Although this is a book about drugs and how people become hooked on drugs, it is also about all of our appetites; therefore, it can help us understand other potential addictions such as eating and gambling. For example, if someone overeats, craves carbohydrates every day, and has withdrawal symptoms when he stops cold turkey, then he may have a problem with carbohydrates. If such a person seeks help, then this book can help with understanding the problem and the needs for treatment. More is said later about food, gambling, and sexual drives.
Another point is that some therapeutically useful medicines (not addicting drugs), such as antidepressants, need to be taken over long periods of time and should not be stopped abruptly because of the danger of recurring disease. Studies of abused drugs, which also involve taking drugs over a long period of time, can inform us not only about how the useful medications produce their beneficial actions in the brain, but also about the problems in abruptly stopping their use.
Brain Structure and Functions
Before embarking on a study of the addicted brain, it is necessary to be aware of the brain and its organization. Different parts of the brain have different functions. Seventy-five percent of the human brain is made up of the wrinkled outer covering referred to as the cerebral cortex, which has different functional areas. Strokes or lesions of the motor cortex result in paralysis, the extent of which is dependent on the extent of the motor area involved. Patients with strokes in the association cortex have deficits of perception and attention. When the temporal lobe is damaged, the ability to recognize or name objects is impaired. Lesions or strokes of the frontal lobe result in personality changes, planning deficits, and inabilities to carry out complex behaviors. Strokes or tumors in other parts of the brain have many other effects as well (see Figure 1-3).
Figure 1-3 A lateral (sideways) surface view of the brain shows some of the more obvious regions, and each region has its own function. The specific functions of the various brain regions have become known after centuries of studies of patients with strokes, injuries, and tumors. Drug addiction also involves certain regions.(Adapted from http://medicalimages.allrefer.com/large/brain.jpg, accessed on December 20, 2010.)
The brain is also the organ of awareness. When general anesthetics are administered, the electrical activity of the brain is reduced, and we lose awareness or go to sleep. If we stimulate the visual cortex, we might have visual images pop into our awareness. If the olfactory cortex is stimulated, then we might perceive odors. If we stimulate other parts of the brain, other events or sensations enter our awareness. Emotional behavior is also based in the brain. A group of brain regions collectively known as the limbic system controls emotional behavior and is partly responsible for feeling good. The following chapters link certain brain regions with feeling good and with drugs.
The Tool Box
Science, like everything else in our lives, has become technology-driven, and there are marvelous new approaches and instruments that allow us to examine the tiniest parts of our chromosomes or peer into the depths of our brains without surgical invasion of the skull. These tools are powerful and interesting in and of themselves.
The science of genetics has advanced, and it is now possible, with a small sample of blood, to examine our genes. Because genes are the basis of heredity, and some aspects of drug addiction are heritable, studies of genes can be informative. The target of these studies is DNA, which is made up of four different chemicals called bases, and it is the order of these chemicals in our DNA that specifies our genes. These chemicals—abbreviated as the letters A, T, G, and C—are lined up in two parallel strands that comprise the structure of DNA. Again, it is the sequence of these bases, in groups of three, that constitutes our genetic code, and certain parts of our genetic code can contribute to the likelihood of our becoming a drug user.
For looking inside our brains, noninvasive brain imaging techniques can be astonishing. Magnetic resonance imaging (or MRI) describes the structure of our brains, such that changes in the size of parts of our brains can be measured. Functional magnetic resonance imaging (fMRI) tells us about the functional activity of various brain regions. Positron emission tomography (PET) scanning is versatile. It can be used to reveal the activity of different brain regions or even the levels of certain brain chemicals and proteins. Overall, genetic and imaging studies are but two of the new tools that have become available over the past 25 to 35 years. These tools are out in front in the attack on drugs.