What cognitive changes result from aging?

Introduction

Cognitive changes refer to those changes that occur in overall mental functions and operations. Cognition
encompasses all mental operations and functions, including attention, intelligence, memory, language and speech, perception, learning, concept formation, thought, problem solving, spatial and time orientation, and motor/behavior control. Psychologists have worked hard to define and measure various areas of cognitive functioning, even though there has been no consensus about these areas. Understanding the progression of cognitive functioning requires an understanding of brain structure and those human functions emanating from the brain and its fullest human potential, the mind. There is considerable debate within the scientific community about what type of cognitive functions actually exist as well as the nature of the mental mechanisms that are necessary to understand cognitive functioning.

There is a common belief that cognitive abilities decline markedly in older individuals. More and more, however, this idea is being shown to be exaggerated. Studies have shown that the diminution of cognitive skills with age may not be significant, especially before the age of about seventy-five. Aging has been found to have different effects on long-term memory
and short-term memory
processes. The capacity of short-term memory (which is quite limited in all age groups) remains essentially the same for older people. Long-term memory, however, does show a decline. This decline can be minimized by various strategies; the use of mnemonic devices is very effective, as is taking extra time in learning and remembering.

Both biological and environmental factors have been studied in regard to aging and cognition. An environment that induces apathy or depression
has been found to have a lowering effect on cognitive abilities. Environments that provide stimuli to interest the individual can reduce cognitive decline. Moreover, at least one study has found that providing challenging stimuli can even reverse cognitive decline. There is a tremendous range of aging effects from individual to individual, with some showing virtually no changes and others showing serious deterioration of functions. It should be noted that this discussion concerns cognition in healthy individuals; diseases such as Alzheimer’s disease and Parkinson’s disease and events such as strokes (cardiovascular accidents) have effects on memory that are considered separately from the normal effects of aging.

Common age-related stereotypes suggest that older adults are slower at performing many tasks and have poorer memories than when they were younger. Other stereotypes suggest that increased knowledge and wisdom come with age. Scientific evidence indicates that as people age, their mental processes become less efficient, but at the same time, they gain growth and experience, which are useful in solving complex problems.

Contemporary research on cognitive changes caused by aging emphasizes the information-processing capabilities of individuals as reflected in memory capacities. Memory is a basic psychological function on which higher-level psychological processes such as speech, learning, concept formation, and problem solving are based. Lester Sdorow describes the brain’s information-processing capacities as the human being’s active acquisition of information about the world. Sensory stimuli are transmitted to the brain, where replicas of the external world are stored briefly in the sensory registry (one second for visual stimuli and four seconds for auditory memory). Information is then transferred to short-term memory for about twenty seconds, unless it is actively rehearsed, then into long-term memory, where it is potentially retained for a lifetime.

Information Processing and Memory

Information processing is a view of cognitive development that is based on the premise that complex cognitive skills develop as the product of the integration of a hierarchy of more basic skills obtained through life experience and learning. According to this view, fundamental skills are mastered and form the foundation for more and more complex skills.

Information-processing theories emerged as psychologists began to draw comparisons between the way computers operate and the way humans use logic
and rules about the world as they develop. Humans use these rules for processing information. New rules may be added and old rules modified throughout childhood and adulthood as more information is obtained from interactions with the world and life experiences. The cognitive changes that occur throughout adult life, as more useful and accurate rules are learned, are every bit as important as the cognitive advances that occurred during childhood, as long as the basic rules acquired in childhood were not distorted by aberrant experiences. Each advance refines the ability to process information. Elizabeth F. Loftus points out that the terms “cognition” and “information processing” have supplanted the term “thinking” among contemporary cognitive scientists. Similar efforts have been made to redefine other human abilities such as problem solving (by Herbert Simon) and intelligence (by Robert Sternberg) to describe greater specificity of function.

Researchers have spent much time and effort defining and redefining memory constructs, although theorists remain in the early stages of understanding memory. Much debate has focused on naturalistic versus laboratory methodologies, with few resolutions as to how the results of both can contribute to a permanent knowledge base of memory.

