The Evolution of Neurobiological Research
Typically, research connecting neurophysiology, victimization, and violence has sought to explain the criminal behaviors of offenders rather than the impact of abuse on victims. However, the new specialty of ‘‘developmental traumalogy’’ has evolved within the field of psychiatry in an effort to explain how trauma, abuse, and neglect impact the neurophysiology of victims of abuse. ‘‘During the past 20 years, the development of brain imaging techniques and new biochemical approaches have led to increased understanding of the biological effects of psychological trauma’’ (Solomon and Heide 2005). Technological advances such as functional magnetic resonance imaging (FMRI) and electroencephalogram (EEG) have permitted explorations into atypical concentrations of neurotransmitters, irregularities in brain wave patterns, inadequate integration of the right and left hemispheres, and size discrepancies within regions of the brain. This has allowed researchers to compare the brain activity and chemical responses of those who have experienced a history of abuse or neglect with others who have not experienced such stressful situations. Research inspired by these technological advances has placed a new twist on the age-old debate between whether ‘‘nature’’ or ‘‘nurture’’ more strongly influences the development of an individual’s personality, well-being, and character. Researchers now seem to agree that the ‘‘process of early brain development is constantly modified by environmental influences’’ (Glaser 2000) and that ‘‘‘nature’ and ‘nurture’ interact continuously during the lifespan’’ (McEwen 2003).
The Functioning of the Brain
In order to understand the neurological, biological, and physiological impact of abuse on individuals, one must first establish a basic understanding of the functions of the body’s main control center: the brain. The human brain controls both unconscious functions such as breathing and digestion, as well as more complex, higher-level cognitive activities that include functions such as thought, memory, and reason. In controlling the nervous system, the brain is composed of various critical structures. The cerebral cortex, which consists of four lobes, is responsible for the higher-level conscious functions, including memory, awareness, and language. It receives and processes information from sensory organs such as eyes and ears. The limbic system, also known as the emotional center, consists of a group of brain structures including the amygdala (involved in the response to aggression, fear, and pleasure) and hippocampus (involved in the formation of long-term memory). It is within the limbic system that emotions such as fear, pleasure, and aggression, along with memory formation, are processed. When the amygdala and hippocampus encode information and control behavioral responses, these regions of the brain are also changed structurally and chemically by those experiences (McEwen 2003). The hippocampus is the region of the brain involved in storing short-term memories and retrieving long-term memories. This region is exceptionally sensitive to elevated levels of cortisol which flow through the bloodstream for hours or days after stress. ‘‘The body’s physiologic responses to stress are based on involuntary actions of the brain. Physical and mental abuse during the first few years of life tends to fix the brain in an acute stress response mode that makes the child respond in a hypervigilant, fearful manner’’ (Committee on Early Childhood 2000). As a person experiences a stressful situation, hormones such as adrenaline and cortisol inundate the brain to provide clarity and quick response. Unfortunately, continuous exposure and heightened levels of stress hormones alter the hippocampus, often leading to such ailments as posttraumatic stress disorder. Since childhood stress leads to initially high and damaging cortisol levels, prolonged stress leads to depleted cortisol levels in humans (Mukerjee 1995). Mukerjee describes this process with an analogy of a broken thermostat. As stress instigates a flooding of the brain with cortisol, the body’s internal thermostat resets the threshold at which cortisol is produced, thereby resulting in low levels of future cortisol circulating the system.
Early Life Experiences
Stress, trauma, and abuse in the early years of life can alter the structure and function of the brain by changing the brain’s chemistry. It appears that as the brain develops, excessive stress can stimulate chemical reactions that essentially ‘‘rewire’’ the brain. Since childhood represents the period when most of the brain development takes place, both positive and negative experiences influence how the brain will be ‘‘wired.’’ Although the brain continues to develop and change throughout one’s lifespan, an infant is born with roughly all the brain cells he or she will acquire. ‘‘Early social, emotional and environmental influences exert significant organizing effects . . . on the brain . . . [that] shape and mold all aspects of intellectual, perceptual, social and emotional development’’ (Joseph 1998). Excessive stress ‘‘alters the production of both the stress-regulating hormone cortisol and neurotransmitters’’ (McEwen 2003), leading to chemical imbalances that may result in anxiety, depression, substance abuse, poor response to stress, aggression, and suicide. Brain scans reveal that those who have endured abuse and neglect are more likely to experience decreased brain activity and lack the ability to maintain a sense of emotional balance.
