The brain possesses a life-long capability to adapt to new challenges and circumstances. This chapter looks at ways of giving the brain its best chance to retain its powers. During adult life, the number of neurons in the brain slowly diminishes. However, the connections between brain cells – which provide the physical basis for everything we know, think, feel, and do, constantly evolve. While these links are made most rapidly when we are young, the brain never stops refining its connections – strengthening old ones and creating new ones as it learns from experience.
Protecting the brain from physical damage, taking regular mental and physical exercise, and avoiding substances and activities that can harm brain tissue are just some of the ways to ensure your brain stays in good condition. Your brain is your most precious possession: by taking good care of it, you improve the likelihood of enjoying a long and fulfilling life.
Your brain through life
Although our brains become more complex during our lives – primarily by forming millions of connections between nerve cells – most of the brain’s structure is already present at birth. The greatest change and the most rapid growth occurs in the first couple of years of our lives.
At birth, after a normal in-month gestation, there are around the same number of neurons (nerve cells) present in a baby’s brain as there will be in adulthood. Most of these cells will not be replaced if they die, although there are a few exceptions. For example, the set of nerve cells involved in smell and taste in the olfactory nerve is continuously replaced throughout life. However, the number of neural connections between brain cells is relatively small at birth, and it is not until a child is around six years of age that the density of neural connections will be about the same as in adulthood. In this way, the learning that takes place in early childhood has a chance to shape the growing brain.
During the first years of life, there is a massive increase in the brain’s size. By the years of age, the size of the brain and the relative proportions of its parts are basically the same as those of an adult. The brain of a typical full term infant weighs 350g (11 oz) at birth; 1kg (216 4oz) at the end of the first year; 1.2kg (216 11oz) at age 6; about 1.3k g (316) at puberty; and about 1.5kg (316 5oz) at adulthood. The virtual trebling of brain weight during the first year is a growth rate unique to humans, owing to the fact that all human babies are born with relatively immature brains – if the brain was any larger, the baby’s head would be unable to pass through the mother’s birth canal. The rapid increase in size is mainly due to three changes:
- The growth of pre-existing neurons.
- The production of the many supporting glial cells between the neurons.
- The thickening of the sheaths (myelination) around the axons that link neurons together.
Mental development
In early childhood, many important changes occur in the brain that explain the way we behave, remember, and think about ourselves. In general, the process of mental maturation starts in the more primitive structures in the middle of the brain and continues upwards and outwards. For example, young babies display simple emotional reactions owing to activity in the limbic system (which is involved in instinct and mood), even though they are not yet conscious of their emotions. Older babies develop the ability to recognize and understand simple spatial relationships, such as when adults play ‘peek–a–boo’ – hiding an object and surprising the baby when it reappears. This occurs when the parietal cortex (the outer side part of the brain) becomes active. The frontal lobes also become active during the first year so that a baby will start to make simple decisions, such as choosing between two toys.
Language and memory
During the second year, development in Wernicke’s area (a part of the cortex on the left side of the brain ) enables a child to begin to understand spoken language. Some months later, the increasing maturity of Broca’s area, which is situated close by, allows the child to start to speak. This is why children are usually able to understand what is said to them before they can speak for themselves. It may also partly explain why, around the age of two, toddlers are prone to frustration and even tantrums – they don’t yet have the verbal abilities to explain what they want. However, this is usually a brief period of just a few months. Children then go on to develop impressive verbal skills in a very short time: by the age of six, they will have a large vocabulary and, even more impressively, be able to understand and use the majority of grammatical rules – such as creating plurals and using past, present and future tenses, without even being aware of what they are doing.
One reason why most of us cannot remember much of our first two or three years of life is that the hippocampus – where the brain stores long-term memories – does not mature until then. However, some emotional experiences from early childhood may be stored in the amygdala, which may be functioning shortly after birth – although these will only ever be recalled as emotional states rather than explicit memories. The fact that our earliest conscious memories generally date from the age of two or three may also be connected to the development of language and the emergence of a sense of self-awareness, which occurs from around 18 months of age onwards.
Puberty and young adulthood
Puberty is a vital time for brain development, but the hypothalamus (which is central to the body’s endocrine and nervous systems) must mature before puberty begins. Although small amounts of sex hormones circulate from the time of birth, during childhood, these appear to inhibit the hypothalamus. At puberty, the hypothalamic cells become less sensitive to sex hormones. So new hormones – gonadotrophins – are released, which stimulate the production of testosterone by the testes in boys and estrogen by the ovaries in girls. The sex hormones are then allowed to reach high enough levels to stimulate the growth of secondary sex characteristics and to support mating behavior.
Certain areas of the brain do not mature for many years. For example, one reason that children often have a short attention span may be due to the fact that the reticular formation (at the base of the brain) does not fully develop until puberty or even later. Similarly, the reason that younger adults are often more emotional and impulsive than older people may be because of the relatively late development of prefrontal lobe areas, where rational processing of emotion takes place.
The older brain
Between the ages of 20 and 75, it is estimated that an average of 50,000 neurons die each day. In a healthy person, this loss adds up to roughly 10 percent of the original neuronal complement. By the age of 75, the physical weight of the brain is about tenths of its maximum, and blood flow through the brain has reduced by almost one-fifth. A loss of neurons does not necessarily mean a comparable loss of function, however – some loss may be compensated for by the formation from viable neurons of new branches of nerve fibers and by the production of new synapses. Thus, by learning new things and solving problems, we can maintain or even improve brain function – new connections are created whenever we learn something new. Still, if we do not stimulate our brains, the connections will become depleted. As we get older, our brains become less adaptable, but there are no known limits to the amount of information we can store or the amount of learning we can enjoy in life. One reason why people sometimes feel less capable as they get older is that, in the West, there is often a belief that aging causes a decline in intellect.
In contrast, elderly Chinese people are held in high esteem and valued for their lifelong knowledge and wisdom. A 1994 study found that a group of older adults in China performed much better on memory tests than an equivalent US group. The researchers concluded that negative stereotypes about aging can become self-fulfilling prophecies. In other words, the low expectations of elderly Americans meant that they were not inclined to continue with activities that would help them maintain good memories.
Differences between the sexes
There are some sex differences in aging: overall, men lose their brain tissue earlier than women and lose more of it. This particularly applies to the frontal and temporal lobes – areas concerned with thinking and feel ing. This could account for some of the personality changes that often characterize older men, such as irritability. Women, on the other hand, tend to lose brain tissue in the hippocampus and parietal areas – where memory and visual-spatial abilities are located. This could explain why some older women have difficulty remembering things and finding their way about them.
Dementia-Facts and Fallacies
The term ‘dementia’ covers a group of diseases that affect the normal functions of the brain, causing memory loss, confusion, and personality changes.
- Some degree of dementia is thought to exist in about 10 percent of people over 65 and 20 percent of over-75s. Alzheimer’s disease – a progressive form of dementia – is diagnosed in 80 percent of these cases.
- The main symptom of Alzheimer’s is intellectual impairment, the first indication being defective short-term memory. Loss of other intellectual functions, such as an inability to concentrate, follows, together with personality changes.
- It is a myth that Alzheimer’s disease only affects older adults. Although usually diagnosed later in life, particularly over the age of 70, initial signs may appear as early as the mid-30s. Early diagnosis may help prevent further problems, and many symptoms can be treated with modern drugs that boost neurotransmitter function.
- Evidence suggests that Alzheimer’s patients who keep mentally active can maintain their thinking abilities. Reading, writing, and attending adult education classes could all help.
