Biology, in An Introduction to Vocational Psychology

Research in developmental neuropsychology suggests the following "most likely" areas with applications to vocational psychology.

Neuronal and synaptic selection models (especially coupled with critical periods). The young baby's brain sprouts many more dentritic connections than it will requireand massively prunes these connections, with such pruning being especially aggressive at about one year postnatal. However, the creation of new dentritic connections, coupled with continued pruning, presumably continues into adulthood. It is likely that at all ages, pruning is associated with lack of appropriate environmental stimulation, in a massive "use it or lose it" system. Although no one knows exactly what environmental stimulation will prune exactly which dentrites, and what the effects of this would be on subsequent skill acquisition and adult vocational behavior, it is likely to be both subtle and profound in its effects in these areas. In addition to dentritic connections, it possible, and perhaps even likely, that there exists postnatal neurogenesis in humans (just as there is in other mammals (e.g., rats), and in many other species (e.g., birds). For the most part, it is the smaller, Type II neurons (granular cells) that continue to form postnatally; these often are created in some central locations and migrate to other positions in the brain. Type II neurons then insert themselves into neurological structures and allow for more complex, fine-tuned behavior. They appear to be especially important in learning and memory functions. To the degree that they are formed postnatally, including as recent evidence suggests all through adulthood, raises the possibility of adding to specific types of processing capacity to support various skills. This is important because limitations in processing capacity are often blamed for such things as low intelligence, poor job performance, and so on. Whether by adding and then pruning dendrites, or by adding and then connecting neurons, the brain may pass through "critical periods" in which environmental stimulation of particular kinds may have disproportionately great influence on the developing neural systems. However, this is largely hypothetical.

Functional amplification models (again, especially as combined with critical periods). Those who have studied the brain traditionally fall into two camps: those who believe in localization of function and those who do not. Early on, this debate shifted to a debate as to localization in the cortex as other areas (limbic system, brain stem) clearly served different and fairly localized functions. This debate hearkens back to the 19th (and even early 20th century) use of phrenology as a basis for, among other things, providing career counseling on the basis of bumps on and shape of the head, presumably reflecting individual differences in the neurological substrate. Although abandoned as quackery earlier this century, the argument now seems pretty well established that the cortex does in fact have fairly well-defined localized functions, and many of these have vocational implications. A good example is the region normally found in the left hemisphere associated with perfect pitch; it is larger in individuals with perfect pitch. However, we do not know whether increased practice and therefore (presumably) use of the region causes the increase in size. This is entirely possible. Brain imaging research has also identified patterns of brain regions that appear to be involved with performing complex tasks of the sort involved in actual job performance, e.g., spatial reasoning and rotation tasks. Finally, research has identified a number of interesting neuropsychological states that may underly vocational performance, e.g., "aha" experiences are often accompanied by a "quieting" of the brain's general activity.

Staged system models. The increasing evidence of fairly strong brain localization for some functions, and for patterns of cross-function (and cross region) coordination to complete more complext tasks, requires a good means of communicating across brain regions. The brain appears to accomplish this by a complext information routing system; often, information has more than one path it can follow from one region to another, much as packets of information on the Internet may travel from one point to another through any of several paths. These paths are not all "built" at birth, and communcation trunk lines between several key regions evidently continue to be laid throughout childhood. Local communication lines -- think of them as the local phone company -- appear to be fairly well established across functionally similar and continuous cortical regions (e.g., speech related regions in the left hemisphere) by age six. Many of the more distal cabling systems -- think of them as the long-distance lines -- take longer, and in some cases are not fully completed until about the onset of sexual maturity. One of the most important of these completion points is the cabling between the hippocampus and the prefrontal cortex; this appears to be important for linking intention and will to memory, and this line is fully operational by between ages 10-14. Coincidentally, this is the age that Piagetians traditionally ascribe to the onset of formal operations. However, the key point here is not that this or that long distance neural cable is completed by a certain age; rather it is to address the question of why, when the child appears to have so many of the discrete neural functions available for use (e.g., perfect pitch, arithmetic calculation), so many more abstract reasoning skills (often required for successful job performance) are not yet accessible. The staging model suggested by the delayed completion of long-distance neural cabling appears to provide an answer to this question, namely, that young children's brains do not support as facile a coordination and communication of discrete skills across distant brain regions required for many aspects of adult vocational performance. Thus, ease of communication and coordination across brain regions becomes perhaps the critical limiting factor in acquisition of expertise in elementary school-age children, because by age 6 they have completed enough of the local cabling system to support the sustained practice required for acquiring fairly "neurologically focused" and discrete skills, but they must wait until later (and the completion of longer distance neural cables) to acquire expertise in more complex, "neurologically diffuse" skills.

Brain laterialization, and more specifically individual differences in relative reliance on the left or right hemispheres in thinking, may play some role in vocational behavior. There are individual differences in so-called hemisphereic activation, essentially the overall level of cortical electric power than an individual maintains in either brain hemisphere. Results on differences across domains or occupations in such differential activation have thus far been inconclusive, but do tend to support the notion that individuals in domains requiring mainly verbal skills tend to have a more active left hemiphere, while individuals in domains requiring mainly spatial skills tend to have a more active right hemisphere.

Adult neurological changes that may make new learning more difficult. The adult brain may undergo changes, such as loss of neurons, or damage to them or the systems by which they communicate with one another. Such changes may have vocational consequences, usually negative, although it is also possible that the brain compensates for loss of so-called fluid intelligene through a continuous expansion of crystallized intelligence (also known as long-term memory). If the expertise for a domain depends mainly on such crystallized intelligence, and if an individual continues to add to that store of knowledge, then aging need not be associated with declines in vocational performance, at least until physical disease and related infirmities take their toll. For example, writers, historians, columnists, reporters, painters, and judges are some of the occupations in which workers continue on until old age; these are generally "cultural" occupations, in which mastery is slow to arrive and expertise late to depart.