by Quinn O’Connor
art by Cindy Jin
Content Warning: physical and emotional (including domestic and sexual) trauma
What is intergenerational trauma, where does it come from, and how can it be averted?
The apple doesn't fall far from the tree. Much of our identities can be traced back to adversities we experienced during childhood or the parenting styles of our guardians. This fact allows us to blame our mom for our procrastination habits or our dad for our poor driving skills. Interestingly, recent studies have found that perhaps these tendencies are due not only to socialization throughout our upbringing, but also to our neuroanatomy. In fact, it is actually those with a larger amygdala (the brain's emotional processing center) who are more likely to procrastinate, and those who produce less BDNF, a protein which assists in linking memory to physical responses, who start off with a poorer driving ability and have more difficulty with correcting mistakes—such as driving through a stop sign . In other words, perhaps the experiences of our parents somehow become our own through the structure of our brains. This concept has been dubbed intergenerational trauma (IGT): the epigenetic transmission of traumatic events from parents to offspring .
To break down this definition, it is helpful to contextualize epigenetics: the study of how particular experiences impact the body’s gene expression . The genetic code itself isn't altered by experiences, but the way each strand of DNA is interpreted changes from its original meaning. Epigenetics is a relatively new concept, and has only begun to be heavily researched for the last 50 years . To provide a general outline of how the process of epigenetics occurs, consider the following: a developing fetus is exposed to the chemicals in cigarettes while in the womb. When introduced to the body, nicotine is known to cross the placenta and interferes with placental function by reducing blood flow, ultimately limiting the availability of oxygen and other nutrients necessary for the development of the fetus’ brain [4, 5]. Several animal studies have shown that prenatal nicotine exposure leads to abnormalities in the dopaminergic system, with lower levels of dopamine being observed after birth . Dopamine is a neurotransmitter that plays a role in several neural mechanisms, including memory, motivation, attention, pleasure, and reward. This neuromodulatory molecule is required for optimal brain function and decreased dopaminergic levels can have several cognitive consequences. Within this framework, when the fetus is born, they will likely have a harder time processing instructions from the brain due to the lack of dopamine . This effect on the fetus was caused by epigenetics, because it was the presence of cigarettes in the mother’s life that caused this change in the child’s brain. A lack of dopamine in the brain is associated with attention-deficit hyperactivity disorder (ADHD), a disorder that can affect mood regulation, emotions, and communication between neurons in the brain . Therefore, in this example the development of ADHD might be partially attributable to the exposure to cigarettes in the womb [4, 7].
Understanding Trauma as a Whole
In order to discuss IGT, we must first understand what trauma is. While trauma is often associated with a specific event or chain of events that trigger an intense emotional response, it can be broken up into further categories that help to fully articulate the extent and severity of its effects.
Three types of trauma are physical, emotional, and environmental. Physical trauma is just as it sounds: serious bodily harm (which can include domestic or sexual violence), vehicular accidents, or injury in a natural disaster . Emotional trauma is the brain's response to a disturbing event in which the individual feels unsafe and/or helpless . It can occur as the result of stressful social situations like verbal abuse, bullying, or humiliation . One final type of trauma is environmental trauma, classified as the physical and emotional adverse effects of long-term residence in areas with poor air or water quality, high rates of light or noise pollution, or lack of nutritious food . For example, there has been a drastic increase in asthma in urban communities due to not only pollution, but also proximity to violence and chronic stress . This type of environmental trauma in urban communities often leads to physiological trauma manifesting as chronic stress and asthma, as well as emotional stress due to heightened violence.
