OVERALL AGE-RELATED CHANGES IN MEMORY

Retrieval of information is an important part of daily functioning.

With normal aging, memory deficits are associated

primarily with the storage of long-term episodic memories.

Information that places little demand on attention, such as

implicit memory tasks, results in very little age-related changes

in performance. The advantage that older adults experience

on recognition tasks indicates that their memory storage and

retrieval may be much less efficient than that of younger

adults. A processing speed perspective illustrates that normal

aging is accompanied by a slowing in overall cognitive processing

and it is accepted that older adults process information

at a slower rate compared with younger adults. Salthouse19

found that after statistically controlling for processing speed,

age was only weakly related to memory. Memory functioning

in normal aging is thus mediated by processing speed.

The reduced attentional resources concept18,40 suggests that

a limited amount of cognitive resources are available for a

given task and consequently, a more complex task requires

more attentional capacity than a simpler task. It follows that

because the amount of attentional resources is reduced with

aging, the processes of encoding and retrieval of information

use a larger proportion of available resources for older adults

than for younger adults. In sum, research suggests that overall

cognitive slowing and changes in attentional ability account

for much of the change in memory functioning as we age.

Verbal Abilities

Most verbal abilities remain intact with normal aging.41

Therefore vocabulary and verbal reasoning scores remain

relatively constant in normal aging and may even show

minor improvements. The two main areas of verbal abilities

that are frequently discussed in terms of aging are verbal fluency

(semantic and phonemic) and confrontation naming.

Verbal fluency is the ability to retrieve words based on their

meaning or their sounds. Confrontation naming describes

the ability to identify an object by its name.

Two common tests used to assess verbal fluency are the

Controlled Oral Word Association Test (COWAT)42 and

the semantic fluency test.31 The COWAT is perhaps the

most widely used test of phonemic fluency. The COWA task

requires an individual to generate as many words that begin

with a specific letter as quickly as they can. The semantic fluency

task is a timed-test that requires the individual to generate

examples in a specific category (e.g., animal naming test).

The Boston Naming Test32 is a commonly used test to measure

confrontation naming ability as individuals are required

to name the object in the presented picture. Confrontation

naming is composed of several different processes; an individual

must perceive the object in the picture correctly, identify

the semantic concept of the picture, and retrieve and

express the appropriate name for the object.43 Confrontation

naming ability is associated with the tip-of-the-tongue

(TOT) phenomenon. The TOT phenomenon occurs when

an individual knows the name of a person or object and is

able to retrieve the semantic information about the object,

but cannot retrieve the name of the object.44 Although an

individual is unable to retrieve the target word, he or she will

often try to describe the term using other words.45 Throughout

all of adulthood, proper nouns comprise the majority of

TOT experiences. However, the increase in TOT phenomenon

among older adults is due to their greater difficulty in

retrieving proper nouns.44 There is not a significant age difference

in the frequency of TOT episodes for simple words.

However, older adults have significantly more TOT experiences

than younger adults for difficult words.45 Thus, wordfinding

difficulty and TOT moments are the most common

cognitive complaints of older adults.

The majority of cross-sectional studies have found that

older adults have lower scores on the Boston Naming Test

compared with younger individuals. It should be noted that

while subjective complaints of word-finding difficulties

increase with age, significantly lower performance on tasks

of confrontation naming only emerges after age 70.44 Zec

et al46 found that confrontation naming ability as measured

by the Boston Naming Test improves when individuals are in

their 50s, remain the same in their 60s, and decline in the 70s

and 80s; it should be noted that the magnitude of these agerelated

changes is relatively small. It was found that there

was an approximate one word improvement in the 50s age

group and a 1.3 word decline in the 70s age group. There is

some indication that there is an accelerated rate of decline in

confrontation naming ability with age.44

Normal aging is associated with a decline in verbal fluency.

It is important to note that the normal age-related decline

seen in verbal fluency performance may be partially mediated

by reduced psychomotor speed rather than true deficits

in verbal ability. Slowed handwriting and reading speed in

the elderly was predictive of poorer performance on verbal

fluency tests.47 Rodriguez-Aranda and Martinussen48 found

a decline in verbal fluency as measured by the COWAT

after age 60. The ability to generate words beginning with

a particular letter improves until the third decade of life and

remains constant through the 40s. Subsequently, a significant

decline occurs in phonemic naming ability and continues to

worsen gradually until the late 60s. Phonemic verbal fluency

ability continues to decline rapidly through the late 80s. Gender

and education may impact one’s phonemic verbal fluency

across the lifespan. Women may slightly outperform men on

tasks of phonemic verbal fluency. Individuals with higher levels

of education (beyond high school) show greater verbal

fluency ability as measured by the COWAT compared with

individuals with lower levels of education (12 years or less).49

Executive Functions

Executive functions describe a wide range of abilities that

relate to the capacity to respond to a novel situation.16

Executive functions include abilities such as mental flexibility,

response inhibition, planning, organization, abstraction,

and decision-making.50,51 Executive function can be thought

of as having four distinct components: volition, planning,

purposive action, and effective performance.3 Volition is a

complex process that refers to the ability to act intentionally.

