Childhood Trauma: The Effects on Brain Development, Mental Disorders, and Memory
This literature review explores the affects that childhood trauma has on the structural development of the brain, psychiatric disorders, and memory. Trauma experienced in childhood alters the structural development of the corpus callosum, hippocampus, and amygdala. Although many other regions of the brain are altered by trauma exposure, these three regions are strongly affected. The brain alterations, stress, and emotional and physical toll that childhood trauma takes on individuals increases the risk of developing mental illnesses. The mental illnesses associated with childhood trauma covered in this literature review are post-traumatic stress disorder (PTSD), bipolar disorder, and depression. Coping with negative effects that childhood trauma has is associated with overgeneral autobiographical memory retrieval and psychiatric disorders. This literature review covers intertwining issues that childhood trauma can have on indivdiuals.
Childhood Trauma: The Effects on Brain Development, Mental Disorders, and Memory
The Impact of Childhood Trauma on Brain Development
The human brain is remarkably complex and the development of this organ can be heavily impacted by the experiences and individual lives through. Stress is a life factor that is commonly known to alter the functions and development of the brain. Childhood trauma is a source of toxic stress that can be a strong determinant in how a child’s brain will be developed.
The corpus callosum is the part of the brain that connects the right and left hemisphere and is in charge of communication between the two hemispheres (Rinne-Albers, et al., 2013). Due to the fact that the myelination of the corpus callosum starts approximately between 6 months of age to 3 years and then continues to develop into adulthood suggests that childhood trauma, specifically early childhood trauma, can affect the structural development of the brain (Jackowski, et al., 2009). Rinne-Albers et al. (2013) compared results from six studies researching the effect of childhood trauma on the structural development of the corpus callosum and out of those six studies, five found significant results suggesting that trauma can affect the structure of the corpus callosum. As cited by Rinne-Albers et al. (2013), De Bellis et al. found that children diagnosed with post-traumatic stress disorder (PTSD) had a smaller sized middle and posterior regions of the corpus callosum which is not surprising due to the finding that PTSD and dissociation, which are both common in individuals who have experienced childhood trauma, is associated with a reduced size of regional and total corpus callosum measurements.
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Rinne-Albers et al. (2013) also suggests that varying types of abuse and gender have an impact on how the corpus callosum in affected by childhood trauma. Teicher et al. found that in a population of child psychiatric patients who had either experienced abuse or neglect that the cross-sectional of the corpus callosum was reduced in size in compared to a control group (as cited in Rinne-Albers, et al., 2013). It was found that girls who had experienced sexual abuse had a reduced cross-sectional area located in the rostral region of the corpus callosum while boys more commonly experienced neglect and had a reduction of the cross-sectional area in the caudal region of the corpus callosum (Rinne-Albers, et al., 2013). It is possible that commonality of neglect occurring early in life and the rostral-caudal pattern that myelinization occurs in the corpus callosum is responsible for the differences in gender (Rinne-Albers, et al., 2013). The corpus callosum has hundreds of millions of axons and plays an essential role in cognition (Hinkley, et al., 2012). It is suggested that abnormal structural development of the corpus callosum affects intelligence, processing ability, and problem solving in children and is associated with developmental disorders such as autism and attention-deficit disorder (Hinkley, et al., 2012). The importance of the corpus callosum and the negative effects that childhood trauma can potentially have on the development of this brain structure, demonstrates the detrimental effects trauma and violence can have on an individual.
The hippocampus is a structure of the brain that is important to study in correlation with childhood trauma due to the crucial involvement of the development and retrieval of memories, the susceptibility of the structure to be impacted by stress, and the abnormalities of the structure present in individuals with mental illness (Teicher & Samson, 2016). Teicher and Samson (2016) composed a research review regarding the effects of childhood abuse and neglect on the brain and found that the structural development of the hippocampus is effected by childhood trauma. The hippocampus is highly comprised of glucocorticoid receptors and is prone to damage from an excess of glucocorticoids (Teicher & Samson, 2016). An example of a glucocorticoid is cortisol, which spikes when experiencing stress, so it is logical to assume that individuals who experience childhood trauma would have heightened cortisol levels due to the stress of the maltreatment they experience and this stress would alter the structure of the hippocampus (Teicher & Samson, 2016).