During the first 3 to 4 years of life, the anatomic brain structures that govern personality traits, learning processes, and coping with stress and emotions are established, strengthened, and made permanent. . . . The nerve connections and neurotransmitter networks that are forming during these critical years are influenced by negative environmental conditions, including lack of stimulation, child abuse, or violence within the family. (Committee on Early Childhood 2000)
According to Schore (2001), ‘‘There is extensive evidence that trauma in early life impairs the development of the capacities of maintaining interpersonal relationships, coping with stressful stimuli, and regulating emotion.’’ Schore claims that strong, stable, and healthy attachments between an infant and his or her caretaker are critical to the baby’s neurological development and ultimately his or her mental health as an adult. Furthermore, Solomon and Heide (2005) claim that ‘‘[a]n infant’s relationship with its primary caregiver has a direct effect on the hard wiring of neural circuits in the developing brain. Many of the neural circuits affected by early experience connect areas of the brain critical for emotional, physiological, psychological, and social development. Some of these circuits are necessary for adaptive coping in emotional and stressful situations’’ (Solomon and Heide 2005).
Prolonged and sustained stress causes the infant to experience negative emotions which trigger processes that alter the biochemistry of the infant’s brain and alter the child’s future coping capabilities. Schore claims that ‘‘the primary caregiver acts as an external psychobiological regulator of the ‘experience-dependent’ growth of the infant’s nervous system.’’ Greenough and Black (1992) explain ‘‘experience-expectant’’ development as growth that will not take place unless a specific experience occurs during its critical developmental period (Glaser 2000). These early social events are imprinted into the neurobiological structures that are maturing during the brain growth spurt of the first two years of life, and therefore have far-reaching effects (Schore 2001). Since the limbic system is thought to be ‘‘experience-expectant,’’ normal infant development anticipates attachments between the infant and the caretaker (Joseph 1999). ‘‘The ability to form emotional attachments requires not just emotional stimulation, but the capacity to remember faces, people, objects, and even locations; functions associated with the amygdala and hippocampus. . . . However, as the amygdala and hippocampus may be injured by deprivation or abnormal rearing experiences, not just emotionality, but all aspects of short-term and long-term memory functioning may be disrupted as well’’ (Joseph 1999). Infants deprived of attachments to caretakers behave in ways similar to those whose limbic system has been damaged or destroyed.
Dr. Martin Teicher, a developmental neuropsychiatrist at Harvard University and director of the Biopsychiatry Research Program at McLean Hospital, has been at the forefront of research that compares the makeup and operation of the brains of individuals with and without a history of abuse and neglect. In his research, Teicher and his team expose how abuse provokes various neurobiological outcomes that alter the structure and function of specific regions of the brain, ultimately causing several identified abnormalities resulting from maltreatment.
These identified abnormalities include damage to the temporal lobe and cerebellar vermis, which represents the region of the brain involved in regulating language and the limbic system (the brain’s emotional processing center). In studies comparing the MRI scans of those with no history of abuse and those who have endured abuse or neglect, the size of the left hippocampus or amygdala is smaller in size than that of persons with no history of abuse (Teicher et al. 2004). When comparing abused or neglected children with a control group, Teicher and colleagues (2004) discovered a distinct difference in the size of the collection of nerve cells that connect the right side of the brain with the left side. In a comparison of the brain structure of twenty-two women reporting childhood sexual abuse with those of twenty-one women without a history of abuse, Murray B. Stein of the University of California at San Diego also uncovered an average 5 percent reduction in the size and volume of the left hippocampus (Mukerjee 1995). Furthermore, victims of abuse and neglect were less successful in integrating the functions of the left and right hemispheres when compared with those lacking a history of abuse. Harm to the left hemisphere resulted in abnormal brainwaves that mimic seizures. ‘‘Studies of the brains of human and animal subjects who have been victims of traumatic stress reveal differences in their brains when compared with control subjects who have not experienced trauma’’ (Teicher et al. 2004). These changes in brain structure and physiology are thought to affect memory, learning, ability to regulate affect, social development, and even moral development (Solomon and Heide 2005). Experiments at McLean Hospital have revealed that patients with a history of abuse are twice as likely to experience abnormal brain waves, or electrical activity, and five times more likely to experience suicidal thoughts than those who do not have a history of abuse. An abnormally developed left hemisphere of the brain is also linked to memory problems and depression (Teicher et al. 2004).