The mediation school of thought suggests theoretical mechanisms of encoding, retention, and retrieval to explain memory functioning. Consequently, concerted efforts have been made to attribute memory changes across the life span to the specific deterioration of such mechanisms. Researchers continue to debate the importance, even existence, of such constructs. Similarly, the dichotomy of long-term versus short-term memory continues to be debated. To test the empirical validity of such theories, constructs must be able to be disproved if false, and these metaphorical constructs have proved difficult or impossible to test because of their abstract nature.

The greatest controversy in memory research focuses on laboratory versus naturalistic experiments; some researchers, such as Mahzarin R. Banaji and Robert G. Crowder, state that naturalistic experiments have yielded no new principles and no new methods of memory research and should be abandoned. Others, such as H. P. Bahrick, however, claim that the naturalistic approach has provided in ten years what the laboratory has not in a hundred years. Banaji and Crowder criticize naturalistic experiments for their lack of control and thus their lack of generalizability. Yet confining a study to a specific population in a contrived laboratory setting does not seem to generalize any further. S. J. Ceci and Urie Bronfenbrenner emphasize the need to focus on the process of understanding, whatever that process might be. As Endel Tulving notes, the polemics that have ensued from this debate are not going to advance the science of memory. He concludes that there is no reason to believe that there is only one correct way of studying memory.

Information Processing in the Elderly

Learning, memory, and attention are all aspects of cognition. Learning is the acquisition of information, skills, and knowledge measured by improvement in responses. Memory involves retaining and retrieving information for later use. Attention is the mechanism by which individuals process information. Cognition is how sensory input is transformed, stored, and retrieved from memory.

Major stages of information-processing models of learning and memory include memory registration (input), memory storage (retention), and memory retrieval (processing of input for response). Attention is a major component of registration in that focusing on stimuli and processing of information begin at this stage. Environmental influences, age-related sensoriperceptual changes, and pacing of instruction affect the processing of information.

Environmental influences can produce negative responses from the elderly because older adults are less comfortable in unfamiliar settings and with unfamiliar people and have difficulty performing multiple tasks. Additionally, the ability to block out extraneous information and to focus on multiple instructions decreases with age.

Sensoriperceptual changes include age-related vision deficits such as altered color perception as a result of yellowing of the eye lens, difficulty seeing at various distances as a result of presbyopia, difficulty adjusting from light to dark, and decreased peripheral vision and depth perception. Sensorineural hearing loss affects the ability to hear high-frequency sounds and consonants and hinders communication. Also, excessive noise interferes with the ability to hear in the elderly.

Pacing of instruction includes both the time it takes to present and the amount of information presented. With age, there is slowing of physiological and psychological responses. Reaction time increases. Studies have shown that the elderly learn more efficiently when they are able to learn and respond at their own pace. The total number of brain cells in the healthy elderly decreases only slightly, but a lifetime of activity causes the cells to be less efficient than they once were because of decreased blood flow and other physiological changes. Decreases in cognitive function are likely because of these deficiencies. The amount of decrease varies widely, however, ranging from insignificant to troublesome.

Studies in Age-Related Cognition

In examining cognitive changes in aging populations, aside from the theoretical debates, researchers have reported that cognitive processes progressively decline as chronological age advances. Studies have tended to describe the cognitive declines as gradual and general, rather than being attributable to discrete cognitive losses in specific areas of functioning.

Several studies have supported the existence of age-related cognitive decline, while other studies dispute the severity of such declines. Research interest is increasing in the areas of identifying factors related to cognitive decline and interventions to abate them. Under the direction of Ronald C. Petersen and Michael Grundman, the National Institute on Aging is studying whether daily doses of vitamin E or donepezil can prevent those with mild cognitive impairment from developing Alzheimer’s disease. Vitamin E is also being researched in conjunction with B vitamins. A 2005 study found that healthy people who consumed more than 400 micrograms of the B vitamin folate (the recommended daily amount for adults) cut their risk of developing Alzheimer’s in half. Gingko biloba, the so-called memory herb, appears to help slow cognitive decline for some people in the early stages of Alzheimer’s. Research studies making this claim have been criticized, however, and further studies are necessary. Other studies are investigating cholinesterase inhibitors and anti-inflammatory agents as a means to slow the progression of mild cognitive impairment.

