It is not news that people abused as children are more exposed to clinical depression, anxiety, and a higher risk of death from suicide. But now, researchers have begun to reveal what happens in the brain following this kind of trauma.

According to data provided by the Children's Bureau of the United States Department of Health and Human Services, there was a 3.8 percent increase in reported child abuse cases in the country between 2011 and 2015. This amounts to 683,000 cases of child abuse in 2015 alone in the U.S.

Research suggests that this type of trauma in childhood leaves deep marks, giving rise to issues including post-traumatic stress disorder, depression, anxiety, and substance abuse.

Now, a team from the McGill Group for Suicide Studies at the Douglas Mental Health University Institute and McGill University in Montreal, Canada, aims to decipher how a history of abuse can impact key brain mechanisms, affecting mental health.

Dr. Pierre-Eric Lutz and colleagues noted that in adults who went through severe abuse as children, the neural connections in an area of the brain associated with the regulation of emotion, attention, and various other cognitive processes are critically impaired.

The researchers' findings were published recently in The American Journal of Psychiatry.

White matter affected after childhood abuse

Previous research has pointed out that individuals who experienced neglect and abuse as children have decreased volumes of white matter in various areas of the brain.

White matter consists in myelinated axons, which are the projections of nerve cells allowing electric impulses to "travel" around and carry information, while myelin is the isolating "coating" in which these tracts are sheathed. Myelin helps these electrical impulses to travel faster, allowing information to propagate efficiently.

The volume and structure of white matter correlate with an individual's capacity for learning, and this component of the brain keeps on developing throughout early adulthood - unlike gray matter.

Although these changes - regarding the volume of white matter in people who have undergone abuse as children - have been noted before, other studies used MRI to scan the brains of the participants.

Dr. Lutz and team instead decided to study brain samples collected postmortem, in order to better understand what happens at a molecular level.

Myelination of axons was disrupted

The researchers analyzed samples collected from the brains of 78 individuals who had died due to suicide. All the brain samples were obtained using the Douglas Bell Canada Brain Bank.

Of these people, 27 had been diagnosed with depression and had undergone severe abuse in their childhood, 25 had been diagnosed with depression but had no history of childhood abuse, and 26 had not been diagnosed with any mental disorder and had no history of child abuse.

The brain tissue from the three groups of people were studied and compared. Alongside these, the researchers also looked at brain samples from 24 mouse models illustrating the impact of environment on the early developmental stages of the nervous system.

People who had undergone abuse as children exhibited thinner myelin coating in a large percentage of nerve fibers. This was not true for the other two brain sample types studied.

Also, the researchers noted that abnormal development at a molecular level specifically impacted the cells involved in the production and maintenance of myelin, which are called oligodendrocytes.

Connectivity of key brain areas impacted

The team also found that some of the largest axons affected were unusually thickened. They say that these peculiar alterations may all act together to negatively impact the connectivity between the anterior cingulate cortex, which is a region of the brain implicated in processing emotions and cognitive functioning, and associated areas of the brain.

These affiliated areas include the amygdala, which plays a key role in regulating emotions, and the nucleus accumbens, which is involved in the brain's reward system, "telling" us when to anticipate pleasure.

This could explain why people who underwent abuse in childhood process emotions differently and are more exposed to negative mental health outcomes, as well as substance abuse.

The researchers' conclusion is that experiencing abuse in early life "may lastingly disrupt" the connectivity between the areas of the brain that are key in cognitive and emotional processes.

However, they admit that the full mechanism involved is not yet clear, and they hope that further research could shed additional light on the impact of childhood trauma on the brain.