Neuroimaging studies have shown that childhood abuse or maltreatment is associated with structural brain changes. The four main categories of child abuse are: neglect, physical abuse, emotional abuse, and sexual abuse. Neglect is a failure by a child’s caregiver to meet a child’s basic needs, including adequate shelter, safety, health care, supervision, or nutritional requirements. In physical abuse, the child is injured by hitting, punching, kicking, shaking, burning, stabbing or choking. The emotional abusers ignore, isolate, terrorize, and reject their victims. Child sexual abuse refers to any sexual activity with a child, including sexual intercourse, attempted intercourse, touching of genitals directly or through clothing, exhibitionism, exposure to adult sexual activity or pornography, and using the child for prostitution or pornography.
The human brain is still developing during childhood through processes of synaptic remodeling, which affects both gray and white matter organization. Child abuse is a serious stressor that has the potential to disrupt these neurodevelopmental processes due to physiological, neurochemical, and hormonal changes.
Brain regions most frequently affected by childhood abuse include the prefrontal cortex, anterior cingulate cortex, hippocampus, amygdala, corpus callosum, and cerebellum. This suggests that fronto-limbic circuits may be most affected.
Picture from original article by Hart H and Rubia K. Frontiers in Human Neuroscience March 2012.
Early adversities can have detrimental effects on the mental health of the child. Experiencing abuse put children at risk of developing mental health consequences and psychiatric disorders. Internalizing behavioral problems include limited stress tolerance, anxiety, affective instability, depression, suicidality, post-traumatic stress disorder (PTSD), dissociative disturbances and hallucinatory phenomena. Externalizing behavioral symptoms include poor impulse control, episodic aggression, substance abuse, attention deficit hyperactivity disorder and conduct disorder. Abuse usually leads to PTSD, with incidence ranging from 36% to 63%.
A significant concern in interpreting the neuroimaging findings in individuals who had experienced childhood abuse is that the majority of studies investigate subjects with associated psychiatric conditions. The results showing that survivors of childhood abuse with PTSD have more pronounced structural brain changes than survivors without PTSD make it difficult to determine the cause of these changes.
About the study
Researchers from Turkey studied the effects of sexual abuse on the limbic and prefrontal cortex structures in adolescent brains. Based on previous research, the authors hypothesized that the volumes of amygdala and hippocampus, as well as the cortical thickness of the prefrontal cortex would be altered in sexually abused adolescents compared to non-abused participants.
The study included 57 adolescents who had been sexually abused and 33 healthy controls (mean age: 16.5± 0.2). All the participants were female. The following exclusion criteria applied for both study groups: a score of 70 or less on the intelligence quotient, a history of perinatal complications, a history of head injury with transient loss of consciousness lasting more than three minutes, a neurological disorder, a developmental disorder, and a personal or family history of psychotic disorders or bipolar disorder. Participants who had taken antidepressants within four weeks before the study were also excluded.
The psychiatric evaluation process included the Kiddie schedule for affective disorders and Schizophrenia present and lifetime, the Beck depression inventory, the State-trait anxiety inventory, and the Childhood trauma questionnaire. A psychologist used the Wechsler intelligence scale for children aged 9-16 and the Wechsler adult intelligence scale for participants after the age of 16.
Results
The results of magnetic resonance imaging scans showed that participants who had been sexually abused had larger volumes of the right and left hippocampus compared to healthy controls. The volumes of the right amygdala in the sexually abused group were significantly greater in comparison to those in the control group. Despite the larger volumes of the left amygdala in the participants who had been sexually abused, the difference did not reach a statistically significant level. The cortical thickness of the inferior frontal gyrus was significantly reduced in the sexually abused group compared to controls.
There was no correlation between scores on the Childhood trauma questionnaire and the observed changes in brain structure, including the thickness of the prefrontal cortex or the volumes of the hippocampus or amygdala. According to the authors, the results showed that neuroimaging data correlated only with history of sexual abuse and not with other types of abuse or psychiatric diagnoses.
The hippocampus is a part of the limbic system and plays an important role in the processes of learning and memory. Data from previous studies on childhood abuse and structural brain changes have shown that hippocampal volume is particularly sensitive to sexual abuse occurring between the ages of 3–5 years and 11–13 years. Some studies have reported a significant correlation between hippocampal volume and the onset or duration of child abuse. The amygdala plays a key role in emotional processing, assessing threatening information, controlling behavior, and memorizing emotional events. As memory and emotion processing are of extreme importance in threatening situations, child abuse may be associated with structural amygdala changes. There is conflicting evidence of structural abnormalities of the amygdala in abused children. One study found that amygdala volume increased in a small sample of postinstitutional adolescents with severe early deprivation. This increase correlated with time spent in the institution.
The prefrontal cortex plays a major role in all functions that characterize mature adult behavior, including higher level motor control, attention, working memory, personality expression, emotion, and motivation regulation. The prolonged development of the prefrontal cortex makes it an important target for abnormal development in children who have been exposed to severe environmental stressors, such as abuse. Numerous studies have shown that lateral prefrontal cortex, particularly the inferior frontal gyrus, is thinner in children with adverse childhood experiences. One study using tensor-based morphometry found smaller volumes of dorsolateral prefrontal cortex, medial prefrontal cortex, and orbitofrontal cortex in children who had been physically abused and did not have PTSD. An MRI study of women who had been sexually abuse in childhood found reductions in gray matter volume in whole frontal cortex, left dorsolateral prefrontal cortex and right medial prefrontal cortex.
The prefrontal cortex has regulatory and inhibitory functions on the limbic cortex. These functions could be maladaptive in children who are exposed to hazardous experiences. The previous research has shown that the limbic system is hyperactive in children who had experienced childhood abuse. Therefore, greater volumes of amygdala and hippocampus combined with a reduction in cortical thickness in the inferior frontal gyrus may represent maladaptive response to dangerous experiences.
The authors concluded that this study provided structural evidence of threat appraisal and response in children with a history of sexual abuse.
Journal Reference
Bulut Demir MH et al. The effects of sexual abuse on female adolescent brain structures. Scandinavian Journal of Child and Adolescent Psychiatry and Psychology 2023; Vol. 11: 87-94. (Open Access). https://doi.org/10.2478/sjcapp-2023-0009
Hart H and Rubia K. Neuroimaging of child abuse: a critical review. Frontiers in Human Neuroscience March 2012; Volume 6, Article 52. (Open Access). https://www.frontiersin.org/articles/10.3389/fnhum.2012.00052/full