Psychologists who studied memory change identified diminished memory capacity in the elderly as attributable to a number of processes, such as slowed semantic access and a reduced ability to make categorical judgments. Other researchers concluded that older subjects were slower in mental operations but were not less accurate. Some researchers hypothesized that slower speed tied up processing functions, resulting in apparent memory impairment. Still others hypothesized that older adults have more trouble with active memory tasks because of increased competition for a share of memory processing resources, whereas others linked the aged’s poor performance on working memory tasks to an actual deficiency in processing resources. Finally, some researchers concluded that older adults might simply have less mental energy to perform memory tasks. These studies accept gradual memory decline, or a slowing of processing, as a normal by-product of aging.

There are some who believe that mild cognitive impairment is a neurological disorder. This belief stems from the identification of atrophy of the left medial lobe and small medial temporal lobe, low parietal/temporal perfusion, and asymmetry of the brain as revealed by computed tomography. One study identified those with small hippocampi as prone to developing Alzheimer’s disease. Additionally, electroencephalogram tracings of the brains of patients with mild cognitive impairment and patients with Alzheimer’s disease showed similarities.

R. A. Hock, B. A. Futrell, and B. A. Grismer studied eighty-two elderly people, from sixty to ninety-nine years of age, who were living independently in the community. These normal adults were tested on a battery of eight tasks that were selected to reflect cognitive functioning, particularly measuring primary and secondary memory, memory for nonverbal material, span of attention, the capacity to divide attention between competing sources of stimulation, and two motor tasks requiring psychomotor integrity. This study found a gradual, progressive decline in cognitive functioning but found that the decline did not reach statistically significant levels. The decline was general, suggesting that it may have been a function of reduced attention rather than more discrete losses. This finding appears to be consistent with the notion that crystallized intellectual or abstract processes are well maintained across time. There were suggestions that speed of information processing is a sensitive measure of the aging process.

It is possible, however, that the tasks selected for this study did not discriminate between younger and older aging adults because the tasks may be more reliable for assessing brain injuries and psychologically impaired persons, who were not included in the population studied. Consequently, further studies on the same cognitive tasks with impaired aged adults would be necessary to see if the same relationships and conclusions would apply. Individuals with impaired cognitive functioning offer a unique opportunity to determine whether the brain continues to show the same propensity to function as a unitary, global system as is observed with individuals who experience the normal aging process.

Although the brain does exhibit localization of functions, with specialization of certain brain cells for specific functions, its overall mode of operation is as a total unit. The brain has an exceptional capacity to compensate for the loss of some specific functions and continue the rest of its mental operations. This capacity or flexibility in brain function has been termed equipotentiation. Further studies of individuals with brain impairments will help to show how the brain attempts to carry out its overall functions when more specific impairments have been sustained. When cognitive disorders result in faulty information processing, actual observable changes may occur in a person’s daily behavior. The previously neat person, for example, may neglect personal hygiene. The person who previously exhibited exceptional verbal abilities may speak in a socially inappropriate manner. The staid conservative businessperson may act impulsively, make unreasonable decisions about personal finances, and show impaired social judgment.

Mild Cognitive Impairment

Studies of cognitive changes across the life span must distinguish between normal gradual change in the elderly and change that is associated with disordered functioning. Studies must also respect the complexity of the human brain. Morton Hunt notes that cognitive scientists have concluded that there may be 100 billion neurons in the interior of the brain. Each of these neurons may be interconnected to hundreds of others by anywhere from one thousand to ten thousand synapses, or relay points. This may enable the average healthy person to accumulate five hundred times as much information as is contained in the entire Encyclopedia Britannica, or 100 trillion bits of information. The circuitry in one human brain is probably sixty times the complexity of the entire United States telephone system. Given this complexity, even the daily estimated loss of 100,000 brain cells from the aging process may leave human beings capable of sound cognitive functioning well into old age.