The altered structure of the hippocampus in individuals exposed to childhood trauma who later developed psychiatric disorder was recognized in the research review conducted by Teicher and Samson (2016). Teicher and Samson (2016) found that 30 out of 37 research studies reported significant results of adults having a reduction in size of their hippocampi compared control groups who had no experience of childhood maltreatment or an inverse correlation between the severity of the childhood maltreatment and hippocampus volume. A reduction in hippocampal volume is the most reported finding in studies comparing individuals with Major Depression Disorder to a healthy control group (Teicher & Samson, 2016). Research that examined right and left hippocampal differences in individuals with Borderline Personality Disorder found right side differences, which may suggest that right side structural alteration of the hippocampus due to trauma may put individuals at risk for the development of Borderline Personality Disorder (Teicher & Samson, 2016). A lower than normal volume of the hippocampus has been linked to eight psychiatric disorders and trauma is a prominent risk factor in the development of all of these disorders (Teicher & Samson, 2016). Overall, the structural alteration of the hippocampus is associated with the stress created by the experience of trauma which can increase the risk of the development of psychiatric disorders (Teicher & Samson, 2016).
The amygdala is a brain structure that encodes implicit emotional memories and detects stimuli and threats (Teicher & Samson, 2016). The number of glucocorticoid receptors in the amygdala is extremely high so similarly to the hippocampus this brain structure is susceptible to the effects of stress (Teicher & Samson, 2016). The amygdala experiences a developmental spurt directly after birth and between ages 9-11 and after these period of growth, pruning occurs (Teicher & Samson, 2016). A study conducted by Marusak et al. (2015) researched if there would be a difference in the automatic regulation of emotional processing in youth who have endured trauma compared to healthy controls.14 youth had a functional MRI while participating in an emotional conflict test that consisted of categorizing facial expressions with an overlying emotional word present (Marusak, et al., 2015). Marusak et al. (2015) found that the individuals who experienced trauma had a higher amygdala reactivity when presented emotional conflict and had a harder time regulating emotional conflict. Additionally, it was found that youth who had been exposed to maltreatment displayed an increase in conflict-related amygdala reactivity which is related with a decrease in trait reward sensitivity (Mausak, et al., 2015). These findings by research conducted by Mausak et al. (2015) suggest that individuals that have experienced childhood trauma have a decrease in their automatic regulations of emotional processing and overly process emotional conflict that are involved in the detection of threats.
Similarly, Teicher and Samson (2016) found in their research review that childhood trauma can lead to an increase in the size of the amygdala during early childhood or lead to a decrease in amygdala volume later in life when exposed to an influx of stress. Research findings and the association of the structural differences of the amygdala in individuals with psychiatric disorders that are commonly present in people who have experienced childhood mistreatment such as post-traumatic stress disorder, borderline personality disorder, and schizophrenia displays that childhood trauma and violence can impact the development of the brain’ structure (Teicher & Samson, 2016).
Mental Health in Relation to Trauma Exposure
Childhood trauma is an extremely common risk factor in the development of mental illness. The altered brain structure, the toxic stress, and the negative impacts that trauma has emotionally and physically can cause serious implications in an individual’s life. One of these negative implications is the development of psychiatric disorders.
Posttraumatic Stress Disorder
According to the American Psychiatric Association, Posttraumatic Stress Disorder (PTSD) is a disorder that occurs when a person experiences traumatic events and has symptoms that persists for more than a month and in most cases lasts for many months or year. The symptoms listed are intrusive thoughts, avoiding reminders, negative thoughts and feelings, and arousal and reactive symptoms and these symptoms are problematic in typical functioning (American Psychiatric Association, 2013). Adverse childhood experiences (ACEs) are events such as physical, sexual, and emotional abuse, neglect, household violence, poverty, etc. that cause individuals to experience trauma. The lifetime prevalence rate of PTSD is about 7.8% while the lifetime prevalence rate of PTSD in adults who has experienced traumatic events as children is anywhere from 30% to 38% (Messman-Moore & Bhuptani, 2017). In a population of 3,936 women, Schneider et al. studied the effect that childhood sexual abuse, physical abuse, and emotional abuse had on PTSD (as cited in Messman-Moore & Bhuptani, 2017). Although each type of childhood abuse is associated with PTSD, having experienced two types of the abuse listed above doubled the risk of probable PTSD, and experiencing all three types correlated with a 23-fold increased risk of probable PTSD (Messman-Moore & Bhuptani, 2017). Childhood trauma is associated with an increased risk of PTSD and unsurprisingly the more types or number of childhood traumatic experiences the risk grows exponentially.
