**2. Age-associated changes**

the increase in life expectancy. However, aging is not only a population phenomenon but also an individual reality [1], which involves a series of changes in people at biological, psychological and social levels. In the psychological field, changes in the domains related to personality, affectivity, emotions, emotional control, and interpersonal relationships have been reported [2]. Regarding cognitive functioning, the changes that occur during aging are of increasing interest for gerontology because of the implications they could have in case they finally appear in

Historically, the research of cognitive functions has its epistemological origin in the studies carried out by the philosopher Galenus, who argued that in the ventricles of the brain, the consciousness of the human being was found as a set of different capacities: perception, intellect, and memory. From the philosophy of Rene Descartes (1596–1650) arises the neurophysiological theory, which defined the relationship between body and spirit and tried to find the explanation of mental function in the ventricles as the basis of psychic functions, later setting

Later, Flourens (1794–1867) argued that all neural tissues are involved in the different cognitive functions. But it was until Gall's studies (1758–1828) with his Frenology theory, that on one side, cognitive functions were associated with structures by examining the skull, and on the other side, the role of the cerebral cortex in relation to cognitive functions was presented. It was until the nineteenth century, with the establishment of the neuropsychology, when the correlation of anatomo-clinical structures with the alterations in cognitive functions was clearly set up [3, 4]. During the nineteenth century, the first stage of neuropsychology was established. Its study object is the relationship between the cerebral organization and the behavior in its broadest sense: actions, emotions, motivations, and social relations. The unit of analysis of neuropsychology is the individual, including his personal history, and his social and cultural environment. The founders of this approach are Luria, Vygotsky, and Leontiev, with the concern of locating psychological functions within circumscribed parts of the brain, defined higher mental human functions as complex reflex-like processes of social origin whose functioning is both conscious and voluntary and are possible due to their structure and functioning [5]. Later, in 1981, Luria proposed that cognitive functioning analysis should be done by looking for what is located outside the individual, the place where the origins of conscious activity are found. He also developed the idea that several macroanatomical areas and brain regions help each other to ensure control of the so-called human cognitive functions [6]. The cognitive psychology perspective studies the cognitive functioning as the way to know the world, through the construction of reality guided by experience. From there, the cognitive structure is formed and the concept of a cognitive scheme arises [7].

Piaget's theory can be found under this perspective, where the study of structures is left aside to focus on the development of cognitive functioning and its schemes, from a constructive approach of knowledge that at the same time disproves empiricists and innatists theories,

Neuropsychology is a discipline with an integrative view, which today contributes decisively to our knowledge about how the brain and the alterations of its functioning work, focused on

The conceptualization of cognitive functioning functions had several meanings.

their most pathological form: dementia.

144 Gerontology

the pineal gland as related to mental disorders.

based on a psychogenetic perspective [8].

the cognitive development in relation to sociocultural factors.

During the last decades, several scientific efforts have been focused on the study of normal cognitive aging. This has resulted in agreements, as well as numerous discrepancies around the topic, mostly regarding the use of different research methodologies, as well as the little control of other variables that are considered to be closely related to cognitive functioning.

In addition, finding differences between normal cognitive aging and a cognitive impairment involving pathology is clinically difficult, since the limits of diagnosis are not precise. This task becomes even more complicated if these differences are also associated with other variables such as age, schooling, and other population differences [15].

It is important to emphasize that attention control is related to other cognitive functions such as processing speed, which suggests that older adults are less involved in tasks of anticipatory

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Changes associated with age have been studied from the different domains of cognitive

Memory is a neurocognitive function that allows us to record, encode, consolidate, retain, store, retrieve, and evoke information [21]. This cognitive function has a sequence of three types of memory, from sensory to short-term (which is a transitory, fragile and sensitive storage to interfering agents) to long term memory (responsible for the more permanent storage of information and involves a process of consolidation); each have their own particular mode of operation but they all cooperate in the process of memorization and can be seen as three necessary steps in forming the lasting memory. There are also three main processes involved

Memory is one of the most studied cognitive domains because it is a frequent complaint that older adults make during normal aging. Kral's research since 1962 has led to evidence of the existence of a slowly progressing memory loss characterized by the inability to remember, sometimes relatively unimportant parts of the experiences of the past. The affectation of this domain in its processes of acquisition, consolidation, and spontaneous evocation is related to the cerebral biological functioning that will depend on variables such as quality of life.

