In the course "Dynamics of Individual Differences", students write a blog post on a topic of their interest that is related to an aspect that differs between individuals and changes across the lifespan. Daphne shared her blog post with us, enjoy!
10th of May, 1940. Under Hitler’s command, the German army invaded the Netherlands during the Second World War. At the time, Piet was 15 years old and Johanna was 10. They are my grandparents, and unfortunately, they both suffered under Nazi rule in their own ways. In 1943, Piet turned 18 and was required to go into hiding on a farm, to prevent being sent off to work in Germany. In exchange for his refuge, he worked on the land. When the German officers held razzias with the aim to find people in hiding, he had to hide at the back of the fields. In that same year, Johanna lost family members in the bombardment of Enschede, the city that she knew as her home, while she was at boarding school. Clearly, they both experienced highly traumatic events during their teenage years, by which they were largely affected. For example, think of how these experiences could have impacted their level of anxiety, how they approached stressful situations, or just how they behaved in general. After the war, the two met, fell in love, and became the parents of four children. Their story raises the question: Did these traumatic experiences of the war impact their children? And if so, does this mean that the effect of trauma transmissible across generations? Am I, as their grandchild, affected by the Second World War?
Your parents have a great impact on your life, through how they raised and took care of you, but also through the genes that they passed along. Also, your parents’ past life experiences influence your life to quite an extent. Their life course and experiences impact their parenting style, how they view the world, and where you grew up, among others. Therefore, their past has shaped your childhood environment, which in turn, shaped you to become the person you are today (Guajardo et al., 2009). Unfortunately, just like Piet and Johanna, most parents have experienced traumatic events, as 87% of the people experience at least one traumatic event in their life (Kilpatrick et al., 2013). Do these traumatic experiences our parents had also impact us, as their children? People show differences in how they respond to traumatic events, this is called heterogeneity. For example, despite the majority of people being exposed to traumatic events, not everyone develops posttraumatic stress disorder (PTSD; lifetime prevalence: 9.8%). PTSD is an impactful and exhausting disorder, that develops in response to direct, indirect, and/or repeated exposure to traumatic events. Because of it, people experience symptoms of involuntary thoughts about the trauma (i.e., ‘intrusion’), avoidance of reminders of the traumatic event, and alterations in cognition and mood, among others (North et al., 2016). Identifying explanations for why some people develop PTSD and others do not, is relevant in the prevention the disorder. Since our parents have a great impact on who we become and how we develop, an important question is: How is your susceptibility to posttraumatic stress disorder (PTSD) influenced by the traumatic events your parents experienced?
Parents can pass along their response to trauma to their children and later generations. Thus, in their offspring, we might observe symptoms of having experienced a traumatic event, even when they did not actually experience something traumatic. This transference is called transgenerational trauma, and it has been identified as a contributor to PTSD susceptibility (Danieli, 1998). The finding that children from traumatized parents had an increased risk for psychopathology, especially for PTSD, demonstrates this (Danieli, 1998). Developing PTSD might thus be influenced by traumatic events that the individual did not experience directly, but that their parents experienced. To understand how trauma is passed along to younger generations, epigenetics must be explained.
The field of epigenetics focuses on variations in cells that are the result of environmental events, these events could include someone’s experiences, diet, exposure to toxic chemicals, or even the prenatal environment (Krippner & Barrett, 2019). Variations in cells determine how our genes are read and interpreted: are the genes switched ‘on’ or ‘off’? A useful analogy to explain epigenetics was proposed by Nessa Carey (2011), in which you have to view your life course as a movie. DNA is the script of your movie, with cells being the actors. Genes are represented by the specific blocks in the script that instruct important actions or events to take place. Within this analogy, epigenetics can be best understood as ‘directing’ the movie. For instance, if you would give the same script to Steven Spielberg or Woody Allen, you could get two different movies even though the script remains the same. The function of epigenetics works similarly, because epigenetics change how a gene expresses itself, even though the gene stays the same. Epigenetics can be placed on our genes by the environment, for example by the experiences we have. Accordingly, how our parents behave, and the environment they create for us, also affects our epigenetics. Epigenetics are useful adaptations to the environment. For example, when under stress, epigenetics can help the individual to adaptively deal with the stressors (Stankiewicz et al., 2013). This explains why epigenetic changes take place within our parents in response to their traumatic experience(s), changing their gene expression. However, epigenetic markers are not a guarantee for a healthy response, and may result in experiencing psychopathological symptoms. For instance, it has been found in Holocaust survivors that trauma affects a region on the gene related to cortisol, which is associated with stress and trauma recovery (Yehuda, 2011). Alterations in this specific region could then explain differences in PTSD susceptibility and PTSD symptoms (Yehuda et al., 2014).
Interestingly, cortisol alterations are not only found in traumatized Holocaust survivors themselves, but also in their children and grandchildren (Yehuda, 2011). Moreover, it was found that Holocaust survivors with PTSD had children with an increased likelihood of developing PTSD, anxiety and depression (Yehuda et al., 1998). In this study, there were no differences in the amount or intensity of traumatic events between children with and without traumatized parents. Therefore, differences in susceptibility to PTSD could be explained by the trauma of earlier generations. These studies provide evidence for effect of the parents’ trauma on the child’s epigenetics, which is in line with what was discussed earlier. There are two ways of transgenerational trauma transmission: indirect and direct (Krippner & Barrett, 2019). Indirect represents transmission through parental behaviour, for example anxious behaviour by the parents is adopted and internalized by the child (Danieli, 1998). Direct transmission refers to how epigenetic markers are directly passed on to the next generation.