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PTSD is a disorder that is comorbid with other mental health disorders and overall causes difficulty in mental functions. Messman-More and Bhuptani (2017) state that 93% of people who have PTSD have one other mental disorder, 54% have two or three comorbid disorders, and 11% have four associated disorders. Substance abuse disorders, eating disorders, and Borderline Personality disorder are three disorders that have a high comorbidity with PTSD according to Messman-Moore and Bhuptani (2013). The lifetime prevalence of having a substance use disorder is increased in those who have a diagnosis of PTSD by 17.2% and in adolescents by 2 to 4 times (Messman-Moore & Bhuptani, 2017). It was found in clinical studies that about 37 to 68% of people diagnosed with PTSD also have Borderline Personality Disorder (Messman-Moore & Bhuptani, 2017). PTSD due to childhood trauma affects the quality of life of many individuals and the high comorbidity rates with other disorders only worsens mental health.
An additional mental illness that has been found to be associated with childhood trauma is bipolar disorder. Roughly 30 to 50% of individuals with bipolar disorder have endured some type of childhood maltreatment, with the most frequent type being emotional abuse (Brietzke, et al., 2012). Those who have bipolar disorder and have experienced childhood trauma are more likely to experience repeated symptoms of depression and have difficulty with successful treatment, which indicates the bipolar symptoms in trauma victims can be especially difficult (Brietzke, et al., 2012). Brietzke et al. (2012) suggests that experiencing sexual and physical abuse in childhood is associated with an increase in manic symptoms which is a key characteristic in bipolar disorder and profoundly impacts an individual’s life. Conversely, when examining the impact of other life stressors and factors on bipolar disorder, childhood trauma can act as a catalyst to the first episode when experienced with these factors (Brietzke, et al., 2012). Moreover, childhood abuse is suggested to be associated with an earlier onset age, higher comorbidity, and worsened symptoms such as higher incidences of suicide attempts, depressive symptoms, and manic episodes (Brietzke, et al., 2012).
Research by Larsson et al. (2013) studied 141 individuals diagnosed with bipolar disorder and their childhood history in order to assess the correlation between bipolar disorder and childhood trauma. Results found that trauma is significantly correlated with bipolar disorder and different types of trauma are correlated with different symptoms of bipolar disorder (Larsson, et al., 2013). The three types of childhood trauma identified that are associated with the development of bipolar of disorder were emotional abuse and neglect, physical abuse, and sexual abuse (Larsson, et al., 2013). Sexual abuse in particular was associated with a heightened number of mood episodes in the participants with bipolar disorder and emotional abuse and neglect was associated with low Global Assessment of Function scores (Larsson, et al., 2013). The data of individuals who experienced physical abuse had data that was found to be significantly associated with low Global Assessment of Function scores, an inflated number of mood episodes, and self-harm (Larsson, et al., 2013). Overall, Larsson et al. (2013) suggests that childhood trauma is associated with a higher severity of bipolar disorder and increases the rate at which bipolar is developed.
Depression is a mental illness is that is known to be associated with childhood maltreatment due to the stress and trauma that children experience when facing adversity. Bernet and Stein (1999) found in comparing a group of adults with a diagnosis of major depression to a control group of healthy adults and both groups childhood traumas that participants with major depression recalled significantly higher severity of emotional abuse and neglect and physical abuse compared to the control group. The recall of childhood abuse is associated with a higher level of depression that also has an earlier onset, a higher number of depressive episodes, a higher comorbidity with other illnesses (Bernet & Stein, 1999). The work of Bernet and Stein (1999) suggests in their sample populations that emotional abuse accounted for 25 to 28% of the depressive episodes and the age of major depression onset.
