Mohammed T. Abou-Saleh

20 PRINCIPLES AND PRACTICE OF GERIATRIC PSYCHIATRYenvironment and having favorable living habits influence most ofthe lifespan.Inherent in our functioning are the biological rhythmsobserved at the hormonal levels. Many of the biological rhythmsare synchronized by control centers within the brainstem. Thehypothalamus plays a particularly important role in the losses ofhomeostatic mechanisms in the body. The responsible nuclei(clusters of cells within the hypothalamus) change with aging.These cells decline not only in number but also in efficiency.Sleep changes in late life are clearly associated with alteration ofcontrol centers within the brainstem. Van Gool and Mirmiran 12propose that our biological rhythms become desynchronized aswe age.The Free Radical TheoryA free radical is often considered a molecular fragment, as it hasan unpaired electron. It is unstable and highly reactive. Freeradicals are ubiquitous in living substances and are produced bynormal metabolic processes as well as by external causes such asionizing radiation, ozone and chemical toxins. Free radicals havebeen linked to DNA damage, the cross-linkage of collagen and theaccumulation of age pigments 13,14 .The Accumulation of WasteWith the passage of time, certain pigments such as lipofuscinaccumulate in neurons and other cells. While there is no directevidence that these pigments may be harmful to these cells, there isan association with the wear and tear of aging. Interestingly, theaccumulation of lipofuscin is limited to the cells that are capableof dividing 15 .The Immune System and AgingThe autoimmune theory of aging was proposed by Burnett 16 ,Walford 17 and Comfort 18 . It was suggested that a small number ofimmunologically competent cells may mutate in such a fashion asto lose their tolerance to their host antigen and subsequently giverise to a clone of ‘‘renegade’’ cells 19 , producing antibodies thatmight result in death or damage in a large number of cells,including neurons. ‘‘Anti-brain antibodies’’ are believed to berelated to neuronal injury in senile dementia of the Alzheimertype. Autoimmunity to vascular antigens has also beenreported 20 .The immune system is a complex network, but it has beenfound that restoring certain components can improve immunity.Interleukin-2 (IL-2) declines with age and it appears that theadministration of IL-2 may retard the human aging processes 21 .Caloric Restriction and AgingIt is well established that physical inactivity and overeatingcontribute to obesity, which in turn increases morbidity andmortality 22 . Determining the pathophysiology of overeating isbeing given considerable attention. It appears that oxidative stressassociated with excess caloric intake results in damage thatimpacts on the process of senescence and various diseasescommon in late life. In contrast, a calorie-restricted diet inlaboratory animals results in an increase in average lifespan.However, it is unclear whether further caloric restrictions in nonobesehumans will add to life expectancy.Other Biological Theories of AgingThe disposable soma theory holds that nature’s demand forreproduction takes precedence over a demand for longevity 23 .Nature gives a priority to those traits that are inherent in theorganism that favor reproductive success—traits that enhancetheir fecundity. Hence, somatic cells are disposed of afterachieving reproductive success. However, it appears that theselection of traits that are favorable for reproduction mayindirectly influence lifespan because the increased reserve capacityto carry an animal to and through a longer reproductive life alsoadds to the animal’s capacity to live longer.The brain–body weight theory is based on evidence that theheavier the brain when compared to the weight of the body, themore likely the organism is to be inclined to longevity 24 . Thisrelationship of brain and body is called ‘‘the index of cephalization’’.Naturally there are deviations from this correlation and thisin turn has made the theory of limited validity.Biophysicists have proposed a theory of aging that aims toexplain why larger living organisms tend to live longer thansmaller organisms. One explanation is that ‘‘lifespan tends tolengthen and metabolism slows down in proportion to the quarterpower of the animal’s body weight’’, or what might be called a‘‘scaling theory’’ of aging 25 . The theory is sometimes linked to thesystem of distributing nutrients. The rate of a heartbeat is relevantto the distribution of nutrients. For example, the elephant livesmuch longer than the chicken and has a much slower heart rate.However, the capillaries of elephants are the same size as thosefound in the chicken.PSYCHOLOGICAL THEORIES OF AGINGPsychologists have accumulated a wealth of information regardingmental stability and change in late life. As in biology, thisinformation has not been integrated into a viable comprehensivetheory. The main areas that have been studied by psychologistscan be placed in three broad categories: cognition, personality andcoping mechanisms.Cognitive PsychologyThe term ‘‘cognition’’ subsumes the range of human intellectualfunctioning 26 . Cognition is to perceive, to remember, to reason, tomake decisions, to solve problems and to integrate complexknowledge. Measures of various types of cognition are influencedby chronological age, environment, task characteristics and otherinfluences. With advancing age, individual differences in cognitivefunctions seem to increase. A comprehensive coverage of thestudies on intelligence and memory in old age is beyond the scopeof this chapter and will be presented at greater length in SectionBIII, while basic concepts in those areas will be introduced in thischapter. In general, adults with high intelligence and educationwill show minimum decline in their performances with increasingage, while a significant decline is observed in adults with lowerintelligence and age. However, older adults in general tend toperform less well in new or novel situations 26 .Loss of memory is a common complaint of old age and hasreceived considerable attention by psychologists. There are severaltheoretical models of memory functioning. Such theories attemptto define various stages of information processing. Often attemptsare made to distinguish short-term from long-term memory.Other theorists talk about primary, secondary and tertiarymemory.Research on intellectual functioning has been under way formany years and has been productive. Intellectual performance