Читать книгу New hope for ADHD in children and adults - Helena Bester - Страница 21

For almost a century scientists suspected that brain injuries caused ADHD. Later it was determined that only between five and ten per cent of ADHD sufferers may have suffered brain damage in utero or at birth. Researchers today agree that ADHD is usually not caused by brain damage. It is also not associated with cognitive disability (a low intellectual ability).

Studies conducted among chimpanzees and other primates (Dr Russell A. Barkley, 1995) have produced interesting results. When the frontal lobes of the brains of the primates were manipulated or injured they manifested behaviour that corresponds with ADHD symptoms. The animals became more hyperactive and had difficulty with concentration and impulse control. Many other studies confirm that the frontal area of the brain is underdeveloped in ADHD sufferers. One of the most common treatments for ADHD using neurofeedback therapy involves inhibiting the activity of excessively slow brainwaves (theta waves) that often occur in underdeveloped frontal lobes.

The social behaviour of ADHD sufferers often seems immature. Neurological tests often show that the electrical activity in the brain of ADHD sufferers looks like that of a younger person. In neurofeedback therapy, this situation is addressed by boosting faster brainwaves (by means of a process of visual and auditory feedback) and inhibiting slower ones, for example. Evaluations also often show delayed motor co-ordination in ADHD sufferers.

Although numerous studies have been done to try to determine differences in brain structure and anatomy between ADHD suffers and non-sufferers, to the best of my knowledge there is as yet no certainty about this. However, the brainwaves do appear to be slower in the frontal area of the brain of ADHD sufferers.

Most researchers agree that there is a biochemical imbalance in the brain of ADHD sufferers and that in most cases (80%) it is hereditary. There is no clarity on what causes this imbalance.

The biochemical imbalance results in inadequate stimulation of the brain in the areas that control the person’s concentration and impulse control. According to Dr John F. Taylor (1997), the brain of the ADHD sufferer underproduces the neurotransmitters dopamine (which controls alertness and motivation), noradrenaline (responsible for concentration and memory) and serotonin (the feel-good chemical), with the result that there may be a deficiency of these substances in the person’s brain.

In recent years the dopamine deficiency in particular has been receiving attention. The dopamine structure in the prefrontal cortex does not function properly in ADHD sufferers, and stimulant medication such as Ritalin aims to encourage the production of dopamine. Drugs such as cocaine and methamphetamine (also known as “tik” and “meth”) have the same effect. The ADHD sufferer sometimes displays stimulation-seeking behaviour because excitement has an effect on the dopamine transfer in the brain. This is why ADHD sufferers can sometimes play computer games for hours on end, but cannot remain focused enough to read a book. The action on the computer screen influences dopamine transfer. Dr Rykie Liebenberg, a psychiatrist specialising in ADHD, believes that ADHD sufferers can become addicted to the dopamine reaction that takes place in their brain when playing computer games.

Research conducted by the Howard Hughes Medical Institute at Duke University in Durham, North Carolina, USA, indicates that stimulant medication may also influence serotonin levels. Non-stimulant medication such as Strattera affects noradrenaline transmission.

Neurotransmitters play an important role in the transmission of information from one brain cell to the next. These chemical substances are secreted in the space between two brain cells and are partially taken up by the next one. Enzymes destroy the surplus molecules so that the neurons don’t keep sending messages. Ritalin and other stimulants influence this process. (We will go into this in more detail in chapter 8, and also investigate whether diet may promote or change the production of neurotransmitters.)

Among the approximately twenty per cent of ADHD sufferers who have not inherited the condition, other factors are involved. A number of researchers have found a link between the mother’s stress levels during pregnancy and the prevalence of ADHD among children. Professor André Venter of the department of paediatrics and child health at the University of the Free State was quoted in an article in the magazine Sarie as saying that there is a higher incidence of ADHD in children born during wartime because the stress levels of pregnant women are higher then. This leads to a higher level of the stress hormone cortisol in the baby’s brain. According to Professor Venter, HIV and meningitis or anything else that causes inflammation of the brain, could also be non-genetic causes of ADHD.

Near drowning or suffocation or a brain injury suffered in a car accident, for example, or even as a result of a blow to the head during play, could lead to the symptoms of ADHD. Brain damage, particularly as a result of a lack of oxygen, could also easily occur during birth. ADHD symptoms occur especially when the damage occurred in the frontal lobe of the cerebral cortex.

Although environmental factors cannot cause ADHD, they can exacerbate the symptoms. For instance, a child with a tendency to hyperactivity and impulsivity could learn to regulate her behaviour more easily in a calm, orderly environment. However, if there is a hyperactive father in the household who regularly encourages the child to display active behaviour in situations where it is more appropriate to be calm, the child’s hyperactive behaviour patterns will be strengthened and become more prominent and problematic. Managing the behaviour of ADHD sufferers both at home and in the school environment is therefore very important, and is discussed later in this book.