Planning is the process and the steps involved in achieving

the goal. Purposive action refers to the productive activity

required to execute a plan. Effective performance is the ability

to self-correct and monitor one’s behavior while working.

All of the components of executive functioning are necessary

for problem solving and appropriate social behavior.

Another term for executive functions is frontal lobe functions

because these abilities are localized in the prefrontal

cortex.52 The frontal aging hypothesis refers to the idea

that normal aging leads to deterioration of the frontal lobes.

Deterioration is due to a loss of volume in the prefrontal

cortex and is associated with cognitive deficits. Prefrontal

deterioration plays a key role in many of the age-related

changes in cognitive processes, such as memory, attention,

and executive function.53

Like many cognitive processes, it is difficult to assess pure

executive function as many of the measures used in its assessment

rely on other cognitive processes such as working memory,

processing speed, attention, and visual spatial abilities.

The Wisconsin Card Sorting Test (WCST)54 is a popular test

used to measure executive function. The WCST requires an

individual to sort a set of cards based on different categories.

Individuals are not informed about how to sort the cards

and must deduce the correct sorting strategies through the

limited feedback that is provided. After a particular category

is achieved (i.e., a set number of correct responses) based

on a particular characteristic (e.g., color or shape), the sorting

strategy changes and the individual must shift strategies

accordingly. Once the test is completed, the examiner is provided

with several measures related to executive function, for

example, categories and perseverative errors. A category is

achieved when a specific number of cards have been sorted

correctly based on the particular criterion such as color. Perseverative

errors occur when an individual continues to give

the wrong response when provided the feedback that the

strategy is not or is no longer correct, thus demonstrating a

lack of cognitive flexibility.

On the WCST older adults achieve significantly fewer categories

than younger adults.52 The most significant decline

in performance on this test is seen in adults age 75 and older.

Individuals of this age group achieve significantly fewer categories

and more perseverative errors compared with younger

individuals. However, changes in executive functioning as

measured by neuropsychological assessments, such as the

WCST, can be seen in adults aged 53 to 64, but adults ages

53 to 64 do not show deficits on more real-world executive

tasks.55 Thus although individuals in midadulthood may

show a decline in executive functioning on structured neuropsychological

tests, their real-world executive skills remain

intact.

Other measures used in the assessment of executive functioning

included Trail Making Test, Part B5 and the WAIS-III

subtests,4 Matrix Reasoning and Similarities. Trail Making,

Part B, is a timed visual-spatial sequencing task requiring

an individual to draw connecting lines alternating between

numbers and letters in numerical and alphabetical order.

Matrix Reasoning is an untimed task that measures one’s

nonverbal analytic thinking abilities. The Matrix Reasoning

task requires an individual to identify the missing element

of an abstract pattern from a variety of choices. Wechsler’s

Similarities subtest measures an individual’s verbal abstract

reasoning skills by asking an individual to describe how two

different objects/concepts are alike.

Normal aging is generally associated with a decline in

executive functioning.56 When reasoning and problem-solving

involve material that is novel, complex, or requires

the ability to distinguish relevant from irrelevant information,

the performance of older adults suffers because they

tend to think in more concrete terms and the mental flexibility

required to form new abstractions and concepts

declines.3 Compared with younger adults, older adults also

show a decreased capacity to form conceptual links as mental

flexibility diminishes.3 Executive functions serve as the

overseer of brain processing and are essential for purposeful,

goal-directed behavior. Deficits in executive functioning

can be seen in difficulties with planning and organizing,

difficulties implementing strategies, and inappropriate social

behavior

or poor judgment.

Lifestyle Factors Associated with

Cognitive Functioning

LEISURE ACTIVITIES

The mental exercise hypothesis refers to the notion that

keeping mentally active will help maintain an individual’s

cognitive functioning and prevent cognitive decline. Many

activities, such as playing bridge, doing crossword puzzles,

studying a foreign language, and learning to play an instrument,

have been suggested to help in preventing cognitive

decline.57 The research regarding the mental exercise

hypothesis has been varied and there is currently not a

definitive answer regarding the role of leisure activities in

preventing cognitive decline.