The most frequent cognitive complaint made by and about the elderly is loss of memory, especially short-term memory. Researchers are finding that staying active and engaged in a challenging activity requiring mental concentration, such as learning a new language, taking music lessons, doing crossword puzzles, playing games such as chess, or reading books, may help to combat or slow the onset of dementia and keep the mind alert. Not everyone loses the same skills at the same time, but by the eighties, nearly everyone has experienced some cognitive loss. A study in the late 1990s by Gerald E. McClearn of the Center for Developmental and Health Genetics at Pennsylvania State University examined the influence of genes on aspects of cognition in the elderly. Using 240 sets of twins averaging eighty-three years of age, the twins were tested for verbal meaning, figure logic, block design, and picture memory. Genetic inheritance accounted for 55 percent of the individual differences in ability, a result similar to that of middle-aged people. The study concluded that the relative influence of genetics and environment (half and half) extends into advanced age, contrary to the commonly held belief that environmental influences increase throughout the life span as genetic influences decrease.

Mild cognitive impairment is a term used to describe isolated memory loss without changes in activities of daily living. There is some support for the theory that mild cognitive impairment represents a transitional stage between normal aging and Alzheimer’s disease and may be a precursor to Alzheimer’s disease. However, a significant proportion of patients with mild cognitive impairment do not progress to Alzheimer’s disease. One research study followed a group of mildly cognitively impaired patients and reported they developed Alzheimer’s disease at a rate of 10 to 15 percent per year, while individuals without mild cognitive impairment developed Alzheimer’s disease at a rate of 1 to 2 percent per year. Individuals who have a memory problem but do not meet clinical criteria for Alzheimer’s disease are considered to have mild cognitive impairment with memory loss. One study supported that those who carried the gene apolipoprotein E-4 (APOE-4) were more likely to develop Alzheimer’s disease. Studies involving molecular brain activity have contributed to understanding normal and abnormal memory activities. Another study linked poor performance on a memory test that provided cues to help participants at time of recall as indicating a cognitive decline. There is no cure for mild cognitive impairment. However, treatment of coexisting conditions such as depression and high blood pressure can help cognition. Also donepezil (Aricept) has been used to try to slow the progression of mild cognitive impairment to Alzheimer’s disease. Awareness and early identification are important in management of mild cognitive impairment.

Paul Baltes notes that it used to be considered common knowledge that cognitive abilities decline with age, but this view has become highly debatable. When the effects of disease and injury are separated out in studies of the healthy elderly, no drastic decline in cognitive ability is found. This conclusion may be one reason that studies of cognition and aging have begun to make a distinction regarding intelligence. The distinction is between crystallized intelligence, involving the accumulation of facts and knowledge, which holds up with age, and fluid intelligence,
which is the rapid processing of new information, a function that appears particularly associated with the young, and vulnerable to the effects of age or disease. Studies of neurologically healthy aging adults have revealed no consistent evidence of a reduced ability to learn. Studies have further shown that very little practice may be required to substantially improve an elderly person’s ability to perform some cognitive tasks, reflecting a motivational factor. Studies of mentally active persons in their eighties have concluded that loss of cognitive ability stemmed more from intellectual apathy or boredom than from actual physical deterioration.

John Darley and his colleagues concluded that on average, the decline of intellectual capability with age is slight and probably does not occur before age seventy-five. When declines do occur, they do not occur equally across cognitive functions. Vocabulary and verbal skills may actually improve with age, whereas skills involving spatial visualization and deductive reasoning are more likely to diminish. In general, verbal skills and accumulated knowledge are maintained with aging, while tasks that require quick responses are more susceptible to aging.

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