Childhood Abuse, the Hippocampus, and Memory Damage

Introduction to the Limbic System and Hippocampus

The limbic system within the brain consists of structures involved in emotion, motivation, and emotional association with memory. It influences the formation of memory by linking and integrating emotional states with stored memories of physical sensations. It has been observed to be more active and larger in extroverts and risk-takers than in introverts and fearful, cautious people. The key anatomical structures of the limbic system include: the hippocampus, responsible for the formation of long-term memories; the amygdala, associated with aggression and fear; the nucleus accumbens, linked to reward, pleasure, and addiction; the cingulate gyrus, involved in cognitive and attentional processing; the hypothalamus, which regulates the autonomic nervous system; the mammillary body, also involved in memory formation; the parahippocampal gyrus, involved in spatial memory; the orbitofrontal cortex, associated with decision-making; and the broader cingulate gyrus region. Circumstantial evidence suggests that the proper functioning of the limbic system is necessary for maintaining a healthy, conscious state of mind (Wikipedia, 2006).

Psychologists and neuroscientists generally agree that the hippocampus plays an essential role in the formation of new memories about experienced events, and that it operates as part of a larger medial temporal lobe memory system responsible for facts and episodes (Wikipedia, 2006). These memories last a lifetime, but the role of the hippocampus ceases after a period of consolidation. Damage to the hippocampus makes the formation of new memories — anterograde amnesia — very difficult, and also impedes access to memories stored before the damage occurred — retrograde amnesia. It is believed that older memories are transferred out of the hippocampus to other parts of the brain as a result of this process. However, damage to the hippocampus does not affect all aspects of memory; learning new skills, for instance, involves procedural memory, which relies on different neural structures.

Other evidence suggests that the hippocampus is essential in storing and processing spatial information, functioning as a cognitive map — a neural representation of the layout of the environment. Studies have shown that human beings require a fully functional hippocampus to successfully store and recall the places they have visited and to navigate to new ones. It is responsible for finding shortcuts and new routes to already familiar places. Individuals with greater navigating skills, such as taxi drivers, have been shown to have more active hippocampi than those without such skills (Wikipedia, 2006).

It is hypothesized that abused, non-autonomous persons have greater hippocampal deficits — less active or smaller hippocampi — than autonomous abused individuals, autonomous non-abused individuals, and non-autonomous non-abused individuals. This study attempts to determine how autonomy and abuse together affect the hippocampus, using the results of a survey alongside information gathered from authoritative sources.

Childhood Abuse and Hippocampal Damage

Research has shown that those who suffer abuse, especially as children, often "forget" it (Al-Kurdi, 2006) because the body produces high levels of neurochemicals that erase the painful experience from conscious memory. Under severe stress, the hippocampus becomes inactive and is disabled from placing a memory into its memory bank; instead, the memory is dissociated and recorded elsewhere in the brain. Experts at the University of California Medical School in San Francisco, such as Dr. Lenore Terr, have stated that survivors of repeated abuse by people they love often repress these painful memories until they are grown and away from home. A group called the False Memory Syndrome Foundation has been active in attempting to discredit the accounts of childhood abuse survivors. The Foundation is alleged to have support from the Central Intelligence Agency in a shared objective of manipulating public perception and blaming victims (Al-Kurdi, 2006).

Neglect of a child during early brain development deprives that child of the input needed for healthy maturation, and abusive experiences affect brain development at critical experience-dependent stages (IPCE, 2006). Early neglect and abuse can potentially affect subsequent brain functioning, and studies have found that deprivation elicits a stress response and causes developmental deficits. Reduced hippocampal activity and post-traumatic stress disorder observed in studied adults suggest that the integrative function of the hippocampus — particularly for emotionally charged memories of trauma — may be seriously affected. Evidence has shown that damage or shrinkage of the hippocampus following traumatic events is usually confined to processing of subsequent events. A study of 22 women who were victims of prolonged and severe childhood sexual abuse revealed a measurable reduction in the volume of the left hippocampus (IPCE, 2006).

