Childhood trauma is defined as a psychological consequence of sudden or ongoing external blows that temporarily leave the child helpless, damage coping mechanisms, or a series of ongoing external injuries (1). Bernstein and Fink (2) proposed a definition that includes child abuse and neglect, which includes verbal attacks on a child's sense of self-worth, bodily attacks that pose a risk of injury, sexual contact with a child, failure to provide basic psychological and emotional needs, and failure to meet basic needs. Terr (1) emphasized that 4 features are important in traumatized children regardless of their age. These were expressed as visualized or repeatedly perceived memories, repetitive behaviors, fears associated with trauma, changing attitudes about people, life and the future. There is broad evidence that childhood trauma and different subtypes are frequent in various populations. In a study conducted with a German sample, 2510 participants aged 14–94 completed the Child Trauma Questionnaire (CTQ); as a result, 2.6% of the participants stated that they were subjected to severe emotional abuse, 3.3% physical abuse, 2.3% sexual abuse, 7.1% emotional neglect, and 9% physical neglect (3). In the meta-analysis study where the prevalence of physical and emotional neglect was examined, it was pointed out that physical neglect based on self-report was 16.3%, emotional neglect was 18.4% (4). In a meta-analysis study that examined 217 studies published between 1982 and 2008, it was concluded that 118 out of 1000 children were exposed to sexual abuse. Another meta-analysis study including studies conducted in 22 countries on the prevalence of childhood sexual abuse showed that 7.9% of men and 19.7% of female were exposed to sexual abuse before the age of 18 (5). This situation reveals that sexual abuse is a universal problem (6). In another study conducted with students of the Faculty of Medicine (n = 192), 32.3% of the students stated that they experienced emotional abuse, 14.6% physical abuse, and 8.9% sexual abuse (7).
The knowledge of childhood trauma and other forms of violence is difficult to access due to social taboos, studies show that traumatic childhood experiences are common (8). In addition to the prevalence of this condition, traumatic childhood experiences have developmental and long-term effects in many areas of functionality (8). Childhood traumas can interrupt developmental processes and lead to neurological, physiological and psychological consequences (9). Adults who experienced childhood trauma developed many psychopathologies in life. Most of the adults suffering from mood disorders (10, 11, 12, 13, 14, 15) and anxiety disorders (16, 17, 18, 19) experience trauma during childhood. Childhood trauma increases the likelihood of post-traumatic stress disorder (PTSD) (11, 20), obsessive-compulsive disorder (21), personality disorders (22, 23, 19), psychotic symptoms (24). Individuals with childhood trauma have higher risk of suicide, suicide probability, suicide attempts and self-harming behaviors (25, 26, 27, 28). Childhood trauma appears to have a significant impact on the emergence of many psychological disorders, including the risk of suicide. Also, childhood trauma negatively affects alcohol and substance abuse in adulthood (11, 19). In addition to these, traumatic experiences in childhood are also closely related to physical symptoms such as chronic fatigue (29), pain disorders (30), sleep problems (31) and cognitive impairment (32) in adulthood.
There are various theories explaining the development of psychopathology in individuals who experience childhood trauma. One of these is the hypothalamic-pituitary-adrenal axis (HPA). Stress is defined as stimuli or experiences that cause negative emotional reactions or feelings such as fear and loss of control. Maltreatment from parents in early childhood is one of the most important sources of stress (33). The HPA axis, sympathetic nervous system and immune system play an important role in the stress response (33). Traumatic events in childhood cause damage to the neurobiological and neuroendocrine system, which significantly affects social, emotional and cognitive development (34). For example, childhood maltreatment causes disruptions in the HPA axis, which is an important factor in the development of psychological disorders (35, 36, 37).