Regarding the different types of memory, aging has a significant effect, on one hand, on the decline of immediate and episodic memory rather than on semantics and, on the other hand, on evocation rather than consolidation. Aging also affects the codification of new information,

Perception is the mental capacity that allows us to integrate and recognize through our senses. It allows us to recognize those objects to which we pay attention and to create our own knowledge patterns. In that sense, there must be an encounter between the sensorial information

It is often difficult to dissociate spatial skills from constructional ones, being the latter defined as the ability to integrate elements into an organized whole (examples of these skill are copying geometric figures and the construction with cubes), since it requires the handling of space. According to the Pan-American Health Organization, changes in these cognitive functions in aging are due to the decline of visual acuity and processing, which causes problems of sensitivity to illumination and vision difficulties in poorly lit places, problems to distinguish colors, to focus at different distances and deficits related to spatial perception in general.

The executive functions (or meta-cognitive processes) would be those processes involved in the planning and supervision of cognitive processing. The term "executive" encompasses a series of cognitive processes, including updating and tracking information and inhibiting responses [24]. This kind of functions could be understood as a set of high-level operations that sequence and control the basic operations and, at the same time, make decisions in the moments of choosing among alternatives. Because they are linked with other cognitive functions, it is difficult to evaluate them in a specific way. At the same time, it is more complicated to find tasks that

and the memory files that leads to the perception or interpretation of reality.

attentional resources due to the slower reaction time during aging [22].

in the human memory: encoding, storage and recall (retrival) [23].

especially when strategic processing is needed [24].

refer only to the performance of each one of them.

functioning.

The concept of cognitive functioning in normal aging has been defined as "the functioning of the cognitive system, either in adaptation or alteration, which can generate a regression or successful management of the functions of daily life in older adults" [16].

The study of the changes that occur in the cognitive domains has found a close relationship between the physiological and social aspects. On one hand, research focused on the study of the human brain through different techniques (brain mapping, electroencephalogram and cerebral magnetic resonance among others) has reported that the mechanism behind successful cognitive aging may be the preservation of the hippocampal function combined with a high responsiveness in the frontal area [17].

Likewise, studies developed with electroencephalogram and neuropsychological tests found a reduction in age-dependent cerebral electrical power in cortical areas such as the parietal, temporal, and occipital lobes, causing a decline in functions such as memory, attention, visuospatial skills, and processing speed, concluding that the physiological aging of the brain is characterized by a loss of synaptic contacts and neuronal apoptosis that causes a dependent decline in sensory aspects, processing, motor performance, and some cognitive functions.

On the other hand, Steffener et al. [18] conducted a study which reported that cognitive changes during normal aging are due to the slow decrease across different ages of cerebral blood flow and the gray matter volume, mainly in areas such as the prefrontal cortex and the temporal convolutions of the putamen and occipital regions. On the other hand, the social aspects that have been described in different longitudinal studies and were related to the changes of the cognitive functioning in older adults are the schooling, the good health, the social participation, the lifestyle, and the genetic factors [17, 18].

It should be pointed out that socioenvironmental variables can contribute to an individual's cerebral aging and therefore modify his cognitive and behavioral profile. This causes that while some of these factors can affect negatively, precipitating cognitive deterioration in normal aging, others can soften or even slow their effects.

To recognize which cognitive functions normally decline in older adults and when they occur is a complicated task, however, research has agreed that the domains generally involved in it are attention, verbal memory, visuospatial and visuoconstructive skills, processing speed and some of the executive functions such as inhibition, working memory and mental flexibility, while functions such as semantic memory and language are preserved, and even the latter can improve over the years [19–21].

Attention is a complex, dynamic, multimodal, and hierarchical functional system that makes easier the processing of information, selecting the relevant stimuli to perform a certain sensory, cognitive, or motor activity [21]. According to data, cognitive changes are particularly difficult for older adults, mainly in activities that involve orienting them between several elements or constantly changing between different successive testing options, due to the decrease in selective visual attention, which in part is due to the degradation of sensory processing.

It is important to emphasize that attention control is related to other cognitive functions such as processing speed, which suggests that older adults are less involved in tasks of anticipatory attentional resources due to the slower reaction time during aging [22].

