCE OF HUMAN AMYGDALA–PREFRONTAL CONNECTIVITY AFTER MATERNAL DEPRIVATION
This study provides convincing evidence for the Stress Acceleration model. The researchers investigated the impact of institutionalisation – which included maternal deprivation – on a group of children and adolescents. They found that this group relative to peers showed a pattern of amygdala hyper-reactivity as well as an altered trajectory of amygdala and prefrontal cortex connectivity. Connectivity refers to how these two brain regions worked together. Surprisingly, children with a history of maternal deprivation displayed a pattern of connectivity that resembled what was seen in older adolescents. This suggests a pattern of accelerated maturation of this brain system that may reflect adaptation to early adversity.
Memory System
ALTERED DEVELOPMENT OF HIPPOCAMPUS-DEPENDENT ASSOCIATIVE LEARNING FOLLOWING EARLY-LIFE ADVERSITY
Children and young people exposed to different kinds of violence (sexual, physical and witnessing domestic violence) were compared to a control group who had not had these experiences. Children were asked to engage in a simple learning task in the scanner. Those who had been exposed to violence showed memory difficulties (particularly in relation to threat cues) that became more pronounced with age. These difficulties were associated with reduced activation of the hippocampus – a key region involved in learning and memory. It is suggested that this difficulty in learning new information, particularly in relation to emotion, may contribute to poorer outcomes for these children in respect of academic attainment and mental health.
AUTOBIOGRAPHICAL MEMORY: A CANDIDATE LATENT VULNERABILITY MECHANISM FOR PSYCHIATRIC DISORDER FOLLOWING CHILDHOOD MALTREATMENT
Children with and without documented abuse and neglect recalled positive and negative personal memories while their brain activity was being measured. Maltreatment experience was associated with reduced neural activation in several brain regions, including the hippocampus when children recalled positive memories. There was also an increased engagement of the amygdala and other brain regions signalling salience while remembering negative memories. This suggests that the experience of maltreatment can bias how the brain processes memories, making negative past personal experiences more detailed and arousing, and positive ones less prominent.
Reward System
NEUROBEHAVIORAL MARKERS OF RESILIENCE TO DEPRESSION AMONGST ADOLESCENTS EXPOSED TO CHILD ABUSE
Studies have linked altered reward processing and risk of depression. In this study, reactivity to reward was assessed in a task where adolescents viewed facial expressions, including positive facial expressions and neutral facial expressions. Those with histories of abuse and neglect who had low reactivity for reward (positive vs. neutral facial expressions ) were found to have had higher symptoms of depression two years later. Although the sample size was small for this group, this finding suggests that greater reactivity to positive and rewarding environmental cues may be associated with resilience to depression among adolescents who have experienced abuse and neglect in the past.
A NEUROCOMPUTATIONAL INVESTIGATION OF REINFORCEMENT-BASED DECISION MAKING AS A CANDIDATE LATENT VULNERABILITY MECHANISM IN MALTREATED CHILDREN
Children with and without documented exposure to abuse and neglect performed a decision-making task during an MRI brain scan. They had to learn what stimuli presented on the screen were associated with a higher likelihood of winning points (i.e. reward). Children exposed to abuse and neglect showed decreased activity in brain regions such as the striatum and the orbitofrontal cortex, which are important to predict and process reward. This suggests that children exposed to maltreatment may not respond in the same way as non-maltreated peers to rewarding events, activities and relationships. This may increase the risk of several mental health problems, such as depression and addiction.