It is suggested that engaging in leisure activities, especially

ones that are cognitively demanding, maintains or improves

cognitive functioning.58 However, there is also evidence

that individuals with high levels of intellectual functioning

engage in more cognitively demanding activities, making it

difficult to discern the exact role of mental activities in preventing

cognitive decline. This line of research suggests that

it is not the activity per se that is responsible for maintaining

cognitive functioning, but rather specific lifestyles and living

conditions.58

Although there is not conclusive evidence regarding

the protective factors of leisure activities, several research

studies59,60

have shown that leisure activities reduce the risk

of dementia in the elderly. Reading, playing board games,

learning a musical instrument, visiting friends or relatives,

going out (i.e., to movies or a restaurant), walking for pleasure,

and dancing are associated with a reduced risk of

dementia.59,60 Such leisure activities have been shown to

protect against memory decline even after controlling for

age, sex, education, ethnicity, baseline cognitive-status, and

medical illness. Participation in an activity for 1 day per

week was found to reduce the risk of dementia by 7%.59 Individuals

who participated in many leisure activities (i.e., six or

more activities a month) had a 38% less risk of developing

dementia.60

It has been also hypothesized that leisure activities reduce

the risk of cognitive decline by enhancing cognitive reserve.

A decrease in activity results in reduced cognitive abilities.61

Engaging in leisure activities may also provide structural

changes in the brain that protect against cognitive decline

given that certain areas of the adult brain are able to generate

new neurons (i.e., plasticity). Stimulation, such as engaging

in social, intellectual, and physical activities, is suggested

to promote increased synaptic density. Enhanced neuronal

activation has been proposed to hinder the development of

disease processes, such as dementia.60 However, research has

also shown that changes in cognitive reserve are more likely

to occur early in life; it is primarily the early experiences of

education and intellectual activity that increases cognitive

reserve the most.11 Despite the varied findings,

“people should continue to engage in mentally

stimulating activities because even if there is

not yet evidence that it has beneficial effects

in slowing the rate of age-related decline in

cognitive functioning, there is no evidence that it

has any harmful effects, the activities are often

enjoyable and thus may contribute to a higher

quality of life, and engagement in cognitively

demanding activities serves as an existence

proof—if you can still do it, then you know that

you have not yet lost it.”57

PHYSICAL ACTIVITIES

It has been hypothesized that engaging in physical activities

may enhance cognition and prevent decline in late life

as physical activities enhance blood flow to the brain and

oxygenation, processes which are known to slow biologic

aging.11 Physical activities reduce cardiovascular and cerebrovascular

risk factors, which may reduce the risk of vascular

dementia and Alzheimer disease.62 There is also evidence

that physical activity may directly affect the brain by preserving

neurons and increasing synapses.63

Moderate and strenuous physical activity is associated

with a decreased risk of cognitive decline. Moderate activity

includes playing golf on a weekly basis, playing tennis

twice a week, and walking 1.6 m/day. Research has found

that long-term regular physical activity, such as walking, is

associated with less cognitive decline in women.64 The benefits

of walking at least 1.5 hr/wk at a 21 to 30 min/mile pace

are similar to being about 3 years younger and are associated

with a 20% reduced risk of significant cognitive decline

SOCIAL ACTIVITIES

Social support has also been suggested to serve as a protective

factor in cognitive decline. Social support may serve as a

buffer against stress and may lead to decreased cortisol production

in the brain. Lower levels of cortisol result in better

performance on tests of episodic memory.65 Interacting

with others may also prevent cognitive decline by providing

an individual with increased mental stimulation66 and

may also protect an individual from depression, which has

been shown to negatively impact cognition.67 Depression

and mood disorders are associated with an accelerated cognitive

decline as people age.68 Processing speed, attention,

and consequently, memory may all be affected by depression.

In addition, a lack of social interaction also impacts an

older adult’s well-being. It has been found that individuals

who live alone or have no intimate relationships are at an

increased risk of developing dementia; those individuals

who are classified as having a poor social network are 60%

more likely to develop dementia.69 Individuals in their 70s

who report having limited social support at baseline show

greater cognitive decline at follow-up assessments.67 On the

other hand, individuals with greater emotional supports have

better performance on cognitive tests.67 Rowe and Kahn70

proposed a model of successful aging as being composed of

three main components: avoidance of disease-related disability,

maintenance of physical and cognitive functioning,

and active engagement in life. Active engagement with life

involves maintaining interpersonal relationships and it has

been found that social environment and emotional supports

may be protective against cognitive decline and result in a

slower decline in functional status.

