The Ever Changing Brain
Do you consider your brain to be fully matured?
When do you think the brain reaches full maturity?
The answers to these questions might surpraise you.
In fact, the brain grows in spurts from conception until well into adulthood (Fisher & Rose, 1994). In childhood and adolescence, many of these spurts are correlated with major advances in physical and intellectual skills, such as the aquisition of fluency in language that happens around age 4 for most children. Each growth spurt also seems to involve a different brain area. For example, the spurt that begins around 17 and continues into the early 20s mainly affects the frontal lobes, where, you'll recall, the abilities to plan and to control one's emotions are located. Differences between teens and adults in these abilities may be the result of this growth spurt.
Changes in brain function are influenced by several development processes.
Synapsis develop as a result of the growth of both dendrites and axons. This process, known as Sinaptogenesis, occurs in spurts throughout the life span. Each spurt is followed by a period of pruning, the process through which the developing brain eliminates unnecesary or redundant synapses. The activity of neurotransmitters within the synapses also varies with age. For example, acetylcholine is less plentiful in the brains of children than in teens and adults. This difference may help explain age differences in memory and other functions influenced by this excitatory neurotransmitter.
The process of Myelination, or the development of myelin sheats around axons, begins prior to birth but continues well into adulthood. For example, the brain's association areas are not fully myelinated until age 12 or so (Tanner, 1990). And the reticular formation, which, as you'll recall, regulates attention, isn't fully myelinated until the mid-20s (Spreen et al., 1995). Thus, differences in myelination may account for differences between children and adults in processing speed, memory, and other functions.
Some degree of Hemispheric Specialization is present very early in life. Languge processing, for example, occurs primarily in the left hemisphere of the fetal and infant brain just as it does in the adult brain (Chilosi et al., 2001; de Lacoste et al., 1991). Other functions, such as spatial perception, aren't lateralized until age 8 or so. Consequently, children younger than 8 exhibit much poorer spatial skills than do those who are older (Roberts & Bell, 2000). For instance, children younger than 8 have difficulty using maps and distinguishing between statements such as "It's on your left" and "It's on my left".
The ability of the brain to reorganize, to reshape itself in response to input of both internal (within the brain) and external (environmental) sources(Clifford, 2000), and to compensate for damage is termed Plasticity. Plasticity is greatest in young children within whom the hemispheres are not yet completely lateralized. In one case study, researchers found that a prenatal hemorrhage that prevented the development of the left side of the cerebellum in one child was evidenced only by a slight tremor at age 3 (Mancini et al., 2001). As you might suspect, an adult who lost the left side of his or her cerebellum would probably experience much more functional impairment.
However, it is probably also true that the brain retains some degree of plasticity throughout life. For example, researchers have found that the correction of hearing defects in late-middle-aged adults results in changes in all the areas of the brain that are involved in sound perception (Giraud et al., 2001). Moreover, the brains of these individuals appear to develop responses to sounds in areas in which the brains of people with normal hearing do not.
Aging and the brain
Does the brain ever stop changing? No, the brain both gains and loses synapses throughout life. At some point in adulthood, however, losses begin to exed gains (Huttenlocher, 1994). Studies show that almost all areas of the brain lose volume across the early, middle, and late adult years (Raz et al., 2006). One brain-imaging study showed that grey matter, but no white matter, is lost with normal aging in both hemispheres of the cerebellum (Sullivan et al., 2000). Age-related deficits resulting from the loss of gray matter are common. For example, elderly people tend to experience problems with balance, they become less steady on their feet, and their gait is affected.
However, as is true in childhood, intellectual and motor skill training can positively influence the brains of older adults.
The World of Psychology p. 68 -69
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