Solomon and Heide (2005) explain that nontraumatic memories are processed much like a roll of film. Personal experiences and events are temporarily stored in the limbic system and include a sense of time and self, such as in a photo of oneself at Disneyland with Mickey Mouse on a third birthday. The cognitive aspects of these memories are stored in the hippocampus, while the emotion attached to the memories is stored in the amygdala. ‘‘As the brain processes these memories over time, aspects of them are abstracted and transferred to the neocortex’’ (Solomon and Heide 2005). Upsetting experiences are processed at a much slower rate and linger in the limbic system for longer periods of time. ‘‘Because traumatic experiences are terrifying, the survivors avoid thinking and talking about what happened. This avoidance prevents processing. [As a result,] trauma alters physiology and gives rise to images, feelings, sensations, and beliefs that may persist throughout life’’ (Solomon and Heide 2005). The memories of traumatic events overwhelm the brain and become accumulated in the limbic system indefinitely. Those who suffer trauma through abuse or neglect experience impaired brain development, leaving them with an inability to cope with stress appropriately (Solomon and Heide 2005).
Traumatic events not only affect an individual’s brain functioning and memory capabilities, but they affect his or her physical health as well. ‘‘During the past few years, [researchers] have dramatically increased [their] understanding of the effects of traumatic stress on the brain, sympathetic nervous system, and endocrine system. Through a physiological domino effect, these changes affect many other body systems, including the cardiovascular system, respiratory system, and muscular system’’ (Solomon and Heide 2005). Although the negative consequences of abuse generate the greatest amount of damage during the early formative years, Solomon and Heide clearly articulate how maltreatment at any juncture of the lifespan impacts the vital organs of the body and produces negative health consequences even into adolescence and adulthood. In studies with adolescents, Juang and colleagues (2004) examined the existing correlations between adversity, depression, and headaches. Juang et al. found that ‘‘increased morbidity to depression and other psychiatric disorders is a long-term consequence of childhood adversity such as abuse and neglect’’ (Juang et al. 2004). Juang and colleagues’s research also showed that chronic daily headache (CDH) in young people is ‘‘associated with family adversity, physical abuse, and parental divorce occurring during childhood.’’ Researchers in countless studies have noted that abused women report experiencing inferior physical and mental health compared with women with no history of abuse (Garimella et al. 2000). In a study of 444 women responding to self-administered surveys in a small northeastern Italian town, Romito, Turan, and De Marchi (2005) examined the relationship between past and present abuse across ‘‘three indicators of current women’s health—psychological distress, the use of psychoactive drugs, and a subjective evaluation of health’’ (Romito et al. 2005). The results showed that female ‘‘victims of partner violence were around six times more likely to be depressed and to feel in bad health, and four times more likely to use psychoactive pills than other women’’ (Romito et al. 2005), who had not endured any form of abuse.
It is difficult to study the impact of abuse on a person, since one may become a victim of abuse at various points throughout his or her life. Additionally, it is difficult to assess the time order of the symptoms and causes of abuse, since many trauma survivors do not seek assistance. It is possible that those born with a smaller hippocampus are more susceptible to acquiring disorders, including posttraumatic stress, rather than the abuse causing a decrease in the size of the hippocampus, which leads to physical or mental ailments. In addition, acts of neglect and physical, sexual, or emotional abuse during childhood also increase the risk of further victimization later in life (Romito et al. 2005), making it difficult to isolate the effects of each episode of abuse. A lack of interdisciplinary collaboration between various academic fields complicates the quest for knowledge further by yielding isolated bits of information that remain unknown to researchers in other academic fields.
