Drugs, Malnutrition, and Stress

A User's Guide to the Brain: Perception, Attention, and the Four Theaters of the Brain
by John J. Ratey, M.D.

(Page 6 of 12)

Though we should all heed the lesson to follow, expectant mothers should take it very seriously. The developing brain in the fetus is extremely sensitive to its environment. Most pregnant women are aware of the dangers they can pose to their unborn babies. But they may not realize just how potent their actions can be. Let's consider a few of the most striking cases of environmental influence.

Smoking

Cigarettes are probably the "drug" most commonly used during pregnancy. Despite warnings, 20 to 25 percent of pregnant women still smoke. Nicotine can reduce blood flow in the uterus and placenta by causing constriction of the blood vessels. It decreases the fetus's heart rate and breathing movements and exposes it to carbon monoxide.

Smoking raises considerably the risk that a baby will be born premature and underweight. The risk of spontaneous abortion is 1.7 times higher for smoking than for nonsmoking mothers. The risk of congenital abnormalities is 2.3 times higher. Research also shows that there is a 50 percent greater incidence of mental retardation among the children of mothers who smoked during pregnancy and that the more a woman smoked when she was expecting, the greater the chance of retardation. Importantly, the children of mothers who smoke show a threefold increase in attention deficit disorder (ADD), and a well-known reduction in birth weight, which is thought to have a great effect on the development of the brain. The incidence of sudden infant death syndrome is also higher among babies whose mothers smoked during pregnancy. Prenatal use of marijuana has similar effects. A mother's smoking affects her unborn baby because certain substances in her blood are passed to the fetus across the placenta. Research indicates that nicotine actually concentrates in the fetus, exposing it to an even higher level of the drug than the mother experiences.

The leading theory as to how nicotine affects the fetus's brain development is that the drug interferes with the natural migration of neurons, their connections, and their proper pruning during fetal development, although a direct link has not yet been proven. There is also evidence that nicotine can deregulate the dopamine system, undermining the modulating effect dopamine has on the brain's development.

Alcohol

Alcohol consumption during pregnancy can have devastating consequences. Microscopic studies of fetal brains show that alcohol causes faulty cell migration. Once they begin to travel, the neurons do not know when to stop, miss their proper destinations, and often die. As a result, the brains of babies whose mothers drink regularly are frequently small, shrunken, and malformed, with a lower density of neurons. These fetal alcohol syndrome (FAS) babies have low IQ scores in childhood and severe reading and math disabilities by the time they reach high school and adulthood, as well as maladaptive behavior, hyperactivity, and depression. The really unfortunate news is that, as with every other developmental toxin, the most significant effects of alcohol come early in pregnancy: the first six weeks are the most crucial. If a woman is drinking during this period, by the time that she becomes aware that she is pregnant the damage may have been done. Given this, there may be hundreds of thousands of people who have some degree of mental or physical impairment owing to in utero exposure to alcohol.

Research also shows that the effects associated with FAS continue and indeed increase as children become adults. There is also a more subtle version of fetal damage known as fetal alcohol effects (FAE). A recent study of 253 people diagnosed with FAS and FAE found that 90 percent had mental health problems; 60 percent experienced disrupted educations; 60 percent had trouble with the law; 50 percent had been accused of inappropriate sexual behavior. This points to a theme that will be repeated time and again in this book: Some types of antisocial and even criminal behavior could be linked to, if not caused by, physical problems in the brain.

Meanwhile, as treatments develop, society can do a great deal to prevent FAS and FAE in the first place, by educating all its citizens about the risks of drinking during pregnancy.

Cocaine

Only a few studies of cocaine use during pregnancy have been completed. More are needed. But the early results indicate effects similar to those of alcohol. Cocaine interferes with the transfer of nutrients and can shrink the amount of oxygen that travels from the placenta to the fetus, causing impaired growth of the fetus's body and brain. However, most recent studies show that many of the effects of cocaine disappear as the infant matures.

Malnutrition

During pregnancy, the fetus is more readily harmed by foreign substances than by poor nutrition. Nonetheless, a shortage of certain nutrients in the mother's diet, such as iron, vitamin B12, folic acid, and essential fatty acids, can retard the brain's development. For example, research has shown a clear correlation between an insufficient intake of folic acid and a high incidence of spina bifida. If essential nutrients are not available, neurons stop forming, resulting in smaller brains, less overproduction of neurons in the fetus and subsequently less pruning or fine-tuning, and less cognitive development. Once born, these babies have lower birth weights, slower rates of growth, less coordination, a higher incidence of poor sight, and more learning difficulties. Malnutrition in young children also slows the brain's development, impairing cognition.