Exposure to trauma in childhood and infancy is associated with dysfunction in the HPA axis (38, 39, 40). Irregularity caused by childhood trauma in the HPA axis affects suicidal behavior in adulthood (41). When danger is perceived, corticotropin releasing factor is released from the hypothalamus. In this case, the pituitary gland is stimulated and cortisol release from the adrenal glands begins. The release of cortisol causes anxiety symptoms such as an increase in heartbeat and increased blood pressure. Exposure to stress for a long time causes a continuous release of cortisol, which affects learning, memory and other cognitive functions (42). Exposure to trauma in childhood causes shrinkage in the brain. This has important effects on psychopathology such as impulse control and inability to regulate emotions (43). In a study with young people exposed to different types of childhood trauma, it was stated that fast or slow HPA reactivity increased internalization and externalization symptoms (36). Early and chronic adversities are associated with more hypocortisolism patterns (44). As a result of child maltreatment, significant changes occur in brain functions. As can be seen, most of these changes are related to the stress response. In addition, these changes in the brain cause aggressive responses and problems in executive functions (33). Brain structures affected by the secretion of chronic stress hormones in childhood are differently involved in various cognitive functions such as memory and emotion regulation (45).
Impairments in the HPA axis are determined by changes in cortisol levels (46, 36, 47). In the literature, alexithymia, sensory sensitivity, and emotion recognition skills are related to cortisol. Studies indicate that alexithymia is associated with elevated cortisol levels (48, 49, 50). Similarly, high cortisol levels appear to be associated with sensitivity in sensory processing (51). The relationship between the ability to recognize emotions and cortisol level is different. Although some studies indicate that individuals who are good at recognizing emotions have high cortisol levels (52), some do not report a relationship between emotion recognition and cortisol levels (53). Considering the concept of trauma on the HPA axis, it is thought that trauma causes a significant deterioration in cognitive, executive functions, emotional skills, and sensitivity to stress, and this relates possible pathways to psychopathology. Therefore, it was thought that the possible mediators of childhood trauma to cause psychological distress might be emotional and mental processes (EYES test), alexithymia associated with skills in understanding and expressing emotions, and sensory processing sensitivity associated with sensitivity to stimuli.
The concept of alexithymia is a concept introduced by Sifneos and it means that there is no word for emotions (54). Alexithymic individuals have difficulty in defining their own emotions, and their thinking styles are impoverished in terms of imagination, reality-based and embodied (55). It was found that individuals with childhood trauma had higher alexithymia levels (56, 57, 58). In addition, studies show that individuals with high levels of alexithymia also develop more psychological symptoms (59, 60).
The term mentalizing, one of the cognitive and emotional functions, refers to the process in which inferences are made about mental states. People's faces become an important resource for inference (61). Children with trauma have difficulties in understanding and recognizing emotions from facial expressions (62, 63, 64). In addition, studies reveal that people with psychological symptoms in adulthood have difficulty recognizing emotions from facial expressions (65, 66, 67).
Sensory processing sensitivity, thought to be another possible mediator variable, is a term introduced by Aron and Aron (68) that defines the sensitivity of the individual to the perception of social and emotional stimuli against internal and external stimuli. For example, the individual is sensitive to sensations such as pain, hunger, and stimuli such as loud sounds and sharp odors. The fact that the individual perceives and interprets such stimuli faster and responds faster to these stimuli indicates that the individual has a high sensitivity to sensory processing. There are findings in the literature that individuals with childhood trauma decrease in pain threshold and increase in sensitivity towards stimuli in adulthood (69, 70, 71). Individuals with increased sensitivity to stimuli and high level of sensory processing sensitivity are at increased risk of developing various psychological problems (72, 73).
Although there are studies supporting the relationship between childhood trauma and psychological distress in the literature, that similar concepts are studied in mediation models that have been created. It has been observed that the relationship between alexithymia and childhood trauma and psychopathology has been studied extensively. However, the number of studies involving sensory processing sensitivity and emotional mental processes is limited. In this context, this study aims to present up-to-date and comprehensive information to the literature by considering all these variables together. It is predicted that the findings of the study may serve to understand the predisposing factors in the relationship between childhood trauma and psychopathology. In this context, our study has a hypothesis. Our hypothesis claims that emotional-mental processes, sensory processing sensitivity and alexithymia mediates the relationship between childhood traumatic experiences on adult psychopathology.