Impact on the cortex and limbic system
Research shows that children and adults with histories of child abuse often respond excessively to minor triggers. Traumatised children (and adult survivors) become increasingly responsive to relatively minor stimuli as a result of decreased frontal lobe functioning (learning and problem solving) and increased limbic system (amygdala) sensitivity (impulsiveness) (Streeck-Fischer & van der Kolk, 2000).
Decreased cortex activity
The cortex or the more rational, outer-layer of the brain is the seat of our thinking capacity. The cool, rational cortex is in constant communication with the amygdala and the hippocampus (the limbic system). The frontal lobes are situated in the cortex and are responsible for learning and problem solving. The capacity to learn from experience requires events to be registered in the prefrontal cortex, compared with other experiences and evaluated for an appropriate response (Streeck-Fischer & van der Kolk, 2000).
When children are under threat, the fast tracts of the limbic system are likely be to activated before the slower prefrontal cortex has a chance to evaluate the stimulus (Streeck-Fischer & van der Kolk, 2000). Only a state of non hyper-arousal allows activation of the prefrontal cortex needed for learning and problem solving.
Increased limbic system sensitivity
The limbic system is sometimes called 'the emotional brain'. It controls many of the most fundamental emotions and drives for survival (McLean Hospital, 2000). The limbic system initiates the fight, flight or freeze responses to threat. The amygdala and the hippocampus are part of the limbic system. A study by Teicher et al. (1993) found a 38% increased rate of limbic abnormalities ('emotional brain') following physical abuse, 49% after sexual abuse, and 113% following abuse of more than one type combined (cited in Streeck-Fischer & van der Kolk, 2000).
The amygdala processes emotions before the cortex gets the message that something has happened. For example, the sound of a loved one's voice is communicated to the amygdala, and the amygdala generates an emotional response to that information (for example, pleasure) by releasing hormones. When someone is threatened, the amygdala perceives danger and sets in motion a series of hormone releases that lead to the defensive responses of fight, flight or freeze. Because the amygdala is immune to the effects of stress hormones it may continue to sound an alarm inappropriately, as is the core of PTSD (Rothschild, 2004).
The amygdala's role in the encoding, storage and retrieval of emotionally-arousing material (and corresponding hormonal changes) primes animals to remember emotionally charged or threatening events better than every-day events (Howe, Cicchetti and Toth, 2006).
Decreased hippocampal volume
The hippocampus helps to process information and lends time and spatial context to memories and events. The hippocampus assists the transfer of initial information to the cortex which works to make sense of the information. However the hippocampus is vulnerable to stress hormones, in particular the hormones released by the amygdala's alarm. When those hormones reach a high level, they suppress the activity of the hippocampus and it loses its ability to function. Information that would make it possible to differentiate between a real and imagined threat never reaches the cortex and a rational evaluation of the information isn't possible (Rothschild, 2004).
If a particular stimulus is misinterpreted as a threat, this leads to immediate fight/flight/freeze responses (to non-threatening stimuli). This causes this system to respond to minor irritations in a totalistic manner (Streeck-Fischer & van der Kolk, 2000).
Research shows that environments of extreme stress lead to increased cortisol levels (Murray-Close, Han, Cicchetti, Crick, & Rogosch, 2008) which can lead to decreased hippocampal volume. Decreased hippocampal volume has been associated with poorer declarative memory which places adults at greater risk of developing PTSD-like symptoms, and is closely correlated with experiences of depression and physical inflammations (Danese, Pariante, Caspi, Taylor & Poulton, 2006).
Impact on the left and right hemisphere
Underdevelopment of left brain
A study by McLean Hospital (2000) found that children with histories of abuse were twice as likely as non-abused children to have abnormal electroencephalograms (EEGs). EEG is a medical test used to measure the electrical activity of the brain, via electrodes applied to your scalp. Research shows evidence of deficient development of the left brain hemisphere in abused patients (which controls language), suggesting that the right hemisphere may be more active than in healthy individuals.
