Article summary of Decreased cortical representation of genital somatosensory field after childhood sexual abuse by Heim et al. - Chapter

Introduction

Unfavorable childhood conditions lead to an increased risk of developing various psychiatric disorders and medical illnesses in later life. A clinical consequence of sexual abuse in childhood is the development of sexual dysfunction. Examples of this are anorgasmia, no experienced pleasure in sexuality and / or chronic genital pain or pelvic pain in adulthood. Various studies state that the human brain is plastic (= cortical / neural plasticity). This means that the brain adapts to the environment as a reaction to certain (life) events. There may be either an enlargement or a reduction in cortical areas and it is known that events that are not good for development can cause cortical areas to shrink and that enriching events can cause cortical areas to enlarge. In the case of shrinkage of cortical areas, this means that the brain tries to limit the harmful effects of the negative experiences and tries to protect itself against this. This is the case with sexual abuse during childhood. In this study, the cortical thickness was analyzed by MRI (magnetic resonance imaging).

Methods

Participants

51 healthy African-American, white and other women participated in this study. Among them there were women with and without a history of abuse and / or neglect before puberty and with and without depression. All women had a normal menstrual cycle, had no medical illnesses and did not use any medication. Women with a history characterized by psychosis, bipolar disorder, substance abuse, or alcohol abuse were excluded from this study.

Clinical assessment

The Childhood Trauma Questionnaire (CTQ) was used in this study. The CTQ is a form of self-report that assesses emotional, sexual and physical abuse and emotional and physical neglect. The five subscales each contain five items and a positive score on a subscale means that events are most often answered as 'true'. This showed that moderate to severe mistreatment occurred in 28 women and that 23 women experienced little to no abuse. 

A semi-structured clinical interview was also used to map the starting age and duration of the trauma, and this correlated highly with the CTQ. To map the current mental health, the Structured Clinical Interview for DSM-IV-TR was conducted. This revealed that twelve women were depressed during the study and that nine women suffered from post-traumatic stress disorder.

MRI: a 3D MRI technique was used.

Cortical thickness analysis: an analysis of cortical thickness was also performed.

Statistical analysis: cortical thickness was used in the statistical analysis as a dependent variable with respect to the total CTQ score as an independent variable. Furthermore, the age of the start of the abuse and the duration thereof were also taken into account.

Results

A regression analysis was conducted to compare cortical thickness to the total CTQ score. This analysis showed that people who had experienced difficulties during childhood, had cortical shrinkage. This was most visible in the lateral somatosensory cortex located in the left hemisphere. This area is connected to the female clitoris, the genital area and the area around the mouth. The same was true for the anterior cingulate gyrus, the precuneus and the gyrus parahippocampalis (also known as seahorse winding). These are cortical areas that play a role in emotion regulation, self-awareness and the coding of memories.

The effects were less clear for the right hemisphere. However, a maximum was found in both the lateral area of ​​the right motor cortex, as well as in the gyrus parahippocampalis and in the central area of ​​the posterior cingulate cortex. A separate analysis for the effect of experiences with sexual abuse on cortical shrinkage revealed a shrinkage of the somatosensory cortex. This area is associated with the female clitoris and with the area around it in the left hemisphere. Furthermore, the gyrus parahippocampalis appeared to be affected by sexual abuse in both hemispheres.

There also appeared to be an effect of emotional abuse on cortical shrinkage. This was seen in the left and right precuneus and in the left anterior and posterior cingulate cortex. These areas are important for self-reflection, self-awareness, and one's own perspective of the self. At an earlier start of the abuse / abuse, effects of cortical shrinkage were found in the right temporal strain, the left parietal lobe, the left frontal lobe and the right frontal strain. These areas are important in autobiographical memory. Finally, there was also a shrinkage of the anterior cingulate cortex. This provides an explanation for the phenomenon that people who have been abused in their youth often cannot remember this afterwards. No effects were found for the duration of the abuse.

Discussion

This research has shown that childhood abuse causes changes or adaptations in the brain. This often involves cortical shrinkage and there appears to be a specific effect for each area as a result of a specific type of abuse. This is the result of a protection mechanism of the brain. 

Different mechanisms can explain the changes in brain structures. The shrinkage of the primary somatosensory cortex observed in this study would be the result of both top-down and bottom-up mechanisms. Cognitive adjustment plays a role in the top-down mechanism. This is explained on the basis of an example about pain perception. Several studies showed that by diverting attention from the painful stimuli, attention to experiencing the pain and thus the activation of the somatosensory cortex was reduced. It is stated that if this same mechanism comes into effect during the development and formation of the synapses, as is the case in childhood, the final formation of the synaptic compounds in the neocortex will be significantly less. The bottom-up mechanism assumes that physical and sexual abuse during the synapse period can lead to inhibition and that this could reduce the number of synapses in the somatosensory cortex.

Inadequate development of the genital somatosensory region in the brain could lead to reduced sexual perception and / or sexual dysfunction in later life. Women who have experienced sexual abuse in childhood will probably have a lower pain threshold due to the reduced thickness of their somatosensory cortex. This will cause them to experience more genital and pelvic pain. In the case of poor development of the precuneus and the cingulate cortex, which play a role in emotion regulation, there is likely to be cognitive avoidance and inhibition of emotional processes. Studies conducted into childhood trauma showed that in this case there was a reduced volume of the anterior cingulate cortex, but there was no distinction made between the different types of trauma.

An alternative explanation is that people who are sexually abused in childhood are more likely to avoid sexual activity in adulthood. This can lead to a reduced size of the somatosensory cortical area. Emotional abuse in childhood would ensure that these children would later become refusal-sensitive adults who avoid assessment situations and thus use this cortical area too little, which in turn will lead to shrinking of this area. There was no longitudinal MRI and behavioral data in this study, so this hypothesis could not be tested. Another limitation of this investigation is that retrospective self-reporting has been used. Issues such as forgetting childhood events can yield bias. However, meta-analysis has shown that this would lead to false-negative rather than false-positive self-reporting.