However, anxious pregnant mothers must also be careful not to overindulge. The vitamin craze that continues to sweep Western cultures makes it too easy, and seemingly imperative, to take massive doses of vitamins. Consumption of excessive amounts of some vitamins, particularly A and D, can lead to toxicity, which interferes with the brain's neurochemistry. A recent study shows that the consumption of too much vitamin A by pregnant women may cause birth defects. Large quantities of retinol and retinyl esters, the forms of vitamin A commonly used in dietary supplements, cause birth defects in tests on many animals. Pregnant women, with their doctors, should make sure they are getting enough vitamins, but not too many.

Toxins

Most of us remember the frightening warnings we received as children about not eating paint. Toxins such as lead can severely disrupt brain chemistry. During pregnancy, lead, pesticides, anesthesia gases, antibiotics, over-the-counter and prescription medications, and even acne medicine containing large amounts of vitamin A can all act as toxins on the fetus's brain. Ionizing radiation, such as X-rays and drugs used in treating cancer, have the same effect.

Some chemicals may not interfere with the brain's development. A small 1996 study at the University of Toronto of three widely used antidepressants-paroxatine, sertraline, and fluvoxamine-showed that these drugs do not appear to cause birth defects, which agrees with research in animals and previous studies of the antidepressant Prozac among pregnant women. However, because the study looked at only 267 expectant mothers, it was far too limited to establish that these drugs are safe during pregnancy. The study also did not explore behavioral differences in the babies born.

A previous study of Prozac found no effects on IQ, language, or behavior among babies exposed to the drug as fetuses. However, other research indicates an increased rate of "minor anomalies" at birth, such as abnormal creases in the palm of the hand. Until more research is done, women who are taking antidepressants or any medication and are considering pregnancy should consult with their doctors about the risks of continuing or stopping medications on the health of mother and fetus.

For their part, would-be fathers would also be wise to avoid exposure to smoking, alcohol, drugs, and toxins for at least three months prior to conception-the life span of the sperm.

Neural Darwinism

in the early stages of development, neurons travel freely in the brain, though guided in general pathways by genetic instruction. As they float around, some divide into more neurons, some die, and others settle down at permanent sites and make connections with neighbors, building the brain's complex circuitry. Genes provide the basic guidelines that control how the neurons form functioning networks. But the precise chemical environment influences which neurons connect with which.

All of our brains have the same general features that make us human, but each neural connection is unique, reflecting a person's special genetic endowment and life experience. Circuit connections are made stronger or weaker throughout a lifetime according to use. Neurologist and Nobel laureate Gerald Edelman, head of the Neurosciences Institute at the Scripps Clinic in La Jolla, California, calls the process neural Darwinism. Connections that cope well with the sensory inputs they receive, which they can convert into effective actions, stay intact and become strong. Those that do not, die off in a process that resembles natural selection. Neurons and the circuits they form part of compete with other neurons for survival, and those that are best adapted to the environment survive. The environment around us-what we ingest and inhale, the amount and type of light and sound-actually changes the physical interconnection of synapses within the brain, providing us with more efficient circuitry, and allowing each of us to develop an exclusive brain suited to our particular needs.

Neural Darwinism is the theory that explains why the brain needs to be plastic, that is, able to change as our environment and experiences change. That is why we can learn in the first place, and unlearn too, and why people with brain injuries can recover lost functions. The concept also underlies two of the mantras of this book. "Neurons that fire together wire together" means that the more we repeat the same actions and thoughts-from practicing a tennis serve to memorizing multiplication tables-the more we encourage the formation of certain connections and the more fixed the neural circuits in the brain for that activity become. "Use it or lose it" is the corollary: if you don't exercise brain circuits, the connections will not be adaptive and will slowly weaken and could be lost.

Excerpted from A User's Guide to the Brain by John J. Ratey, M.D. Copyright © 2002 by John J. Ratey, M.D.. Excerpted by permission of Vintage, a division of Random House, Inc. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.

About the Author

John J. Ratey, M.D., is an associate professor of psychiatry at Harvard Medical School. He has lectured extensively and published many articles on the topic of treating adults with ADD. Dr. Ratey is the author of A User's Guide to the Brain and the co-author of Driven to Distraction. He lives in Cambridge, Massachusetts, where he has a private practice.