This task becomes even more complicated if these differences are also associated with other

The concept of cognitive functioning in normal aging has been defined as "the functioning of the cognitive system, either in adaptation or alteration, which can generate a regression or

The study of the changes that occur in the cognitive domains has found a close relationship between the physiological and social aspects. On one hand, research focused on the study of the human brain through different techniques (brain mapping, electroencephalogram and cerebral magnetic resonance among others) has reported that the mechanism behind successful cognitive aging may be the preservation of the hippocampal function combined with a

Likewise, studies developed with electroencephalogram and neuropsychological tests found a reduction in age-dependent cerebral electrical power in cortical areas such as the parietal, temporal, and occipital lobes, causing a decline in functions such as memory, attention, visuospatial skills, and processing speed, concluding that the physiological aging of the brain is characterized by a loss of synaptic contacts and neuronal apoptosis that causes a dependent decline in sensory aspects, processing, motor performance, and some cognitive

On the other hand, Steffener et al. [18] conducted a study which reported that cognitive changes during normal aging are due to the slow decrease across different ages of cerebral blood flow and the gray matter volume, mainly in areas such as the prefrontal cortex and the temporal convolutions of the putamen and occipital regions. On the other hand, the social aspects that have been described in different longitudinal studies and were related to the changes of the cognitive functioning in older adults are the schooling, the good health, the

It should be pointed out that socioenvironmental variables can contribute to an individual's cerebral aging and therefore modify his cognitive and behavioral profile. This causes that while some of these factors can affect negatively, precipitating cognitive deterioration in nor-

To recognize which cognitive functions normally decline in older adults and when they occur is a complicated task, however, research has agreed that the domains generally involved in it are attention, verbal memory, visuospatial and visuoconstructive skills, processing speed and some of the executive functions such as inhibition, working memory and mental flexibility, while functions such as semantic memory and language are preserved, and even the latter can

Attention is a complex, dynamic, multimodal, and hierarchical functional system that makes easier the processing of information, selecting the relevant stimuli to perform a certain sensory, cognitive, or motor activity [21]. According to data, cognitive changes are particularly difficult for older adults, mainly in activities that involve orienting them between several elements or constantly changing between different successive testing options, due to the decrease in selective visual attention, which in part is due to the degradation of sensory

variables such as age, schooling, and other population differences [15].

successful management of the functions of daily life in older adults" [16].

social participation, the lifestyle, and the genetic factors [17, 18].

mal aging, others can soften or even slow their effects.

improve over the years [19–21].

processing.

high responsiveness in the frontal area [17].

functions.

146 Gerontology

Changes associated with age have been studied from the different domains of cognitive functioning.

Memory is a neurocognitive function that allows us to record, encode, consolidate, retain, store, retrieve, and evoke information [21]. This cognitive function has a sequence of three types of memory, from sensory to short-term (which is a transitory, fragile and sensitive storage to interfering agents) to long term memory (responsible for the more permanent storage of information and involves a process of consolidation); each have their own particular mode of operation but they all cooperate in the process of memorization and can be seen as three necessary steps in forming the lasting memory. There are also three main processes involved in the human memory: encoding, storage and recall (retrival) [23].

Memory is one of the most studied cognitive domains because it is a frequent complaint that older adults make during normal aging. Kral's research since 1962 has led to evidence of the existence of a slowly progressing memory loss characterized by the inability to remember, sometimes relatively unimportant parts of the experiences of the past. The affectation of this domain in its processes of acquisition, consolidation, and spontaneous evocation is related to the cerebral biological functioning that will depend on variables such as quality of life.

Regarding the different types of memory, aging has a significant effect, on one hand, on the decline of immediate and episodic memory rather than on semantics and, on the other hand, on evocation rather than consolidation. Aging also affects the codification of new information, especially when strategic processing is needed [24].

Perception is the mental capacity that allows us to integrate and recognize through our senses. It allows us to recognize those objects to which we pay attention and to create our own knowledge patterns. In that sense, there must be an encounter between the sensorial information and the memory files that leads to the perception or interpretation of reality.

It is often difficult to dissociate spatial skills from constructional ones, being the latter defined as the ability to integrate elements into an organized whole (examples of these skill are copying geometric figures and the construction with cubes), since it requires the handling of space. According to the Pan-American Health Organization, changes in these cognitive functions in aging are due to the decline of visual acuity and processing, which causes problems of sensitivity to illumination and vision difficulties in poorly lit places, problems to distinguish colors, to focus at different distances and deficits related to spatial perception in general.

The executive functions (or meta-cognitive processes) would be those processes involved in the planning and supervision of cognitive processing. The term "executive" encompasses a series of cognitive processes, including updating and tracking information and inhibiting responses [24].

This kind of functions could be understood as a set of high-level operations that sequence and control the basic operations and, at the same time, make decisions in the moments of choosing among alternatives. Because they are linked with other cognitive functions, it is difficult to evaluate them in a specific way. At the same time, it is more complicated to find tasks that refer only to the performance of each one of them.