For these subtypes of trauma, we usually group their severity into one of three levels: acute, chronic, or complex . Acute severity describes the immediate and relatively short emotional response during or after an unnerving event; for example, crying after witnessing a car accident. Chronic severity indicates that there is a continuous and long-lasting trauma response after repeated distress, such as domestic violence or bullying. Lastly, complex trauma encompasses the long-term effects of an individual’s continued exposure to maltreatment and/or traumatic experiences. It is most often developed after the occurrence of acute and chronic traumas, as there is continued distress within the individual. Forms of complex trauma can include emotional, sexual, and physical abuse, as well as witnessing domestic violence or war . As a result, children exposed to complex trauma can experience lifelong issues that place them at risk for additional trauma exposure and cumulative impairment (e.g. psychiatric illness, addictive disorders, and chronic medical illness) . When left untreated, these may continue into adolescence and adulthood . Finally, complex trauma modifies how the instructions within DNA are communicated to cells throughout the body and may kickstart the inheritance of IGT .
Beyond identifying the types of trauma, it is also important to understand how they manifest biologically. Typically, a large portion of neurological growth occurs both in-utero and before the age of five . During this time, there is an overall expansion of brain volume to allow for the development of gray matter structures, which are part of what allows the nervous system to control movement, memory, and emotions [13, 14].
The brain acts as the headquarters for all anatomical systems, and even the smallest of traumatic events can instigate permanent changes in neurological makeup. When a distressing event occurs, the body produces increased cortisol—a steroid hormone that increases in response to stress and low-blood glucose concentration—and norepinephrine—a signaling molecule that results in higher alertness and arousal—to respond to the current stressors [13, 15, 16].
Unfortunately, recent studies have shown that there is often a reduction in brain volume in patients with post-traumatic stress disorder (PTSD): a psychiatric disorder instigated by a significant traumatic event . The areas that have been observed to decrease most in volume are the frontal and parietal cortices . These cortices control memory, attention, and judgment, which has been said to explain why people with PTSD experience increased levels of cortisol and norepinephrine in response to stress, while people without PTSD experience no such increase when confronted with the same stressor [11, 18, 19].
One especially significant consequence of IGT is the potential development of mental illness. A study conducted on mice at the University of California, Irvine showed that trauma exposure during pregnancy often induces social deficits and depressive behavior in offspring . Cells extracted from offspring that were exposed to prenatal trauma had an impaired ability to regulate normal cellular processes, such as regeneration, and showed an abnormal gene expression profile in adulthood. For example, when a pregnant parent has a low body mass due to starvation, the fetus in the womb may be more vulnerable to neuropsychiatric disorders such as PTSD, autism spectrum disorder, and schizophrenia .
These modified genes may also increase an individual’s risk for behavioral disorders, the progression of mental illness, or increased levels of cortisol, all of which can be observed in youth with PTSD . Increased cortisol levels can cause cortisol-sensitive tissues to become cortisol-resistant and lead to uncontrolled inflammation responses . Such responses may decrease the volume of the hippocampus in the parent, which can put the offspring of the individual at a higher risk for dementia, memory loss, and rare genetic disorders .
Historical Examples of Intergenerational Trauma at Work
No matter the type or classification, trauma has a profound effect on health. Though research in this area is relatively recent, studies have begun to examine how historical oppression and distress can manifest both mentally and physically in various demographics . Trauma is often measured using the adverse childhood experience, or ACE test . The ACE test is essentially a list of different types of abuse, neglect, and other trauma experienced. It contains ten yes-or-no questions, with each “yes” equating to one “ACE.” For reference, some studies have shown that within their lifetime, 57.8 percent of people have experienced at least one ACE . A higher score indicates that the individual has a higher predisposition to mental health issues . Studies have shown a positive correlation between high ACE scores and a propensity for chronic illness, specifically in communities that are experiencing or have experienced oppression. For instance, a study conducted at Baylor University found that multiracial individuals had the highest average ACE score (2.39) when compared to other races or ethnicities, whereas white individuals had a significantly lower mean score of 1.53 .