As this research adds a new perspective to the question of nature and nurture’s effect on human development, researchers are now beginning to examine whether there are evolutionary benefits to the physiological changes resulting from abuse. Childhood stress is not a new phenomenon, so new speculations have been raised as to ‘‘whether the increased stimulation for fight or flight may facilitate survival and reproductive success in hostile environments’’ (Cromie 2003).
Methodological impediments in research designs analyzing neurological processes have created numerous challenges in understanding the neurophysiological impact of abuse and neglect; however, understanding the impact of abuse and neglect on the mind and body provides the greatest information toward the development of adequate treatment and prevention. As researchers uncover the potential extent of physiological damage resulting from abuse and neglect, it becomes more evident that the best treatment for survivors is the creation of resources that aid in early intervention and prevention of abuse.
- Committee on Early Childhood, Adoption and Dependent Care. ‘‘Developmental Issues for Young Children in Foster Care.’’ Pediatrics 106, no. 5 (November 2000): 1145–1150.
- Cromie, William. ‘‘Childhood Abuse Hurts the Brain.’’ Harvard University Gazette, May 22, 2003.
- Flinn, Mark V., and Barry G. England. ‘‘Childhood Stress and Family Environment.’’ Current Anthropology 36, no. 5 (December 1995): 854–866.
- Garimella, Ramani, et al. ‘‘Physicians’ Beliefs about Victims of Spouse Abuse and about the Physician Role.’’ Journal of Women’s Health and Gender-Based Medicine 9, no. 4 (2000): 405–411.
- Glaser, Danya. ‘‘Child Abuse and Neglect and the Brain— A Review.’’ Journal of Child Psychology and Psychiatry 41, no. 1 (2000): 97–116.
- Hawley, Theresa. ‘‘Safe Start: How Early Experiences Can Help Reduce Violence,’’ 2000. Practical Parenting Supporting Parents and Professionals. Ounce of Prevention Fund.
- Joseph, R. ‘‘Environmental Influences on Neural Plasticity, the Limbic System, Emotional Development and Attachment: A Review.’’ Child Psychiatry and Human Development 29, no. 3 (Spring 1999): 189–208.
- Juang, K.-D., et al. ‘‘Association between Adolescent Chronic Daily Headache and Childhood Adversity: A Community-Based Study.’’ Cephalgia 24 (2004): 54–59.
- McEwen, Bruce S. ‘‘Early Life Influences on Life-Long Patterns of Behavior and Health.’’ Mental Retardation and Developmental Disabilities Research and Review 9 (2003): 149–154.
- Mukerjee, Madhusree. ‘‘Hidden Scars: Sexual and Other Abuse May Alter a Brain Region.’’ Scientific American, October 1995.
- Raine, Adrian, et al. ‘‘Reduced Right Hemisphere Activation in Severely Abused Violent Offenders during a Working Memory Task: An FMRI Study.’’ Aggressive Behavior 27 (2001): 111–129.
- Romito, Patrizia, Janet M. Turan, and Margherita De Marchi. ‘‘The Impact of Current and Past Interpersonal Violence on Women’s Mental Health.’’ Social Science and Medicine 60 (2005): 1717–1727.
- Schore, Allan N. ‘‘The Effects of Early Relational Trauma on Right Brain Development, Affect, Regulation, and Infant Mental Health.’’ Infant Mental Health Journal 22, no. 1-2 (2001): 201–269.
- Solomon, Eldra P., and Kathleen M. Heide. ‘‘The Biology of Trauma: Implications for Treatment.’’ Journal of Interpersonal Violence 20, no. 1 (January 2005): 51–60.
- Teicher, Martin H., et al. ‘‘Childhood Neglect Is Associated with Reduced Corpus Callosum Area.’’ Biological Psychiatry 56, no. 2 (July 2004): 6–85.