A smaller corpus callosum
The corpus callosum is a major information pathway connecting the two hemispheres of the brain (McLean Hospital, 2000). A number of studies have found that the corpus callosum is smaller in abused children than in healthy children (De Bellis et al., 1999; McLean Hospital, 2000; Teicher, Ito, Glod, & Andersen, 1997). Furthermore, McLean Hospital (2000) found that abused patients shifted the degree of activity between the two hemispheres to a much greater extent than normal. They theorised that a smaller corpus callosum leads to less integration of the hemispheres. This can lead to dramatic shifts in mood or personality.
Brain development is affected by stress early in development. Extensive research has been carried about the neuro-biology of stress. The link between a history of childhood abuse and neglect and neuro-endocrine impacts is well established. Research tells us that the bodies of children who are being abused react and adapt to the unpredictable dangerous environments to which they are exposed. Stress can set off a ripple of hormonal changes that permanently wire a child's brain to cope with a malevolent world (Teicher, 2002). Through this chain of events, violence and abuse pass from generation to generation (Teicher, 2002).
The neuro-endocrine system refers to the system of interaction between our brain/ nervous system and the hormones in our bodies. This system helps regulate our moods, our stress response, our immune system, and our digestion, amongst other things. Any disruption to the neuro-endocrine system affects a range of basic psychological and physiological functions.
Research suggests that many of the long-term impacts of child abuse experienced by adult survivors result from the chronic neuro-endocrine dysregulation caused by prolonged exposure to abuse and violence (Kendall-Tackett, 2001).
Impact on stress hormones (including impact on cortisol production)
A number of studies have identified alterations in cortisol production in both children and adults who experienced childhood abuse (Carpenter et al., 2007; Joyce et al., 2007; Linares et al., 2008; McLean Hospital, 2000). Alteration in cortisol levels, either an increase or decrease, can cause a number of long-term physical and psychological health concerns.
Even in utero foetuses experience stress (Cozolino, 2002). Tests have found that foetuses express a biological response indicative of a stress response well before birth (Gunnar, 1998).
The nervous systems of children who are abused run on a constant high because they are constantly anticipating further danger. Their bodies are flooded with fight-or-flight hormones (Cozolino, 2002). A study by Linares et al. (2008) shows alterations in cortisol production in children with histories of abuse and neglect. This state of chronic 'hyper-arousal' persists for many survivors throughout their adult years as well. Even when the abuse and violence has ceased and the environment is 'safe', many adult trauma survivors still perceive the threat to be present; their fear is maintained and becomes pathological (Giarratano, 2004b). A study by Joyce et al. (2007) found that experiences of childhood abuse were associated with high cortisol levels in depressed adult survivors.
Impact on Thyroid production
Studies conducted by McLean Hospital (2000) have found that neglect can also decrease production of thyroid hormone. This can lead to a number of health concerns as the thyroid gland secretes hormones which modulate metabolism.
Trauma is biologically encoded in the brain in a variety of ways. Changes in structures like the hippocampus, and the coordination and integration of neural network functioning have been identified. These changes are reflected in the victim's physiological, psychological and interpersonal experiences (Cozolino, 2002). Deficit in psychological and interpersonal functioning then create additional stress which further compromises neurobiological structures. In this way, adaptation to trauma, especially early in life, becomes a "state of mind, brain, and body" around which subsequent experience organises (Cozolino, 2002).
Impact on gene expression
A research study, led by Michael Meaney from Douglas Mental Health University Institute in Montreal examined samples from the hippocampus region of the brain, which is associated with memory function, and is known to develop differently in abused children. (Meaney, 2009) They found a gene - NR3CI, which influences the brain's susceptibility to stress hormones - was less likely to be activated in people who have been abused. This study as the first to demonstrate that a genetic process appears to underlie such changes. Those who have been abused had lower levels of expression of the gene for the glucocorticoid (cortisol) receptor, which is critical for the stress response pathway. Children who are abused early are flooded with stress hormones like adrenaline and cortisol, impacting on how the brain develops and the stress regulation method. This in turn impacts on the hippocampus, the area which controls feelings, meaning that adult survivors will be more likely to be highly stressed, have difficulties with anger and emotions, and be prone to self-harm, anxiety, suicide and depression.