Some of the tasks that have been considered as executive functions are the working memory, the majority of everyday cognitive tasks that require the establishment of goals, the implementation and follow-up of the operations to reach those goals, and both the checkup of each one of these operations and of the fulfillment of the final purpose; their relevance could be used as evidence of the importance of executive functions in the lives of people [25]. In normal aging, it has been found that changes in executive functions are mainly observed in: working memory, when keeping information available for a short period of time; in inhibition, because over the years, more problems to concentrate on relevant information are experienced and inhibit attention to irrelevant aspects, in addition inhibitory processes are less efficient to allow the initial entry of information into the operational memory and in mental flexibility [26].

functioning and clinical. The MCI intends to identify this intermediate stage of cognitive impairment that is often, but not always, a transitional phase from cognitive changes in normal aging to those typically found in dementia [32]; in this sense, MCI is considered a pre-

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In 2013, the American Psychiatric Association (APA) proposed new criteria for dementia in the fifth edition of the Diagnostic and Statistical Manual for Mental Disorders (DSM-5) and recognizes the predementia stage of cognitive impairment [34]. The condition, which has many of the features of MCI, is known as mild neurocognitive disorder (NCD). Mild NCD recognizes subtle features of cognitive impairment that are different from aging but do not represent dementia. Furthermore, mild NCD focuses on the initial phases of cognitive disorders and precedes major NCD that is analogous to the previous diagnosis of dementia.

There are several subtypes of MCI, which differ according to the type and number of impaired cognitive abilities, the most common is the amnesic which mainly involves memory problems, while in the nonamnesic, memory operation is not compromised. Likewise, when only one dimension of cognitive functioning is affected, it is called DCL of a domain or multidomain if more than one cognitive ability (e.g., memory, reasoning, executive functions, etc.) is affected [32]. These MCI subtypes are usually related to different pathological processes, for example, it has been found that people with amnestic DCL are more likely to progress to Alzheimer's disease (AD) [35, 36], while people with nonamnestic MCI are more likely to develop Lewy

According to this definition, MCI is operationalized based on clinical data of changes in cognitive abilities (see **Table 1**). The subjective cognitive complaint needs to be confirmed by objective cognitive measures, such as neuropsychological test batteries. Objective cognitive impairment is defined as a poor performance in one or more cognitive measures, which suggests deficits in one or more cognitive areas or domains. There is no gold standard to specify which neuropsychological test battery to use, but it is important that all the main cognitive areas are examined. Typically, executive functions, attention, language, memory, and visuospatial skills are taken into account. Functional abilities are investigated by means of a thorough interview with the person and with the next of kin and registered in terms of activities

of daily living (ADL) and instrumental activities of daily living (IADL) scales [32].

ing (ADL) and instrumental activities of daily living (IADL) scales [32].

According to this definition, MCI is operationalized based on clinical data of changes in cognitive abilities (see **Table 1**). The subjective cognitive complaint needs to be confirmed by objective cognitive measures, such as neuropsychological test batteries. Objective cognitive impairment is defined as a poor performance in one or more cognitive measures, which suggests deficits in one or more cognitive areas or domains. There is no gold standard to specify which neuropsychological test battery to use, but it is important that all the main cognitive areas are examined. Typically, executive functions, attention, language, memory, and visuospatial skills are taken into account. Functional abilities are investigated by means of an in-depth interview with the person and with the person's next of kin and registered in terms of both activities of daily liv-

It has been shown that a significant proportion of people with MCI progresses to dementia in periods of 1–2 years and approximately 50% progresses toward dementia over a 5-year period [37].

demential syndrome [33].

Body Dementia [36].

Processing speed has been defined as the reaction time that produces a global effect on cognition [27]. It is one of the functions in which a decline has been found as part of normal aging, and it has even been associated with the cause of cognitive changes in other domains such as care and executive functioning.

Moreover, as a cognitive task becomes more complex, older adults may not have the necessary resources of mental operations to carry out the later phases of it because cognitive functioning is slower and sometimes does not allow them to complete some mental operations that are needed for a correct final task performance [28]. Other studies compared two groups, one of young adults and other of older adults, and applied neuropsychological tasks to measure executive functioning and found a lower performance in inhibitory control, abstraction, and working memory but not the rest of this kind of functions [29].

The subjective perception of adults about their cognitive functioning (also called meta-memory) is another factor that significantly influences the activities of daily living (ADL) during aging, a recent study showed that a third of the evaluated population reported memory problems, thinking skills, and their ability to reason, all of them associated with their overall health [30].

Finally, it is important to note that the cognitive changes that occur in normal aging are presented as a slight decline and do not interfere with the level of independence during aging; if these changes appear in the opposite way, it is possible to suspect deterioration or cognitive change related to a pathology.