In regard to tangible examples of ACEs and historical oppression, we can examine the history of Indigenous individuals, whose scores have been consistently higher than average . When examining the adversity of Indigenous people, researchers typically recognize three phases: the infliction of mass trauma, the community’s response, and the trauma that is conveyed to successive generations. For example, government boarding schools forcibly took Native children from their families at the developmental ages of four or five, without any notice or parental consent. This atrocity led to complex feelings of shame, subordination, and inferiority in the children that later developed into inheritable psychiatric disorders . Significant adversity can produce physiological disruptions that hinder the development of the body’s stress response systems . Researchers now believe that prolonged stress associated with discrimination and historical trauma can create negative epigenetic expression in the genes that regulate stress response, causing difficulty in handling stress [27, 28]. Negative epigenetic expression is not unique to groups experiencing collective emotional trauma: it can also be a consequence of environmental trauma in general, as seen in those who have experienced famine, such as the one experienced in Ireland in the 19th century.
The postcolonial Irish society today can be characterized by a generational cycle of dependency, fear, and vulnerability, giving rise to some of the most tangible indicators of IGT . Many of these emotions are theorized to have originated from the “Great Hunger,” or Irish Potato Famine (circa 1845), in which a crop disease caused mass starvation and exodus throughout Ireland. The Irish still experience the repercussions of the famine retroactively, partially due to the way in which the psychological effects of hunger impeded emotional development in their communities/families . Recent studies have found that 18.5 percent of the current Irish population were diagnosed with a mental health illness (anxiety, bipolar disorder, depression, or addiction), and the schizophrenia incidence rate amounts to around six in every 100 people, which is 2.4 times higher than the average in Europe . Concurrently, the Republic of Ireland has risen to fifth place in the World Health Organization's global rankings for alcohol consumption, which is often correlated to the mental illness and maladaptive coping mechanisms mentioned prior . The connection between famine and IGT has only been identified within the last decade, but two theories potentially explain the prominence of mental illness in Ireland today.
One theory, proposed by Dr. Oonagh Walsh of Glasgow Caledonian University, states that the nutritional deprivation endured by the Irish during the potato famine created an epigenetic change that led to a higher likelihood of developing mental illness at some point in life . Another theory originates from an Irish independent author, Patrick Tracey, who examined his own family history. Tracey believes there is a correlation between parental age disparity and schizophrenia rates. In mid-19th century Ireland, it was often financially inadvisable for a man to marry until later in life .These older men would then strive to marry the youngest girls of age. Interestingly, a recent study has found some alterations to sperm DNA methylation (a chemical modification to gene expression that does not alter the sequence) associated with age [32, 33]. Tracey believes that the difference in age between two spouses and the increase in sperm mutations as age increases possibly contributed to a spike in schizophrenia .While a gap exists within research that specifically delves into the origins of schizophrenia, it is apparent that it could be a crucial lead in developing a better understanding of IGT.
While less studied than the Irish, some descendants of enslaved individuals have been shown to have a decreased ability to regulate or control emotions as a result of reduced activity in the frontal cortex . Due to this reduction in frontal-lobe activity and excess cortisol produced through stress, a fetus’s neurological makeup in the womb can be disrupted, thus continuing the physiological effects of the trauma in offspring . This prenatal instance of IGT is often referred to as “intergenerational gendered racialized trauma,” and this phenomenon has prompted studies on the origins of mental illness within Black communities . In Holocaust survivors and their offspring, studies have observed that parents are oftentimes unable to provide physical and emotional care, which may be a reflection of past trauma . Children of Holocaust survivors also showed increased vulnerability to psychological disorders. Having two parents who were survivors of the Holocaust has even been directly correlated with increased intrusive memories and other posttraumatic symptoms, and adult children of survivors have a predisposition to PTSD . Most interestingly, some descendants of Holocaust survivors even report persistent nightmares of war and torture despite never experiencing the horrific events themselves . Due to the recency of IGT research and the prioritization of Eurocentric demographics, a gap exists within research on marginalized groups, but this is an important connection to make as we progress in conceptualizing IGT.