HEALTH FACTORS

Several medical conditions are associated with cognitive

decline. Hypertension is the most prevalent vascular risk factor

in the elderly.71 Chronic hypertension has been shown to

result in deficits in brain structure including the reduction of

white and gray matter in the prefrontal lobes, atrophy of the

hippocampus, and increased white matter hypertensities.72

Research has found that uncontrolled hypertension can lead

to cognitive decline that is independent of normal aging,71,73

aside from posing a risk for stroke. Older adults with hypertension

have mild but specific cognitive deficits in the areas

of executive function, processing speed, episodic memory,

and working memory.73

Diabetes mellitus has also been associated with cognitive

decline.74,75 Lipids and other metabolic markers may play a

role in the relationship between diabetes and cognition.76

Diabetes may also impact cognition through confounding

factors such as hypertension, heart disease, depression,

and decreased physical activity.76 Individuals with type 1

diabetes display a slower processing speed and a decline

in mental flexibility.75 Type 2 diabetes is also associated

with cognitive decline; longer duration of type 2 diabetes

results in greater cognitive decline.77 Elderly women

with type 2 diabetes have a 30% greater risk of cognitive

decline compared with those without diabetes, with a 50%

greater risk for individuals with a 15-year or greater history

of diabetes.

Dietary factors and vitamin deficiencies have also been

associated with cognitive decline in the elderly population.

Individuals with cognitive decline associated with normal

aging should be investigated for B12 deficiency. Research

has demonstrated that vitamin B12 injections may improve

executive and language functions in patients with cognitive

decline, but will rarely reverse dementia.78 Low vitamin

B levels may be associated with impaired cognitive

performance through several possible mechanisms including,

multiple central nervous system functions, reactions

involving DNA, and the overproduction of homocysteine

that could potentially damage neurons and blood vessels.79

Low levels of vitamin B12 and folic acid result in poorer

performance on tasks of free recall, attention, processing

speed, and verbal fluency.80 Overall, research suggests that

the effects of vitamin deficiency are most likely seen on

complex cognitive tasks that demand greater executive

functions.

Conclusion

Cognitive decline is a natural part of aging. However, the

extent of decline varies across individuals and across the

specific cognitive domain being assessed. The cognitive

reserve perspective maintains that individual differences

with regard to cognitive aging are related to an individual’s

reserve built upon early life factors (i.e., educational and

intellectual experiences).9

Although cognitive reserve can be increased in later life, it

is more amenable to change in early life. Although cognitive

decline is inevitable, all areas of functioning do not

change equally. It is well established that older adults process,

store, and encode information less efficiently than

younger adults. The cognitive functions related to fluid

intelligence, such as the ability to solve novel or complex

problems, tend to decline with aging, whereas cognitive

functions related to crystallized intelligence, such as

school-based knowledge, vocabulary, and reading, generally

remain stable throughout life. Processing speed and

attentional capacity are particularly vulnerable to aging,

especially on more challenging tasks, and mediate multiple

areas of cognitive functioning. For example, a memory

problem is often, more accurately, a problem with poor

attention and/or slowed speed of processing information.

KEY POINTS

Normal Cognitive Aging

• Variability exists across individuals in their ability to compensate

for cognitive changes as they age.

• An active, engaged lifestyle, emphasizing mental activity and educational

pursuits in early life, has a positive impact on cognitive

functioning in later life.

• In normal aging there is typically a decline in sustained attention

and selective attention and an increase in distractibility.

• Older adults’ response time is approximately 1.5 times slower than

younger adults.

• Most verbal abilities remain intact with normal aging.

• Normal aging is generally associated with a decline in executive

functioning.

• Memory deficits associated with normal aging are primarily

related to the storage of long-term episodic memories.

• Implicit memory tasks, results in very little age-related changes in

Performance

Although research has found cognitive decline in the

areas of attention, processing speed, episodic memory,

and executive function, research has also shown that older

adults have cognitive (or brain) plasticity and may benefit

from cognitive training and other mental activities.81 However,

the results of cognitive training with normal aging

adults has been varied; although improved performance on

a specific task can be found, there is a lack of generalizability

to daily functioning in the long term.82 Nevertheless,

maintaining an engaged and healthy lifestyle (social,

physical, and intellectual) improves one’s quality of life and

may add to successful aging. One problem is the assumption

that “successful aging” means that there is no discernable

change in memory and overall cognitive functioning from

one’s previous level of functioning. Changes in cognition

are a normal part of aging and not something that is necessarily

a cause for concern or precursor to dementia. Older

adults need to adjust their idea of normal aging to a more

realistic standard.

ACKNOWLEDGMENT

Material in this chapter contains contributions from the previous

edition, and we are grateful to the previous author for

the work done.

For a complete list of references, please visit online only at

www.expertconsult.com