The following rat study serves as an example of how parental behaviour influences offspring, which reflects the indirect transmission of trauma. Female rats usually lick their offspring, which can be seen as an equivalent to hugging or comforting a child in humans. Traumatized female rats licked their pups less often than non-traumatized female rats. The offspring’s epigenetics were affected by this in such a way that caused the pups to show less explorative and more anxious behaviour (Weaver et al., 2004). Therefore, trauma in the mother rat changes her behaviour in a way that increases stress susceptibility in her offspring. Likewise, in the earlier mentioned example of the Holocaust survivors and their children, anxious parental behaviour might have resulted in the epigenetic markers that have been found in the children. This caused the children to be more anxious, more depressed, and more likely to develop PTSD.
All the evidence mentioned above discusses indirect transmission of trauma, so through parental behaviour. However, evidence for the direct transmission of epigenetic markers is less available. One rat study showed that direct transmission of the epigenetic markers is possible in animals (Dias & Ressler, 2014). In this study, the first generation of rats was conditioned to fear a specific smell, by means of shocks. This conditioned fear was also found in their offspring two generations later, who were not raised by their parents. Since the fear responses could not have been transferred through parental behaviour, a direct transmission of the fear response was established. In humans, this direct transmission has not yet been identified. Does this mean that it is not possible in humans to pass on stress-related epigenetic markers to their offspring, or is it simply yet to be discovered? It is not impossible, however epigenetic modifications are usually not passed on in humans, as they are deleted or altered (Walter & Hümpel, 2017). Additionally, the epigenetic markers that have been identified in humans could also be explained by parental behaviour (indirect transmission). Research on epigenetic trauma transmission in humans is plagued by this problem, because detangling the effect of parental behaviour (environmental influence) from direct transmission of epigenetic markers (genes) appears to be a difficult task. No human studies have investigated the presence of epigenetics in offspring when they were not raised by their traumatized parents (i.e., in adoption studies).
Evidently, research has shown that the effect of traumatic events can be experienced throughout generations. Offspring of traumatized individuals is more vulnerable for the development of PTSD, and shows increased levels of anxiety. Therefore, it is wise to identify children and grandchildren of traumatized (grand)parents and to implement prevention programs for them. Prevention of the effects of transgenerational trauma is two-fold: with focus on the (grand)children, and focus on the parents. Most prevention strategies for PTSD are targeting the appropriate processing of the traumatic experience. However, since the offspring did not directly experience the traumatic event, this does not apply. Therefore, it is recommended to teach these (grand)children how to appropriately regulate their emotions, so that they will be able to deal with stressful and traumatizing situations they might encounter. It was found that adaptive emotion regulation has the power to influence a variety of unhealthy, psychopathological thinking patterns (Sheppes et al., 2015). By targeting inefficient emotion regulation strategies, offspring of traumatized individuals can more adaptively deal with stressful situations. Additionally, having a fear of experiencing emotions has been identified as a risk factor for PTSD development (Bomyea et al., 2012). Thus, teaching children about emotions and how to deal with them can lower their risk of developing PTSD. Another point of action is related to the traumatized individual themselves. Parents can try to prevent their trauma from transferring onto next generations, for example by adjusting their behaviour. Like mentioned previously, when parents show anxious behaviour, their children are likely to mimic this and portray anxious behaviour themselves as well (Danieli, 1998). Being more sensitive to anxiety has been shown to be one of the cognitive aspects that increases an individual’s vulnerability for PTSD (Elwood et al., 2009). As a parent, preventing your child from being exposed to these dysfunctional behaviours can help them in becoming more effective in dealing with stress. In conclusion, there are two recommended ways of decreasing the susceptibility of PTSD: improving the child’s abilities to effectively cope with emotions, and adjusting parental behaviour to prevent an indirect carry-over of the effects of trauma onto the children.
Thankfully, having a traumatized parent (or grandparent) does not have to be the end of the world, and is not a guarantee of developing PTSD. Several protective factors may decrease your likelihood of being strongly affected by traumatic events, like peer and parental support, but your resilience (Hébert et al., 2014). Personality traits like extraversion, conscientiousness, and openness were identified as protective factors as well (Weinberg et al., 2021). Another point pertains to epigenetics, because it was shown that we can still positively influence our epigenome with a healthy lifestyle (Walter & Hümpel, 2017).
How to specifically target the dysfunctional epigenetic markers that are related to PTSD susceptibility is still unknown, and thus, must be further investigated. Also, to what extent traumatized people and their children benefit from prevention strategies requires more attention, in order to prevent transgenerational transmission of trauma. Additionally, an important question is if direct transmission is also found in humans, and if so, what does this mean for PTSD prevention in the offspring? Clearly, many questions regarding transgenerational trauma and how it relates to PTSD susceptibility in offspring remain unanswered. Nevertheless, what you should take-home from this is that not everything we inherit from our parents is fixed, or unchangeable. What we experience throughout life, and how we cope with that all plays a role in the risk of PTSD development. This is what I, as a granddaughter of Piet and Johanna, must keep in mind as well. In this blogpost I wanted to shed light on their story, and with that, also of many others that are affected by traumatic experiences. Their trauma may play a role in who I am today, but my response to traumatic events is not set in stone.
References
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