In no way is IGT unique to the few demographics discussed in this article, but it is important to identify a few of the ways in which it may manifest based on different types of adversity experienced. However, while mental health disorders in succeeding generations are an unforeseen aftermath to trauma, they are not impossible to reverse.
Reversing the Effects
After reading an array of situations regarding the way IGT manifests itself, you may be curious as to how—or even if—we can reverse the effects of IGT that have become so prevalent within society. Our brains are plastic, meaning they have the ability to adapt and change in structure and function throughout our lifetimes [37, 38]. The brain is most plastic during childhood and other critical developmental stages, with the most significant window being up until the age of 25, by which point the prefrontal cortex is more fully formed. This high level of plasticity during critical stages in development helps to explain some of the reasons why the brain can be epigenetically changed in the first place, and why neurological disorders can develop and be treated throughout life.
One case study followed a cohort of individuals and monitored changes in their brain before, during, and after complex trauma . After a series of traumatic events occurred, the researchers ensured that all participants had adequate resources to care for both their physical and mental health, whether that be through exercise, medication, therapy, or some combination of these treatments. The findings found that initially, participants exposed to adversity early in life had widespread brain volume reductions. However, by age 45, the effects had been mitigated and/or improved . These findings indicate that the brain worked to heal itself as the individuals made a conscious effort to care for their mental and physical health, even during adverse experiences [37, 38]. Similar studies have observed that early pharmacological interventions, such as antidepressants, produced long-lasting protection against depression . Therefore, intentional efforts to care for mental illness and address individuals’ needs appear to be able to reverse the changes caused by trauma. Furthermore, there were no adverse IGT effects inherited by the offspring of these treated participants [37, 38]. While this does not mean this outcome is guaranteed in all cases, it is encouraging to see that improvement is a possibility.
Insights from non-medical fields, such as sociology, also suggest other possible mechanisms for the reversal of IGT. Evidence shows that strong identification with one’s heritage creates a positive cultural identity and can act as a protective factor against trauma. It has been shown that the infusion of cultural practices into one’s life (e.g. traditional music, dance, language, etc.) can improve one’s overall mental health and functioning . For instance, the more involved that an individual became with their Native tribe, the easier it was to overcome traumas and to reduce the inclination to seek maladaptive coping mechanisms such as substance abuse. In the same vein, the Irish are also making strong efforts toward renewing culture, especially via language, music, sports and traditional arts, such as river dancing  Reengaging with culture can even better support the family unit: attachment research shows that after having developed healthy relationships with others throughout their lifetimes, parents were able to raise children without the explicit psychiatric disorders that once prevented them from developing healthy social connections. This research demonstrated an instance in which the chain of IGT was broken .
Most often, the diagnosis of mental illness is conducted through the Diagnostic and Statistical Manual of Mental Disorders (DSM) . The DSM is written by primarily highly-educated, white individuals from what the authors believe to be an academic and purely quantitative lens. While the phenomenon of IGT is widely agreed upon among mental health professionals, the term itself is never specifically mentioned in the DSM. It is often broken down into more specific categories, such as anxiety disorders or PTSD, which may discount the origin and magnitude of effects the patient is experiencing .
The restriction of addressing trauma through the DSM guidelines alone “virtually excludes notions of history and collective, community, or cultural trauma” . Therefore, mental health workers should have an understanding of IGT as well as its particular effects and associated intervention strategies . One proposed solution is that when treating a specific demographic, the health facility should have a professional with a similar background on staff . For example, Black mental health professionals should be present within discussions surrounding historical racism within society, along with the necessary mental health resources for all participants . This culturally-representative staffing would allow for a better understanding of the individuals with trauma.
While IGT is difficult to reverse due to its interconnectedness with genetics, its effects are no longer inevitable or untreatable. With decades of research behind us and more to come, we can unite as advocates, neuroscientists, and sociologists to combat the inheritance of trauma and allow for upcoming generations to encounter life as it was experienced prior to historical oppression and adversity.
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