Doctor of Philosophy (PhD)
Department of Psychology - Faculty of Health & Behavioural Sciences
Fox, Geoffrey A, Effects of aging on functions of the prefrontal cortex, PhD thesis, Department of Psychology, University of Wollongong, 2004. http://ro.uow.edu.au/theses/213
Primary Aging is a term used to describe the effects of the passage of time on the human body, particularly after 50 years of age. The effects may be contained or reversed. Secondary Aging describes the effects of a pathological process, commonly associated with the passage of time. The effects are difficult to contain, cannot be reversed, and progress to death. The thesis addresses two issues, namely can the two conditions be accurately differentiated by neuropsychological tests, and are the effects of Primary Aging first observed in functions commonly associated with the prefrontal cortex. The research technique is that of Real World Research (Robson, 1993), using mostly clients of the author�s private practice, with volunteers whose ages were greater than 59 years. After discussing the various theoretical positions concerning prefrontal functions and the dysexecutive syndrome, the thesis addresses the evidence that supports or queries the influence of primary aging on prefrontal functions. The general consensus of authors is that the prefrontal cortex supports a wide range of brain systems by reciprocal connections. It is emphasised that dysfunction in one part of a system remote from the prefrontal cortex is capable of producing behaviour which suggests a disorder of the prefrontal cortex. It is also emphasised that the prefrontal cortex is a system of connections, and three of these critical circuits are described. Because one of the functions of the PFC is to activate alternate circuits, the PFC system may be able to compensate for damage in one part of the circuit, thus masking the effects of damage. It is proposed that white matter demyelination may play a significant role in the process of disconnection between systems. Measures employed in the research are detailed, and their use justified by systematic analyses of the relevant scores, using the records of past clients of the practice. The research database comprised 184 new clients and volunteers. Four main factors were extracted from the database of 14 test scores, namely Verbal Working Memory, Non-verbal Working Memory, Inhibitory Process and Sensori-motor Speed. The results of the primary aging group suggested a selective decrement in skills. On the other hand, results of the secondary aging group clearly demonstrated global deficits, even when a client showed no obvious symptoms of mild dementia. This distinction was clarified by showing that primary aging effects were more similar to the effects of selective brain damage, as in mild traumatic head injury, and that secondary aging effects were more similar to the effects of a global pattern, as seen in clients with long-standing intellectual deficits. A battery of twelve tests employed demonstrated 100 percent discrimination between the clients assigned to the primary aging group and those assigned to the secondary aging group.