The legacy of maltreatment on the brain

The World Health Organization defines childhood maltreatment as the abuse and neglect of children, including all types of physical and emotional abuse, sexual abuse, neglect, negligence or other forms of exploitation.

And it’s a major problem with potential life-long consequences.

International studies have found almost 40 per cent of children experience some form of maltreatment. A recent Australian study found that 18.5 per cent of children had been the subject of a report to Child Protection Services by the age of five or six.

Those with a history of childhood maltreatment are two to four times more likely to develop a mental health disorder – like depression or substance dependence.

Given the scale of the issue, it’s important to understand why victims of maltreatment are vulnerable to poor mental health throughout their lives.

The developing brain

During childhood and adolescence, the human brain is undergoing dynamic development and, for this reason, it’s considered particularly vulnerable.

As well as changes in brain structure, the connectivity (or communication) between different regions of the brain evolves significantly as it becomes increasingly refined.

Early adverse experiences, like maltreatment, may trigger a cascade of physiological reactions that can alter the course of brain development. These alterations can, in turn, contribute to poor mental health.

This ‘developmental miswiring’ – or alterations in the connectivity between different regions of the brain – is increasingly recognised as an important vulnerability marker for mental health disorders.

Maltreatment and ‘developmental miswiring’

Our recent research looked at the associations between childhood maltreatment and widespread alterations in brain functional connectivity.

We found evidence for an effect of childhood maltreatment (particularly neglect) on the brain’s connectivity development in 130 Australian adolescents.

Although earlier research has found links between childhood maltreatment and brain structure and function, ours is the first longitudinal study into the effects of childhood maltreatment on brain functional connectivity in adolescents.

Longitudinal studies use repeated measures that follow particular people over prolonged periods of time — sometimes years or decades – in order to get a fuller picture of trends or patterns.

For our research, this approach was critical, as it allowed us to investigate how maltreatment may lead to deviations from typical developmental trajectories, which was important for our understanding of mental health outcomes for this group.

Stress-related acceleration vs delay

One theory – known as the ‘stress acceleration hypothesis’ – suggests that the experience of maltreatment can accelerate brain development during childhood and adolescence to reach ‘adult like’ functioning earlier.

This is thought to reflect evolutionary adaptation – faster brain development may enable a person to regulate emotions and behaviour independently, which could be advantageous in high-stress conditions.

To test this, our team undertook normative modelling which entails examining how connections in the brain change across the whole sample, regardless of maltreatment experiences.

Our aim was to examine the overlap between connections in the brain that develop with age across our whole sample group, and those changes associated with maltreatment. This would allow us to investigate whether maltreatment accelerates or delays normal development of brain connectivity.

Contrary to the stress acceleration hypothesis, we found that exposure to childhood maltreatment was associated with delayed (or immature) brain development during adolescence. This is consistent with other research which found that maltreatment is associated with delays in cognitive ability, language and other key aspects of a child’s development.

Childhood maltreatment, particularly neglect, may lead to delayed brain development as an evolutionary adaptive response to prolong the period during which the brain can be shaped by environmental inputs ­– such as language and cognitive stimulation.

Unfortunately, in most cases, the neglected child doesn’t receive this cognitive or language input at home, which has ongoing consequences for their development.

Our research also found that males who experienced maltreatment as children had a specific pattern of changes in brain connectivity that wasn’t present in females.

These changes were observed primarily in the brain systems involved in emotion regulation, cognition, as well as the processing of stimuli from the environment.

This may (cautiously) indicate that male brains could be particularly vulnerable to the effects of childhood maltreatment during adolescence.

Childhood maltreatment and mental health

Our study suggests that childhood maltreatment may lead to depression in adolescence in part by altering the development of brain connectivity.

The alterations in connectivity we found related to maltreatment and depression were primarily in brain networks important for ‘higher-order’ functions like planning, decision-making, goal setting and self-reflection.

Importantly, these alterations may partially explain the association between maltreatment and depressive symptoms in late adolescence, and the impairments often reported in individuals with depression and maltreatment history.

Our finding that maltreatment may derail brain development during the ‘sensitive’ period of adolescence is important knowledge as it’s a crucial time that can set the stage for healthy brain function throughout life

But it also sheds light on why childhood maltreatment can have such long-term negative consequences and, hopefully, help inform ways of tackling the legacy of maltreatment.

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