December 14, 2000 -- Belmont, MA -- McLean Hospital researchers have identified four types of brain abnormalities linked to child abuse and neglect, providing the first comprehensive review about the multiple ways in which abuse can damage the developing brain. In the Fall 2000 issue of Cerebrum, the researchers also review evidence that suggests this early damage to the developing brain may subsequently cause disorders like anxiety and depression in adulthood.
"The science shows that childhood maltreatment may produce changes in both brain function and structure," says Martin Teicher, MD, PhD, director of the Developmental Biopsychiatry Research Program at McLean, and author of the paper. Although a baby is born with almost all the brain cells (neurons) he will ever have, the brain continues to develop actively throughout childhood and adolescence. "A child's interactions with the outside environment causes connections to form between brain cells," Teicher explains. "Then these connections are pruned during puberty and adulthood. So whatever a child experiences, for good or bad, helps determine how his brain is wired."
The McLean team identifies four types of abnormalities caused by abuse and neglect. "These changes are permanent," says Teicher. "This is not something people can just get over and get on with their lives."
Limbic irritability: The limbic system is a network of brain cells sometimes called the "emotional brain." It controls many of the most fundamental emotions and drives important for survival. The McLean researchers found evidence that abuse may cause disturbances in electrical impulses as limbic nerve cells communicate, resulting in seizures or significant abnormalities on an EEG, a diagnostic test that measures brain waves. The researchers studied 253 adults who came to an outpatient mental health clinic for psychiatric assessment. A little more than half reported being physically and/or sexually abused as children. The researchers developed a checklist (the Limbic System Checklist-33 or LSCL-33) to determine how often the patients experienced symptoms similar to those that occur in patients with temporal lobe epilepsy. They found that patients who experienced abuse scored much higher suggesting an underlying disturbance in the limbic system. Follow-up studies of 115 children admitted to McLean were conducted to measure EEG disturbances. Patients with a history of abuse were twice as likely as non-abused patients to have an abnormal EEG. Interestingly, all of the extra EEG abnormalities affected the left hemisphere of the brain. EEG abnormalities were associated with more self-destructive behavior and more aggression.
Arrested development of the left hemisphere: The brain is divided into two hemispheres, with the left controlling language and the right responsible for visual-spatial ability, perception and expression of negative affect. In six separate studies and analyses, the smallest involving 20 people and the largest involving 115, the researchers reviewed medical records, conducted neuropsychological tests to measure left- and right-brain abilities, examined the results of MRI scans to provide pictures of the brain at work, and studied the results of sophisticated EEG coherence tests, which provided information on brain structure as well as function. These studies provide evidence of deficient development of the left brain hemisphere in abused patients, so that the right hemisphere may be more active than in healthy individuals. The researchers speculate that the left hemisphere deficits seen in abused patients may contribute to the development of depression and increase the risk of memory impairments.
Deficient integration between the left and right hemispheres: The corpus callosum is a major information pathway connecting the two hemispheres of the brain. The researchers reviewed MRI brain scans from 51 patients admitted to McLean's Child and Adolescent Psychiatry Program, and compared them to 97 MRIs of healthy children obtained from the National Institute of Mental Health. In abused children, the corpus callosum was smaller than in healthy children. After reviewing the medical records, the researchers found that neglect was associated with a 24 percent to 42 percent reduction in the size of various regions of the corpus callosum in boys, but sexual abuse had no effect. In girls, sexual abuse was associated with an 18 percent to 30 percent smaller size in the corpus callosum, but neglect had no effect. They also found that abused patients shifted degree of activity between their two hemispheres to a much greater extent than normal. They theorize that a smaller corpus callosum leads to less integration of the hemispheres. This in turn can result in dramatic shifts in mood or personality.
Increased vermal activity: The cerebellar vermis is a part of the brain that is involved in emotion, attention and the regulation of the limbic system. The McLean researchers used a new functional MRI technique known as T2 relaxometry, which provides information about blood flow to the brain during a resting state, to measure vermal activity in both abused and healthy individuals. Thirty-two adults participated, including 15 with a history of sexual or intense verbal childhood trauma but no physical trauma. The higher a participant's LSCL-33 score, the greater the degree of vermal activity or blood flow. The researchers theorize that the abused patients had higher vermal activity in order to quell electrical irritability within the limbic system. They hypothesize that the cerebellar vermis helps to maintain emotional balance, but that trauma may impair this ability.
After documenting these four types of brain abnormalities, the McLean researchers examined animal studies to determine how such damage might occur. Such studies show that neglect and trauma increase production of cortisol and decrease production of the thyroid hormone, which affect development of neurochemical and neurotransmitter receptors in the hippocampus, amygdala and locus coeruleus, parts of the brain that regulate fear and anxiety. Based on these studies, the McLean team theorizes that the stress caused by child abuse and neglect may also trigger the release of some hormones and neurotransmitters while inhibiting others, in effect remolding the brain so that the individual is "wired" to respond to a hostile environment.
"We know that an animal exposed to stress and neglect early in life develops a brain that is wired to experience fear, anxiety and stress," says Teicher. "We think the same is true of people."
McLean Hospital established the nation's first laboratory dedicated to studying the role of biological factors in mental illness. Today, the hospital is listed by the Institute for Scientific Information as among the most commonly cited sources of publications on neuroscience. McLean is the largest psychiatric teaching affiliate of Harvard Medical School.