Childhood adversity and the brain: What have we learnt?
Eamon McCrory is professor of developmental neuroscience and psychopathology at UCL. He is a member of the EIF evidence panel, and was a contributor and member of the expert advisory group for our report on adverse childhood experiences. In this post, Eamon shares the theory of latent vulnerability and considers whether biology can shed light on the link between childhood adversity and mental health.
It’s widely acknowledged that child abuse and neglect can have a negative impact on mental health – even many years after the event, as the findings described in the new EIF report on adverse childhood experiences (ACEs) make clear. Emerging findings from the biological sciences tell us that this link may be explained by processes occurring in the body and brain which remain hidden or ‘latent’ when children are young, but increase their vulnerability to mental health problems as they develop. Understanding what these processes are has important implications for understanding how early intervention can stop and potentially reverse the negative impact of childhood adversity, especially when it involves experiences of abuse and neglect.
The brain as an adaptive learning organ
We can think of the brain as a collection of interconnected and interdependent brain systems. Each system has a particular role or function. Together, these brain systems allow us to navigate a complex physical and social world. The brain is also a learning organ. This means that our earlier experiences – including adverse experiences – shape brain development. These changes, or ‘adaptations’, may help children cope with the environments that they are having to negotiate.
Brain imaging findings
Over the last decade, together with Essi Viding, our team at UCL and other teams across the world have focused on how experiences of abuse and neglect affect brain function. We have used fMRI scanners to produce images of the brain and indirectly measure neural activity.
We have recruited children from social services with documented experiences of abuse and neglect and carefully matched them with peers. This means that our findings are specific to those ACE categories which involve child maltreatment, but not all ACE categories. Our neuroimaging work has focused primarily on brain systems implicated in how children process information about environmental threats and rewards, as well as their recall of daily experiences (also referred to as autobiographical memory). Altered activity in these three brain systems has been implicated in common mental health disorders such as anxiety, depression and conduct disorder.
For example, studies have found that children who have experienced abuse and neglect show patterns of hypervigilance, involving a hyper-awareness to potential threats in the child’s environment. Our neuroimaging work has observed that this altered amygdala activity is similar to that observed in soldiers after they have been exposed to combat. Studies in addition to our own have observed altered neural response in brain areas associated with reward, potentially reducing children’s experiences of satisfaction and motivation. Finally, studies of autobiographical memory indicate that abuse and neglect are associated with a pattern of over-general (or less detailed) memories of everyday experience, as well as a privileging of negative over positive memories. Importantly these all these brain differences have been observed even in children with no presenting mental health disorder.
On the basis of these findings, we have put forward the theory of ‘latent vulnerability’. This theory argues that children adapt to early chaotic, unpredictable or violent home or community settings in ways that help them cope and survive. In other words, the brain changes we observe may be helpful for a child in the short term in an unpredictable or dangerous home environment. For example, becoming vigilant to threat may help a child survive in a violent household. Indeed, very similar brain changes are seen in soldiers exposed to combat. However, in the longer term, in more ordinary environments, such as school or a safe foster placement, these changes can play out in ways that increase risk of mental health problems. We call this latent vulnerability.
We know that a child doesn’t suddenly wake up one day with a mental health problem. We believe that vulnerability and resilience is created over time. In part this may be due to how brain adaptation impact a child’s social behaviour. Below we consider three ways that brain changes may increase vulnerability to mental health problems.
First, they can make everyday life more stressful – we call this stress susceptibility. Changes in the threat, reward, and memory systems can mean everyday life takes a greater toll. Being on ‘high alert’, for example, may also reduce attentional capacities to learn new things. Over time this can lead to chronic stress responses in the body and this may even affect the functioning of the immune system.
Second, brain adaptations may impact the child’s future social experience. In particular, they may increase the likelihood that they experience future stressful events. We call this stress generation. It is well established that children who have experienced abuse and neglect are more likely to be bullied, experience relationship problems or face exclusion than their peers. Why this happens is not straightforward. Scientists are working to understand what is likely a complex process, involving a child’s genetic make-up, alterations in brain systems and social behaviour – and how these may contribute to stress generation over time.
Third, we believe that brain changes following abuse and neglect can impact everyday relationships. Studies have shown that abuse and neglect in childhood can lead to reduced social support over time – even into adulthood. We call this social thinning. We have suggested that changes in the threat, reward, and memory systems may make harder for children to build and maintain relationships. Yet supportive relationships are key to a child’s wellbeing and mental health.
While scientists have documented evidence of differences in brain structure and function in children who have experienced abuse and neglect, the practical implications of these findings are less clear. However, we are beginning to delineate complex biological and social mechanisms whereby latent vulnerability unfolds over time. It is clear that biological and social pathways to vulnerability following abuse and neglect are intricately intertwined. There is much work to do in order to better specifiy these mechanisms so that they can inform frontline practice.
One take-home message from the research to date is that brain changes associated with abuse and neglect are evident even before mental health problems emerge. This should act as a wake-up call in our efforts to develop effective preventative approaches – and help children before mental health problems emerge.