Carloff (2002) observes that antisocial behavior resulting from childhood abuse appears to derive from over-excitation of the limbic system — specifically the hippocampus and the amygdala. The hippocampus plays an important role in determining which memories are stored long-term, while the amygdala filters and interprets incoming sensory information according to the person's survival and emotional needs and helps initiate appropriate responses. Studies have revealed that adults who were abused as children had a 113% higher chance of developing and exhibiting symptoms of temporal lobe epilepsy, which disrupts the functioning of both the hippocampus and the amygdala. A review of brain-wave abnormalities in 115 patients showed that 54% had a history of early trauma, compared with only 27% who had none. A cross-study of 17 adult survivors of childhood abuse and 17 healthy matched respondents showed that 12% of abuse survivors had smaller left hippocampi. A 1997 study of adult women who were sexually abused as children reflected the same finding of significantly reduced hippocampal volume. A 2001 study by the Gilead Hospital in Bielefeld, Germany also reported a 16% reduction in hippocampus size. Psychologists generally concur today that mistreatment during childhood leads to stunted psychological development and destructive or dysfunctional psychic defense mechanisms in adulthood. Current brain imaging surveys and other experiments also present evidence that child abuse can permanently damage the neural structure and functioning of the developing brain (Carloff, 2002).

Post-traumatic stress disorder (PTSD) is a psychiatric disorder arising from exposure to actual or threatened death, serious injury, or threat to physical integrity. Its manifestation depends on a person's coping skills, psychological resilience, and interpersonal support (Coleman, 2004). Core symptom areas include re-experiencing traumatic events through intrusive thoughts, images, and memories; avoidance and emotional numbing; and heightened arousal in response to reminders of those events. The part of the brain that regulates the processing of memories for storage and retrieval is the hippocampus. Slow processing of high-affect experiences — such as intense fear — leads to a rigid memory that is toned down but easily released as a nightmare or flashback, with its original emotional intensity intact each time it surfaces. The severity, duration, and repetition of the stressful event over time interact with an individual's vulnerability to produce varying levels of symptoms (Coleman, 2004).

Trauma, Memory, and Post-Traumatic Stress Disorder

New studies reinforce the theory that those who experience severe stress early in life, such as childhood abuse, tend to have an unusually small hippocampus, which plays a central role in regulating memory (Bower, 1996). However, scientists have remained uncertain as to whether reduced hippocampal size is a consequence of severe trauma or instead represents a pre-existing vulnerability to trauma. Earlier studies conducted on 29 women who survived repeated childhood sexual abuse showed hippocampal volumes approximately 5% smaller than those found in women who reported no sexual abuse or psychiatric disorder. Hippocampal volume was lowest in those who reported the most dissociation — that is, feelings of detachment from oneself and other alterations of consciousness. Young children appeared to be more resilient than teenagers or adults in this regard. A separate study conducted by the Veterans Affairs Medical Center in Manchester, New Hampshire, discovered hippocampi that were 24% smaller in combat veterans suffering from PTSD than in those without PTSD and those who had not served in the military. The smallest hippocampi belonged to those who had experienced the most severe combat (Bower, 1996).

A research study conducted by James Golomb and colleagues at New York University on 54 healthy persons aged 55 to 87 demonstrated that recall fails when the hippocampus shrinks (Pennisi, 1993). The researchers measured the size of participants' hippocampi and a comparable brain lobe not involved in memory or learning. They tested participants on immediate recall and delayed recall after a few minutes, and found that the poorer an individual's ability to recall words and pictures after a delay, the smaller his or her hippocampus (Pennisi, 1993).

Sherry (1997) adds that injury to the small brain tissue of the hippocampus can produce profound amnesia, such that the source of a stressful encounter is perceived by the affected person as a stranger, even though they may have met and spoken only minutes earlier. Reasoning and intelligence remain intact; only the recent experience of stress disappears from accessible memory. This condition can destroy the possibility of a normal life (Sherry, 1997).