Research conducted by Rehan et al. (2017) studied if individuals that experienced severe forms of child abuse had a greater likelihood of developing depression, anxiety, and alcohol abuse. It was found that men participating in this study that had experienced severe emotional and physical abuse and physical neglect were significantly associated with clinical depression and/or anxiety (Rehan, et al., 2017). For women, all types of severe maltreatment examined in this research study (emotional, physical and sexual abuse, and emotional and physical neglect) were associated with clinical depression and/or anxiety (Rehan, et al., 2017). Vitriol et al. (2017) states that the higher intensity of the trauma experienced, the higher the risk of developing depression. Depression in individuals who have experienced severe childhood trauma is associated with an increase in endurance and occurrence of depressive symptoms, higher rates of suicide, and an increase in comorbidity with other psychiatric disorders (Vitriol, et al., 2017). In conclusion, childhood trauma is a risk factor for the development of depressive symptoms and disorders which have a high comorbidity with other psychiatric disorder, suicide, and cost societies an immense amount of money (Vitriol, et al., 2017).
Memory and Childhood Trauma
Overgeneral Autobiogrpahical Memory Retrieval
A study conducted by Ono and Devilly (2013) studied self-discrepancy and the effect it has on overgeneral memory retrieval. In Ono and Devilly’s (2013) research, three groups were studied; a group of 29 individuals who experienced childhood trauma, a group of 17 individuals who experienced adulthood trauma, and a group of 26 people who had no trauma experience. The participants were given cue words that were wither positive, negative, threatening, or a neutral control word and were asked to write down a memory for each word listed and were given 30 seconds to do so (Ono & Devilly, 2013). Results found that participants in the childhood trauma group had significantly greater memory retrieval for the negative cue words presented and those in the adulthood trauma group had significantly higher level of memory retrieval of threatening cue words in comparison to the non-trauma exposed control group (Ono & Devilly, 2013). The results found by Ono and Devilly (2013) suggest that individuals exposed to trauma affects their overgeneral memory retrieval. The self-discrepancy of people who have lived through trauma is associated with negative and threatening memory retrieval, which is logical considering trauma creates negative and harmful memories (Ono & Devilly, 2013).
Psychopathology is thought to be a reason why overgeneral autobiographical memory exists. People may not want to remember the traumatic experiences they have endured so they may suppress their memories in order to protect themselves. Similar to Ono and Devilly, Griffith et al. (2016) studied overgeneral autobiographical memory by using positive and negative cue words and having their participants record their memories. The research was conducted on individuals diagnosed with major depressive disorder, because it is difficult to declare if overgeneral autobiographical memory is caused from trauma or depression so Griffith et al. (2016) experimented with individuals who had both major depressive disorder and had experienced trauma. It was found that there was a significant association between people who had experienced physical abuse as a child and overgeneral autobiographical memory (Griffith, et al., 2016). The association was still existent when covarying out effects of psychiatric disorders, suggesting that there is strong evidence between childhood maltreatment and autobiographic memory. There was not a significant association between childhood sexual abuse and overgeneral autobiographical memory, but the results of research on childhood maltreat and autobiographical memory is extremely varied and has found opposite of what Griffith et al. (2016) found. Due to the varying results of the research it is possible that overgeneral autobiographical memory occurs for many reasons which could be the avoidance of reliving emotional trauma, rumination leading a person to be more susceptible to the pain of trauma, and low executive capacity leading to poor coping skills (Griffith, et al., 2016). It is suggested that overgeneral autobiographical memory is significantly associated with childhood trauma and mental disorders and is another aspect of life that is altered due to maltreatment.
Childhood trauma is a factor that immensely affects an individual’s life. Trauma affects the development of the brain, especially when experienced in early childhood. The cerebral cortex, hippocampus, and amygdala are all structurally impacted by childhood trauma and therefore abnormal brain functioning can occur. Childhood trauma is known to be a common risk factors for many mental illnesses and typically can worsen the symptoms of these illnesses. Cognitive processes are affected by the brain alterations, stress, and the attempt to cope with childhood trauma. There are many more aspects of life that are affected by adverse experiences and should continue to be researched. Further in-depth research on how trauma affects the structural development of the brain would be beneficial and would lead to more knowledge on mental illness and cognition. With additional research on how trauma affects the brain and it’s cognitive processes would lead to many more discoveries and methods of healing and coping.
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